The journal is partially supported by the Ministry of Scientific ...

This issue o f Optica Applicata
has been in partfi.nancially supported
by t he Offi.ce o f Naval Research GZobal
(grant N62909-09-1-1095)

Optica Applicata, Vol. XL, No. 2, 2010
High porosity materials as volumetric receivers
for solar energetics
THOMAS FEND
German Aerospace Center, Institute of Technical Thermodynamics, Solar Technology Department,
Linder Hoehe, 51143 Köln, Germany; e-mail: Thomas.Fend@dlr.de
This paper gives a brief overview on the research activities of the Solar Technology Department
of the German Aerospace Center on porous materials for solar tower technology. Firstly, a brief
introduction to solar tower technology is given. Then, the function of the central component of
tower technology, the volumetric air receiver, is described in detail and examples as well as
experimental results of receiver tests are given. Results of numerical studies are presented, which
have been carried out to characterize air flow stability in receiver systems. Approaches presently
used to model the interior temperatures of the receiver are described. Next spin-off applications
such as particle filters or cooling systems are presented, which are dominated by similar physical
phenomena and which can be treated with the same experimental and numerical methods. Finally,
information is given about the Jülich Solar Tower, which is the first test power station that makes
use of the solar air receiver technology.
Keywords: solar tower technology, porous materials, volumetric air receiver, concentrating solar power.
1. Introduction
Solar tower technology is a promising way to generate large amounts of electricity
from concentrated solar power in countries with high solar resources such as North
Africa and the Middle East, India, Australia or parts of North and South America,
countries known to belong to the so-called “sun-belt” of the Earth.
The concentrated radiation is generated by a large number of controlled mirrors
(heliostats), each of which redirects the solar radiation onto the receiver as a common
target on the top of a tower. Here, at the focal point the so-called “solar air receiver”
is located, which absorbs the radiation and converts it into high temperature heat.
Cellular high temperature resistant materials are used as receivers. As a heat transfer
medium air is used, which is heated up by flowing through the open cells of the hot
receiver material and which then feeds a conventional boiler of a steam turbine.
As an example, a 3 MW solar tower test plant in Almería, Spain, as well as a sketch
of the working principle are shown in Fig. 1. A typical flow chart is shown in
Fig. 2. This idea of the “solar air receiver” was first presented in 1985 [1]. Since then,

272 T. FEND
Fig. 1. Solar tower technology: photograph of the CESA 1 test plant in Almería, Spain (a) and working
principle (b).
Fig. 2. Flow chart of a steam turbine driven by solar tower technology.
a
b

High porosity materials as volumetric receivers for solar energetics 273
the technology has been successfully proven in a number of projects during the last
25 years [2–4]. A ceramic receiver with a thermal power of 3 MW was successfully
tested by a European consortium in 2002 and 2003 within the SOLAIR-project [5].
Recently, a 1.5 MW E 1 test plant was erected in Jülich, Germany, which is the first
plant connected to the grid equipped with a solar air receiver [6]. A detailed description
of the solar air technology is provided in [7].
2. The solar air receiver
The solar air receiver is often also called volumetric air receiver, because due to
the porosity of the material the concentrated solar radiation is absorbed in part of
the volume of the material. Its principle is illustrated in Fig. 3. A simple tubular
absorber is shown for comparison. Because cold ambient air enters the material at
the front of the volumetric absorber, where it is facing the radiation, the material can
be kept relatively cool. In an ideal operation, the temperature distribution should be
as shown on the lower right-hand side of Fig. 3. The low temperature level at the front
minimizes thermal radiation losses.
Reaching the inner absorber volume the temperature increases and the temperature
difference between fluid and solid vanishes. Usually, this is already the case after
a couple of cell diameters, for example, in the case of an 80 ppi 2 ceramic foam after
1–2 millimetres. In contrast to this increasing temperature distribution from the inlet
to the outlet of the absorber module in the case of an ideal volumetric absorber
the temperature distribution of a simple tubular absorber is disadvantageous. This is
shown in the graph on the lower left-hand side of Fig. 3.
1 Megawatt electrical power.
2 The unit ppi (pores per inch) is a measure of the pore density of a foam.
Fig. 3. The volumetric receiver principle
compared to a tube receiver.

274 T. FEND
Here, the fluid which has to be heated flows inside a tube. The solar radiation heats
the tube which in turn heats the fluid. The temperature at the outer tube surface is
significantly higher, leading to higher radiation losses. The temperature at the outer
tube surface is limited by the temperature resistance of the material employed. To
avoid destruction of the tube material, the intensity of the concentrated radiation must
be kept low compared to volumetric absorbers. This makes it necessary to install larger
absorber apertures to achieve similar amounts of total power.
The material requirements of volumetric absorbers are resistance to temperatures
of 1000 °C and more and a high porosity needed to allow the concentrated solar
radiation to penetrate into the volume of the cellular material. Further requirements
are a high cell density to achieve large surface areas necessary to transfer heat from
the material to the gaseous fluid flowing through the channels and a high thermal
conductivity. Even though the extinction volume, that is, the volume of the receiver,
in which the solar radiation is absorbed, decreases with smaller cell size, the increased
surface area and the increase of heat transfer by smaller hydraulic diameters leads to
the desire for structures with cells as small as possible.
3. Results of solar air receiver experiments
Within several recent projects the performance of solar air receivers has been tested
experimentally. The most interesting quantity of solar air receivers is their solar-to-
-thermal efficiency
η =
Q · air
----------------
POA
It may be calculated by dividing the useful thermal power inside the air circuit after
the receiver Q by the power of the concentrated solar radiation penetrating into
the aperture area of the absorber POA (power-on-aperture). is usually determined
with the temperature difference, the air mass flow and the heat capacity:
· air
Q · air
Q · air m · =
CPL( Tout – T0) The experiments were carried out in a 20 kW solar installation capable to generate
concentrated radiation of up to 5 MW/m 2 peak flux. Figure 4 shows the principle of
the set-up used for efficiency measurements. Figure 5 shows examples of materials
tested: a fiber mesh material, which is commercially available from SCHOTT under
the name Ceramat (fiber ∅ =25μm), the HITREC-material, a siliconized silicon
carbide (SiSiC) catalyst carrier with parallel channels of approximately 2 mm in width
made by Saint-Gobain, a 20 ppi SiC foam and an 80 ppi/20 ppi SiC sandwich-like
foam with the 80 ppi layer at the front being responsible for absorption and heat
transfer, both made by the Fraunhofer Institute for Ceramic Technologies (IKTS).

High porosity materials as volumetric receivers for solar energetics 275
Fig. 4. Set-up used for efficiency measurements.
Advanced
fiber material
Hitrec
Fig. 5. Examples of porous materials tested as solar air receivers.
The results are shown in Figs. 6 and 7. The best performance was achieved by
the fiber mesh absorber and by the 80 ppi foam. This indicates that at a given level of
flux density the efficiency increases with increasing cell density. However, the HITREC-
-material was the material of choice for the modular receiver in the SOLAIR-project
(Fig. 8) to be tested in a 3 MW th 3 scale although it has shown limited efficiency results
(Fig. 6) compared to the fiber mesh or the 80 ppi foam. The reason for that was a higher
reliability as far as corrosion resistance and durability are concerned.
Some other materials did not withstand the high temperature exposure during
the tests. This happened although the mean air outlet temperature was significantly
lower than the allowed temperature for the material. As an example, a cordierite
3 Megawatt thermal power.
Foam 80/20 ppi
Foam 20 ppi

276 T. FEND
Fig. 6. Results of efficiency test of a receiver made out of silicon carbide (SiC) catalyst carrier material
(HITREC) and a combined receiver additionally covered with an SiC fiber mesh material.
Fig. 7. Results of efficiency test of an SiC 20 ppi foam receiver and a combined receiver additionally
covered with an 80 ppi SiC foam.
Fig. 8. Solar air receiver test within the European project SOLAIR. Each of the 150 mm HITREC modules
absorbs 15–20 kW of solar power (left); photographs show a cordierite material before (middle) and after
being tested as a solar air receiver in concentrated radiation (I 0 ≈ 2MW/m 2 ).

High porosity materials as volumetric receivers for solar energetics 277
receiver melted, when the air outlet temperature was 900 °C, although the melting
temperature of cordierite is 1450 °C (Fig. 8, right).
This effect is mainly due to flow instabilities, which have to do with the temperature
dependent viscosity of air, which increases with increasing temperature. If there are
temperature inhomogeneities at the front side of the receiver hot parts of the receiver
have a lower permeability due to the more viscous air in these channels. Consequently,
this kind of self-reinforcing effect may lead to hot spots and a material failure in
severe cases. The occurrence of flow instabilities has been investigated in more
detail in a recent study [8]. It turned out that a number of measures are efficient to
prevent the occurrence of hot spots. These are a good thermal conductivity in
the direction perpendicular to the main direction of flow, a high inertial coefficient
in the Darcy–Forchheimer equation describing the pressure loss inside the porous
material and the capability of the materials to allow fluid flow perpendicular to
the main direction of flow (mixing). This last property is especially fulfilled for
ceramic foams.
4. Numerical prediction of gas flow and temperature distributions
A sophisticated way to describe the problem in Fig. 9 is a numerical approach, which
has been carried out by a research group at the University of Erlangen within
the common project SOLPOR [14]. This approach provides a numerical solution of
the basic conservation equations of mass, momentum and energy in a number of
distinct control volumes. The heat transport in the porous material, which is composed
out of heat conduction in the solid, grid, heat conduction in the fluid and heat
conduction by mixing effects, is described by an effective heat conductivity, which
has to be determined experimentally. The experimental method as well as data of
various porous materials have been published by DECKER et al. [10]. The numerical
method is described in more detail in an earlier publication by BECKER et al. [8]. As
the method is a two phase calculation, solid-to-fluid heat transfer has to be treated
as a separate physical quantity. A transient technique has been employed to
determine this quantity for porous materials. It is described in more detail in [11].
An overview on experimental data of a number of various porous materials is given
Fig. 9. Flow problem through a heated porous medium with P out < P 0 .

278 T. FEND
Fig. 10. Volumetric heat transfer data determined for a set of ceramic foam materials. (Various pore
diameters were investigated.)
in [12]. As an example, heat transfer data of a series of silicon carbide foams is shown
in Fig. 10.
Performing a detailed numerical study as roughly described in the last paragraph
enables us not only to show a rough tendency how certain properties influence
the probability of hot spots but also to generate two dimensional distributions of
the front temperature of the porous sample. Such an investigation has been carried out
within the German SOLPOR-project by researchers from the University of Erlangen.
It is described in more detail in [8]. They considered the situation shown in Fig. 9
and assumed a cylindrical geometry. The external radiant heat source of 1 MW/m 2 ,
a typical value for a solar tower installation, was assumed to be absorbed in some
thin layers of the porous body corresponding to the extinction coefficient of
the material employed. It was further assumed that the heat flux is homogeneously
distributed on the circular front of the sample. The resulting flow and temperature
distribution were calculated. To study possible flow instabilities a “static hot spot”
was created by using a small area of higher flux as starting conditions. After a while
the flux was switched to homogenous flux but the temperature calculation continued.
Depending on the material properties, the hot spot maintained or it vanished. In this
way, a parameter study was performed and it could be observed at which levels of
thermal conductivity and inertial coefficient flow instabilities occurred. An example
is shown in Fig. 11. On the horizontal axis the inertial coefficient was varied, on
the vertical axis, the thermal conductivity. For K 2 10 Wm –1 K –1 ). By varying three parameters and looking
for permanent hot spots, a detailed parameter field could be determined, in which no
hot spots can occur.
The results confirm the experimental results, which were obtained from a test with
the cordierite catalyst carrier material already mentioned in Section 3. Here the sample

High porosity materials as volumetric receivers for solar energetics 279
Fig. 11. Temperature distributions at the front side of various homogenously heated porous material
samples obtained from numerical calculations.
melted although the average air outlet temperature was 800 °C and the melting point
of cordierite is 1450 °C. The thermal conductivity (λ ≈ 1Wm –1 K –1 ) and the inertial
coefficient (K 2 = 0.05 m) of the cordierite sample were in a range where hot spots are
allowed.
5. The Solar Tower Jülich
In Section 2, the technology of the solar air receiver was described in detail.
The most recent application of the HITREC Technology (Fig. 8) is the Solar Tower
Jülich, a power plant of 1.5 MW electrical power erected in Jülich in West Germany.
It was launched in June 2009 and since then it has been delivering electrical power
into the German electricity grid. It was erected by the company Kraftanlagen München
with financial and scientific support of DLR. It is currently operated by Stadtwerke
Jülich, the local utility.

280 T. FEND
It works according to the principle shown in Fig. 2. The total number of heliostats
needed is more than 2000 and they comprise a mirror surface area of more than
20000 m 2 . The receiver consists of 1080 HITREC receiver elements and covers a total
area of 20 m 2 .
6. Spin of applications
a b
Fig. 12. The Solar Tower Jülich in operation (a), HITREC receiver element (b), view from the test
platform of the tower (c).
6.1. Cross-flow particle filter
Particle filters for Diesel engines (DPF), which are going to be obligatory in the future
for passenger cars and large vehicles, are object of an intensive research activity all
over the world. Most of the DPFs consist of inlet channels, a porous ceramic or metal
wall, which enables flow of the exhaust gas through it and outlet channels. Particles
are filtered and remain outside the walls in the inlet channels. In regular time intervals
the DPF has to be regenerated to remove the particles. In this process, which is carried
out during regular use of the engine, soot particles in the inlet channels of the filter are
burned, partly with catalyst support. After burning, ashes remain in the channels. In
many existing filters this leads to a slow blocking of the inlet channels (Fig. 13, left).
Fig. 13. Cross-flow particle filter principle.
c

High porosity materials as volumetric receivers for solar energetics 281
During the regeneration heat is generated inside the channels. In so far, the physical
processes are comparable to the processes inside the solar air receiver. In the common
project INNOTRAP, which is carried out by the company DEUTZ AG, the University
of Erlangen, the Fraunhofer IKTS, the Solar Institute Jülich, the DLR and some
smaller industrial partners, these processes are investigated in more detail.
Additionally, a cross-flow filter is proposed, which enables the ashes being removed
from the inlet channels and entering into an ash container. This principle is shown
in Fig. 12.
The cross-flow filter may be realized with ceramic foil technology, which has been
approved for water filtering before, or with an advanced ceramic printing technology,
which has been developed by the German company Bauer Technologies. Also this
technology has been approved in a hot gas application as a solar receiver before [13].
An example of a possible filter design is shown in Fig. 14 (right).
Fig. 14. State-of-the-art particle filter principle (left) and advanced cross-flow principle.
Besides testing new filter designs experimentally the objective of the project is to
develop tools for a numerical simulation of the air and particle flow inside the filter.
6.2. Gas turbine cooling
To achieve higher temperatures in the combustion chamber of combined cycle power
stations, the Collaborative German Research Project SFB 561 has been founded in
1998. One of the main objectives of the project is to investigate an active cooling of
the combustion chamber walls by effusion of air into the chamber (effusion cooling).
The principle is shown in Fig. 15. The wall is covered with metal foam and a thermal
barrier coating (TBC). Cooling air is pressed through the foam and through thin
Fig. 15. Combustion chamber cooling with μm-scale porous metal foams.

282 T. FEND
holes in the TBC. In 2004, DLR joined the project and took over the responsibility for
the characterization of the flow through the foam. Until now, a number of foam
materials have been characterized concerning heat transfer and thermal conduction
properties. Results are presented in more detail in [15] and [16]. Also this application
deals with an external heat source, which is transferred into the porous material by
convection and by radiation.
6.3. Cross-flow/counter flow heat exchanger
A new approach manufacturing a compact high temperature heat exchanger is shown
in Fig. 16. A modified honeycomb structure was used to lead two separate gas flows
through the open pores of the material. Every second row of channels was closed at
the inlet and outlet with a high temperature cement. These closed rows were then
opened from the side in the green state of the ceramics, as can be seen on the right
photograph of Fig. 16. By using an appropriate canning a second flow could be led
through the lateral openings. First experimental results as well as results of numerical
calculations show excellent performance of prototypes of this technology.
Cold gas II in
Hot gas II out
Cold gas I out
Hot gas I in
Fig. 16. Extruded SiC honeycomb-structure used as a cross-flow/counterflow heat exchanger.

High porosity materials as volumetric receivers for solar energetics 283
7. Conclusions
Flow through hot porous materials has been investigated for a number of different
applications. In the case of the solar air receiver physical phenomena like
the occurrence of hot spots, which have been observed experimentally, could be
explained theoretically and it could be shown how material properties such as thermal
conductivity and permeability influence this phenomenon. From the design point of
view the desired properties of an ideal solar air receiver are known, however, future
activities have to focus on durability, corrosion resistance and simplicity of
manufacturing to achieve low costs for the whole receiver system, which at last lowers
the generation costs of solar electricity. In the case of the particle filter, the ceramic
mixer and the effusion cooling of the gas turbine numerical approaches are subject of
current research activities and first results should be expected within the next months.
Acknowledgments – The support of the Deutsche Forschungsgemeinschaft (DFG) for the projects
PORENKÖRPER and SFB 561, the German Ministry of Education and Science for the projects SOLPOR
and 3DKeSt as well as the German Ministry of Economy for the project INNOTRAP is gratefully
acknowledged. Additionally we thank the European Commission for having funded the collaborative
project SOLAIR.
References
[1] FRICKER H., Studie über die Möglichkeiten eines Alpenkraftwerkes, Bulletin SEV/VSE 76, 1985,
pp. 10–16 (in German).
[2] WINTER C.J., SIZMANN R.L., VANT-HULL L.L. [Eds.], Solar Power Plants, Springer-Verlag, Berlin,
1991.
[3] MEINECKE W., BOHN M., BECKER M., GUPTA B. [Eds.], Solar Energy Concentrating Systems,
C.F. Miller Verlag, Heidelberg, 1994, pp. 18–19, 68.
[4] CHAVEZ J.M., KOLB G.J., MEINECKE W., Second Generation Central Receiver Technologies –
A Status Report, [Eds.] Becker M., Klimas P.C., Verlag C.F. Müller, Karlsruhe, Germany.
[5] HOFFSCHMIDT B., DIBOWSKI G., BEUTER M., FERNANDEZ V., TÉLLEZ F., STOBBE P., Test results of
a 3 MW solar open volumetric receiver, Proceedings of the ISES Solar World Congress 2003
“Solar Energy for a Sustainable Future”, June 14–19, 2003, Göteborg, Sweden.
[6] KOLL G., SCHWARZBÖZL P., HENNECKE K., HARTZ TH., SCHMITZ M., HOFFSCHMIDT B., The Solar Tower
Jülich, a Research and Demonstration Plant for Central Receiver Systems, Proceedings of the 2009
SolarPaces Conference, Berlin, September 15–19, 2009.
[7] FEND T.D., PITZ-PAAL R., HOFFSCHMIDT B., REUTTER O., Solar radiation conversion, [In] Cellular
Ceramics: Structure, Manufacturing, Properties and Applications, [Eds.] Scheffler M.,
Colombo P., Wiley-VCH Verlag GmbH & Co. KgaA, Weinheim, 2005.
[8] BECKER M., FEND T., HOFFSCHMIDT B., PITZ-PAAL R., REUTTER O., STAMATOV V., STEVEN M.,
TRIMIS D., Theoretical and numerical investigation of flow stability in porous materials applied as
volumetric solar receivers, Solar Energy 80(10), 2006, pp. 1241–1248.
[9] KRIBUS A., RIES H., SPIRKL W., Inherent limitations of volumetric solar receivers, Journal of Solar
Energy Engineering 118(3), 1996, pp. 151–155.
[10] DECKER S., MÖßBAUER S., NEMODA S., TRIMIS D. ZAPF T., Detailed experimental characterization
and numerical modelling of heat and mass transport properties of highly porous media for solar
receivers and porous burners, Sixth International Conference on Technologies and Combustion for
a Clean Environment (Clean Air VI), Vol. 2, Porto, Portugal, 9–12 July 2001, paper 22.2.

284 T. FEND
[11] FEND T., REUTTER O., PITZ-PAAL R., Convective heat transfer investigations in porous materials,
International Conference Porous Ceramic Materials, Brügge, October 20–21, 2005.
[12] FEND T., HOFFSCHMIDT B., PITZ-PAAL R., REUTTER O., RIETBROCK P., Porous materials as open
volumetric solar receivers: Experimental determination of thermophysical and heat transfer
properties, Energy 29(5–6), 2004, pp. 823–833.
[13] FEND T., REUTTER O., PITZ-PAAL R., HOFFSCHMIDT B., BAUER J., Two novel high-porosity
materials as volumetric receivers for concentrated solar radiation, Solar Energy Materials and
Solar Cells 84(1–4), 2004, pp. 291–304.
[14] REUTTER O., BUCK R., FEND T., et al., SOLPOR Charakterisierung von Strömungsinstabilitäten in
volumetrischen Solarreceivern, Statusseminar Vernetzungsfond “Erneuerbare Energien”, Stuttgart,
February 17–18, 2004, Projektträger Jülich, 2004.
[15] SAUERHERING J., REUTTER O., FEND T., ANGEL S., PITZ-PAAL R., Temperature dependency of
the effective thermal conductivity of nickel based metal foams, Proceedings of ASME
ICNMM2006, 4th International Conference on Nanochannels, Microchannels and Minichannels,
June 19–21, 2006, Limerick, Ireland, paper no. ICNMM2006-96136.
[16] REUTTER O., SAUERHERING J., SMIRNOVA E., FEND T., ANGEL S., PITZ-PAAL R., Experimental
investigation of heat transfer and pressure drop in porous metal foams, Proceedings of ASME
ICNMM2006, 4th International Conference on Nanochannels, Microchannels and Minichannels,
June 19–21, 2006, Limerick, Ireland, paper no. ICNMM2006-96135.
Received November 12, 2009
in revised form January 13, 2010

Optica Applicata, Vol. XL, No. 2, 2010
The influence of thermal treatment
of the porous glass plates on the character
of their scattering in visible spectral region
TATYANA V. ANTROPOVA * , IRINA N. ANFIMOVA
Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences,
Nab. Makarova, 2, Saint Petersburg, Russia
* Corresponding author: antr2@yandex.ru
The pore structure and light transmission of the high-silica porous glasses in visible spectral
region are investigated depending on a temperature of their thermal treatment and composition of
the initial two-phase alkali borosilicate glasses. The character of light transmission in porous
glasses is analyzed considering the features of their pore space structure and processes occurring
in porous glass upon heating. It is shown that with an increase in temperature of thermal
treatment of the porous glasses of different composition the pore size increases, and their
specific surface decreases (at practically constant common porosity), which is due to the processes
of pore overcondensation, that occur owing to the regrouping and change of packing density of
the secondary silica particles. It is shown that introducting phosphate and fluoride ions in the basic
alkali borosilicate glass results in an increase in the light attenuation factors of the porous glasses
owing to an increase in the sizes of liquation areas of heterogeneity in initial two-phase glasses,
formation of larger pores and presence of the nanostructured microcrystalline phases in the porous
glasses.
Keywords: phase-separated alkali borosilicate glasses, porous glass, light transmission.
1. Introduction
Porous glasses (PGs) based on the phase-separated alkali borosilicate (ABS)
glass-forming systems represent the chemically, biologically and thermally steady
nanostructured porous materials with controllable parameters of the structure and
properties [1]. PGs are the matrices for creation of the high silica materials with
adjustable properties, such as the spectral-optical sensors of sorption type for
optoelectronic analyzers of structure of the gas environment; the microoptical elements
for creation of integrated microcircuits working in an optical range and used for
transfer, storage and processing of information; the functional nanoporous elements
for microfluidic devices, etc. [2, 3]. In connection with the availability of PG’s
application in optical technologies information on their optical properties, namely,
light transmission τ in visible spectral area and τ change depending on various factors,
is necessary.

286 T.V. ANTROPOVA, I.N. ANFIMOVA
Generally, a light transmission of the PG plates is defined by absorption and
dispersion on inhomogeneities in PGs [4].
Spectral dependences of the light transmission allow us to obtain data on
the scattering of a light flux from the boundary of the media, as well as from
the structure inhomogeneities and surface. Depending on the size, form and
distributions of the inhomogeneities the various variants of light scattering are
possible. When the inhomogeneity sizes are smaller than the wavelengths λ,
the Rayleigh scattering is observed [5, 6]. In this case, the light extinction factor
K λ = A/λ –β (A =const, β is a parameter, which is determined as a tangent of angle of
inclination of dependence –log(–logτ )=f (logλ) [7]) is proportional to the quantity
λ β =4 [8, 9]. The presence of large inhomogeneities results in diffraction scattering.
The absence of a strict connection between PG’s τ values (in a wavelengths range
λ = 350–800 nm) and the pore sizes (at pore radius r < λ) testifies to the complex
mechanism of light scattering in PG [10]. Besides the pores the sizes of which are less
than a wavelength and the inhomogeneities of liquation type which are inherent to
two-phase ABS glasses there are larger heterogeneities, namely silica gel
precipitations and microcrystalline inclusions [4, 11]. These heterogeneities poorly
absorb light, but bring about the essential contribution to the weakening of a light
stream because of light scattering [6] and can influence the light transmission
character [4, 5, 7, 10, 12, 13]. The observed dependences of τ values on the various
factors which influence the glass leaching process and the structure of the PGs obtained
are connected to these facts (see the review in [14]).
Earlier we investigated the τ values of the porous glasses depending on the ABS
glass composition and its leaching conditions (i.e., the concentration and temperature
of an acid solution) [10], thickness of samples [10], an angle of the light stream
falling on a glass plate surface [12], PG’s thermal background [4]. In the present work,
the light transmittance of the PG plates (thickness L = 3 mm) at λ = 400–800 nm is
investigated depending on the composition of the initial two-phase ABS glasses and
the values of temperature of subsequent thermal treatment (T tt ) of the PG samples
obtained.
2. Technique
The composition and pore parameters of the PGs, obtained as a result of through acid
leaching of two-phase ABS glasses that are a base glass (PG-1) and the glasses of
modified composition (PG-2a, PG-2b, PG-3), and the following PG’s thermal
treatment at T tt = 120–750 °C, are presented in Tabs. 1 and 2. Values of porosity W
are determined by a weight method; sizes of a specific surface pore S (m 2 /g) – by
porosimetry BET method using a SORBTOMETER-M (Russia) analyzer. The values
of average pore diameter D were calculated with the formula [15]:
D =
4
-------
S
⎛ 1 1 ⎞
⎜---------------------- – ----------- ⎟
⎝ ⎠
ρ seeming
ρ Si

The influence of thermal treatment of the porous glass plates ... 287
where ρ Si =2.18g/sm 3 is the density of silica skeleton; ρ seeming = P/V is a seeming
density of PG, g/sm 3 ; P [g] – weight of the sample, g; V [sm 3 ] – volume of the sample.
Spectral dependences of the values τ have been measured on a SF-26
spectrophotometer relative to air (PG/air) or a sample of corresponding two-phase
T a b l e 1. Composition of the porous glasses under study.
Composition as-analyzed [wt%]
Glass Na2O B2O3 SiO2 R x (Oy ) *
PG-1 0.22 4.25 95.53 –
PG-2a
0.17 5.96 93.75 0.07 P2O5 0.05 |F|
PG-2b
0.30 5.48 94.08 0.08 P2O5 0.06 |F|
PG-3 0.09 6.29 93.49 0.13 K2O T a b l e 2. The pore structure parameters of the porous glasses under study.
Glass
Thermal treatment
temperature T tt
[°C]
Porosity W
[sm 3 /sm 3 ]
Parameter of pore structure [15]
Diameter D
[nm]
PG-1 120 0.28 3.9 160
400 0.28 4.9 135
600 0.29 5.0 137
650 0.29 5.9 117
700 0.31 7.3 95
750 0.27 8.4 83
PG-2a 120 0.27 9.9 65
400 0.27 17.6 35
600 0.28 17.9 37
650 0.27 20.0 31
700 0.28 24.9 27
PG-2b 120 0.28 14.3 45
400 0.28 18.7 36
600 0.27 18.2 38
650 0.29 25.3 28
700 0.27 27.4 26
750 0.27 27.5 25
PG-3 120 0.43 9.3 149
400 0.43 10.4 136
600 0.44 12.4 115
650 0.45 14.3 102
700 0.44 17.3 83
750 0.44 26.6 54
Specific surface area S
[m 2 /g]

288 T.V. ANTROPOVA, I.N. ANFIMOVA
glass (PG/two-phase glass). Transmittance spectra of the PG samples, which were
thermally treated at T tt ≥ 400 °C (PG T ), have been measured relative to PG samples
with T tt =120°C (PG 120).
The obtained spectra have been used to reveal the scattering type by parameter β.
3. Experimental results and discussion
The pore parameters of the PGs investigated depend on the initial two-phase glass
composition and their thermal background (Tab. 2). Upon heating of PG samples
in interval T tt ≤ 750 °C the pore size increases, and their specific surface decreases
(at practically constant common porosity) as a result of processes of the pore
over-condensation, caused by the regrouping and change of packing density of
the secondary silica particles [16].
Some results of the measurement of the spectral dependences of porous glasses
under study are given in Fig. 1. The PG plates having larger pores are characterized
by smaller τ values (Fig. 1, Tab. 2). This result is adjusted with data [10] about
an increase of turbidity of the PGs at increase in the sizes of scatterers, which is
caused by the pore over-condensation processes at T tt increase. At the same time, for
similar D values the various values τ of the PG plates from modified glasses are
a b
c d
Fig. 1. Spectral dependences of light transmission of the porous glasses after drying at 120 °C (a–c) and
after thermal treatment at 600 °C (d).

The influence of thermal treatment of the porous glass plates ... 289
observed. The PG-2 samples made from two-phase ABS glass with P 2 O 5 and fluoride
ion additives possess a practically zero light transmission in the wavelength area
λ ≤ 550 nm (Fig. 1b).
The low light transmission of PGs from the two-phase glasses with additives is
most likely caused (besides both an increase in the sizes of the liquation areas of
heterogeneity in initial two-phase glasses [5, 7] and a presence of larger pores) by
the presence of the nanostructured microcrystalline phases [13]. In certain λ intervals
for PGs from two-phase glasses with additives the value τ (PG T /PG 120 ) is greater
than τ (PG T/air) and τ (PG T/two-phase glass) values (Fig. 1d). This fact can also serve
as a proof of the presence of such phases in PG and gives grounds for judging their
sizes and temperatures of their fusion (decomposition).
According to Fig. 1, light transmittance of the PG samples, measured relative to
air is a little bit less than that measured relative to two-phase glass, and to PG 120 in
long-wave region (λ > 600 nm). It was shown that the presence of fluoride-ions in
initial two-phase glass results in an increase in K λ (at the same T tt) [15]. For these
PGs an increase of T tt up to 600 °C is accompanied by reduction of K λ , contrary to
PGs from the glass without fluoride-ions. At T tt > 600 °C the light attenuation of PGs
decreases. In the long-wave spectral region (λ ≈ 700–800 nm) the character of T tt
influence on K λ is maintained, but absolute sizes of K λ values decrease by 1.5–2.5
times (at the same λ). Under such conditions, for PGs from the glasses with
the additives of fluoride-ions a Rayleigh scattering is inherent (β ≈ 4) (Tab. 3). In other
cases, a more complicated character of scattering (β ≈ 0.3–1.9), which is caused by
the features of PG’s porous space structure [17] is observed. An increase of T tt value
from 120 °C up to 600 °C–750 °C is accompanied by a small increase in β values
(Tab. 4).
T a b l e 3. The values of factor β of the porous glasses (T tt = 120 °C) in different spectral regions.
Factor β
Glass λ = 400–550 nm λ = 550–750 nm
PG-1 1.4 0.4
PG-2a 3.7 4.0
PG-2b 0.3 3.7
PG-3 3.3 1.3
T a b l e 4. The values of factor β of the porous glasses treated thermally at different temperatures.
Glass λ [nm] Ttt = 120 °C
Factor β
Ttt =600 °C Ttt = 750 °C
PG-1 400–550 1.4 1.9 1.7
550–750 0.4 0.6 0.9
PG-2b 400–550 0.3 0.4 0.8
550–750 3.7 3.8 4.1

290 T.V. ANTROPOVA, I.N. ANFIMOVA
4. Conclusions
A study of an influence of the composition and temperature of thermal treatment of
the porous glass plates on their light transmission in visible spectral area has been
carried out.
Temperature ranges have been determined of the thermal treatment of the porous
glass plates in which a change of light attenuation, a character of which is defined by
the pore over-condensation processes and depend on an initial glass composition, is
observed. A complex character of the light scattering caused by the structural features
of a pore space has been shown.
The results obtained can be used for optimization of the technological modes of
creating the high-silica porous functional elements of the devices with optical
detection.
Acknowledgements – This work was supported by the Russian Foundation for Basic Research (project
No. 08-08-00733a) and by the Department of Chemistry and Material Science of the Russian Academy
of Science (project PFI OXNM-02).
References
[1] ANTROPOVA T.V., Nanostructurized porous glasses, Proceedings of Nanotechnology International
Forum “Rusnanotech’08”, December 2–6, 2008, Moskow, Russia, Abstracts: 4.5. Chemistry and
Chemical Technology of Nanomaterials 1, 2008, pp. 485–486.
[2] MESHKOVSKIJ I.K., Composite Optical Materials on the Basis of Porous Matrixes, Saint-Petersburg
State University of Information Technologies, Mechanics and Optics, 1998, p. 332.
[3] EVSTRAPOV A.A., ESIKOVA N.A., RUDNITSKAJA G.E., ANTROPOVA T.V., Application of porous glasses
in microfluidic devices, Optica Applicata 38(1), 2008, pp. 31–38.
[4] ANTROPOVA T.V., DROZDOVA I.A., YASTREBOV S.G., EVSTRAPOV A.A., Porous glass: inhomogeneities
and light transmission, Optica Applicata 30(4), 2000, pp. 553–567.
[5] EVSTRAPOV A.A., MURAVIEV D.O., ANTROPOVA T.V., YASTREBOV S.G., Study of optical properties
of the two-phase and microporous glasses, Optical Journal 75(4), 2008, pp. 71–77 (in Russian).
[6] EVSTRAPOV A.A., ANTROPOVA T.V., DROZDOVA I.A., YASRTEBOV S.G., Optical properties and
structure of porous glasses, Optica Applicata 33(1), 2003, pp. 45–54.
[7] ROSKOVA G.P., MOROZOVA E.V., BAKHANOV V.A., Light transmittance of the porous plates received
from two-phase sodium borosilicate glasses with different structures, Fizika i Khimiya Stekla 17(4),
1991, pp. 623–630 (in Russian).
[8] ANDREEV N.S., Small-angle X-ray scattering and visible light scattering in inorganic glasses upon
metastable phase separation, Abstract of Doctoral Dissertation, Leningrad, 1981.
[9] BOHREN C.F., HUFFMAN D.R., Adsorption and Scattering of Light by Small Particles, Wiley, New
York, 1983.
[10] SMIRNOVA I.S., ANTROPOVA T.V., SIDOROVA M.P., ERMAKOVA L.E., ROSKOVA G.P., The effect of
synthesis conditions on the transmittance and coefficient of structural electrical resistance of
microporous glasses, Glass Physics and Chemistry 22(4), 1996, pp. 388–392.
[11] ANTROPOVA T.V., DROZDOVA I.A., Influence of the conditions of manufacturing of the porous glasses
on their structure, Fizika i Khimiya Stekla 21(2), 1995, pp. 199–209 (in Russian).
[12] ANTROPOVA T.V., KRYLOVA N.L., BAKHANOV V.A., Physic-and-chemical interpretation of
the anomalous light transmittance of porous glasses, Fizika i Khimiya Stekla 18(1), 1992,
pp. 113–122 (in Russian).

The influence of thermal treatment of the porous glass plates ... 291
[13] ANTROPOVA T.V., DROZDOVA I.A., Physic-and-chemical features of a porous glass and their
influence on its light scattering, J. Applied Chemistry 69(3), 1996, pp. 393–396 (in Russian).
[14] ANTROPOVA T.V., Physic-and-chemical processes of creation of the porous glasses and high-silica
materials on a base of the two-phase alkali borosilicate glasses, D.Sc. Thesis, Saint Petersburg,
2005, p. 588 (in Russian).
[15] ANTROPOVA T.V., ANFIMOVA I.N., GOLOVINA G.F., Influence of the composition and temperature of
heat treatment of porous glasses on their structure and light transmission in the visible spectral
range, Glass Physics and Chemistry 35(6), 2009, pp. 572–579.
[16] ANTROPOVA T.V., DROZDOVA I.A., VASILEVSKAYA T.N., VOLKOVA A.V., ERMAKOVA L.E.,
SIDOROVA M.P., Structural transformations in thermally modified porous glasses, Glass Physics
and Chemistry 33(2), 2007, pp. 109–121.
[17] DROZDOVA I., ANTROPOVA T., Features of the structure of the phase-separated and porous
borosilicate glasses with/without an impurity of fluorid-ions according to electron microscopy,
Optica Applicata 38(1), 2008, pp. 17–24.
Received November 12, 2009
in revised form January 5, 2010

Optica Applicata, Vol. XL, No. 2, 2010
Application of high resolution microscopy
and optical spectroscopy for study
of phase separation in phosphorus- and
fluorine-containing sodium borosilicate glasses
TATYANA V. ANTROPOVA 1* , IRINA DROZDOVA 1 , IGOR KUKHTEVICH 1 ,
ANATOLY EVSTRAPOV 2 , NADYA ESIKOVA 2
1 Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences,
Nab. Makarova, 2, Saint Petersburg, Russia
2 Institute for Analytical Instrumentation of Russian Academy of Sciences,
Rizhski Pr., 26, 198103 Saint Petersburg, Russia
* Corresponding author: antr2@yandex.ru
The kinetics of phase separation in glass-forming Na 2O–B 2O 3–SiO 2–P 2O 5–|F| system and
structure parameters of the two-phase glasses have been investigated by transmission electron
microscopy (TEM) and optical spectroscopy methods. The TEM images were analyzed with
the help of specially designed software for the purpose of determination of the relative volume
and size of the phases. An influence of duration of a glass heat treatment on the parameters of
their structure was investigated at a temperature of 550 °C which is necessary for prompting
a two-network structure and is most frequently used for manufacturing porous glasses. The time
of glass heat treatment necessary for achieving phase equilibrium was established. A deviation of
the phase inhomogeneity growth rate from theoretical one was determined. It was revealed that
a certain third phase, the composition of which can include α-quartz, is formed in glass during
the heat treatment. Fluorescence of the two-phase glass which has been subjected to heat treatment
for a long time can be caused by the presence of this phase.
Keywords: alkali borosilicate glasses, phase separation, transmission electron microscopy, optical
spectroscopy.
1. Introduction
Phosphorus- and fluorine-containing (PF) glasses are of interest for various
technological applications due to a combination of the useful qualities inherent in
fluorine and metaphosphate glasses [1–9]. In particular, the PF-glasses are
characterized by unique optical and laser properties, that, alongside with high chemical
stability and big opportunities on introduction of the alkaline-earth and rare-earth

294 T.V. ANTROPOVA et al.
elements into a glass matrix, makes theirs by perspective material for the decision of
the applied tasks of optoelectronics. Successful application of PF-glasses is promoted
by their technological properties (a good glass-forming ability, the high thermal
expansion coefficients, a low viscosity) which have a positive effect in industrial
production of the glass, shown in the lowering of a liquidus temperature and
temperature of glass melting.
The important direction is practical use of PF-glasses for creation of the porous
glasses (PGs). Even small additives of fluorine and phosphorus in the glasses of
sodium borosilicate (SBS) system significantly influence the process of phase
separation during their heat treatment [5, 6], which ultimately determines the course
of acid leaching of two-phase glasses and structural parameters of PGs [10]. Using
the two-phase fluorine- and phosphorus-containing SBS glasses in some cases helps
to reduce cracking of the leached samples [6]. This accelerates the process of alkaline
etching of the microporous [11] glasses during manufacture of the macroporous [11]
glasses, and facilitates the process of obtaining PGs with bigger pore radiuses [7, 8].
The last circumstance is extremely important because the functional elements from
macroporous glasses are promising for use as electroosmotic pumps in microfluidic
analytical systems [12–14]. With proper conduct of alkaline etching of the microporous
glass a silica skeleton structure of the macroporous glass obtained corresponds
to the phase structure of the initial two-phase glass.
To optimize the structural parameters of PGs the directional choice of the initial
glass composition and its heat treatment regime are necessary to regulate the structure
of the coexisting phases in two-phase glass. The most important condition for solving
this problem is the availability of information about the structure of two-phase glass
and PGs.
A comparative study of the structure of the phase-separated SBS glasses with and
without additives of fluorides and phosphorus oxide has been initiated by us through
the use of electronic microscopy and X-ray phase analysis methods [15]. There were
found out the distinctions of phase morphology of the two-phase glasses which either
contain or not a fluorine and phosphorus additives. Since the purpose of the research
was to identify the influence of the initial glass composition on the morphology of
two-phase glasses, the experiments were conducted under condition of only one regime
of the thermal treatment of glass. At the same time, the processes of phase separation
in the Na 2 O–B 2 O 3 –SiO 2 –P 2 O 5 –|F| (NaBSiPF) system have been little studied,
making it difficult to directionally select the regimes of heat treatment of the initial
glasses for future manufacture of the macroporous glasses with the predicted structure
of a pore space.
This governs the statement of this work, which is aimed at studying the effect of
temperature and duration of heat treatment of the NaBSiPF-glasses (in comparison
with the base SBS-glass [10, 15, 16]) on structure of coexisting phases in the phase-
-separated glasses with high resolution microscopy and optical spectroscopy methods.

Application of high resolution microscopy and optical spectroscopy ... 295
2. Technique
The objects of investigation were the samples of NaBSiPF-glass (see the Table).
The initial glasses were clarified at temperature T = 810 °C for 15 min, were roughly
annealed to room temperature at a rate of 100 °C/min, and then heat treated at
temperature T ht = 550 °C during a time t ht = 0.5–500 hrs, or at 700 °C during 1–6 hrs.
The choice of such T ht values is caused by the fact of using them in practice for
production of the two-phase glasses suitable for manufacture of PGs.
T a b l e. The compositions, density ρ and glass transition temperature Tg values of the glasses
H2O under investigation.
Glass
Initial glass composition as-analyzed [mol%]
Na2O B2O3 SiO2 Al2O3 P2O5 |F|
20
ρ 20
H2O [g/sm 3 ]
t ht at 550 °C
[hrs]
T g
[°C] *
NaBSi 7.6 20.4 71.9 0.1 – – 2.262 [17] 140 495 [17]
NaBSiPF 6.8 22.1 70.4 – 0.2 0.5 2.200 [17] 40 468 [19]
454 [18]
140 458 [19]
449 [18]
500 450 [18]
* Dilatometer measurements in a mode of heating a sample at a speed of 3 °C/min [17, 18], or 7 °C/min [19].
The transmission electron microscopy (TEM) study of the two-phase glasses was
performed via electronic microscope EM-125 at an accelerating voltage 75 kV with
the resolution at 5 Å. A well-known method of platinum–carbon replica [15] prepared
from freshly cleaved surface etched in 5% solution HF at room temperature during
5–7 seconds has been used.
An analysis of TEM images including calculation of relative volume and the sizes
of co-existing phases in a glass was carried out with the help of special software
[20, 21], which had been developed in MatLab system. In these programs
the histograms of analyzed grey images are used [5]. To estimate a relative volume of
boron-rich phase (V) the cross-section of areas selected on the appropriate image of
glass structure is made. An approach for the choice of rules for a section (in the center
span of the histogram, the peak of the histogram, the half-width at half-height, etc.)
depends on the morphology of the phases. To smooth the origin image the filtering
operation was carried out.
X-ray analysis of all glasses was previously executed on DRON-3 device with
monochromatic CuKα-radiation.
The transmission spectra of the two-phase glass samples were measured on Hitachi
U-3410 spectrophotometer in the wavelength range of 250–850 nm with a step of

296 T.V. ANTROPOVA et al.
10 nm. Fluorescence spectra of the samples were measured on Hitachi F4010
spectrofluorimeter, within the spectral range from 220 to 800 nm, with the speed of
scanning of the spectrum of 120 nm/min and spectral width of the slit of 2 nm.
a b c
d e f
g h i
j k l
Fig. 1. TEM images of the NaBSiPF-glass: after annealing (a) as well after heat treatment at 550 °C
(b–k) and 700 °C (l). Heat treatment time t ht: 1 hrs – b, 6 hrs – l, 10 hrs – c, 40 hrs – d, 65 hrs – e,
90 hrs – f, 198 hrs – g, 240 hrs – h, 344 hrs – i, 500 hrs – j, k.

Application of high resolution microscopy and optical spectroscopy ... 297
3. Experimental results and discussion
It is possible to obtain some notions about the course of the glass phase separation
process on TEM images on which there are precise phase borders between the sites of
the various structures [22, chapter 5]. This can be readily done under the circumstances
where a nucleation mechanism takes place and there is a distribution of one phase
drops inside a matrix of another phase. In the case of a drop-matrix structure it is
possible to estimate the relative volume V values and the size (average radius R) of
co-existing phases on TEM images. The TEM data can be used for the description
of glass phase separation kinetics [22, pp. 29–34]. According to the Lifshitz–Slyozov
theory (see review in [22], Chapter 2), the growth of the radius of the germs formed
of the second phase is proportional to a root square of time of heat treatment, and to
a root cubic of time for the over-condensation stage. The parameter α, determined
on a tangent of an angle of inclination of dependences R = f (tht ) in logarithmical
coordinates, is accordingly equal to 1/2 and 1/3. In the first case the size α is
characteristic of diffusion on an inter-phase surface, in the second case, it is
characteristic of the growth controllable by volumetric diffusion; for diffusion through
an interface α = 1/4 [23]. However, in our case, as is apparent from Fig. 1, on which
TEM images of the glasses investigated are submitted, the structure variant
described is not characteristic even at small values tht . At the same time, it is known
that the laws described according to the Lifshitz–Slyozov theory are carried out for
qualitatively similar structures in base SBS system [24, 25]. Results of our estimation
of the phase parameters in the two-phase glasses on their TEM images are presented
in Figs. 2–4.
According to the results obtained, formation of a micro-heterogeneous structure in
the glass-forming NaBSiPF system occurs already during the cooling of glass melt
(Fig. 1a). It is probable that at this stage a heterogeneity of glass structure is caused
mainly by the occurrence of composition fluctuations, namely by formation of
the high-polymerized silica-oxygen anionic groupings constructed from structural units
PO 4 3–
Q 3 and Q 4 [26], the depolymerizated ortho-phosphate structural groupings [9]
and oxyfluoride polar [BO 3/2 F] – ones [27, 28], and also the germs of a new phase (for
example, [BO 4/2 Me] structural complexes, compatible with SiO 4/2 [22, pp. 24–28]).
These fluctuations result in formation of the areas strongly distinguished on composition
from an initial melt at the following heat treatment of glass [22, pp. 28–45].
It is visible from Fig. 1 that at early stages of phase separation up to t ht

298 T.V. ANTROPOVA et al.
a b
Fig. 2. Dependences of the phase inhomogeneity diameters D (a) or radius R (b) versus heat treatment
time t ht in the common coordinates (a) or in logarithmical coordinates (b).
is a formation of a structure with interpenetrating silica and alkali-borate phases,
the channel diameters of which are D channel =15–20nm (Figs.1c and 1d; Fig. 2a,
dependence 1). At the beginning of the t ht interval mentioned the sizes of the third
phase particles D particle are commensurable with the sizes of the liquation channels
(Fig. 2a, dependence 2).
As the t ht value increases it is possible to observe some increase of the D channel
values as well as structure condensation due to the increase of the third phase
amount. The occurrence of the third phase particles the sizes of which surpass the sizes
of the channels occupied with a boron-rich phase is marked.
At t ht = 65 hrs the sharp changes of a two-phase glass structure are observed
(Fig. 1e) which undergo further development with an increase of t ht (Figs. 1f–1j).
The sizes of the silica phase areas are essentially increased. Along with occurrence
of new fine particles of the third phase its larger part is presented by particles, for
which D particle > D channel .
The fact of so-called “crushing” of the silica phase (an occurrence of the “cracks”
in the areas contacting the particles of the third phase which considerably increases in
size) at t ht ≥ 198 hrs has engaged our attention. In the long heat treatment of a glass
(t ht = 500 hrs) a faceting of the third phase particles (Fig. 1j) and their substantial
growth (Fig. 2a, dependence 2) are observed.
The TEM image of glass structure, generated at elevated temperature T ht =700°C,
at which the phase separation processes occur much faster [24, 25], demonstrates
the growth in the size of areas of silica phase and the faceted crystalline particles of
the third phase (Fig. 1l). It should be noted that at longer etching of the cleaved surface
of glass in 5% HF solution before a replica manufacturing these particles are dissolved
as evidenced by the image of a spongy structure with a rounded through pores,
corresponding to the size of liquation channels (Fig. 1k).
An example of construction of the histograms accordingly to [20] is shown in
Fig. 3a. The histograms, constructed for TEM images of the two-phase glasses with
different time of heat treatment which are combined so that all maxima are at zero, are

Application of high resolution microscopy and optical spectroscopy ... 299
Fig. 3. An illustration of histogram designed by software (a). Overlapping of the histograms of the two-
-phase NaBSiPF-glass samples after heat treatment at 550 °C during different times t ht (b). Dependence
of a relative volume of boron-rich phase in the two-phase NaBSiPF-glasses versus the time t ht of glass
heat treatment at 550 °C (c).
c
a
b

300 T.V. ANTROPOVA et al.
presented in Fig. 3b. It is seen that the form of histograms depends on the time of glass
heat treatment: the tendency towards reduction of a maximum height at essential
increase of t ht value is marked.
For small t ht values the histograms look like an asymmetrical parabola. With
increasing t ht , the narrowing of the peak with maximum and the appearance of strong
skewness (a two-peak distribution) are observed. For t ht ≥ 198 hrs there appear
reflexes (the small peaks) at the end of distributions. These reflexes correspond to
the lightest gradations that are adequate to the lightest areas on TEM images, which
can be correlated to areas of the third phase.
Figure 3c shows a dependence V = f (t ht ), obtained under the condition of choosing
the histogram section as a half-width on half-height after filtering. It is seen that when
t ht ≥ 25–40 hrs an equilibrium value V ~ 55% is achieved. The fluctuations of V around
this value are caused by a process of formation and reorganization of the particles of
third phase, which is denser in comparison with a boron-rich phase, which is
manifested in the analysis of grey images.
It is worthwhile to note that, that judging by glass transition temperature T g , a glass
heat treatment during t ht = 40 hrs is enough to achieve equilibrium composition of
boron-rich phase in the NaBSiPF-glass investigated (the Table), whereas in the case
of base NaBSi-glass not less than 100 hrs are required for this purpose [24]. From
the Table, it is seen that the density and T g value (for the same t ht value) of the modified
glass is much less than for base glass [17–19]. Most probably, this reflects
the influence of fluoride ions, which are mainly in the boron-rich phase and reduce
the degree of connectivity of a skeleton of the second glass-former B 2 O 3 due to
the formation of the oxyfluoride polar structural groupings [BO 3/2 F] – [10, 27, 28].
On the curves representing the dependences of the sizes of phase inhomogeneities
in two-phase glass versus t ht value (taking into account the error caused by
a sufficiently high degree of coherence of heterogeneity regions) in log–log
coordinates there are points of inflection separating the initial and later stages of
growth (Fig. 2b). The results of determining the α values indicate that the growth
of the sizes of the heterogeneity areas in SBS glass with phosphorus and fluoride
additives (under conditions of phase equilibrium) cannot be unambiguously explained
within the framework of the mechanisms mentioned previously, because the α values
do not correspond to any of the above.
Qualitatively similar results were obtained in research of phase separation kinetics
in SBS glasses with ZrO 2 , CaO and Sb 2 O 5 additives [23, 29]. According to the author
of [23, 29] we can assume that in this case, it is not the over-condensation which is
the late stage of phase separation, but the transitive stage of formation of the disperse
system state called a metastable colloidal equilibrium [30] that takes place. At this
stage, the growth of particles can be either slowed down or stopped for some time, as
exemplified by our results (Fig. 2a). The occurrence of such a state in the phase
decomposition of the metastable systems may be due to the simultaneous processes
of nucleation, dissolution and growth of the particles that complicates the kinetics of
a process [23].

Application of high resolution microscopy and optical spectroscopy ... 301
a
Fig. 4. Optical density spectra of the two-phase NaBSiPF-glass samples after heat treatment at 550 °C
during different time t ht , hrs (a). Dependences of the first derivative of transmission spectra of the two-
-phase NaBSiPF-glass samples after heat treatment at 550 °C during different time t ht , hrs (b).
The results of research of the two-phase glasses with the help of optical
spectroscopy (Fig. 4) reflect the structural transformations in glass with an increase in
duration of its heat treatment (Fig. 1).
From the dependences of the first derivative of the transmission spectra of
the samples it is seen that at t ht = 25–90 hrs the maximum of the first derivative
of transmission decreases smoothly and gradually shifts to longer wavelengths. This
may indicate the appearance and enlargement of the scattering particles in the samples.
With an increase in duration of the heat treatment of samples (t ht ≥ 140 hrs) there is
a significant decrease in the peak of the derivative and its shift to longer
Fig. 5. Fluorescence spectra of the two-phase NaBSiPF-glass samples after heat treatment at 550 °C
during different time t ht (hrs).
b

302 T.V. ANTROPOVA et al.
wavelengths, which may be due to a significant enlargement of the structure. Thus
observed broadening of a peak, in all probability, is caused by transition from a system
with prevalence of disseminating and absorbing particles of equal size in a system with
diffusers of different sizes.
The important question is identification of the third phase. Such compounds as, for
example, sodium fluoride and Na 2SiF 6 [15], can be present at the microcrystalline
phase revealed. Allocation of the fluorides in a separate phase can be caused by
the known fact of their small solubility in silicate glass and propensity to crystallization
[2, 3]. In the case of the introduction of P 2O 5 in SBS glass, formation of
phosphates in the form of the teardrop-shaped particles the crystallization of which is
improbable because of propensity to glass formation [3] is quite possible. Apparently,
this explains the fact that accordingly to X-ray analysis data there is only a crystalline
modification of silica, namely α-quartz (ICPDS, no. 33-116) in the samples of
the two-phase glasses under investigation.
The intensity of crystallization increases at great t ht values. This fact can be
evidenced by the spectra of fluorescence which can be caused by presence of
α-quartz in the two-phase glass: the expressed peaks of fluorescence are observed
at t ht = 344–500 hrs (Fig. 5).
4. Conclusions
The structure of the phase-separated glasses of Na 2 O–B 2 O 3 –SiO 2 –P 2 O 5 –|F| system
subjected to heat treatment at 550 °C during 0.5–500 hrs is investigated using
electronic microscopy and optical spectroscopy techniques. The programs developed
in MatLab environment in which the histograms of analyzed grey images are used
have been applied for the processing of TEM images, which enabled us to analyze
the kinetics of phase separation in system under study. The deviation of growth rate
of the liquation heterogeneity areas from theoretical dependence is established.
Propensity to formation of micro-heterogeneous structure in the glass-forming
system during the cooling of glass melt is revealed.
There was found the generation of the particles of a third phase in the glasses with
a two-frame structure which is formed by coexisting silica and alkali borate phases.
The growth of the third phase particles with an increase in duration of the heat treatment
of a glass is shown. The presence of crystal modification of silica (α-quartz; ICPDS,
no. 33-116) in this phase is established.
It is shown that the light transmission spectra and fluorescence spectra of the two-
-phase glasses under study are influenced by the structural transformations in glass
with an increase in duration of its heat treatment.
Acknowledgements – This work was supported by the Russian Foundation for Basic Research (project
no. 08-08-00733a) and by the Department of Chemistry and Material Science of Russian Academy of
Sciences (project PFI OXNM-02 PAN, 2009). The authors thank Irina Anfimova for carrying out the heat
treatments of the glasses.

Application of high resolution microscopy and optical spectroscopy ... 303
References
[1] VIDEAU J.-J., PORTIER J., PIRIOU B., Raman specrtoscopic studies of fluorophosphate glasses, Journal
of Non-Crystalline Solids 48(2–3), 1982, pp. 385–392.
[2] BROW R.K., TALLANT D.R., OSBORNE Z.A., YANG Y., DAY D.E., Effect of fluorine on the structure
of phosphate glass, Physics and Chemistry of Glasses 32(5), 1991, pp. 188–195.
[3] MÖNCKE D., EHRT D., VELLI L.L., VARSAMIS C.P.E., KAMITSOS E.I., Structure and properties of mixed
phosphate and fluoride glasses, Physics and Chemistry of Glasses – European Journal of Glass
Science and Technology Part B 46(2), 2005, pp. 67–71.
[4] VELLI L.L., VARSAMIS C.P.E., KAMITSOS E.I., MÖNCKE D., EHRT D., Structural investigation of
metaphosphate glasses, Physics and Chemistry of Glasses – European Journal of Glass Science and
Technology Part B 46(2), 2005, pp. 178–181.
[5] YONG WAN PARK, Method of leaching high silica glass having 0.5–2.0% P 2 O 5 , Patent USA
no. 3.785.793 (15.01.1974).
[6] TAKUSAGAWA N., YAMAMOTO K., KITAJIMA K., Structure of porous glass prepared from fluorine-
-containing sodium borosilicate glasses, Journal of Non-Crystalline Solids 95–96(Part 2), 1987,
pp. 1055–1062.
[7] EXNAR P., Macroporous glass with P 2 O 5 and fruorides content, Proceedings of 5th ESG Conference,
June 21–24, 1999, Prague, Czech Republic, p. 184.
[8] EXNAR P., Makroporézní skla, Informativní přehled, Hradec Kralove 32(1), 1989, pp. 1–55.
[9] MULEVANOV S.V., MINYIN’KO N.I., KEMENOV S.A., OSIPOV A.A., BJKOV V.N., Investigation of
the complex phosphorus-containing silicate glass by oscillation spectroscopy methods, Glass and
Ceramics (4), 2009, pp. 3–5 (in Russian).
[10] ANTROPOVA T.V., LURIE S.V., KOSTYREVA T.G., SIRENEK V.A., DORONINA L.A., DIKAIA L.F., Features
of making process and a structure of the porous membranes on the basis of two-phase fluorine- and
phosphorus-containing alkali borosilicate glasses, Glass Physics and Chemistry – to be published.
[11] ZHDANOV S.P., The porous glasses and their structure, WissZtschr. Friedrich-Schiller-Univ., Jena,
Math.-Naturwiss. Reihe 36(5/6), 1987, pp. 817–830.
[12] YAO S., SANTIAGO J.G., Porous glass electroosmotic pumps: Theory, Journal of Colloid and Interface
Science 268(1), 2003, pp. 133–142.
[13] YAO S., HERTZOG D.E., ZENG S., MIKKELSEN JR. J.C., SANTIAGO J.G., Porous glass electroosmotic
pumps: Design and experiments, Journal of Colloid and Interface Science 268(1), 2003,
pp. 143–153.
[14] EVSTRAPOV A.A., ESIKOVA N.A., RUDNITSKAJA G.E., ANTROPOVA T.V., Application of porous glasses
in microfluidic devices, Optica Applicata 38(1), 2008, pp. 31–38.
[15] DROZDOVA I.A., ANTROPOVA T.V., Features of the structure of phase-separated and porous
borosilicate glasses with/without an impurity of fluorid-ions according to electron microscopy,
Optica Applicata 38(1), 2008, pp. 17–24.
[16] ANTROPOVA T.V., DROZDOVA I.A., The influence of synthesis conditions of porous glasses on their
structure, Glass Physics and Chemistry 21(2), 1995, pp. 131–140.
[17] ANTROPOVA T.V., DROZDOVA I.A., VASILEVSKAYA T.N., VOLKOVA A.V., ERMAKOVA L.E., SIDOROVA
M.P., Structural transformations in thermally modified porous glasses, Glass Physics and Chemistry
33(2), 2007, pp. 154–170.
[18] STOLYAR S.V., private communication.
[19] STOLYAR S.V., ANTROPOVA T.V., PETROV D.V., ANFIMOVA I.N., Viscosity and shrinkage of the porous
and quartz-like glasses received on the basis of Na 2O–B 2O 3–SiO 2 system, Journal of Applied
Chemistry 81(6), 2008, pp. 935–938 (in Russian).
[20] KUKHTEVICH I.V., ANTROPOVA T.V., EVSTRAPOV A.A., DROZDOVA I.A., Investigation of
the nanoporous glass structure on the images received by high resolution microscopy methods,
Proc. III Russ. Conf. on Nanomaterials “NANO-2009” (in Russian), Ural Pbl., Ekaterinburg, 2009,
pp. 850–853.

304 T.V. ANTROPOVA et al.
[21] EVSTRAPOV A.A., ESIKOVA N.A., KLOKOV M.V., KUKHTEVICH I.V., ANTROPOVA T.V., Research of
the porous glasses by methods of confocal laser scanning microscopy and optical microscopy of
a near field, Nauchnoe priborostroenie (Scientific instrument making) 19, 2009 (in Russian)
(in press).
[22] MAZURIN O.V., ROSKOVA G.P., AVER’ANOV V.I., ANTROPOVA T.V., Two-phase glasses: Structure,
Properties, Application, Nauka, Leningrad 1991, p. 276 (in Russian).
[23] MOROZOVA E.V., Phase separation in sodium borosilicate glass with additions of ZrO 2 and CaO,
Fizika i Khimiya Stekla (Physics and Chemistry of Glass) 17(5), 1991, pp. 726–739 (in Russian).
[24] ROSKOVA G.P., ANTROPOVA T.V., TSEKHOMSKAYA T.S., ANFIMOVA I.N., Influence of the volumes and
radiuses of channels of alkali borate phases of the liquation sodium borosilicate glasses for rate of
their interaction with an acid, Fizika i Khimiya Stekla (Physics and Chemistry of Glass) 11(5), 1991,
pp. 578–586 (in Russian).
[25] VENZEL’ B.I., ZHDANOV S.P., Kinetics of growth of the sizes of boron-phase areas in the sodium
borosilicate glasses, Fizika i Khimiya Stekla (Physics and Chemistry of Glass) 1(2), 1975,
pp. 122–127 (in Russian).
[26] MCMILLAN P., Structural studies of silicate glasses and melts – Applications and limitations of
Raman spectroscopy, American Mineralogist 69(6–8),1984, pp. 622–644.
[27] PRONKIN A.A., NARAEV V.N., TSOI TONG BEEN, ELISEEV S.U., Electroconductivity of the sodium
borate glasses containing fluorine and chlorine, Fizika i Khimiya Stekla (Physics and Chemistry of
Glass) 18(4), 1992, pp. 52–63 (in Russian).
[28] KIPRIANOV A.A., KARPUKHINA N.G., Influence of fluorine additives on electric characteristics of
the alkali-silicate electrode glasses, Fizika i Khimiya Stekla (Physics and Chemistry of Glass) 27(1),
2001, pp. 108–115 (in Russian).
[29] MOROZOVA E.V., Influence of stibium oxide on phase separation in alkali borosilicate glass, Fizika
i Khimiya Stekla (Physics and Chemistry of Glass) 17(5), 1991, pp. 717–725 (in Russian).
[30] KATSNEL’SON A.A., OLEMSKOI A.I., The microscopic theory of non-uniform structures, Moskow
1987, p. 328.
Received November 12, 2009
in revised form January 4, 2010

Optica Applicata, Vol. XL, No. 2, 2010
Effect of restricted geometry on structural phase
transitions in KH 2PO 4 and NH 4H 2PO 4 crystals
VLADISLAV TARNAVICH 1* , LEONID KOROTKOV 1 , OLJA KARAEVA 1 ,
ALEXANDER NABEREZHNOV 2 , EWA RYSIAKIEWICZ-PASEK 3
1 Voronezh State Technical University, 394026, Voronezh, Russia
2 Ioffe Physical Technical Institute, 194021, St Petersburg, Russia
3 Institute of Physics, Wrocław University of Technology, 50-370 Wrocław, Poland
* Corresponding author: tarnavich@mail.ru
The dielectric response of crystalline NH 4 H 2 PO 4 and KH 2 PO 4 –SiO 2 and NH 4 H 2 PO 4 –SiO 2
composites prepared by embedding salts into porous glasses with the average pore diameter of
320 nm has been studied at the temperature range of 85–300 K. An increase of the structure phase
transition temperatures in embedded salts has been observed, which is supposedly due to tensile
deformations of embedded crystalline particles. The antiferroelectric phase transition in confined
ADP particles becomes diffuse in the temperature region around 10 K.
Keywords: ferroelectrics, antiferroelectrics, composite material, porous glass, phase transition, dielectric
permittivity.
1. Introduction
The porous structures filled with various substances are suitable material for optical
devices [1]. The use of optically active ferroelectric fillers allows us to create optical
devices operated by electrical voltage. However, it is known that the physical
properties of ferroelectric materials in confinement are essentially different from
the properties of the bulk. For example, the temperature of ferroelectric phase transition
T C in NaNO 2 embedded into porous glasses decreases [2] upon reduction of average
pore diameters. On the contrary, for potassium dihydrogen phosphate (KH 2 PO 4 –
KDP) T C increases [3] with a decrease of pore diameters. These experimental facts
could be explained by both the size effect and interaction between the intrinsic surface
of pores and the material embedded.
It was suggested [3] that the observed increase of T C for embedded KDP
particles with a decrease of pore diameters (and sizes of particles) is caused by
tensile deformations, which appear owing to different temperature coefficients of

306 V. TARNAVICH et al.
linear expansion of embedded material and matrix. Cooling the sample leads to
the appearance of elastic stresses in embedded nanoparticles, and it is possible
to interpret this process as an influence of “negative” hydrostatic pressure P. Due to
the strong dependence T C (P) [4] it could be a reason of growth of T C for KDP
nanoparticles.
To check this assumption [3] it is expedient to study the effect of “restricted
geometry” on phase transition (PT) temperature for other crystals of KDP family.
For comparative studies we have used the potassium dihydrogen phosphate and
ammonium dihydrogen phosphate (NH 4H 2PO 4 – ADP) embedded into the identical
porous glasses. This selection has been determined by the following reasons:
1. Both compositions are crystallized in a tetragonal phase.
2. The values of dT C/dP for these substances differ essentially (dT C/dP ≈
≈ –4.5 K/kbar for KDP and dT C /dP ≈ –3.4 K/kbar for ADP [4]).
3. Not only dT C /dP but the linear expansion coefficients for ADP (α 1 ≈
≈ 34.0–39.3×10 –6 K –1 and α 3 ≈ 1.9–5.3×10 –6 K –1 within temperature range
203–407 K) are smaller than for KDP (α 1 ≈ 20–26.6×10 –6 K –1 and α 3 ≈
≈ 34.3–44.6×10 –6 K –1 for KDP within temperature range T ≈ 123–363 K) [5]. This
lightens the interpretation of experimental results.
4. Both materials are used as active elements of optical convertors.
5. The effect of restricted geometry on antiferroelectric phase transition in
KDP-family crystals has not been studied up-to-now.
2. Experiment
The experiments were performed with the samples of composites KDP–SiO 2 and
ADP–SiO 2 and polycrystalline ADP. The composites were prepared by embedding at
363–368 K during 4–5 hours a KDP (ADP) saturated water solution into previously
annealed porous glass with average pore diameter of 320 nm. The volume fraction of
the salts embedded into the porous glass was about 12–17%. The samples were
in the form of rectangular plates ≅ 10×5×1 mm 3 . Every time before measurements
the samples were annealed at ~ 373 K during 4 hours for removing remnant water.
Then the samples were clamped between two aluminum electrodes and placed in
a cryostat, where the temperature varied from 85 to 300 K and was measured with
an error not more than ±0.2 K. The measurements of dielectric permittivity ε were
carried out in the cooling and heating regimes (1–2 K/min) in nitrogen atmosphere,
using LCR-meter at the frequency of 1 kHz.
3. Results and discussion
The temperature dependence of dielectric permittivity for KDP–SiO 2 composite
sample is presented in Fig.1. The well defined maximum of ε(T ) dependence near
125 K indicates the ferroelectric phase transition. One can see that the transition
temperature for embedded material is ≈ 125 K, i.e., 3 K higher than for KDP single

Effect of restricted geometry on structural phase transitions ... 307
Fig. 1. Dielectric permittivity vs. temperature for KDP–SiO 2 composite obtained at heating regime.
crystal (T C ≈ 122 K [4]). The increase of T C in confined KDP in comparison with
the bulk material is in a good agreement with data obtained in reference [3].
It should be noted that the shape of the ε(T) maximum for composite material has
qualitative similarity to the shape of ε 33 (T) dependence observed for KDP single
crystal [4] and for polycrystalline KDP [6] in the vicinity of T C .
Below T C the so-called plateau region is observed. Usually, the plateau region
in ε(T) dependence is explained by high domain structure mobility which is
a characteristic feature of KDP type ferroelectrics [4]. Thus, one can assume
the existence of high domain structure mobility in embedded KDP particles within
a broad temperature region below the Curie temperature.
The analysis of ε(T ) dependences for polycrystalline ADP sample and composite
ADP–SiO 2 (Figs. 2 and 3, respectively) has shown their qualitative similarity.
One can see the step-like ε(T ) dependence and a wide temperature hysteresis of
dielectric permittivity for polycrystalline ADP in the vicinity phase transition
temperature. Such behavior of ε unambiguously shows that the crystal under study
Fig. 2. Dielectric permittivity vs. temperature for polycrystalline ADP (1 – cooling, and 2 – heating).

308 V. TARNAVICH et al.
Fig. 3. Dielectric permittivity vs. temperature for ADP–SiO 2 composite (1 – cooling, and 2 – heating);
insert: ε(T) dependences for polycrystalline and ADP–SiO 2 composite, obtained during heating.
undergoes the first order phase transition near T C ≈ 150 K that is in agreement with
reference data [4, 5].
A similar ε(T) dependence is observed for ADP–SiO 2 composite. However,
the temperature hysteresis of dielectric permittivity for composite material is
essentially smaller and the anomaly of ε(T) near T C broadens evidently. So, PT in
confined ADP becomes diffuse, and we have observed the “rounding” of phase
transition as is typical of nanostructured materials. It is possible to suggest that with
a decrease of sizes of ADP particles the crossover of PT from the first to the second
order will take place. We are going to check this supposition in the future using
the porous glasses with smaller average pore diameters.
The broadening of ε anomaly in the phase transition region makes determination
of the precise point of T C complicated. Taking into account the fact that the appearance
of a nonzero order parameter leads to a decrease of dielectric permittivity in
antiferroelectric crystals [4], we find the T C ≈ 151 K to be the temperature at which
the dependence ε(T) decreases rapidly.
4. Conclusions
Having analyzed the experimental results we can conclude what follows:
– An increase of the structure phase transition temperatures in KDP and ADP
salts embedded into the porous glass matrices (d ~ 320 nm) in comparison with
the bulk materials has been found. More pronounced effect of “restricted geometry”
on transition temperature is observed for KDP particles. This speaks in favor of
the assumption [3] that an increase of phase temperature in embedded crystals of KDP
family is caused by tensile deformations effect.
– The antiferroelectric PT in confined ADP particles becomes diffuse in
the temperature region of about 10 K.

Effect of restricted geometry on structural phase transitions ... 309
– The presence of the so-called plateau region in ε(T) dependence below T C
observed for KDP–SiO 2 composite speaks in favor of the existence of a high mobile
domain structure in embedded KDP salt below T C.
Acknowledgements – This work was supported by the Russian Foundation for Basic Research (Grants
N 08-02-01089-a and N 09-02-97503-p_a) and by the Wrocław University of Technology (Poland).
References
[1] KUMZEROV YU., VAKHRUSHEV S., Nanostructures within porous materials, [In] Encyclopedia of
Nanoscience and Nanotechnology, [Ed.] H.S. Nalwa, American Scientific Publishers, Vol. 10, 2003,
pp. 1–39.
[2] NABEREZHNOV A., FOKIN A., KUMZEROV YU., SOTNIKOV A., VAKHRUSHEV S., DORNER B., Structure and
properties of confined sodium nitrite, The European Physical Journal E: Soft Matter 12(Supplement 1),
2003, pp. 21–24.
[3] COLLA E.V., FOKIN A.V., KUMZEROV YU.A., Ferroelectric properties of nanosize KDP particles, Solid
State Communications 103(2), 1997, pp. 127–130.
[4] LINES M.E., GLASS A.M., Principles and Applications of Ferroelectrics and Related Materials,
Claredon, Oxford, 1977.
[5] SHASKOLSKAJA M.P., Acoustic Crystals, M. Nauka, 1982, pp. 402–425 (in Russian).
[6] ZOLOTUKHIN I.V., SPITSINA S.V., YANCHENKO L.I., KOROTKOV L.N., Preparation, structure and
dielectric properties of fractale aggregates of KH 2 PO 4 , Fizika Tverdogo Tela 41(11), 1999,
pp. 2059–2061 (in Russian).
Received November 12, 2009
in revised form December 6, 2009

Optica Applicata, Vol. XL, No. 2, 2010
Aggregation of dyes in porous glass
OLEXANDR V. TYURIN 1* , YURY M. BERCOV 1 , SERGIY O. ZHUKOV 1 , TETIANA F. LEVITSKAYA 1 ,
SERGIY A. GEVELYUK 2 , IGOR K. DOYCHO 2* , EWA RYSIAKIEWICZ-PASEK 3
1 Institute of Physics, I.I.Mechnikov Odessa National University,
Pasteur St. 27, 65-082 Odessa, Ukraine
2 Non-Crystalline Media Department (NDL-11) of I.I. Mechnikov Odessa National University,
Dvorianska St. 2, 65-082 Odessa, Ukraine
3 Institute of Physics, Wrocław University of Technology,
Wybrzeże Wyśpiańskiego 27, 50-370 Wrocław, Poland
* Corresponding authors: tyurin@onu.edu.ua, viknawsvit@gmail.com
The research examines the interaction of dye molecules with their dimers (H aggregates) and
the more complex formations (J aggregates) developing in porous glass. The use of porous
glass when dealing with dye aggregation has resulted in obtaining photoluminescence dimers of
the J aggregating dye, the formation of which is difficult under normal conditions. In addition,
the porous glass matrix contributes to a substantial reduction in the interaction of photoexcited
states of both a molecular and an aggregated dye, thus helping maximize the luminescence
efficiency of porous glass-distributed dyes.
Keywords: dye, porous glass, luminescence, aggregates.
1. Introduction
Dyes absorb light selectively and efficiently, as they have a high quantum efficiency
of irradiation. This property of dyes is used in spectral sensibilisation of halogen-silver
emulsions [1], in photoelectric transducers based on nanoparticles and nanotubes
(organic dye-sensitized solar cell, DSSC) [2], and in laser equipment [3–5].
The efficiency using dyes in laser equipment, during the emission of radiation from
the first singlet level of dye molecules is significantly complicated by the interaction
between particular dye molecules at high concentrations. This leads to the emergence
of ordered dye dimers of the so-called H aggregates and polymolecular structure,
the so-called J aggregates which absorb light in spectral ranges shifted relative to
the absorption spectrum of the molecular dye [6], promoting a decrease in the transfer
of photoelectrons to singlet levels of the dye molecules.
The emergence of associate dye molecules implies an opportunity for their
interaction, which also has a significant impact on the efficiency using dye for laser
equipment.

312 O.V. TYURIN et al.
The research related to the possibility of controlling the process of aggregation of
the dye is quite significant.
It is especially important that predominant emergence of H or J aggregates in a dye
is not only related to the special structure and concentration of dye molecules in
the solution, but also the dimension and state of the sorption surface, the special
limitation and change of state of which may change the type of dye molecules
aggregation, thus enabling one to control this process.
The latter point has served as the subject of this study dealing with peculiarities of
the H and J aggregation of dyes, and photoexcitation of these aggregates interaction
with dye molecules in case of spatial limitation and different states of the porous glass
matrix which is a sorption surface.
2. Experiment
One of the techniques of studying the internal conversion of dye photoexcitation is
the luminescent method with a temporal resolution of spectra [7]. The experimental
facility that was used to perform low-temperature (T = 77 K) luminescent studies is
able to measure spectral values not only in continuous exciting light irradiation, but
also in case of discontinuous (modulated) excitation, when the time of excitation of
the specimen is equal to the time of registration of its luminescence, which is
0.1×10 –4 s, while the interval between the end of irradiation and luminescence
registration was 1.1×10 –3 s.
This choice of the measuring technique was made because in continuous excitation,
luminescence includes all major glows of luminescence centres: fluorescence,
anomalously retarded fluorescence and phosphorescence. In modulated excitation,
the glow is only caused by anomalously retarded fluorescence and phosphorescence
of luminescence centres.
The luminescence studies were performed for two J aggregating dyes of cation and
anion type, whose structural formulas are presented in Fig. 1.
A porous glass matrix was chosen to be the absorption surface with two
predominant pore dimensions in the range of nanometres: matrix type A – mid-size
pore diameters d 1 =10nm and d 2 = 20 nm (conditionally “small”) and matrix
type C – mid-size pore diameters D 1 =20nm and D 2 = 50 nm (conditionally “large”),
which appeared ideal in view of the limitation of the dimension of the sorption surface
that displayed the aggregation and interaction of dyes. The procedure of measuring
the medial sizes in the nanometre range of pores is given in [8].
The implantation of the dye into the porous glass was performed by dipping it in
the dye solution and holding it there for 3 minutes, excessive dye being removed from
the specimen surface by filter paper.
The dye solutions were made in isopropyl and polyvinyl alcohol (PVA) with
a percentage of three weight percent and 5×10 –4 gmol/liter of dye concentration.
The choice of these solvents was made because in transition from isopropyl alcohol
to polymeric solvent, PVA, apart from doing its primary job as a solvent, can contribute

Aggregation of dyes in porous glass 313
a
Fig. 1. The 1,1'-diethyl-2,2'-cyanineiodine, hereinafter referred to as Dye-I (a); pyridine salt 3,3'-di-
-(γ-sulphopropyl)-4,5,4',5'-dibenzo-9-ethyltiacarbocyaninebetaine, hereinafter referred to as Dye-II (b).
to a change to the state of the internal surface of pores of microporous glass, as
was mentioned in the paper, thus changing the nature of dye aggregation in porous
glass [9].
Pursuant to our studies and known experimental data [10–12] for the two selected
dyes, we have designed a table presenting maxima of absorption and glow of molecules
(M) of dimers (H) and aggregate dyes (J), in a solution of isopropyl (Tab. 1) and
polyvinyl (Tab. 2) alcohol excited by light in the range of 400–700 nm.
T a b l e 1. Position of band maxima (nm). Solution dyes in isopropyl alcohol. (A dash means no data
available.)
Absorption Fluorescence
Luminescence
Anomalously retarded
fluorescence
Phosphorescence
H M J H M J H M J H M J
Dye-I 440 510 540 620 570 550 – – – – 700 –
Dye-II 490 600 640 570 610 650 – – 650 – 760
T a b l e 2. Position of band maxima (nm). Solution dyes in PVA. (A dash means no data available.)
Absorption Fluorescence
Luminescence
Anomalously retarded
fluorescence
Phosphorescence
H M J H M J H M J H M J
Dye-I 470 510 540 650 570 550 – – – – 700 –
Dye-II 490 600 640 570 620 650 570 – 650 – 780 –
b

314 O.V. TYURIN et al.
3. Results
In excitation with either continuous (Fig. 2a, curves 1, 2) or modulated (Fig. 2c,
curve 3) light at λ = 450 nm, the luminescence spectra for the specimens of porous
glass having Dye-I in isopropyl alcohol, regardless of the size of pores of the glass
matrix, are only characterised by one glow maximum, the position of which fits
the same wavelength, and which are only different from each other by the glow
maximum intensity.
The luminescence maximum of the given band fits a wavelength of λ max ≈
≈ 610–620 nm and, consequently, the glow can be referred to as fluorescence, also
including anomalously retarded fluorescence of the H aggregates of Dye-I in the case
of continuous excitation, otherwise to anomalously retarded fluorescence H aggregate
of Dye-I in the case of modulated excitation (see Tab. 1).
Compared to the luminescence of the solution not distributed in porous glass,
the following should be mentioned: in the glow of Dye-I in porous glass, there is no
phosphorescence of Dye-I molecules (λ max ≈ 700 nm), with only anomalously retarded
fluorescence of the H-aggregates of Dye-I (λ max ≈ 610–620 nm).
b
d
a
c
Fig. 2. Spectra of low-temperature (T =77 K) luminescence (a, c), excitation of luminescence (b, d),
in continuous (a, b) and modulated (c, d) excitation of isopropyl alcohol solution with Dye-I in porous
glass matrix type A (solid line) and matrix type C (dashed line). Spectra of luminescence recorded in light
excitation at λ = 450 nm (curves 1, 2) (a). Spectra of excitation recorded for luminescence at λ = 610 nm
– curves 1', 2' (b). Spectra of luminescence recorded in light excitation at λ = 450 nm – curve 3 and
λ = 550 nm – curves 4 and 5 (c). Spectra of excitation recorded for luminescence at λ = 650 nm – curves
3', 5' and at λ = 750 nm – curve 4' (d).

Aggregation of dyes in porous glass 315
While the solution had phosphorescence of Dye-I molecules only, there is no
anomalously retarded fluorescence of H-aggregates of Dye-I.
In the spectrum of continuous excitation of the fluorescence of H-aggregates of
Dye-I at λ max ≈ 610 nm, only three overlapped bands are observed with maxima at
λ max ≈ 440 nm, λ max ≈ 510 nm, and λ max ≈ 540 nm which are most distinct for porous
glass matrix type A (Fig. 2b, curve 1' ). These bands are related to the area of absorption
of H dimers, molecular M and J-aggregated Dye-I, respectively (see Tab. 1).
In the spectrum of modulated excitation of anomalously retarded fluorescence of
H aggregates of Dye-I (λ max ≈ 610 nm), four overlapped bands are observed at
λ max ≈ 440 nm, λ max ≈ 470 nm, a low-intensity band at λ max ≈ 510 nm, and the most
intensive amongst excitation bands at λ max ≈ 540 nm (Fig. 2d, curve 3' ).
These bands may be classified as follows: the bands at λ max ≈ 510 nm and
λ max ≈ 540 nm, as in the case of continuous excitation, fit the absorption of molecular
and J-aggregated Dye-I. Concerning the two bands at λ max ≈ 440 nm and
λ max ≈ 470 nm which fit the Dye-I dimers’ absorption region, it is for the first time
that we have seen them in the excitation spectrum of anomalously retarded
fluorescence of H-aggregates of Dye-I; their nature being ambiguous, we suggest
dealing with this issue during a later discussion.
When looking at the spectrum of low-temperature (T = 77 K) luminescence of
a specimen of porous glass matrix type A having a solution of isopropyl alcohol at
Dye-II in continuous excitation at λ = 500 nm, an intensive glow band at
λ max ≈ 610 nm (Fig. 3a, curve 2) is visible and typical of the fluorescence of Dye-II
molecules. For the spectrum of continuous excitation of this glow band, a maximum
is visible at λ max =600nm (Fig.3b, curve 2' ), which coincides with the absorption
maximum of molecular Dye-II (see Tab. 1).
On exposure to modulated light excitation at λ max = 600 nm from the absorption
region of molecular Dye-II, the above specimen’s luminescence spectrum displays
a vivid band at λ max = 760 nm (Fig. 3c, curve 5) which relates to the phosphorescence
of molecular Dye-II (see Tab. 1).
The spectrum of modulated excitation of the phosphorescence of molecular
Dye-II (λ max = 760 nm) does not form a vivid maximum unlike in the case of
continuous excitation. Apart from the maximum related to the absorption of molecular
Dye-II (λ max ≈ 600 nm), it also displays maxima in the absorption regions of Dye-II
dimers (Fig. 3d, curve 4' ) (see Tab. 1).
On exposure to modulated light excitation from the absorption region of Dye-II
dimers (λ max ≈ 450 nm), the luminescence displays a glow band at λ max ≈ 610 nm
(Fig. 3c, curve 4) which coincides with that in continuous excitation (Fig. 3a, curve 2)
and, consequently, in the case of modulated excitation, it pertains to anomalously
retarded fluorescence of molecular Dye-II (see Tab. 1).
When taking a matrix of porous glass matrix type C having a solution of isopropyl
alcohol with Dye-II, the luminescence spectrum in continuous light excitation at
λ = 500 nm displays an overlap of three bands of luminescence at λ max = 570 nm,
λ max = 610 nm and λ max =670nm (Fig.3a, curve 1), which may be naturally related

316 O.V. TYURIN et al.
b
a
d c
Fig. 3. Spectra of low-temperature (T = 77 K) luminescence (a, c) and excitation of luminescence (b, d)
in continuous (a, b) and modulated (c, d) excitation of a porous glass matrix type A (solid line) and matrix
type C (dashed line), impregnated with a solution of isopropyl alcohol with Dye-II. Spectra of
luminescence recorded in light excitation at λ = 500 nm curves 1 and 2 (a). Spectra of excitation recorded
for luminescence at λ = 700 nm – curve 2' and at λ = 670 nm – curve 1' (b). Spectra of lumines-cence
recorded in light excitation at λ = 450 nm – curves 4 and at λ = 600 nm – curves 3 and 5 (c). Spectra of
excitation recorded for luminescence at λ = 750 nm – curves 3' and 4' (d).
to the luminescence of dimers, molecules and J aggregates of Dye-II, respectively. In
the spectrum of continuous excitation for the long-wave glow band J aggregates of
Dye-II (λ = 670 nm), there are three bands at λ max ≈ 490 nm, λ max ≈ 600 nm and
λ max ≈ 650 nm (Fig. 3b, curve 1' ) which fit the absorption of dimers, molecules and J
aggregates of Dye-II, respectively (see Tab. 1). This indicates that the photoexcitation
of dimers and molecules of Dye-II is transferred to the J aggregates of Dye-II.
In modulated light excitation at λ = 490 nm, the luminescence spectrum has two
bands at λ max ≈ 670 nm and λ max ≈ 760 nm (Fig. 3c, curve 3) which pertain to the
anomalously retarded fluorescence of J aggregates and phosphorescence of molecular
Dye-II, respectively. In the spectrum of modulated excitation of these glow bands at
λ max ≈ 760 nm, bands are found at λ max ≈ 440 nm, λ max ≈ 490 nm, λ max ≈ 600 nm and
λ max ≈ 650 nm (Fig. 3d, curve 3' ).
The nature of three bands with maxima λ max ≈ 490 nm, λ max ≈ 600 nm and
λ max ≈ 650 nm is clear and based on the absorption of dimers, molecules and J
aggregates of Dye-II, respectively (see Tab. 1). As to the maximum at λ max ≈ 440 nm
from the absorption region of Dye-II dimers, we have seen this maximum for the first

Aggregation of dyes in porous glass 317
b
d
a
c
Fig. 4. Spectra of low-temperature (T = 77 K) luminescence (a, c) and excitation of luminescence (b, d)
in continuous (a, b) and modulated (c, d) light excitation of a porous glass matrix type A (solid line) and
matrix type C (dashed line) impregnated with a PVA solution having Dye-I. Spectra of luminescence
recorded in light excitation at λ = 450 nm – curve 1, 2 (a). Spectra of continuous excitation recorded
for luminescence at λ = 700 nm – curves 1', 2' (b). Spectrum of luminescence recorded in excitation
by the modulated light at λ = 550 nm – curve 3 (c). Spectra of modulated excitation recorded for
luminescence at λ = 750 nm – curve 3' (d).
time displayed in the excitation spectrum of the phosphorescence of molecular
Dye-II, so its origin requires classifications.
The luminescence spectrum of porous glass matrix type A holding a PVA solution
with Dye-I in continuous light excitation at λ = 450 nm is characterised by one glow
band at λ max ≈ 570 nm (Fig. 4a, curve 2), which is typical of the fluorescence of
molecular Dye-I (see Tab. 2). In the spectrum of continuous excitation of the above
luminescence band, one band of glow excitation is seen with a maximum at
λ max ≈ 510 nm which fits the absorption region of molecular Dye-I (see Tab. 2).
The specimen under study in modulated light excitation from the range of
400–700 nm does not glow and, consequently, there is no phosphorescence and
anomalously retarded fluorescence of H aggregates of Dye-I.
The spectra of luminescence of porous glass matrix type C having Dye-I in PVA
in continuous light excitation at λ = 450 nm are based on two glow bands at
λ max ≈ 570 nm and λ max ≈ 650 nm (Fig. 4a, curve 1) pertaining to the luminescence of
molecular and H aggregated Dye-I, respectively (see Tab. 2).
In the spectrum of continuous excitation of a long-wave luminescence band at
λ max ≈ 650 nm, there are three bands at λ max ≈ 470 nm, λ max ≈ 510 nm and
λ max ≈ 540 nm, which in their spectral absorption coincide with the absorption rage of
dimers, molecular and J-aggregated Dye-I, respectively (see Tab. 2).

318 O.V. TYURIN et al.
b
a
Fig. 5. Spectra of low-temperature (T = 77 K) luminescence (a) and excitation of luminescence (b) with
continuous light in porous glass matrix type A (solid line) and matrix type C (dashed line) impregnated
with a PVA solution with Dye-II. Spectra of luminescence recorded in light excitation at λ = 450 nm –
curves 1 and 2 (a). Spectra of excitation recorded for luminescence at λ = 750 nm – curve 1' and 2' (b).
In modulated light excitation from the range of 400–700 nm, unlike the porous
glass matrix type A having a solution of Dye-I in PVA which does not glow,
the specimen with matrix type C displays a glow at λ max ≈ 650 nm (Fig. 4c, curve 3)
which in its spectral position coincides with the fluorescence of Dye-I H aggregates
in continuous excitation and, consequently, can be referred to as anomalously retarded
fluorescence of Dye-I H aggregates. The spectrum of modulated excitation of the above
glow (λ max ≈ 650 nm) displays two bands at λ max =470 nm and λ max =540nm
(Fig. 4d, curve 3' ) which fit into the absorption region of H and J aggregates of
Dye-I, respectively (see Tab. 2).
Eventually, on treating the porous glass matrixes of both types with a PVA solution
having Dye-II, specimens were only luminescent in continuous excitation.
In the case of the specimen matrix type A in continuous light excitation at
λ = 450 nm, the luminescence spectrum displays a glow band at λ max ≈ 610 nm
(Fig. 5a, curve 1) which can be referred to as the fluorescence of molecular
Dye-II (see Tab. 2). The spectrum of continuous excitation of the above luminescence
band also comprises one band at λ max ≈ 600 nm (Fig. 5b, curve 1' ) which fits
the absorption of molecular Dye-II (see Tab. 2).
For the specimen matrix type C in continuous light excitation at λ =450nm,
the luminescence spectrum also displays one glow band at λ max ≈ 570 nm (Fig. 5a,
curve 2) which in its spectral position fits the fluorescence of Dye-II dimers (see
Tab. 2). In the spectrum of continuous light excitation, this band displays one band
excitation at λ max ≈ 490 nm (Fig. 5b, curve 2' ) which in its spectral position fits
the absorption of Dye-II dimers (see Tab. 2).
It is important that far more intensive glow is seen in the porous glass matrix of
the PVA solution with Dye-II compared to the isopropyl alcohol solution with Dye-II
(versus the intensity of luminescence in continuous excitation – Fig. 5a, curves 1, 2,
and Fig. 3a, curves 1, 2).

Aggregation of dyes in porous glass 319
4. Discussion
The luminescence spectrum of Dye-I in isopropyl alcohol and PVA, excited with
modulated light from the range of 400–600 nm, displays a glow band caused by
the phosphorescence of molecular Dye-I (λ max ≈ 700 nm, see Tab. 2). It is known [13]
that such phosphorescence is only visible when dye molecules are adsorbed on H or J
aggregates of the dye.
In the case of distribution of a Dye-I solution in isopropyl alcohol, the porous glass
matrixes of both types does not display a phosphorescence of the Dye-I regardless of
dimensions of pores – neither in the case of continuous nor modulated light excitation
from the range of 400–600 nm, while displaying a fluorescence of H aggregated
Dye-I, including that anomalously retarded (λ max ≈ 640 nm).
Besides, the point should be made that modulated excitation of luminescence of
H aggregates from the absorption regions of molecular Dye-I (λ max ≈ 510 nm) has
a minor efficiency and is accompanied by a low glow intensity.
Conversely, modulated excitation of luminescence of Dye-I H aggregates from
the absorption regions of Dye-I dimers (λ = 450 nm) is not only accompanied by
a more intensive glow of H aggregates, compared to the excitation from the absorption
bands of molecular Dye-I, but also – for the porous glass matrix type A (with
predominantly “small” mid-size pores) – by the appearance of an extra maximum of
excitation at λ max ≈ 470 nm. It is for the first time that we have recorded the appearance
of a new maximum of luminescence excitation of Dye-I H aggregates, which perhaps
implies the existence of two types of H aggregates in the glass matrix depending on
the dimensions of pores, since, in transition to porous glass matrix type C (with
predominantly “large” pores), the spectrum of modulated excitation of anomalously
retarded fluorescence of Dye-I H aggregates does not display an extra maximum in
the absorption regions of dimers.
These results indicate that porous glass matrix type A has a predominant formation
of Dye-I H aggregates, while in the solution this dye mostly forms J aggregates. In
addition, the interaction of molecular Dye-I and its H and J aggregates forming
in porous glass is minimised.
In the case of distributing the Dye-I solution in PVA in a porous glass matrix
type A, it displays a fluorescence of molecular Dye-I, whilst no fluorescence of dimers.
Consequently, PVA has an impact on the character of Dye-I adsorption, which results
in the fact that the formation of Dye-I dimers in a PVA solution in a porous glass matrix
type A is hindered. For the glass matrix type C the formation of Dye-I dimers in PVA
occurs, while not being predominant, unlike in the case of Dye-I solution in isopropyl
alcohol in porous glass matrices of both types.
The spectrum of luminescence of Dye-II dissolved in isopropyl alcohol out of
a porous glass excited with continuous and modulated light from the range
400–700 nm displays two fluorescent glow bands, including the fluorescence of
anomalously retarded J aggregates and Dye-II molecules. It is important that

320 O.V. TYURIN et al.
the spectrum of excitation of phosphorescence of Dye-II molecules displays
a maximum in the absorption region of dimers, molecules and J aggregates.
When distributing Dye-II dissolved in isopropyl alcohol in porous glass matrix
type A no fluorescence of Dye-II J aggregates is found, while only phosphorescence
occurs, including anomalously retarded fluorescence of Dye-II. Thus, porous glass
matrix type A hinders the formation of Dye-II J aggregates, while they are only formed
in porous glass matrix type C.
The glass matrix has a greater impact on the aggregation of Dye-II in a PVA
solution. In this case, porous glass matrix type A does not form any aggregates,
the luminescence spectrum only having a fluorescence of molecular Dye-II. In porous
glass matrix type C only the dimerisation of Dye-II takes place, with no formation of
J aggregates.
5. Conclusions
Based on our analysis, the following may be concluded:
1. Porous glass has a substantial impact on the aggregation of a dye and, depending
on the size of pores, may lead to complete disappearance of aggregation, even at a high
dye concentration in the solution, which greatly widens the possible category of
the dye used in laser.
2. The use of the matrix of the porous glass contributes to a change of the features
of predominant dye aggregation. An example is the 1,1'-diethyl-2,2'-cyanineiodine
which mostly forms J aggregates in isopropyl alcohol solution and PVA. It is for
the first time that we have seen predominant formation of dye dimers in porous glass,
while the formation of J aggregates was difficult.
3. If a dye solution displays an interaction between aggregates and molecules of
dye which reduces the intensity of luminescence of the dye solution, the use of porous
glass will minimise this interaction, thus to a large extent enhancing the intensity of
luminescence of the dye. This is substantial in the use of the dye in lasers.
References
[1] SHAPIRO B.I., Basis Theory of the Photographic Process, Editorial URSS, Moscow, 2000, p. 646.
[2] O’REGAN B., GRÄTZEL M., Photochemical method for the conversation of light into chemical energy,
Nature 353, 1991, pp. 737–747.
[3] BEZRODNY V.I., DEREVIANKO N.A., ISHENKO A.A., KARABANOVA L.V., Laser of dye on basis of
polyurethane matrix, Zhurnal Tekhnicheskoi Fiziki 71(7), 2001, pp. 72–78 (in Russian).
[4] ALDEG G.R., DOLOTOV S.M., KOLDUNOV M.F., KRAVCHENKO YA.V., MANENKOV A.A., PACHIKO D.P.,
PONOMARENKO E.V., REZNICHENKO A.V., ROSKOVA G.P., TSEKHOMSKAYA T.S., Composite a microporous
glass – a polymeric compound: a new material for solid-state dye laser, Kvantovaya
Elektronika 30(11), 2000, pp. 954–958 (in Russian).
[5] KUZNECOV K.A., LAPTINSKAYA T.V., MAMAEV YU.B. et al., Gereration third harmonic in J-aggregate
immobilization in polymer matrix, Kvantovaya Elektronika 34(10), 2004, pp. 927–929 (in Russian).

Aggregation of dyes in porous glass 321
[6] DIETZ F.J., Zum Stand der Theorie der spektralen Sensibilisierung, J. Signal AM 6(4–5), 1978,
pp. 245–266, 341–361.
[7] SADIKOVA A.A., KOZAKOV B.I., MEYKLIAR P.V., LOGINOVA I.S., Application method of the temporary
of luminescence spectra resolution for examination of microcrystal emulsion, ZNiPFiK 30(6), 1985,
pp. 457–459.
[8] RYSIAKIEWICZ-PASEK E., GEVELYUK S.A., DOYCHO I.K., VOROBJOVA V.O., Application of porous
glasses in ophthalmic prosthetic repair, Journal of Porous Materials 11(1), 2004, pp. 21–29.
[9] ROSSI U.D., DAEHNE S., REISFELD R., Photophisical properties of cyanine dyes in sol–gel matrices,
Chemical Physics Letters 251(5–6), 1996, pp. 259–267.
[10] GILMAN P.B., The luminescent properties of 1,1'-diethyl-2,2'-cyanine alone and absorbed to silver
halides, Photographic Science and Engineering 11(4), 1967, pp. 222–232.
[11] GILMAN P.B., Effects of aggregation, temperature and supersensitization on the luminescence of
1,1'-diethyl-2,2'-ceanine adsorbed to silver chloride, Photographic Science and Engineering 12(5),
1968, pp. 230–273.
[12] COOPER W., Electronic adsorption, luminescence and related properties of resolved J-aggregates
of 1,1'-diethyl-2,2'-cyanine adsorbed to silver halide, Photographic Science and Engineering 17(2),
1973, pp. 217–225.
[13] TYURIN A.V., CHURASHOV V.P., ZHUKOV S.A., MANCHENKO L.I., LEVITSKAYA T.F., SVIRIDOVA O.I.,
Interaction dye molecular and polymolecular formation, Optika i Spektroskopia 104(1), 2008,
pp. 97–103 (in Russian).
Received November 12, 2009
in revised form December 25, 2009

Optica Applicata, Vol. XL, No. 2, 2010
Photoluminescence features of AgBr nanoparticles
formed in porous glass matrices
IGOR K. DOYCHO 1* , SERGIY A. GEVELYUK 1 , OLEXANDR O. PTASHCHENKO 1 ,
EWA RYSIAKIEWICZ-PASEK 2 , TETIANA M. TOLMACHOVA 1 ,
OLEXANDR V. TYURIN 3 , SERGIY O. ZHUKOV 3
1 Non-Crystalline Media Department (NDL-11) of I.I. Mechnikov Odessa National University,
Dvorianska St. 2, 65-082 Odessa, Ukraine
2 Institute of Physics, Wrocław University of Technology,
Wybrzeże Wyśpiańskiego 27, 50-370 Wrocław, Poland
3 Institute of Physics, I.I. Mechnikov Odessa National University,
Pasteur St. 27, 65-082 Odessa, Ukraine
* Corresponding author: viknawsvit@gmail.com
The photoluminescence of AgBr nanoparticles formed by a two stage liquid-gas microsynthesis
technology in two types of porous glass with different sizes of pores was investigated. Polyvinyl
alcohol (Polinol) was used as a binder. It has been found that AgBr nanoparticles in the glasses
with smaller pores luminesce more intensively, and we attribute this phenomenon to the differences
in pore size distributions. The luminescence spectra were shown to have two maxima
corresponding to AgBr nanoparticles formed within the nanopores of two different sizes
characteristic of each of the matrices. In both cases, the spectra excited by xenon lamp irradiation
are more intensive than those stimulated by a 337-nm nitrogen laser. Comparing the maxima shifts
in the phosphorescence excitation spectra with ones in phosphorescence spectra we can conclude
that the luminescence and phosphorescence centers in AgBr nanoparticles are of identical nature
in the matrices of both types. The investigation results fit neatly into the inherently consistent
quantum confinement model and are well correlated with the poroscopic spectra of both types of
glass.
Keywords: porous glasses, silver bromide, nanoparticles, luminescence properties, quantum confinement.
1. Introduction
It is well known [1] that AgBr crystallizes into a face-centered cubic crystal lattice
5
with NaCl structure (space group Oh ) or into a simple cubic crystal lattice with CsCl
1
structure (space group Oh ) depending on the acidity of the medium. The most probable
shape of nanocrystallites are cubes characteristic for these space groups. AgBr is one
of the basic photographic materials and its photographic properties are the result of

324 I.K. DOYCHO et al.
deviations from an ideal crystal structure. Since there is no immediate correlation
between concentration of the ingredients of the reaction and the concentration of
the nanoparticles obtained the latter can be evaluated only qualitatively. The metal
silver phase in this case was not formed as its appearance would be accompanied
by sample blackening, which was not observed. The majority of defects in AgBr are
the Frenkel defects concentrated near the surface of its particles [2].
To provide the high-resolution photographic material with good radiation
sensitivity the task of vital concern is to create AgBr particles within the medium
preventing formation of large conglomerations. The presence of nanodimensional
pores makes porous silicate glasses a good medium for the purpose [3–6]. They are
of interest not only as a model medium for investigating various quantum confinement
effects, etc., but they are also promising as a matrix for creating radiation sensitive,
photoresponsive and photochromic materials with extended range of sensitivity,
resolution and, possibly, optical density. These perspectives come about through
the possibility of introducing into the matrix a considerable amount of sensitive
material avoiding at the same time the danger of large conglomerations developing,
which reduce the material resolution and deteriorate its radiation sensitivity. The pore
size distribution restricts nanoparticle size growth within the pores, whereas
special features of the formation technique ensure nanoparticle fineness. The size of
the nanoparticles being formed is determined by the microsynthesis technique. Small
AgBr particles will tend to form the energetically advantageous crystallites of space
O h 5
group . Energetically unfavorable coral-like “sprouting” of AgBr into the adjacent
pores could occur at the excess concentration of the reaction components within pores,
but we deliberately created a deficient concentration. If, along with the nanoparticles,
large microcrystallites of irregular shape were formed inside the pores, the position of
the photoluminescence spectra peak would correspond to single-crystal AgBr in
polyvinyl alcohol (~800 nm). Therefore, the nanoparticle contribution would become
apparent through additional spikes shifted into the short-wave region. However, we
have observed the system shift of all maxima towards higher energies. Such a shift is
characteristic of the system of nanoparticles without any single-crystal formations.
In the present paper, a technique of silver-halide nanoparticle formation is
suggested, which does not result in the development of such conglomerations.
The photoluminescence centers in AgBr particles are known to be concentrated near
their surface interacting directly with binder molecules, thus the selection of a binder
is crucial. It has been shown earlier [7–9] that gelatin is not a suitable binder because
its molecules are too big to transport AgBr nanoparticles into the nanopores. For this
purpose, we employed polyvinyl alcohol (Polinol), a substance not commonly used
for creation of photosensitive media. Since Polinol molecules are essentially smaller
than gelatin ones, the Polinol being a binder serves also as a delivery vehicle
transporting silver particles into the finest pores. For AgBr particles formed with
Polinol assistance within porous matrices of two types [10] we succeeded in observing
the quantum confinement effect. The results of investigating the phosphorescence
excitation spectra and phosphorescence and luminescence ones can be consistently

Photoluminescence features of AgBr nanoparticles ... 325
explained in terms of the quantum confinement model. The effects induced by
formation of AgBr nanoparticles within the pores of two predominant sizes,
characteristic of each of the two matrices, fit neatly within the frame of the model. At
the same time, all observations demonstrate a good correlation with the poroscopic
spectra for both types of glasses [11].
2. Experiment
The special features of the liquid-gas microsynthesis procedure are such that, in spite
of the wide range of pore sizes in the matrix (from several to hundreds of nanometers),
only small particles (of the order of several nanometers) can develop within the pores.
This should be expected from the minimum total energy principle, and this is confirmed
by the photoluminescence spectra where the position of spectrum peaks, being
substantially different from that typical of a single crystal, shifts into the higher energy
region, which is a manifestation of the quantum confinement effect characteristic of
nanoparticles. Thus, in our investigation, we can consider only small pores since our
technique [12] ensures no contribution of large ones to photoluminescence. Thus
an A-type porous silicate glass was selected as a matrix with pores of minimal sizes
prevailing in the range of pore size distribution under consideration. To trace a possible
system shift we used for comparison a C-type glass as a reference material with
somewhat larger prevalent pore sizes. Both types of glass were produced without silica
gel leaching out [13].
The pore size distributions in both types of glass were obtained earlier [11]; as
can be seen in Fig. 1 they are relatively narrow. We were trying to create
the nanoparticles of AgBr, so our interest is only with the fine pores which should limit
the growth of AgBr particles within a nanometric range of sizes where quantum
confinement effects can be observed. Defining role in our studies was played by two
smallest fractions in pore size distributions, since it is just in such pores that the silver
halide nanoparticles can form. These two fractions in A- and C-type glasses are
distinguishable, as can be seen in Fig. 1, and due to this difference the matrix type
influences the nanoparticle forming conditions and, therefore, their luminescent
Fig. 1. Pore-size distribution spectra for
A- and C-type porous silicate glass.

326 I.K. DOYCHO et al.
spectra. We did not take into account a possible presence of large pores in the matrices
of both types since we extended to AgBr the microsynthesis technique developed for
CdS [12, 14]. Owing to such a technique, on the inner surfaces of large pores only
the islets of binder monolayer can appear containing the same AgBr nanoparticles,
which do not lead to development of additional maxima in photoluminescence spectra.
To create AgBr nanoformations within the matrix we saturated the appropriate
porous glass with one-molar AgNO 3 aqueous solution with a 3% Polinol addition.
After an hour’s holding in the solution necessary for silver ions to penetrate into
the finest pores, the specimen was exsiccated for 30 minutes at approximately 40 °C,
and after that for twenty-four hours it was held in bromine vapors.
In the case of silver haloids, the photoluminescence centers at low temperatures
are the same centers that provide photosensitivity at room temperature. These two
properties of silver haloids are complementary, which means that if there is a photoluminescence
at liquid-nitrogen temperature, at room temperature the photosensitivity
should be expected. However, an increase in the intensity of photoluminescence is not
connected directly with photosensitivity growth, but is only indicative of an increase
in the quantity of silver halide nanoparticles with the suitable relationship between
their volume and their surface area.
Being actually one and the same recombination process the fluorescence and
phosphorescence are distinguished only by the excited-state lifetimes of the luminescence
centers. However, as fluorescence correlates with the size of particles containing
these centers, and phosphorescence characterizes the centers themselves and makes it
possible with sufficiently good resolution to distinguish the traps indistinguishable
within the lifetime range of up to 10 –5 s, both phenomena are conveniently studied
separately in the different sample excitation modes. The luminescence and phosphorescence
spectra excited by a 337-nm nitrogen laser or 1 kW xenon lamp were recorded
at 77 K with standard equipment [15]. The laser and xenon lamp sample excitation
regimes do not require any special calibration for comparison of results. Both sources
of excitation are parts of one and the same installation, use the same register system
and the excitation mode is changed by a simple switch in the exciting unit. We did not
investigate the efficiency of quantum luminescence in this case, since this exceeds
the scope of the problem formulated.
To record the phosphorescence spectra excited by the xenon lamp two
monochromators are used. The first performs a spectral decomposition of the lamp
light, and through the second one a luminescence beam goes from the sample
before hitting a photodetector. A possible internal photoelectric effect as a result of
xenon lamp irradiation could have a significant influence on single-crystal AgBr, but
for the carriers inside nanoparticles the forbidden band is considerably wider and
the photoelectric threshold shifts towards higher energies.
At the beginning, knowing from the photoluminescence spectrum in what spectral
range it is necessary to look for the phosphorescence peak, the sample is excited by
a sufficiently broadband within this range. Having the peak located, the second
monochromator in front of the photodetector is adjusted to the corresponding

Photoluminescence features of AgBr nanoparticles ... 327
wavelength. After that the first monochromator scans the broad spectral band of
the excitation source providing as a result the excitation spectrum of this particular
maximum of the phosphorescence spectrum. Such a procedure makes it possible to
segregate maxima of the phosphorescence spectrum, which can overlap in
photoluminescence investigation. Each separate maximum corresponds to a specific
type of traps, and therefore the spectrum of phosphorescence excitation shows
the excitation energy of this particular trap.
Optical polarization inside such essentially isotropic system as porous glass is
possible only for sufficiently long molecules, for example, organic dyes or liquid
crystals sensitive to the conditions on the surface inside the pores. But in our case, for
sufficiently symmetrical nanoparticles the optical polarization is hardly probable and
was not investigated.
3. Results
For A- and C-glasses with AgBr nanoparticles created with Polinol assistance
the luminescence spectra excited by a 337-nm nitrogen laser are presented in Fig. 2;
and in Fig. 3 are the ones excited by 430-nm xenon lamp. Comparing the spectra in
Figs. 2 and 3 shows that for both types of glass the intensity of luminescence excited
by xenon lamp is almost 10 times higher. The spectra of AgBr nanoparticles in
A-type matrix for both methods of excitation have two characteristic maxima
with approximately 130-nm system shift. The laser-excited spectrum shows a more
intensive short-wave maximum against the background of relatively insignificant
overall luminous intensity. With a xenon lamp excitation the intensity redistribution
between the maxima occurs, they become comparably-intensive and the luminosity of
both sharply increases. The same effect is observed for C-type matrix, but here
�
Fig. 2. Photoluminescence spectra of AgBr nanoparticles excited by 337-nm nitrogen laser in two types
of porous glass.
Fig. 3. Photoluminescence spectra of AgBr nanoparticles excited by 430-nm xenon lamp in two types of
porous glass.

328 I.K. DOYCHO et al.
the system shift between maxima is less almost by half (about 70 nm), the luminescence
intensity is substantially lower and there is no intensity redistribution. With both
excitation methods in the luminescence spectra of AgBr nanoparticles in C-type
matrix only the short-wave maximum is strongly pronounced, while the second one
at 430 nm excitation is diffuse and spread-out, and at 337-nm excitation it is barely
perceptible.
In the photoluminescence spectra we observe the shift of the peak into the short-
-wave region in comparison with the spectra of AgBr microcrystallites, known from
the literature, obtained with the same binding agent. It is precisely a manifestation of
the quantum confinement effect. The phosphorescence spectra and the phosphorescence
excitation spectra do not refer to the quantum confinement effect, and their
comparison just helps to separate the contributions into the luminosity from
energetically close long- and short-lived centers.
The system shift of the spectra can also be traced through comparison of maxima
position in phosphorescence excitation spectra and those in the phosphorescence
a b
Fig. 4. Phosphorescence excitation spectra (a) and phosphorescence ones (b) of AgBr nanoparticles in
A-glass.
a b
Fig. 5. Phosphorescence excitation spectra (a) and phosphorescence ones (b) of AgBr nanoparticles in
C-glass.

Photoluminescence features of AgBr nanoparticles ... 329
spectra of AgBr nanoparticles Polinol-implanted into both types of matrices. For
A-type matrix these spectra are shown in Fig. 4, and for C-type glass in Fig. 5. A single-
-humpedness of all maxima indicates that the corresponding traps are elementary ones
without any fine structure. In the phosphorescence spectra of AgBr nanoparticles in
A-glass two maxima can be seen at a wavelength λ max of approximately 580 and
720 nanometers, for which there are also two corresponding peaks in the spectra
of their phosphorescence excitation with λ max ≈ 420 nm and 550 nm, respectively. In
the phosphorescence spectra of C-glass with AgBr nanoparticles also two maxima of
luminosity are observed (approximately at 570 nm and 660 nm) for which there are
also two corresponding peaks in the spectra of their phosphorescence excitation with
λ max ≈ 440 nm and 465 nm, respectively. Thus, the maxima in the spectra of
phosphorescence excitation, just as the maxima of phosphorescence spectra for both
matrices, are shifted into the long-wave region with an increase in the exciting
wavelength.
4. Discussion
It is known [16] that at 77 K the photoluminescence spectrum of AgBr microcrystals
in a Polinol binder solution demonstrates one strongly pronounced maximum at
680 nm. Both maxima that we observed in the luminescent spectra were shifted from
680-nm into the short-wave region, which is explained by the quantum confinement
effect and confirms that we succeeded in creating AgBr nanoparticles. The presence
of two peaks in the photoluminescence spectra corresponds to the nanoparticles formed
in pores of two basic fractions (see Fig. 1). The absence of any traces of a 680-nm peak
in the spectra confirms that our two stage liquid-gas technique of microsynthesis
prevents the reagents from filling the large pores where the microcrystals could form.
As can be seen in Fig. 1, the luminosity of nanoparticles created in C-type matrix
is considerably weaker, for there are fewer pores of appropriate sizes than in A-type
matrix. The long-wave excitation power of xenon lamp is higher than that of a pulsed
laser, so the intensity of laser-stimulated luminosity for both glasses is 10 times lower.
Because the xenon lamp is more powerful and can activate some radiative
recombination centers in bigger particles, the lamp-excited A-glass photoluminescence
demonstrates the intensity redistribution from the maxima of the AgBr nanoparticles
in favor of those radiative recombination centers. At the same time, since the pulsed
laser UV radiation fades being scattered strongly by the fine pores, the majority of
the carriers in bigger particles recombine nonradiatively. For C-glass nanoparticles
the effect is practically nonexistent because of the weak luminous intensity.
As the wavelength of the exciting radiation shortens the maxima of
phosphorescence the excitation spectra are shifted into the short-wave region
simultaneously with the respective peaks in phosphorescent spectra, for two sizes of
AgBr nanoparticles in the matrices of both types. This is the evidence that
quantum confinement effect takes place for AgBr nanoparticles in pores of appropriate
sizes.

330 I.K. DOYCHO et al.
Presented in Figs. 4 and 5 the phosphorescence spectra and the corresponding
phosphorescence excitation spectra, as well as their system shift with the change in
the excitation wavelength, confirm that luminescence and phosphorescence centers
in AgBr nanoparticles are of identical nature for matrices of both types.
The investigation of light emission by AgBr crystallites [17, 18] has shown
that lattice defects can play the role of luminescence centers. As is known [2],
the luminescence centers in AgBr without binder are the atom-molecule dispersion
centers formed by the elementary combinations of interstitial atoms with silver ions.
They can be distinguished by the presence of cation vacancies in these centers [17].
The only one peak in the phosphorescence spectra (Figs. 4, 5) suggests that there is
only one type of luminescence centers, namely, the inherent in AgBr Frenkel
defects [1], that is, the complexes of interstitial silver ions Ag+ i and silver vacancies
–
Agv [2]. In this case, the Polinol binder molecules stabilize the surface interstitial
luminescence centers in AgBr through their agglomeration. When light falls on
the surface of AgBr nanoparticle a photoelectron is generated in the conduction band
at the expense of the halogen electron [18]:
X – + hν → X + e –
After being generated, the electron tends to be bonded with an interstitial silver
ion Ag+ 0
i to form a neutral atom Agi :
e – + Ag+ i → Agi Simultaneously with a nonequilibrium electron a nonequilibrium hole h + is formed,
which also tends to be neutralized. The lifetime of a nonequilibrium hole, however,
does not correlate with the electron lifetime. This is a consequence of different
trapping mechanisms: it was shown [18] that traps for the holes are the mobile,
–
negatively charged lattice defects, namely, the silver vacancies Agv , with which they
form the hole complexes:
h + + ↔ h·Ag v
Ag v –
0
Formation of the hole complexes h·Ag v reduces energy of the components
sufficiently for their stabilization and reduction in the probability of the hole ejection
back into the valence band. As a result of the concentration gradient creation the holes
diffuse to a nanoparticle surface where their lifetime is much longer than within
the bulk of crystallite, and where they are in equilibrium with the adsorbed bromine.
The final result of this equilibrium is the stimulation of an increase in the number of
holes at the surface, which makes up for the phosphorescence.
The fundamental absorption edge in AgBr can reach 500 nm [3, 19], hence
the subsequent recombination of nonequilibrium carriers is a band-to-band one. Thus

Photoluminescence features of AgBr nanoparticles ... 331
the shift of phosphorescence excitation maximum into short-wave region with
a decrease in the sizes of AgBr nanoparticles makes it possible to speak about such
a manifestation of the quantum confinement effect as the band-gap broadening.
5. Conclusions
For porous glasses a liquid-gas microsynthesis technique is developed for the Polinol
assisted formation of AgBr nanoparticles within the pores.
The technique ensures the uniformity of bulk distribution of AgBr nanoparticles
within the matrix and makes it possible to increase silver halide concentration in
gelatin- or Polinol-type binding solutions. In that way, it opens up prospects both
for creating more responsive radiation sensors and for further development of
photochromic media.
Two maxima in the luminescence spectra of AgBr nanoparticles correspond to
the two fractions of predominant pore sizes. This is confirmed by the system shift of
maxima in the photoluminescence spectra, in phosphorescence excitation spectra, and
in the phosphorescence ones, depending on the prevalent pore sizes in each glass.
Upon transition from AgBr nanoparticles in A-type glass to the ones created in
C-glass a tendency towards weakening the quantum confinement effect takes place,
which manifests itself in the reduced system shift of the luminescence spectra peaks
into the long-wave region with a simultaneous sharp decrease in their intensity.
A single-humpedness of all maxima in phosphorescence spectra and in
the corresponding phosphorescence excitation spectra indicates that the related
traps are elementary ones without any fine structure. And the maxima simultaneous
system shift with the change in the exciting wavelength confirms that luminescence
and phosphorescence centers in AgBr nanoparticles are of identical nature for matrices
of both types.
References
[1] GLAUS S., CALZAFERRI G., The band structures of the silver halides AgF, AgCl, and AgBr:
A comparative study, Photochemical and Photobiological Sciences 2(4), 2003, pp. 398–401.
[2] SLIFKIN L.M., The physics of lattice defects in silver halides, Crystal Lattice Defects and Amorphous
Materials 18, 1989, pp. 81–96.
[3] GLAUS S., CALZAFERRI G., The band sructures of the silver halides AgF, AgCl, and AgBr:
A comparative study, Photochemical and Photobiological Sciences 2(4), 2003, pp. 398–401.
[4] HAILSTONE R.K., DE KEYZER R., Latent-image formation in tabular AgBr grains: experimental studies,
The Imaging Science Journal 52(3), 2004, pp. 151–163.
[5] OVECHKO V., SCHUR O., Size spectroscopy of porous glasses and porous glasses with metal
nanoparticles using UV-VIS and X-ray radiation, Optica Applicata 35(4), 2005, pp. 735–743.
[6] MIKHAYLOV V.N., STASEL’KO D.I., Ipulse defectolyse in the emulsion nanocrystals AgBr:
Recombination processes in the early stadia of defectolyse, Optics and Spectroscopy 102, 2007,
pp. 962–966 (in Russian).

332 I.K. DOYCHO et al.
[7] MESHKOVSKY I.K., Composition of Optical Materials on Base of Porous Matrixes, SPb, 1998,
pp. 148–176 (in Russian).
[8] SUKHANOV V.I., KHAZOVA M.B., SHELEKHOV N.S., ANDREYEVA O.V., KURSAKOVA A.M.,
TSEKHOMSKA T.C., RASKOVA G.P., SOLOMATIN Y.V., Volumetric Phase Diagrams in the Light-
-Sensitive Systems Having a Capillary Structure, Optical Holography with Three-Dimensional
Recording, Nauka, L. 1989, pp. 86–105 (in Russian).
[9] SHORE J.D., Molecular Dynamics Simulation of Nucleation of AgBr from Solution, American
Institute of Chemical Engineering, 1999.
[10] RYSIAKIEWICZ-PASEK E., VOROBYOVA V.A., GEVELYUK S.A., DOYCHO I.K., MAK V.T., Effect of
potassium nitrate treatment on the adsorption properties of silica porous glasses, Journal of
Non-Crystalline Solids 345–346, 2004, pp. 260–264.
[11] RYSIAKIEWICZ-PASEK E., GEVELYUK S., DOYCHO I., VOROBJOVA V.A., Application of porous glasses
in ophthalmic prosthetic repair, Journal of Porous Materials 11(1), 2004, pp. 21–29.
[12] GEVELYUK S.A., DOYCHO I.K., MAK V.T., ZHUKOV S.A., Photoluminescence and structural
properties of nano-size CdS inclusions in porous glasses, Photoelectronics 16, 2007, pp. 75–79.
[13] JANOWSKI E., HEYER W., Porose Glasser, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig,
1982.
[14] RYSIAKIEWICZ-PASEK E., ZALEWSKA M., POLAŃSKA J., Optical properties of CdS-doped porous
glasses, Optical Materials 30(5), 2008, pp. 777–779.
[15] DOYCHO I.K., GEVELYUK S.A., KOVALENKO M.P., PROKOPOVICH L.P., RYSIAKIEWICZ-PASEK E., Small
doses γ-irradiation effect on the photoluminescence properties of porous glasses, Optica
Applicata 33(1), 2003, pp. 55–60.
[16] YEFIMOV S.P., ZAKHAROV V.I., KARTUZHANSKY O.L., MARTYSH G.G., SHUR L.I., Luminescence and
light-sensitivity of primitive AgBr photographical emulsions with absolute and partial substitution
gelatin with polinol, Journal of Scientific and Applied Photography and Cinematography 23(5),
1978, pp. 351–358 (in Russian).
[17] MALINOWSKI J., The role of holes in the photographic process, The Journal of Photographic
Science 16(2), 1968, pp. 57–62.
[18] MAKLAR P.V., Physical Processes by Forming of the Latent Photographic Image, Nauka, M. 1972,
p. 339 (in Russian).
[19] JAMES T., Theory of Photographical Process, Chemistry, L. 1980, p. 646 (in Russian).
Received November 12, 2009
in revised form April 14, 2010

Optica Applicata, Vol. XL, No. 2, 2010
Porous glasses as a substrate for sensor elements
ANATOLY EVSTRAPOV 1 , NADYA ESIKOVA 1* , GALINA RUDNITSKAYA 1 , TATYANA V. ANTROPOVA 2
1 Institute for Analytical Instrumentation, Russian Academy of Sciences,
Rizhsky Pr., 26, 198103 Saint-Petersburg, Russia
2 Grebenschikov Institute of Silicate Chemistry, Russian Academy of Science,
Nab. Makarova, 2, Saint-Petersburg, Russia
* Corresponding author: elpis-san@yandex.ru
The properties of porous glasses are determined by optical spectroscopy and high-resolution
microscopy at different stages of immunoglobulin immobilization and after immune reaction.
The influence of duration and temperature of drying between surface activation and silanization
is studied. The quantity of protein immobilized on the porous glass surface is estimated by
the Coomassie method. Various ways of surface silanization with the use of toluene and acetone
are compared. The possibility of fabricating a microsensor element based on the porous glass for
microchip is presented.
Keywords: porous glass, sensor element, laser scanning confocal microscopy, scanning near field optical
microscopy, optical spectrometry.
1. Introduction
Designing microfluidic chip (MFC) devices is one of the perspective directions in
the development of microanalytical systems. The chips make it possible to manipulate
with picoliter volumes of samples and reagents, including dosing, mixing, carrying
out chemical reactions, etc., [1, 2]. Microanalytical systems with the new properties
and high technical characteristics can be developed by means of integrating the new
elements into an MFC. These may be fabricated on the basis of porous glasses (PG)
(for example, sensors elements, micropumps, columns, reactors, etc.)
Modern technologies made it possible to produce PG with pores of nanometer sizes
(from 2 to 500 nm) and known structural characteristics [3, 4]. PG’s optical properties
allow using high-sensitivity methods for detection and registration of sample
components.
In order to design an element of a sensor on the basis of PG it is necessary to choose
optimal methods of PG surface activation, modification and sensitive substance
immobilization. This requires studying optical and structural characteristics of glasses
at different stages of preparation of the sensor element. So, characterization of glasses
at different stages by methods of high resolution microscopy and optical spectroscopy
is a topical issue.

334 A. EVSTRAPOV et al.
2. Experiment
2.1. Motivation
In order to study the features of biological substance immobilization on a PG surface,
the PG made of biphasic glass 8 V was used. It has a developed surface and high optical
transmittance in visual and infrared spectral ranges (80–93% at a wavelength of
340–850 nm for a 0.2 mm sample thickness). The average pore radius of the samples
is 85.5 nm, the specific pore surface is 88.8 m2 /g (Institute of Silicate Chemistry RAS).
These parameters are suitable for designing sensor elements with good permeability
for liquid probes. The PG size is 8×8×0.2 mm.
Fabrication of the sensor element required: activation of the hydroxyl groups on
the PG surface, with the purpose to silanize the surface, to treat it with bifunctional
reagent (glutaric dialdehyde) and to immobilize the sensitive substance (for example,
biological substances like proteins, antibodies and antigenes).
In this technology, the covalent binding of the silan on the glass substrate is chosen
because this immobilization type allows more firm protein fixation. But this method
has a disadvantage: it makes probe diffusion difficult, so the sensor response time gets
longer. Nevertheless, the PG allows using transportation of the probe to sensitive
substance due to electroosmotic flow produced by the external electric field. It gives
an opportunity to reduce the response time of the sensor.
2.2. Surface modification and sensor working principle
A reaction scheme for protein immobilization is outlined in Fig. 1. It was realized in
static regime in four stages: surface activation (I), silanization (II), treatment with
glutaric dialdehyde (III) and protein immobilization (IV) [5, 6].
For surface activation, samples were placed into 0.5 M NaOH for 0.5 hour.
Silanization was carried out in two ways: i) immersion in a 10% solution of
aminopropyltriethoxysilane (APS) in toluene at 90 °C for 2 hours; or ii) 4% solution
of APS in acetone at 24 °C for 2 hours. Then, sample surfaces were treated with
glutaraldehyde for 2 hours. Protein immobilization is based on Schiff’s base
formation between the amino groups on the protein surface and the aldehyde groups
on a chemically modified surface of PG.
The principle of the sensor element action based on the immune reaction:
IgG + (Insulin-FITC) ↔ IgG – (Insulin-FITC). Anti-insulin immunoglobulin IgG is
immobilized on PG surface. Afterwards the immune reaction with insulin-FITC
followed.
2.3. Measurement and instrumentation
During preparation of glasses the influence of drying conditions (time and temperature)
between glass surface activation and silanization on protein immobilization was
studied. At first, toluene was used for silanization, later – acetone.
At every stage of the protein immobilization and after immune reaction
the characteristics of the samples were detected by transmittance spectroscopy,

Porous glasses as a substrate for sensor elements 335
Fig. 1. Procedures for protein immobilization.
fluorescence spectroscopy, laser scanning confocal microscopy (LSCM) and scanning
near-field optical microscopy (SNOM).
The optical transmittance spectra were measured by a Hitachi U-3410
spectrophotometer (Japan) at a bandpass of 3 nm, in the spectral range 350–850 nm.
The fluorescence spectra were measured by a Hitachi F-4010 spectrofluorimeter
(Japan) at a bandpass of 5 nm, scan speed 120 nm/min, excitation wavelength of
488 nm. Images of the surfaces of the samples were made by the laser scanning
confocal microscopy TCS SL (Leica, Germany) in the mode of registration of
reflection and fluorescence at the excitation wavelength of 488 nm and the scanning
near-field optical microscopy NTEGRA Solaris (NT-MDT, Russia) in the modes of
shear force and reflections at a wavelength of 488 nm.
3. Results and discussion
The influence of drying conditions (duration and temperature) between the surface
activation (stage I) and silanization (stage II) on protein immobilization was studied.
For that purpose, samples were prepared by drying for 2 hours at 50 °C, and for 1, 2
and 3 hours at 100 °C.

336 A. EVSTRAPOV et al.
The images of the sample surfaces were made by laser scanning confocal
microscopy. For the samples dried at 100 °C it visualized relatively large particles
(with a diameter of nearly 10 mkm). After silanization (stage II) and glutaric
dialdehyde surface treatment (stage III) the transmittance of the samples alters in
a wide spectral range. A small “burnt out” site of the surface with lower fluorescence
compared to the background on all the surfaces is observed in the images. The changes
of the sample surface properties are due to laser radiation (for LSCM) at 488 nm
(energy density ~500 W/cm 2 ).
When the sample is dried at 50 °C there are no big particles observed and “burnt
site” is more degraded. Spectrophotometric measurements show that the sample dried
at 60 °C has lower transmittance (~10%) in the spectral range 550–850 nm than
for other samples; the sample dried for 5 hours has higher transmittance in the range
350–600 nm than for other samples. The above observations proved that drying regime
exerts a significant influence on protein immobilization at PG (i.e., on the volume
quantity of the immobilized protein).
Protein immobilization was performed by immersing the pretreated glass samples
in protein solution. The quantity of the immobilized protein was estimated by
spectrophotometric detection of protein in solution before and after immobilization at
PG (Coomassie method) [7]. The method was based on the dye colour change (from
red-brown to blue) corresponding to absorbance peak shift from 465 to 595 nm
after reaction with protein. These measurements show that only 0.202 mg
(~16 mkg/mm 3 ) of the protein was immobilized on the sample, when toluene was used
at the silanization stage (stage II, version a), while 0.302 mg (~24 mkg/mm 3 ) was
immobilized when acetone was used (stage II, version b).
The absorbance peak at ~525 nm was observed at the spectrum of PG treated with
glutaric dialdehyde. There is no such absorbance peak for the spectrum of the glutaric
dialdehyde solution.
From the spectral transmittance dependences for the samples after immune reaction
(Fig. 2) the fluorescence absorbance peak is observed at 495 nm. It confirms that
successful immune reaction has been performed.
The treatment with glutaric dialdehyde results in reduction of sample
transmittance. The immunoglobulin immobilization leads to additional transmittance
reduction. The transmittance of the samples considerably increases (~15% for samples
with the use of toluene for silanization (Fig. 2a) and ~45% with the use of acetone for
silanization (Fig. 2b)) after the immune reaction has been carried out. This effect may
be used for the future detection system design.
Figure 3 presents the normalized transmittance spectra of PG after the immune
reaction and treatment with Coomassie solution. The measurements demonstrate
that silanization with acetone results in immobilization of more protein compared to
silanization with toluene.
Note that no fluorescence was observed in the case of initial (native) porous glass
upon excitation at a wavelength of 488 nm.

Porous glasses as a substrate for sensor elements 337
a b
Fig. 2. Transmittance spectra of PG 8V-MAP: after silanization with toluene (a), after silanization with
acetone (b); solid line – PG, dashed line – after immunoglobulin immobilization, dotted line – after
immune reaction.
Silanization
with toluene
Silanization with acetone
Fig. 3. Normalized transmittance spectra of
PG after immune reaction and treatment with
Coomassie solution.
a b
Fig. 4. Fluorescence spectra of PG: after immunoglobulin immobilization (a), after immune reaction (b);
dashed line – silanization with the use of toluene, solid line – with the use of acetone.

338 A. EVSTRAPOV et al.
Glutaric dialdehyde solution (which was used for protein immobilization) has
a fluorescence peak at 550 nm at excitation wavelength 488 nm (Fig. 4a). This has
made it more difficult to interpret the results obtained by laser scanning confocal
microscopy because of the presence of a few fluorescence substances and not just one.
The fluorescence of insulin-FITS at 523 nm is significantly higher than
the fluorescence of glutaric dialdehyde. Using acetone for silanization leads to
the higher fluorescence peak of insulin-FITS for the samples after immune reaction
than in the case of toluene (Fig. 4b). This proves that using acetone for silanization
results in immobilization of more protein than in the case of using toluene.
Figure 5 presents images of the sample surfaces taken by scanning near-field
optical microscopy in shear force and reflection modes. For the initial glass in both
modes a near-to-smooth surface is obtained at image size 25×25 mkm. But at bigger
magnification (image size 5×5 mkm) a porous structure appears. It corresponds to BET
measurement (Institute of Silicate Chemistry RAS).
Groups of particles with average radius ~0.6 mkm are visualized by shear force
mode after insulin immobilization at the sample surface. After immune reaction there
may also be observed particles at the sample surface, but more uniform.
In the sample surface images after immune reaction (in reflection mode) one can
see not only the particles formed, but the surface structure, too. Probably, this effect
occurs because of the formation of a homogeneous surface film with structural
elements greater than the sizes of the pores in the glass.
Fig. 5. Surface images of PG 8 V by SNOM. Shear force mode: 1 – initial glass, 2 – after insulin
immobilization, 3 – after immune reaction; reflection mode: 4 – initial glass, 5 – after immune reaction.
Images size 25×25 mkm.

Porous glasses as a substrate for sensor elements 339
Fig. 6. Surface images of PG 8 V by LSCM: 1 – initial glass, 2 – after immunoglobulin immobilization
(silanization with toluene), 3 – after immunoglobulin immobilization (silanization with acetone), 4 – after
immune reaction. Image sizes 50×50 mkm.
The measurement by laser scanning confocal microscopy (Fig. 6) shows that
fluorescent substances (glutaric dialdehyde/insulin-FITC) are adsorbed not only on
the surface but diffused through the pores into the deep glass layers.
After immunoglobulin immobilization an PG surface some particles with
significant absorption at excitation wavelength of 488 nm were visualized by laser
scanning confocal microscopy. After immune reaction a homogeneous surface was
observed. Obviously, this is due to the formation of a thin enough and more optically
uniform layer of the immune complex on the surface. This is confirmed by
measurement with the use of scanning near-field optical microscopy (Fig. 5).
4. Conclusions
Porous glass is a suitable material used in designing optical sensor elements for
immune reaction detection.
Sensor element formation consists of four basic stages: surface activation,
silanization, treatment by glutaric dialdehyde and protein immobilization.
Duration and temperature of drying between activation and silanization stages have
a significant influence on immobilization.
According to spectrophotometric (Coomassie method) and fluorometric measurements
using acetone for silanization results in immobilization of more proteins on PG
in comparison with the case of using toluene.
Immune reaction leads to the formation of an optically homogeneous thin layer on
the surface of glass and to an increase of transmittance, which may be used for
the immune reaction detection.
Measurements by scanning near-field optical and laser scanning confocal
microscopy confirmed the complex formation at the sample surfaces and the optical
uniformity increase as a result of the immune reaction.
So, we can draw a conclusion about the possibility of monitoring the immune
reaction with the use of sensors based on the porous glass.
Acknowledgements – This work was supported by the RFBR Grant No. 08-08-00733-a: The processes of
creation, a structure, the colloid-chemical and optical properties of the nano-dimensional membranes

340 A. EVSTRAPOV et al.
from the high silica porous glasses and their application for creation of the microfluid analytical systems;
SPbRC RAS project: Microfluidic analytical systems with integrated nanostructures (porous glasses)
and by the Saint-Petersburg Government grant for undergraduate and postgraduate students of universities
and academic institutes located in Saint-Petersburg.
References
[1] HAEBERLE S., ZENGERLE R., Microfluidic platforms for lab-on-a-chip applications, Lab on a Chip 7(9),
2007, pp. 1094–1110.
[2] HEROLD K. E., RASOOLY A., Lab-on-a-Chip Technology (Vol. 1): Fabrication and Microfluidics,
Caister Academic Press, 2009, p. 410.
[3] KREISBERG V.A., RAKCHEEV V.P., ANTROPOVA T.V., Influence of the acid concentration on
the morphology of micropores and mesopores in porous glasses, Glass Physics and Chemistry 32(6),
2006, pp. 615–622.
[4] ANTROPOVA T.V., DROZDOVA I.A., Influence of the porous glass receiving on it’s structure, Glass
Physics and Chemistry 21(2), 1995, pp. 199–209.
[5] LI XIONG, REGNIER F.E., Channel-specific coatings on microfabricated chips, Journal of
Chromatography A 924(1–2), 2001, pp. 165–176.
[6] PIJANOWSKA D.G., REMISZEWSKA E., PEDERZOLLI C., LUNELLI L., VENDANO M., CANTERI R.,
DUDZIŃSKI K., KRUK J., TORBICZ W., Surface modification for microreactor fabrication, Sensors 6(4),
2006, pp. 370–379.
[7] REIGOSA R.M.J., Handbook of Plant Ecophysiology Techniques, Springer Netherlands,
The Netherlands, 2001, pp. 283–295.
Received November 12, 2009
in revised form February 1, 2010

Optica Applicata, Vol. XL, No. 2, 2010
Determination of electrokinetic potential
of porous glasses by methods of streaming potential,
electroosmosis and electrophoresis
ANNA VOLKOVA 1* , LUDMILA ERMAKOVA 1 , MARIA VOLKOVA 1, 2 , TATYANA V. ANTROPOVA 2
1 Saint-Petersburg State University, Chemical Faculty,
Universitetskii pr., 26, St. Petersburg, 198504, Russia
2 Institute of Silicate Chemistry, RAS, emb. Makarova, 2, St. Petersburg, 199034, Russia
* Corresponding author: vanva2002@mail.ru
Complex research of structural and electrokinetic characteristics of nano- and the ultraporous
glasses prepared from sodium borosilicate (SBG) glass DV1-Sh in KCl background solutions of
various concentrations in a wide pH range has been performed. It is shown that for ultraporous
membranes with the sizes of porous channels r in the range 10–70 nm appreciable electroosmotic
flows and a good agreement of electrokinetic potential values determined by three different
methods are observed. It is established that for nanoporous (r < 10 nm) glass membranes
change of electroosmotic flow velocity with time is due to the development of concentration
polarization.
Keywords: electrokinetic potential, electroosmotic flow.
1. Introduction
It is known that nanostructured porous glasses (PG) with controllable nanometric
range parameters of structure and adjustable adsorptive and optical properties find
a variety of applications [1–3]. In particular, suitability of PGs for their application
as functional membrane elements in microfluidic chip (MFC) systems for the biochemical
analysis [4] is revealed. Depending on the pore size and the secondary silica
contents PGs can be used as electroosmotic pumps or as sensory elements with
indicated complexes being introduced. In this connection definition of electroosmotic
flows and electrokinetic potential values depending on pore space structure of
membranes from PGs, which is defined by composition, thermal treatment of initial
alkali borosilicate (ABS) glasses and conditions of obtaining of PG [5], are actual.

342 A. VOLKOVA et al.
2. Objects and techniques
Porous high-silica glasses were prepared from industrial sodium borosilicate (SBG)
glass DV1-Sh with bithermal treatment (650 °C, 530 °C) and two-frame structure by
leaching in 3 M solution of hydrochloric acid (DV1-Sh (3 M HCl)). Afterwards,
some of the samples were treated by a 0.5 M KOH solution for 10 hours (DV1-Sh
(3 M HCl + 10-KOH)).
For the samples obtained the following electrokinetic characteristics were
determined:
– Specific membrane conductivity κ M by difference method [6]; κ M values
were used for calculating the efficiency coefficient α (α = κ Mβ/κ V , where κ V is
the specific conductivity of bulk solution, β is the structural resistance coefficient,
which characterize the contribution of the non-conducting skeleton to the membrane
conductivity).
– Counterion transport numbers n + by method of membrane potential in a flowing
cell [7].
– Electrokinetic potential ζ by methods of electroosmosis, streaming potential
and ultramicroelectrophoresis; ζ – potential values of membranes were calculated
from experimental data using Helmholtz–Smoluchowski’s equations:
ζ 0
ζ 0
=
=
ηκV ES ----------------------εε0P
ηκ V Q
-------------------εε0I
– method of streaming potential (1)
– method of electroosmosis (2)
(where E S is the streaming potential, P is the applied pressure, η is the fluid viscosity,
Q = V/t is the volume velocity of a liquid, I is the current strength) and taking into
account both electrical double layers overlapping [8], and real specific conductivity
of pore solution [9]:
ζ α *
( ηκVα ES [ Q]
) ⁄ ( εε0P[ I]
)
=
------------------------------------------------------------------------f(
krβ, ζ *
α , β * )
where β * is the parameter, including electrolyte properties, k is Debay’s parameter.
After measurements of electroosmotic flow and streaming potential some of
the membranes were washed with HCl, then watered, dried up and powdered.
The ζ-potential value was also determinated for powders by method of ultramicroelectrophoresis.
(3)

Determination of electrokinetic potential of porous glasses ... 343
The values of ζ-potential were calculated from electrophoretic data using
Smoluchowski’s equation:
ζ
S η
=
εε0 ------------- U ef
(where U ef is the electrophoretic mobility) and also taking into account conductivity
of PG particles (Henry’s equation) [10]:
η ⎛ κM ⎞
ζ = ------------- Uef ⎜1+ -------------- ⎟ =
εε0 ⎝ ⎠
2κ V
ζ S 1
⎛ α ⎞
⎜ + ----------- ⎟
⎝ 2β ⎠
For porous glasses under investigation structural parameters were also determined:
BET surface area S 0 (by thermal desorption of nitrogen with chromatographic
registration), volume porosity W, structural resistance coefficient β, liquid filtration
coefficient G. Measurements of G values were carried out in the range of pressure
0.3–0.5 atm in a 0.1 M electrolyte solution to avoid the influence of electroviscous
effect. Values of the mean pore radius were calculated by the equations
r S0
=
rβ =
2W
----------------------------------
( 1 – W )ρS0 8Gη d M β
where ρ is the glass density, d M is the membrane thickness.
Measurements of colloidal-chemical characteristics of porous glasses were carried
out in KCl background solutions with concentration of 10 –4 –10 –1 M in the pH
range 2–7. All solutions were prepared on bidistilled water with specific conductivity
~2×10 –6 Ω –1 cm –1 .
3. Experimental results and discussions
3.1. Structural parameters of porous glasses
Investigation of the porous glasses obtained began with studying their structural
characteristics in 0.1 M KCl solutions. It is worth noting that the obtained membranes
DV1-Sh (3 M HCl) and DV1-Sh (3 M HCl + 10-KOH) after a sufficiently long-term
storage in air were put to contact with a 0.1 M KCl solution at once, and PG DV1-Sh*
(3 M HCl) and DV1-Sh* (3 M HCl + 10-KOH) (parallel samples) were previously
placed for 2 days in a 0.1 M HCl solution.
(4)
(5)
(6)
(7)

344 A. VOLKOVA et al.
T a b l e 1. Structural parameters of porous glasses under investigation. R init – initial parameter values,
R fin – final parameter values (parameter values at the end of experiment).
Membrane W init W fin β init β fin
DV1-Sh*
(3 M HCl)
DV1-Sh
(3 M HCl + 10-KOH)
DV1-Sh*
(3 M HCl + 10-KOH)
0.25 0.31 7.27 6.03
0.24 * 0.29 * 8.20 * 6.89 *
It can be seen from the data of Tab. 1 that for PGs, leached in HCl, the porosity
value increases and β value decreases during the contact of the membranes with
electrolyte solutions, owing to dissolution and removal of secondary silica from pore
space.
The additional alkaline treatment of PGs for 10 hours leads to an increase in
the size of pore channels and also to a volume porosity growth, which causes a decrease
in the specific surface area and in the structural resistance coefficients.
Note that the structural parameters of ultraporous membranes remain practically
constant during experimental time.
3.2. Specific conductivity of porous glasses
G init ×10 12
[cm 2 s/g]
r β init
[nm]
G fin ×10 12
[cm 2 s/g]
– – 7.71 *
r β fin
[nm]
S 0 fin
[m 2 /g]
r S0 fin
[nm]
The measurements of efficiency coefficients show (Fig. 1a) that for all the porous
glasses investigated α values decrease with increasing KCl solution concentration in
accordance with decreasing contribution of the EDL ions into specific conductivity
of pore solution. A comparison of values α at C =const (C < 0.1 M) shows that
efficiency coefficients increase with the mean pore radius diminishing (in accordance
with the theoretical conceptions), therefore the additional alkaline treatment of PGs
results in essential (especially in the diluted solutions) α values decreasing.
It is necessary to pay attention to that fact that for membranes DV1-Sh (3 M HCl)
and DV1-Sh (3 M HCl + 10-KOH) (not exposed before measurements to 0.1 M HCl
treatment) a decrease of efficiency coefficient values after electroosmotic
measurements (Fig. 1a, curves 1, 2 and 4, 5) is observed, whereas for PG DV1-Sh*
(3 M HCl) and DV1-Sh* (3 M HCl + 10-KOH) no appreciable change of α values has
occurred. It should be noticed that α–logC dependence for PG DV1-Sh (3 M HCl +
10-KOH) coincides with that for membrane DV1-Sh* (3 M HCl + 10-KOH) (Fig. 1a,
curve 5) and earlier obtained data for PG DV1-Sh (3 M HCl + 3.5-KOH) [11].
The analysis of changes of α values for membrane DV1-Sh (3 M HCl) shows that
both before and after electroosmotic measurements α values (at C = const) are greater
than that for the parallel sample. We should notice that initial α values for glass
DV1-Sh (3 M HCl) (Fig. 1a, curve 1) are incredibly high. Such electrokinetic behavior
of nanoporous membranes is apparently connected with changes in the internal
9.2 *
37 11
– 0.44 3.53 3.47 909 71.6 935 71.6 10 70.9
0.42 0.42 4.06 3.64 638 61.4 669 61.7 – –

Determination of electrokinetic potential of porous glasses ... 345
structure of liquate channels, and first of all with the changing of globule packing of
secondary silica. And this difference is most likely connected with the fact that in HCl
solution secondary silica swells and is structured practically at a zero charge of
a surface, and in a salt solution at considerable negative surface charge. Let us notice
that the difference between measured parameters of membranes DV1-Sh (3 M HCl)
and DV1-Sh* (3 M HCl) during contact with KCl solutions considerably decreases,
but does not disappear.
3.3. Counterion transport numbers in membranes
a
Fig. 1. Transport characteristics of the membranes investigated: efficiency coefficient (a) and counterion
transport numbers (b) vs. concentration of KCl solutions.
The results of counterion (K + ) transport numbers measurement show (Fig. 1b) that
an increase in salt level and in pore size leads to a monotonic decrease in the n + values.
These tendencies are in accordance with decreasing contribution of the EDL ions to
the membrane transport. In the most diluted solution membranes, leached in HCl
solution, possess practically ideal selectivity (n + = 0.94–0.98).
Let us notice that for PG DV1-Sh (3 M HCl) n + value after electroosmotic
measurements decreases (at C

346 A. VOLKOVA et al.
3.4. Electrokinetic potential
3.4.1. Method of streaming potential
The analysis of ζ *
α concentration dependences for membranes DV1-Sh (3 M HCl)
and DV1-Sh (3 M HCl + 10-KOH) (Fig. 2a) has shown that the absolute values
of electrokinetic potentials were greater before than after electroosmotic measurements.
It should be noticed that the angular coefficient of dependences ζ *
α –logC
differs, too.
a b
Fig. 2. Electrokinetic potential ζ *
α of the membranes investigated vs. concentration of KCl solutions.
It is seen (Fig. 2b) that for membrane DV1-Sh (3 M HCl + 10-KOH) after treatment
of 0.1 M HCl, | ζ *
α | values coincide with those for membranes DV1-Sh* (3 M HCl +
10-KOH) and DV1-Sh (3 M HCl + 3.5-KOH) [11] (line 1 and points 2). For PG
DV1-Sh (3 M HCl) (after electroosmotic measurements) | ζ *
α | values remain
higher than for membranes DV1-Sh* (3 M HCl) and DV1-Sh (3 M HCl) [11]
(curves 3 and 4), whereas values of electrokinetic potentials for those PGs are similar.
It is worthwhile to notice that the laws obtained in the case of electrokinetic
potential, completely agree with the results of measurement of specific conductivity
of the membranes investigated (see Section 3.2). From Fig. 2 it is also seen that for
the membranes investigated absolute ζ-potential values increase with pore sizes, which
can be connected with a decrease of an ion-permeable layer thickness on the surface
of pore channels.
3.4.2. Method of ultramicroelectrophoresis
The dependences of electrophoretic mobility of particles of PGs being investigated on
pH on the background of 10 –2 M and 10 –3 M KCl are presented in Fig. 3a. A growth
of particle mobility with an increase in the mean pore radius and with a decrease
in concentration of background electrolyte is observed. The analysis of U ef –pH

Determination of electrokinetic potential of porous glasses ... 347
a b
Fig. 3. Electrophoretic mobility (a) and electrokinetic potential (b) of PG particles vs. pH on
the background of KCl solutions.
dependences allows us to conclude that the isoelectric point (IET) lies close to
pH IET = 0.5 that is similar to IET position in HCl solutions [9].
The comparison of ζ-potential values, calculated taking into account own
conductivity of particles, has shown (Fig. 3b) that values of electrokinetic potentials
on the background of 10 –3 M KCl are similar. On the background of 10 –2 M KCl usual
ratio of ζ values is observed – the transition from nanoporous to ultraporous glasses
leads to an increase in |ζ | value. However, it should be noticed that this difference
does not exceed 5 mV in neutral pH range.
3.4.3. Method of electroosmosis – Comparison of the results
obtained with the data of other methods
The determination of ζ values by a method of electroosmosis on nanoporous
glasses was very difficult because of the electroosmotic flow velocity changing with
time. This was due to the presence of secondary silica in the PG pore space, and
was also connected with the concentration polarization increasing with time, owing to
the essential difference in counterion transport numbers between bulk and pore
solutions.
The results of electroosmotic flow measurements and calculated electrokinetic
potentials for the ultraporous membranes are presented in Fig. 4 and Tab. 2. It is seen
that for ultraporous glasses the ζ values measured by the three methods are in a good
agreement. Note that in the diluted solution for glasses with pore radius close to 10 nm
is not enough to take into account only own conductivity of particles (method of

348 A. VOLKOVA et al.
Fig. 4. Electrokinetic potential ζ i determined by various methods vs. concentration of KCl solutions.
T a b l e 2. Results of volume velocity measurements and calculations of electrokinetic potential values.
C [M] κV [Ω –1 cm –1 ] α I [mA] V/It [cm3 /As] –ζ 0 [mV] – [mV]
V1-Sh* (3 M HCl + 10-KOH)
0.98×10-2 1.246×10-3 1.10 8.8 0.151 27.0 32.7
1.15×10 -3 1.518×10-4 1.84 1.2 0.965 20.0 52.1
1.29×10 -3
1.705×10 -4
1.85 1.25 0.772 18.4 47.9
DV1-Sh (3 M HCl + 10-KOH)
1.05×10-1 1.760×10-2 1.00 30 0.017 27.7 28.5
1.08×10 -2 1.326×10-3 1.00 10.4 0.247 45.9 49.8
1.54×10-3 1.635×10-4 2.55 1.25 0.899 20.6 65.5
1.55×10 -4 2.075×10-5 ζ *
α
7.11 0.2 2.042 5.91 81.9
ultramicroelectrophoresis) for calculation of correct ζ-potential values, but it is also
required that polarization phenomena in a electric double layer should be considered.
4. Conclusions
It is established that for ultraporous membranes with the pore sizes ranging from
10 to 70 nm appreciable electroosmotic flows are observed. The constancy of
structural parameters and velocity of electroosmosis in time for those membranes
testifies to the possibility of using them for creation of electroosmotic pumps.
It is shown that for ultraporous membranes, a good agreement of the electrokinetic
potentials found by means of three independent methods is observed. This enables us
to calculate the electroosmotic flow values from the electrokinetic potential values
determined by the method of streaming potential, which is one of the most exact
methods of experimental definition of the ζ-potential value since application of

Determination of electrokinetic potential of porous glasses ... 349
the external electromoving force calling by-effects (heating, polarization) is not
required. For nanoporous glass membranes a change of electroosmotic flow velocity
with time owing to the development of concentration polarizations is observed.
Acknowledgments – This work was supported by the grant of RFBR No. 08-08-00733, SPbSC RAS
(Section 2 Scientific Program 2009) and Russian President Program Leading Scientific Schools, project
No. SSh-3020.2008.3.
References
[1] ENKE D., JANOWSKI F., SCHWIEGER W., Porous glasses in the 21st century – a short review,
Microporous and Mesoporous Materials 60(1–3), 2003, pp. 19–30.
[2] KHANDURINA J., JACOBSON S.C., WATERS L.C., FOOTE R.S., RAMSEY J.M., Microfabricated porous
membrane structure for sample concentration and electrophoretic analysis, Analytical
Chemistry 71(9), 1999, pp. 1815–1819.
[3] SHUHUAI YAO, SANTIAGO J.G., Porous glass electroosmotic pumps: theory, Journal of Colloid and
Interface Science 268(1), 2003, pp. 133–142.
[4] EVSTRAPOV A.A., ESIKOVA N.A., RUDNITSKAJA G.E., ANTROPOVA T.V., Application of porous glasses
in microfluidic devices, Optica Applicata 38(1), 2008, pp. 31–38.
[5] ANTROPOVA T., Abstract of a doctoral thesis, St. Petersburg, 2005, p. 45.
[6] MEDVEDEVA S., Abstract of a Ph.D. thesis, St. Petersburg, 2004, p. 16.
[7] BOGDANOVA N., SEMENOVA O., ERMAKOVA L., SIDOROVA M., Electrokinetic characteristics of
ultraporous membrane in NaCl solutions, Vestnik SPbSU 3(4), 2006, pp. 89–94.
[8] LEVINE S., MARRIOTT J.R., NEALE G., EPSTEIN N., Theory of electrokinetic flow in fine cylindrical
capillaries at high zeta-potentials, Journal of Colloid and Interface Science 52(1), 1975,
pp. 136–149.
[9] ERMAKOVA L., Abstract of a doctoral thesis, St. Petersburg, 2002, p. 33.
[10] DUKHIN S., Non-equilibrium electric surface phenomena, Advances in Colloid and Interface
Science 44, 1993, pp. 1–134.
[11] ERMAKOVA L., VOLKOVA A., ANTROPOVA T., SIDOROVA M., Preparation of nano- and ultraporous
glasses and study of their structural and electrokinetic characteristics in 1:1 electrolyte solutions,
Colloid Journal 69(5), 2007, pp. 563–570.
Received November 12, 2009

Optica Applicata, Vol. XL, No. 2, 2010
Influence of PbX 2 (X = F, Cl, Br) content
and thermal treatment on structure
and optical properties of lead borate glasses
doped with rare earth ions
JOANNA PISARSKA 1 , RADOSŁAW LISIECKI 2 , GRAŻYNA DOMINIAK-DZIK 2 ,
WITOLD RYBA-ROMANOWSKI 2 , TOMASZ GORYCZKA 3 ,
ŁUKASZ GROBELNY 1 , WOJCIECH A. PISARSKI 1*
1 University of Silesia, Institute of Chemistry, Szkolna 9, 40-007 Katowice, Poland
2 Institute of Low Temperature and Structure Research, Polish Academy of Sciences,
Okólna 2, 50-422 Wrocław, Poland
3 University of Silesia, Institute of Materials Science, Bankowa 12, 40-007 Katowice, Poland
*Corresponding author: Wojciech.Pisarski@us.edu.pl
Oxyhalide lead borate glasses doped with rare earth ions have been studied before and after thermal
treatment. The rare earths as optically active ions were limited to the Er 3+ ions. Near-infrared
luminescence due to the main 4 I 13/2– 4 I 15/2 laser transition of Er 3+ was registered. The introduction
of PbX 2 to the borate glass results in a reduction of spectral linewidth and an increase of
luminescence lifetime of 4 I13/2 state of Er 3+ ions. The unusual large spectral linewidth for
4 I13/2– 4 I 15/2 transition of Er 3+ in the oxide glass host was obtained, whereas the luminescence
decay from 4 I 13/2 state is longer for a sample with PbF 2 than PbCl 2 and PbBr 2 . Heat treatment
introduces transformation from a glass to transparent glass-ceramic (TGC). The coordination
sphere around Er 3+ ions is changed, giving important contribution to the luminescence
characteristics. The spectroscopic consequence of this transformation is the increase of
luminescence lifetime and the narrowing of spectral lines of Er 3+ .
Keywords: lead borate glasses, rare earth ions, thermal treatment, luminescence, up-conversion.
1. Introduction
B 2 O 3 is one of the most important forming oxides from the point view of physics and
chemistry of glasses. It was incorporated into the various kinds of glass systems.
Glasses containing B 2 O 3 usually exhibit very good broadband properties, but their
luminescence characteristics are rather not satisfied in comparison to low-phonon
heavy metal oxide and fluoride based glasses. Incorporation of PbO and/or PbF 2 to
the conventional borate glasses leads to an increase of radiative parameters for Ln 3+

352 J. PISARSKA et al.
ions. From this point of view, Ln-doped borate glasses with relatively high PbO/PbF 2
and low B 2 O 3 concentration are of particular interest for optical investigation. They
belong to glass systems, which are promising luminescent materials in relation to
practical applications as solid-state laser active media, near-infrared tunable lasers,
NIR-to-visible up-converters and broadband optical amplifiers.
Several oxide and oxyfluoride lead borate glasses were prepared and extensively
studied by GRESSLER and SHELBY [1, 2] and TAWANSI et al. [3, 4] twenty years ago.
The Ln-doped mixed oxyhalide glasses with B 2 O 3 and PbX 2 (where X = Cl, Br) have
yet not been examined, to the best of our knowledge. From the literature data it can be
gathered that oxyhalide systems such as the undoped alkali haloborate B 2 O 3 –BaF 2 –
–LiX glasses [5] or erbium-doped heavy metal lead halotellurite PbX 2 –TeO 2
glasses [6], where X denotes F, Cl or Br, were successfully prepared and present
interesting optical properties.
The present paper is divided into two parts. The first part contains results for
erbium-doped borate glasses with PbX 2 content (X = F, Cl, Br). The luminescence
spectra at 1.5 μm due to the main 4 I 13/2 – 4 I 15/2 laser transition of Er 3+ ions and
luminescence decay curves from the 4 I 13/2 state have been examined.
The second part is concerned with erbium-doped transparent glass-ceramics.
Thermal treatment introduces transformation from a glass to transparent glass-ceramic
(TGC). The coordination sphere around Er 3+ ions is changed, giving important
contribution to the luminescence characteristics. The spectroscopic consequence of
this transformation is the increase of luminescence lifetime and the narrowing
of spectral lines of Er 3+ . These aspects are presented and discussed in relation to
the previously published results [7].
2. Experiment
Multicomponent mixed oxyhalide glasses with the following composition given
in wt%: 9PbX 2 –63PbO–18B 2 O 3 –6Al 2 O 3 –3WO 3 –1Er 2 O 3 (X = F, Cl, Br) were
prepared by mixing and melting appropriate amounts of metal oxides and lead halide
of high purity (99.99%, Aldrich Chemical Co.). A homogeneous mixture was heated
in a protective atmosphere of dried argon. Mixed reagents were melted at 900 °C.
Then, they were quenched and annealed below T g in order to eliminate internal
mechanical stresses. NIR luminescence spectra were measured with a Continuum
Model Surelite I optical parametric oscillator pumped by a third harmonic of
a Nd:YAG laser. Luminescence was dispersed by a 1-meter double grating
monochromator and detected with a photomultiplier with S-20 spectral response.
Up-conversion luminescence spectra were recorded under excitation by diode laser at
980 nm. Both luminescence and up-conversion spectra were recorded using a Stanford
SRS 250 boxcar integrator controlled by a computer. Luminescence decay curves
were recorded and stored by a Tektronix TDS 3052 oscilloscope. All measurements
were carried out at room temperature. The spectral resolution was equal to 0.1 nm.
Luminescence decay curves were detected with accuracy of ±1 μs.

Influence of PbX 2 (X = F, Cl, Br) content and thermal treatment ... 353
3. Results and discussion
It is interesting to see that glass modification strongly influenced the surroundings
of Ln 3+ ions, bringing about an important contribution to their luminescence
characteristics. Substitution of PbO by PbX 2 (X denotes F, Cl or Br) and/or thermal
treatment of precursor glasses results in the structural changes of the local environment
of Ln 3+ ions. These phenomena are correlated with the optical changes.
3.1. Influence of PbX 2 content (X = F, Cl, Br)
Our preliminary investigations indicate that erbium-doped oxide and oxyhalide lead
borate glasses are promising materials for NIR solid-state laser and broadband
optical amplifiers [8]. An introduction of lead halide PbX 2 (where X = F, Cl or Br) to
the borate glass changes coordination sphere around Er 3+ . The anion electronegativities
(Br – 2.8, Cl – 3.0, F – 4.0) and ionic-type bond character increase in Br → Cl → F
direction, which results in reduction of spectral linewidth and the increase of
luminescence lifetime for Ln 3+ ions. Figure 1 presents NIR luminescence spectra at
1.5 μm due to the main 4 I 13/2 – 4 I 15/2 laser transition of Er 3+ ions in oxide and oxyhalide
lead borate glasses. Figure 2 shows luminescence decay curves from the 4 I 13/2 state of
Er 3+ ions. Spectroscopic parameters for Er 3+ ions strongly depend on PbX 2 content.
The unusual large spectral linewidth (Δλ = 100.5 nm) for the 4 I 13/2 – 4 I 15/2 transition of
Er 3+ in the glass sample without PbX 2 is useful for potential broadband optical
applications. The linewidths for glass samples with PbX 2 are close to 52.5 nm (X = F),
60 nm (X = Cl) and 80 nm (X = Br). Their values are reduced in Br → Cl → F
direction. They are considerably smaller than that obtained for glass sample without
�
Fig. 1. NIR luminescence spectra for Er 3+ ions in lead borate glasses without and with PbX 2 (X = F,
Cl, Br).
Fig. 2. Luminescence decay curves for Er 3+ ions in lead borate glasses without and with PbX 2 (X = F,
Cl, Br).

354 J. PISARSKA et al.
�
Fig. 3. NIR luminescence spectra for Er 3+ ions in lead borate glasses without and with PbF 2 .
Fig. 4. Luminescence decay curves for Er 3+ ions in lead borate glasses without and with PbF 2 .
PbX 2 . This indicates that part of X ions (X = F, Cl or Br) is successfully bridged
with Er 3+ .
On the other hand, the luminescence decay analysis indicates that the 4 I 13/2 lifetime
of Er 3+ ions increases in the glass samples where PbO was partially replaced by PbX 2 .
The relatively long lifetime of the upper 4 I 13/2 state of Er 3+ is demanded for solid-state
laser active media and optical amplifiers (EDFA). The 4 I 13/2 lifetimes for glass
samples with PbX 2 are close to 610 μs (X = F), 500 μs (X = Cl) and 555 μs (X = Br).
The luminescence decays are longer in comparison with the one obtained for the oxide
sample (τ m =400μs). The highest value of τ m was obtained for sample with PbF2. This
is in good agreement with the results of lead halotellurite glasses doped with Er 3+ [6].
Further substitution of PbO by PbF 2 in borate glass enhanced significantly
luminescence intensities (Fig. 3) and lifetimes (Fig. 4) of Er 3+ . The total replacement
of PbO by PbF 2 results in a two-fold increase of the 4 I 13/2 lifetime of Er 3+ ions from
400 μs to 820 μs, which is advantageous from the optical point of view [9].
3.2. Influence of thermal treatment
The influence of thermal treatment on the optical properties of Er 3+ ions in oxyfluoride
lead borate glass was analyzed in detail [10]. During temperature-controlled
crystallization, crystalline domains embedded in the glass matrix are formed. These
new advanced materials with their general properties between crystals and glasses [11]
are known in the literature as transparent glass-ceramics (TGC). Transformation from
glasses to glass-ceramics causes changes in spectroscopic properties of Ln 3+ . Spectral
lines are more intense and narrowed. Luminescence decays from excited states of Ln 3+
ions in glass-ceramics are relatively longer in comparison to precursor glasses. This
behavior can be explained by changes in the environment around Ln 3+ ions.

Influence of PbX 2 (X = F, Cl, Br) content and thermal treatment ... 355
Fig. 5. Thermal treatment of precursor glasses.
The structural changes for borate glasses with PbX 2 (X = F or Cl) induced by
thermal treatment and evidenced using X-ray diffraction are well illustrated in Fig. 5.
It is interesting to see that the Ln 3+ -doped oxide lead borate glasses in the PbO–B 2 O3–
–Al 2 O 3 –WO 3 system, referred to as PBAW, are fully amorphous, except for Er 3+ .
Lead borate glasses singly doped with Er 3+ or doubly doped with Er 3+ and Yb 3+ are
semi-crystalline systems with the presence of ErBO 3 phase. The fully amorphous lead
borate glasses doped with Er 3+ are possible to obtain in the case of replacement PbO
by PbX 2 (X = F, Cl). Thermal treatment introduces the transformation from glass to
glass-ceramic material. The X-ray diffraction analysis indicates that the orthorhombic
PbF 2 crystals are formed during controlled crystallization of precursor lead borate
glass (Fig. 5, part a), in contrast to the other oxyfluoride systems (Fig. 5, part b)
containing cubic β-PbF 2 phase [12, 13]. Quite a different situation is observed for
glasses with PbCl 2 after annealing. The preliminary results suggest larger tendency to
crystallize lead tungstate than lead chloride in the lead borate glasses, which are
promising in the formation of PbXO 4 (X = W, Mo) crystalline phases such as PbMoO 4
crystals in the B 2 O 3 –PbO–MoO 2 system [14].
Near-infrared luminescence and up-conversion spectra for Er 3+ ions in glasses with
PbX 2 (X = F, Cl) before and after annealing were examined. Figure 6 presents NIR
luminescence spectra at 1.5 μm measured for oxyfluoride and oxychloride glasses and
glass-ceramics, which correspond to the main 4 I 13/2 – 4 I 15/2 laser transition of Er 3+ .
The luminescence bands are more intense and narrowed for glass-ceramics than
precursor glasses, which suggests that local structure around optically active ions was

356 J. PISARSKA et al.
Fig. 6. NIR luminescence spectra for Er 3+
ions in oxyhalide lead borate glasses before
and after thermal treatment.
Fig. 7. Green up-conversion spectra for Er 3+ ions
in oxyfluoride lead borate glasses before and after
thermal treatment.
changed and part of Er 3+ ions are incorporated into crystalline phase. The luminescence
decay analysis for oxyfluoride samples indicates that the 4 I 13/2 lifetime of Er 3+ ions
is slightly changed from 610 μs (glass) to 670 μs (glass-ceramic). This suggests
that small amount of Er 3+ ions is incorporated into the orthorhombic PbF2 crystals.
The similar phenomena were observed for Er 3+ ions in borate glass with PbCl 2 before
and after annealing.
The green up-conversion luminescence of Er 3+ ions in oxyfluoride lead borate
glasses and transparent glass-ceramics was registered under excitation with laser diode
at 980 nm (Fig. 7). There were no up-conversion spectra observed for samples with
PbCl2. The luminescence band at about 545 nm corresponds to 4 S 3/2 – 4 I 15/2 transition
of Er 3+ ions. In comparison with the precursor glass the luminescence intensity
is considerably higher, whereas the luminescence linewidth slightly decreases in

Influence of PbX 2 (X = F, Cl, Br) content and thermal treatment ... 357
the oxyfluoride TGC systems under study. This indicates that part of the trivalent
erbium is incorporated into PbF 2 crystalline phase.
Two dominant 2-photon mechanisms are involved in the up-conversion process [15],
namely the excited state absorption (ESA) and energy transfer up-conversion (ETU).
The 4 I 11/2 level is directly excited by 980 nm line. In the ESA process, the Er 3+ ions
( 4 I 11/2 state) absorb photons and then are excited to 4 F 7/2 state. In the ETU process,
two excited Er 3+ ions ( 4 I 11/2 state) interact with each other. One of them is de-excited
to 4 I 15/2 ground state, whereas the other is promoted to 4 F 7/2 state. Both ESA and ETU
processes populate the 4 F 7/2 state, which transfers energy nonradiatively very fast to
4 S3/2 state of Er 3+ . Finally, the green up-conversion luminescence due to 4 S 3/2 – 4 I 15/2
transition of Er 3+ ions has been observed.
In our case, the conversion of near-infrared radiation into visible (green) light is
observed only in the high limit of laser power. The relatively high power of excitation
source was used to register the luminescence spectrum, due to low efficiency of
up-conversion process. In the low power limit of diode laser, the up-conversion process
was not observed for Er-doped lead borate glasses, in contrast to glass samples doubly
doped with Yb 3+ and Er 3+ ions [16, 17].
4. Conclusions
An introduction of PbX 2 (X = F, Cl or Br) to the borate glass changes coordination
sphere around Er 3+ ions. It results in the reduction of spectral linewidth for
the 4 I 13/2 – 4 I 15/2 transition in Br → Cl → F direction and the increase of luminescence
lifetime for the 4 I 13/2 state of Er 3+ . The 4 I 13/2 lifetime is longer for glass sample with
PbF 2 than PbCl 2 and PbBr 2 , which suggests that the F ions might have a special effect
on luminescence lifetime among the halides.
Thermal treatment introduces transformation from glasses to transparent glass-
-ceramics. The spectroscopic consequence of this transformation is the narrowing of
spectral lines and the elongation of luminescence lifetimes of Er 3+ .
Acknowledgment – The Ministry of Science and Higher Education supported this work under the research
project N N507 3617 33.
References
[1] GRESSLER C.A., SHELBY J.E., Lead fluoroborate glasses, Journal of Applied Physics 64(9), 1988,
pp. 4450–4453.
[2] GRESSLER C.A., SHELBY J.E., Properties and structure of PbO-PbF 2-B 2O 3 glasses, Journal of Applied
Physics 66(3), 1989, pp. 1127–1131.
[3] TAWANSI A., GOHAR I.A., HOLLAND D., EL-SHISHTAWI N.A., Some physical properties of lead borate
glasses. I. Influences of heat treatment and PbO content, Journal of Physics D: Applied Physics 21(4),
1988, pp. 607–613.
[4] TAWANSI A., AHMED E., EL-SHISHTAWI N.A., Some physical properties of lead borate glasses.
II. A compensation model for the transition region, Journal of Physics D: Applied Physics 21(4),
1988, pp. 614–617.

358 J. PISARSKA et al.
[5] HAGER I.Z., Optical properties of lithium barium haloborate glasses, Journal of Physics and
Chemistry of Solids 70(1), 2009, pp. 210–217.
[6] YONG DING, SHIBIN JIANG, BOR-CHYUAN HWANG, TAO LUO, NASSER PEYGHAMBARIAN, YUSUKE HIMEI,
TOMOKO ITO, YOSHINARI MIURA, Spectral properties of erbium-doped lead halotellurite glasses for
1.5 μm broadband amplification, Optical Materials 15(2), 2000, pp. 123–130.
[7] PISARSKA J., RYBA-ROMANOWSKI W., DOMINIAK-DZIK G., GORYCZKA T., PISARSKI W.A., Near-
-infrared luminescence of rare earth ions in oxyfluoride lead borate glasses and transparent
glass-ceramic materials, Optica Applicata 38(1), 2008, pp. 211–216.
[8] PISARSKI W.A., PISARSKA J., LISIECKI R., GROBELNY Ł., DOMINIAK-DZIK G., RYBA-ROMANOWSKI W.,
Erbium-doped oxide and oxyhalide lead borate glasses for near-infrared broadband optical
amplifiers, Chemical Physics Letters 472(4–6), 2009, pp. 217–219.
[9] PISARSKI W.A., DOMINIAK-DZIK G., RYBA-ROMANOWSKI W., PISARSKA J., Role of PbO substitution
by PbF 2 on structural behavior and luminescence of rare earth-doped lead borate glass, Journal of
Alloys and Compounds 451(1–2), 2008, pp. 220–222.
[10] PISARSKI W.A., GORYCZKA T., PISARSKA J., DOMINIAK-DZIK G., RYBA-ROMANOWSKI W., Effect of heat
treatment on Er 3+ containing multicomponent oxyfluoride lead borate glass system, Journal of
Non-Crystalline Solids 354(2–9), 2008, pp. 492–496.
[11] MORTIER M., Between glass and crystal: glass-ceramics, a new way for optical materials,
Philosophical Magazine B 82(6), 2002, pp. 745–753.
[12] RYBA-ROMANOWSKI W., DOMINIAK-DZIK G., SOLARZ P., KLIMESZ B., ŻELECHOWER M., Effect of
thermal treatment on luminescence and VUV-to-visible conversion in oxyfluoride glass singly doped
with praseodymium and thulium, Journal of Non-Crystalline Solids 345–346, 2004, pp. 391–395.
[13] KLIMESZ B., DOMINIAK-DZIK G., SOLARZ P., ŻELECHOWER M., RYBA-ROMANOWSKI W., Pr 3+ and Tm 3+
containing transparent glass ceramics in the GeO 2–PbO–PbF 2–LnF 3 system, Journal of Alloys
and Compounds 382(1–2), 2004, pp. 292–299.
[14] KASHCHIEVA E.P., IVANOVA V.D., JIVOV B.T., DIMITRIEV Y.B., Nanostructured borate glass ceramics
containing PbMoO 4, Physics and Chemistry of Glasses 41(6), 2000, pp. 355–357.
[15] AUZEL F., Upconversion and anti-Stokes processes with f and d ions in solids, Chemical
Reviews 104(1), 2004, pp. 139–174.
[16] ZHENGANG SHANG, GUOZHONG REN, QIBIN YANG, CHANGFU XU, YUNXIN LIU, YONG ZHANG, QUN WU,
Spectroscopic properties of Er 3+ -doped and Er 3+ /Yb 3+ -codoped PbF 2 –MOx (M = Te, Ge, B)
oxyfluoride glasses, Journal of Alloys and Compounds 460(1–2), 2008, pp. 539–543.
[17] PISARSKA J., RYBA-ROMANOWSKI W., DOMINIAK-DZIK G., GORYCZKA T., PISARSKI W.A., Energy
transfer from Yb to X (X = Tm, Er) in lead borate glasses, Optica Applicata 35(4), 2005, pp. 837–842.
Received November 12, 2009
in revised form March 23, 2010

Optica Applicata, Vol. XL, No. 2, 2010
The effect of WO 4 2– group in xerogels
doped with Ln 2–x Pr x (WO 4 ) 3 where Ln = La, Gd
BEATA GROBELNA 1* , PIOTR BOJARSKI 2
1 Faculty of Chemistry, University of Gdańsk, Sobieskiego 18/19, 80-952 Gdańsk, Poland
2 Institute of Experimental Physics, University of Gdańsk, Wita Stwosza 57, 80-952 Gdańsk, Poland
* Corresponding author: beata@chem.univ.gda.pl
We present a synthesis of highly efficient xerogels doped with Ln 2–xPrx (WO4 ) 3 , where Ln = La
or Gd as novel phosphors. For comparison, the synthesis of xerogels doped only with Pr(III) and
La(III) ions was made. The photoluminescence properties of Pr(III) ions in xerogels were studied
by means of luminescence spectroscopy. In particular, an efficient energy transfer from to
Pr(III) ions was observed and demonstrated by their enhanced luminescence intensity. Especially
interesting seems to be strong red acceptor emission observed upon excitation at 240 nm (donor
excitation). Therefore, 4f–4f emission makes the system usable for red phosphor applications.
Additionally, the emission intensity of the materials was improved by reducing concentration of
such quenchers as water molecules and OH groups by the thermal treatment.
Keywords: photoluminescence, praseodymium(III) ions, sol–gel method, energy transfer process.
1. Introduction
2–
WO4 Rare earth doped xerogels are being studied for use as lasers, materials for amplifier
devices, phosphors for color television, fluorescent tubes and medical imaging [1]. In
the luminescent materials field, phosphors based on lanthanide ions play an important
role because of the sharp absorption and emissions lines. Nowadays, the three emission
colors: blue, green and red are usually obtained with rare earth ions. Among red
phosphors, materials with Eu(III) and Sm(III) ions are the most extensively studied of
the various luminescent materials [2, 3].
On the other hand, it is known that trivalent praseodymium ion exhibits very
interesting luminescence as an activator ion. The energy levels of Pr(III) ion contain
several metastable multiplets 3 P0, 1, 2; 1 D 2 and 1 G 4 that offer the possibility of efficient
emissions, such as red ( 1 D 2 → 3 H 4 ), green ( 3 P 0 → 3 H 4 ), and blue ( 1 S 0 → 3 H 4 ) in
the spectral region [4, 5]. Additionally, the emission of Pr(III) ions depends on
the kind of host matrix. Oxides with perovskite structure such as CaTiO 3 :Pr 3+ or

360 B. GROBELNA, P. BOJARSKI
SrTiO3 :Pr3+ exhibit usually red emission with maximum placed at about 613 nm [6].
However, to the best of our knowledge, there are no samples doped with Pr(III) ions
that have been emitted at 647 nm. Therefore, we focused our attention on the synthesis
and luminescence properties of materials consisting of Gd(III) or La(III) tungstate in
the presence of Pr3+ ions incorporated into silica xerogels. Pr(III) ions for applications
in solid-state lasers and electroluminescent devices have to be assembled in transparent
composite materials [7]. These xerogels have a wide transmission region, good thermal
stability and high nonlinear refractive index. During the last years numerous xerogel
matrices were obtained by the sol–gel process [8, 9].
The sol–gel process for production of inorganic or hybrid organic-inorganic
amorphous materials occurs at ambient temperature and is an excellent method
for obtaining phosphors for luminescent materials [10]. Moreover, this method has
the advantage of providing negligible diffusion loss, high quality and purity.
In this study, xerogels doped with Ln2–xPrx (WO4 ) 3 showed three major red
emission peaks from 605 to 648 nm. Among them the most intense is the peak placed
at about 648 nm. In order to enhance the Pr(III) emission the energy transfer process
can be achieved by using xerogels doped with Ln2–xPrx (WO4 ) 3 . For comparison
2–
purposes the photoluminescence properties of xerogels without WO4 groups were
studied.
2. Experiment
2.1. Sample preparation
The starting compounds used in these studies were of at least analytical grade. Sodium
tungstate was purchased from POCh (Poland); lanthanide(III) nitrates:
Pr(NO3 ) 3 ·5H2O, Gd(NO3 ) 3 ·6H2O and La(NO3 )·6H2O from Aldrich Co.; disodium
ethylenediamine-tetraacetate, EDTA from POCh (Poland); polyethylene glycol 400,
PEG and tetramethoxysilane Si(OCH3 ) 4 , TMOS from Aldrich Co.
Sodium tungstate was dissolved in warm water (60 °C). The aqueous solutions of
lanthanide(III) nitrates were mixed together. The doping concentration x of the Pr(III)
ions was 0.002–2 molar ratio of praseodymium in the Ln2 (WO4 ) 3 (where Ln = Gd,
La) host. Then, the solutions of lanthanide(III) nitrates and sodium tungstate in
appropriate amounts were mixed. After a while, insoluble white precipitate of
Ln2–xPrx (WO4 ) 3 was obtained. Next, EDTA was added to this mixture to form a stable
2–
complex with Ln(III) ions, while WO4 groups remained dissolved in the solution.
Polyethylene glycol (PEG) and TMOS were added to homogeneous solution upon
continuous stirring and heating; after several hours transparent gel was formed as
a result of the sol–gel process. In the last step, the product was calcined over
the temperature range 600–900 °C for 3 h in the air atmosphere. Finally, we obtained
Ln2–xPrx (WO4 ) 3 entrapped in a silica xerogel as a white powder material.
2–
However, xerogels without WO4 groups were synthesized in a similar manner,
as above. The aqueous solutions of La(III) and Pr(III) nitrates were mixed together.
The doping concentration x of Pr(III) ions was similar to the above one. Next, PEG

The effect of WO 4 2– group in xerogels ... 361
and TMOS were added to homogeneous solution upon continuous stirring and heating;
after several days transparent gel was formed as a result of the sol–gel process. In
the last step, the product was calcined over the temperature range 600–900 °C for 3 h
in the air atmosphere.
2.2. Apparatus
The photoluminescence excitation and emission spectra were recorded on a Cary
Eclipse spectrofluorometer with a reflection spectra attachment. The emission spectra
of the xerogel samples doped with Ln2–xPrx(WO4) 3 were obtained upon excitation at
2–
λexc = 240 nm within the absorption band range of the WO4 group; at that excitation
wavelength acceptors do not absorb. However, the emission spectra of xerogels
2–
without WO4 groups were obtained within absorption bands of Pr(III) ion λexc = 448
or 473 nm.
3. Results and discussion
Previously, all the xerogels doped with Ln2–xLn'x (WO4 ) 3 where Ln = Gd, La and
Ln' = Eu, Sm, Tb were analyzed by the thermal analysis and FT-IR spectroscopy and
they were described in detail in references [2 ,3, 11]. Similar effect we obtained for
xerogels doped with Ln2–xPrx(WO4)3, therefore we do not precent that result in this
paper. The analysis of FT-IR spectroscopic results and estimated relations of the mass
losses suggest that after heating at 600 °C xerogels doped with Ln2–xPrx (WO4 ) 3 were
obtained, which can play the role of phosphors in the luminescent materials [12].
The photoluminescence properties of the xerogels doped with Ln2–xPrx (WO4 ) 3
were examined, keeping in mind their applications as red phosphors for color
television. For each material studied, enhancement of the emission intensity of Pr(III)
ions was observed because of the energy transfer. It is evidenced by the results of
excitation and emission spectra. The high emission intensity of the xerogel samples
doped with Ln2–xPrx (WO4 ) 3 were obtained upon excitation at 240 nm within
2–
the absorption band range of the WO4 group; at that excitation wavelength acceptors
do not absorb. For comparison purposes, the photoluminescence properties of xerogels
2–
WO4 without groups were studied.
The photoluminescence excitation spectra of xerogels doped with
La1.9Pr0.1 (WO4 ) 3 or Gd 1.9Pr0.1 (WO4 ) 3 and annealed at 900 °C are shown in Fig. 1.
The spectra were measured upon the emission wavelength λ =648nm which
corresponds to the Pr(III) 3 P0 → 3 F2 transition. A broad excitation band centering at
about 240 nm with a shoulder at about 250 nm is observed in the UV range. It is
attributed to the charge transfer (CT) transition from oxygen to tungsten in
2–
WO4 group. However, the shoulder at about 250 nm can correspond to the CT transition
between O 2– → Pr 3+ . Along this band, it is also possible to observe several narrow
bands located between 420 and 500 nm, which are ascribed to the f–f transitions of
Pr(III) ion. They are placed at about 448, 473 and 486 nm. The 448 nm photon
absorption causes excitation from 3 H 4 to 3 P 0 level of Pr 3+ ion.

362 B. GROBELNA, P. BOJARSKI
Fig. 1. Excitation spectra of xerogels doped with: La 1.9 Pr 0.1 (WO 4 ) 3 (spectrum a) and Gd 1.9 Pr 0.1 (WO 4 ) 3
(spectrum b).
Fig. 2. Emission spectra of xerogels doped with: La 1.9Pr 0.1(WO 4) 3 (spectrum a) and Gd 1.9Pr 0.1(WO 4) 3
(spectrum b).
Figure 2 shows the photoluminescence emission spectra of xerogels doped with
La 1.9 Pr 0.1 (WO 4 ) 3 or Gd 1.9 Pr 0.1 (WO 4 ) 3 and annealed at 900 °C. Luminescence signals
due to Pr(III) were observed in the red region of the spectrum. These signals are due
mainly to Pr(III) 1 D 2 → 3 H 4 (605 nm), 3 P 0 → 3 H 6 (618 nm), 3 P 0 → 3 F 2 (648 nm),
3 P1 → 3 F 3 (680 nm) and 3 P 1 → 3 F 4 (730 nm) transitions, respectively. It is known that
the emission of Pr 3+ depended strongly on the host lattice. In our case, the most intense
band is placed at about 648 nm and also is regarded as hypersensitive one. The ratio
between 3 P 0 and 1 D 2 emission intensities shows the dominant character of the 3 P 0
transition and is less commonly observed in oxide materials. This suggests that
coordination sphere of Pr(III) ion is of low symmetry.

The effect of WO 4 2– group in xerogels ... 363
Fig. 3. Excitation and emission spectra of xerogels doped with La 1.9 Pr 0.1 .
The influence of tungstate groups on Pr(III) luminescence in silica xerogels was
studied. Figure 3, spectrum a shows excitation spectrum of xerogel doped with Pr(III)
and La(III) ions. The spectrum was measured upon the emission wavelength
λ = 648 nm. The small band observed at 473 nm corresponds to f–f transition of Pr(III)
ion. However, the band placed at around 250 nm is attributed to the charge transfer
between O 2– → Pr 3+ . The emission spectra of low intensity (Fig. 3, spectra c and d )
correspond to a situation where the material is excited by radiation of λ exc = 448 or
473 nm. In the case where λ exc = 240 nm no red emissions at 605, 618 and 648 nm
were observed in Fig. 3, spectrum b.
In order to avoid emission quenching of O–H oscillators the emission intensity of
Pr(III) ion has been studied as a function of annealing temperature in xerogels doped
with mixed tungstate. Figure 4 shows that the emission intensity of Pr(III) ion in
Fig. 4. The dependence of Pr 3+ emission intensity I of the 3 P 0 → 3 F 2 band at 648 nm with annealing
temperature T for xerogels doped with: La 1.9 Pr 0.1 (WO 4 ) 3 (curve a) and Gd 1.9 Pr 0.1 (WO 4 ) 3 (curve b).
The lines are drawn as guide to the eyes.

364 B. GROBELNA, P. BOJARSKI
the materials studied increases with an increase of temperature up to 900 °C. Water
molecules come from both silica matrix and coordination sphere of Pr(III) ion. Thus,
removal of O–H groups leads to an increase of the emission intensity. In our previous
paper [3], we reported that heating at least up to 1000 °C causes the emission intensity
to decrease. This is possible since the formation of mixed lanthanide silicate and
tungstate salt could occur. Additionally, xerogels doped with Ln 2–xPr x(WO 4) 3 heated
up to the temperature around 1000 °C could transform into glassy material.
The second parameter which affects the enhancement of the emission intensity is
the concentration of Pr(III) ion. As we can see from Fig. 5, the highest emission occurs
Fig. 5. The dependence of Pr 3+ emission intensity I of the 3 P 0 → 3 F 2 band at 648 nm with Pr(III)
content x for xerogels doped with: La 1.9 Pr 0.1 (WO 4 ) 3 (curve a) and Gd 1.9 Pr 0.1 (WO 4 ) 3 (curve b). The lines
are drawn as guide to the eyes.
Fig. 6. The dependence of Pr 3+ emission intensity I of the 3 P 0 → 3 F 2 band at 648 nm with time t for
xerogels doped with La 1.9Pr 0.1(WO 4) 3. The lines are drawn as guide to the eyes.

The effect of WO 4 2– group in xerogels ... 365
for x = 0.1 for xerogels doped with Ln 2–x Pr x (WO 4 ) 3 or Gd 2–x Pr x (WO 4 ) 3 . The decrease
above the maximum (x) is due to the concentration quenching.
A good luminescent material should be resistant to UV-Vis radiation and water
absorption from the air atmosphere for a long time. Therefore, it has not shown changes
of emission intensity during illumination by the sun radiation. As can be seen in Fig. 6,
the emission intensity of silica xerogel doped with La 1.9Pr 0.1(WO 4) 3 is constant within
the experimental error for eight months.
4. Conclusions
The materials under study show UV-Vis reflectance spectra with a band placed at about
240 nm, related to O → W charge transfer transition. The Pr(III) ion presents its
enhanced emissions ( 3 P0 → 3 F2) in the materials studied owing to the efficient
energy transfer from the excited W(VI) states in tungstate group via O to Pr(III) ions.
The energy transfer from groups to Pr(III) ions is particularly effective for
xerogels doped with mixed systems of the compositions: La 1.9Pr 0.1(WO 4) 3 and
Gd 1.9 Pr 0.1 (WO 4 ) 3 . The Pr(III) emission intensity in the materials studied increases
with temperature increasing up to 900 °C. This is due to the removal of O–H quenchers
from the coordination sphere of Pr(III) ions. The Pr(III) emission intensity has been
constant for eight months.
Acknowledgments – The financial support of this study by the Ministry of Science and Higher Education
(Poland Grant 3162/B/T02/2009/36) is gratefully acknowledged.
References
2–
WO4 [1] RONDA C.R., JÜSTEL T., NIKOL H., Rare earth phosphors: fundamentals and applications, Journal of
Alloys and Compounds 275–277, 1998, pp. 669–676.
[2] GROBELNA B., Luminescence based on energy transfer in xerogels doped with Tb 2–x Eu x (WO 4 ) 3 ,
Optica Applicata 38(1), 2008, pp. 39–47.
[3] GROBELNA B., SZABELSKI M., KLEDZIK K., KŁONKOWSKI A.M., Luminescent properties of Sm(III) ions
in Ln 2–x (WO 4 ) 3 entrapped in silica xerogel, Journal of Non-Crystalline Solids 353(30–31), 2007,
pp. 2861–2866.
[4] LIANHUA TIAN, SUN-IL MHO, ZHE JIN, Luminescence properties of red-emitting praseodymium-
-activated BaTi 4 O 9 phosphor, Journal of Luminescence 129(8), 2009, pp. 797–800.
[5] VOLOSHIN A.I., SHAVALEEV N.M., KAZAKOV V.P., Luminescence of praseodymium (III) chelates from
excited states ( 3 P 0 and 1 D 2) and its dependence on ligand triplet state energy, Journal of
Luminescence 93(3), 2001, pp. 199–204.
[6] LIANHUA TIAN, SUN-IL MHO, Enhanced luminescence of SrTiO 3:Pr 3+ by incorporation of Li + ion,
Solid State Communications 125(11–12), 2003, pp. 647–651.
[7] BOILOT J.-P., GACOIN T., PERRUCHAS S., Synthesis and sol–gel assembly of nanophosphors, Comptes
Rendus Chimie 13(1–2), 2010, pp. 186–198.
[8] BREDOL M., GUTZOV S., JÜSTEL T., Highly efficient energy transfer from Ge-related defects to Tb 3+
ions in sol–gel derived glasses, Journal of Non-Crystalline Solids 321(3), 2003, pp. 225–230.
[9] GARCIA-MURILLO A., LE LUYER C., GARAPON C., DUJARDIN C., BERNSTEIN E., PEDRINI C., MUGNIER J.,
Optical properties of europium-doped Gd 2 O 3 waveguiding thin films prepared by the sol–gel method,
Optical Materials 19(1), 2002, pp. 161–168.

366 B. GROBELNA, P. BOJARSKI
[10] BRINKER C.J., SCHERER G.W., Sol–Gel Science. The Physics and Chemistry of Sol–Gel Processing,
Chapter 13, Acadmic Press, Boston, 1990.
[11] GROBELNA B., Luminescence based on energy transfer in xerogels doped with Ln 2–xTb x(WO 4) 3,
Journal of Alloys and Compounds 440(1–2), 2007, pp. 265–269.
[12] GROBELNA B., BOJARSKI P., Red emission of Eu(III) ions doped gadolinium or lanthanum tungstate
entrapped in silica xerogel, Journal of Non-Crystalline Solids 355(45–47), 2009, pp. 2309–2313.
Received November 12, 2009
in revised form December 2, 2009

Optica Applicata, Vol. XL, No. 2, 2010
Borate glasses with PbO and PbCl 2
containing Dy 3+ ions
JOANNA PISARSKA
University of Silesia, Institute of Chemistry, Szkolna 9, 40-007 Katowice, Poland;
e-mail: Joanna.Pisarska@us.edu.pl
Oxychloroborate glasses containing Dy 3+ ions in the B 2 O 3 –PbCl 2 –PbO–Al 2 O 3 –WO 3 system
were studied using X-ray diffraction, Raman, FT-IR, absorption, excitation and luminescence
spectroscopy. The results concerning glass preparation, short-range order structure and optical
properties are reported. X-ray diffraction analysis evidently indicates that the fully amorphous
system was prepared. Coexistence of trigonal BO 3 and tetrahedral BO 4 units was evidenced by
Raman and FT-IR spectroscopy. The electronic states belonging to the 4f 9 configuration of
trivalent Dy 3+ were determined from the absorption and excitation spectra. The luminescence
bands at 480, 573 and 662 nm were registered in oxychloride glasses, which correspond to
transitions originating from the 4 F 9/2 state to the 6 H J/2 (J = 11, 13, 15) states of Dy 3+ .
Keywords: glasses, dysprosium ions, optical properties.
1. Introduction
The systematic studies of rare earth ions in different environments indicate that Dy 3+
doped systems are known as a two primary color (yellow/blue) luminescent materials.
Yellow/blue luminescence is related to 4 F 9/2 – 6 H 13/2 and 4 F 9/2 – 6 H 15/2 transitions of
Dy 3+ . Several oxide, oxyfluoride and fluoride glass systems containing Dy 3+ ions were
studied for yellow/blue luminescence [1–15], but dysprosium-doped oxychloride
glasses have not been examined yet. The preparation of oxychloride glasses and their
potential applications are often limited due to low glass forming region and large
tendency towards crystallization. Previously published results for oxychloride
systems singly doped with Ln 3+ are concerned mainly with Er 3+ ions in tellurite [16],
germanate [17], and phosphate [18] glasses containing PbCl 2.
Recently, the NIR luminescence of Nd 3+ ions in B 2 O 3 –PbCl 2 –PbO–Al 2 O 3 –WO 3
glass system was examined [19]. The present work deals with synthesis, short-range
order structure and optical properties of the oxychloroborate glasses containing Dy 3+
ions. The glass structure was investigated using X-ray diffraction, Raman and FT-IR
spectroscopy. Visible emission due to 4 F 9/2 – 6 H J/2 (J = 11, 13, 15) transitions and its
decay from 4 F 9/2 state of Dy 3+ was analyzed in detail. Several spectroscopic parameters

368 J. PISARSKA
for Dy 3+ ions in oxychloroborate glasses were evaluated based on the absorption,
excitation and emission measurements.
2. Experimental techniques
The X-ray diffraction was carried out using INEL diffractometer with Cu Kα
radiation. The Raman and FT-IR spectra were performed by Bruker spectrometer using
standard KBr disc techniques. Absorption spectra were recorded using a Varian 2300
UV-VIS-NIR spectrophotometer. Luminescence spectra and decay curves were
obtained using Jobin Yvon Fluoromax4 spectrophotometer. The spectral resolution
was equal to 0.1 nm. Luminescence decay curves were detected with accuracy of
±1 μs. All spectral measurements were carried out at room temperature.
3. Results and discussion
3.1. Glass preparation and structural studies
Oxychloroborate glass samples singly doped with Dy3+ ions were prepared using
the following composition (in wt%): 18B2O3 –9PbCl2 –63PbO–6Al2O3 –3WO3 –
– 1Dy2O3 .
Anhydrous oxides (B2O3 , PbO, Al2O3 , WO3 , Nd2O3 ) and lead halide PbCl2 (99.99% purity, Aldrich) were used as the starting materials. Due to the hygroscopicity
of the halide components and, in order to minimize the adsorbed water content,
the batches of 4 g were weighted and stored in a vacuum furnace at 100 °C.
Homogeneous mixture was heated in a protective atmosphere of dried argon. Glasses
were melted at 900 °C in Pt crucibles, then poured into preheated copper moulds and
annealed below the glass transition temperature. After this procedure, the samples were
slowly cooled to room temperature. Transparent glassy plates of about 2 mm in
thickness were obtained.
In order to obtain information on the crystallizing phases, the X-ray diffraction
was performed. Figure 1 presents X-ray diffraction pattern of the oxychloroborate
glass singly doped with Dy 3+ ions. The XRD pattern displays two characteristic broad
bands corresponding to the fully amorphous phases and does not show any strong
diffraction lines due to the precipitation of PbCl2 or other crystalline phases. In order
to obtain some information on the short-range order structure of oxychloroborate
glasses, Raman and FT-IR spectra were performed. Figure 2 presents the Raman
spectrum, which was registered in 600–1700 cm –1 region for oxychloride lead borate
glass and then compared to the one obtained for glass sample without PbCl2 . In this
frequency region, the Raman bands are related to the vibrations of borate groups.
Similarly to the previous results [20], several vibration bands at around 620, 720, 870,
925, 1050 and 1280 cm –1 are located, which correspond to the chain- and ring-type
metaborate groups as well as diborate and pentaborate units, respectively.
Two important effects can be observed. Firstly, the intensities of the bands located
at about 870 and 925 cm –1 (assigned to pentaborate groups [20]) due to the stretching

Borate glasses with PbO and PbCl 2 containing Dy 3+ ions 369
Fig. 1. X-ray diffraction pattern for the oxychloroborate
glass.
Fig. 2. Raman spectra for the glasses with and without
PbCl 2.
vibrations of BO 4 units, increase with the presence of lead chloride PbCl 2 . From
the literature data it is known that the PbO 4 units bridge preferentially rather to BO 3
groups than BO 4 ones. Here, the partial substitution of PbO by PbCl 2 results in
an increase of the Raman band intensities related to the formation of BO 4 units.
Similar phenomena were observed for lead fluoroborate glasses doped with Sm 3+ [20]
in the case of BO 4 unit formation, when the oxygen atoms added to the oxyfluoride
glass network reduced the effect of F ions in the PbO 4 units. Secondly, the Raman
band due to the maximal phonon energy of the host slightly decreases from 1301 to
1277 cm –1 in the case of the partial substitution of PbO by PbCl 2 . There is a good
agreement with the results obtained for other oxychloride germanate glass systems,
where the maximum phonon energy slightly shifts from 819 cm –1 to 805 cm –1 with
the replacement of PbO by PbCl 2 [21]. One can deduce that PbCl 2 plays an important
role in the formation of the glass network.
Figure 3 presents FT-IR spectrum of the oxychloroborate glass containing Dy 3+ ,
acquired in the 4000–400 cm –1 range. The spectrum exhibits the low-intense band
near 3445 cm –1 (2.9 μm), which is related to the characteristic stretching vibration
of OH – groups. The infrared bands located between 1500 cm –1 and 400 cm –1 are

370 J. PISARSKA
correlated with the vibrations of borate network. The first group of bands was identified
as the BO 3 bending modes (650–700 cm –1 ).
The second group of bands is associated with the B–O stretching vibrations of
tetrahedral BO 4 groups (800–1050 cm –1 ). The antisymmetric stretching mode causes
that bands are centered at 1050 cm –1 , whereas the symmetric stretching frequency is
located in the 800–900 cm –1 infrared region. The third group of the most intense
bands, centered at 1300–1400 cm –1 , is due to the antisymmetric B–O stretching
vibrations of trigonal BO 3 groups. It can be clearly drawn from Fig. 3 that both trigonal
BO 3 and tetrahedral BO 4 units coexist in multicomponent oxychloroborate glasses.
3.2. Optical studies
Fig. 3. FT-IR spectrum for the oxychloroborate glass.
The absorption spectra of Dy 3+ ions in the glasses without and with PbCl 2 are
presented in Fig. 4. The spectra consist of several inhomogeneously broadened
transitions from the 6 H 15/2 ground state to the 6 H 11/2 , 6 F 11/2 , 6 F 9/2 , 6 F 7/2 , 6 F 5/2 and 6 F 3/2
excited states belonging to the 4f 9 electronic configuration of trivalent dysprosium.
Fig. 4. Absorption spectrum for Dy 3+ in the glasses with
and without PbCl 2.

Borate glasses with PbO and PbCl 2 containing Dy 3+ ions 371
T a b l e. Observed absorption band positions (in cm –1 ) and bonding parameters (β and δ ) for Dy 3+ ions
in the glass samples without and with PbCl 2.
Energy level PbO–B 2O3 PbCl2–PbO–B2O3 Aquo-ion [16]
6
H15/2 – 4 F9/2 22090 22170 22100
6H15/2– 6F3/2 13290 13328 13250
6
H15/2– 6 F5/2 12452 12500 12400
6
H15/2 – 6 F7/2 11101 11101 11000
6H15/2– 6F9/2 9150 9151 9100
6
H15/2– 6 F11/2 7847 7853 7700
6
H15/2 – 6 H11/2 5933 5937 5850
β 1.0078 1.0095
δ –0.77 –0.94
From the absorption spectra of Dy 3+ ions in the glasses without and with PbCl 2,
bonding parameters (β and δ ) were calculated using the relation [22]:
δ =
1 – β
----------------- × 100
β
where β = Σ Nβ * /N and β * = ν c /ν a , β is the shift of energy level position (nephelauxetic
effect), ν c and ν a are energies of the corresponding transitions in the investigated
complex and aquo-ion [23], respectively, and N denotes the number of levels used for
the calculation of β values. Positive or negative sign for the δ value indicates covalent
or ionic bonding between the rare earth ions and surrounding ligands. The observed
absorption band positions and bonding parameters for Dy +3 in the glasses and
aquo-ion are given in the Table. The bonding parameter δ was found to be –0.77,
which indicates that the B 2O 3–PbO based glass exhibits ionic character between Dy 3+
and surrounding ligands. This behavior is connected with the occurrence of [PbO 4/2 ] 2–
as well as [B 3 O 9 ] 9– anions having BO 3 and BO 4 units in the host matrix, which was
evidenced by Raman and FT-IR spectroscopy (see Section 3.1). The partial
substitution of PbO by PbCl 2 results in the change of δ value from –0.77 to –0.94,
which indicates more ionic environment around Dy 3+ .
From the spectra it is also clearly seen that the absorption bands related to
6 H15/2 – 4 F 9/2 and 6 H 15/2 – 6 F 3/2 transitions of Dy 3+ in the visible spectral region are more
intense and resolved for oxychloride glass than oxide one. Moreover, the matrix
absorption in the visible region is higher for oxychloride glass as compared to oxide
glass. The 4 F 9/2 state lies on the UV-VIS absorption edge, whereas higher-lying states
of Dy 3+ in the glass under study are not visible. For that reason, the excitation spectrum
monitored at λ em = 573 nm ( 4 F 9/2– 6 H 13/2 transition) was recorded in 300–500 nm
spectral region (Fig. 5). Several narrowed bands belong to the well known higher-lying
f–f electronic transitions of Dy 3+ . Any broad excitation charge-transfer bands due to
Dy 3+ –O 2– /Cl – interactions were not obtained in the short wavelength spectral region.

372 J. PISARSKA
Fig. 5. Excitation spectrum for Dy 3+ in the oxychloroborate
glass.
This confirms the absence of the energy transfer process from the O 2– /Cl – ligands to
the metal atoms. It also indicates that the interactions between Dy 3+ ions and host
lattice are rather weak. The observed bands are assigned to transitions originating from
the 6 H 15/2 ground state to the 4 F 9/2 , 4 I 15/2 , 4 G11/2, 4 K17/2, 6 P 5/2 and 6 P 7/2 states of
Dy 3+ . Two of them, 6 H 15/2 – 4 K 17/2 (386 nm) and 6 H 15/2 – 4 I 15/2 (450 nm) transitions are
the most intense.
Figure 6 shows luminescence spectrum for Dy 3+ in oxychloroborate glass.
Luminescence spectra were recorded under excitation by 386 nm ( 4 K 17/2 state) or
450 nm ( 4 I 15/2 state) lines. Independently of the excitation wavelengths, two relative
intense bands at 480 nm and 573 nm, and considerably less intense band at 662 nm
have been observed. The luminescence bands correspond to 4 F 9/2 – 6 H 15/2 (blue),
4 F9/2 – 6 H 13/2 (yellow) and 4 F 9/2 – 6 H 11/2 (red) transitions of Dy 3+ ions, respectively. All
transitions are shown in the energy level scheme, which was constructed for Dy 3+ ions
Fig. 6. Luminescence spectrum for Dy 3+ in the oxychloroborate glass. Inset shows luminescence decay
from the 4 F 9/2 state of Dy 3+ .

Borate glasses with PbO and PbCl 2 containing Dy 3+ ions 373
in oxychloroborate glass. Owing to small energy gaps between all states lying above
21000 cm –1 , the 4F9/2 state is well populated by non-radiative relaxation. Then,
quite strong yellow/blue luminescence due to 4 F9/2– 6 HJ/2 (J = 13, 15) transitions
is observed. This phenomenon is related to large separation (~6000 cm –1 ) between
4F9/2 state and the next lower lying 6F1/2 state, and the relative high phonon energy of
the host (~1300 cm –1 ).
The inset shows luminescence decay from the 4F9/2 state of Dy3+ in
oxychloroborate glass. The luminescence decay curve is nearly single exponential.
The measured 4 F9/2 lifetime was determined to be 0.42 ms. It is consistent with values
obtained for similar Dy-doped glasses based on ZnO–PbO–B 2O3 [24].
4. Conclusions
Oxychloroborate glasses containing Dy 3+ ions were studied using X-ray diffraction
and various spectroscopic techniques (Raman, FT-IR, absorption, excitation and
luminescence). The results concerning glass preparation, short-range order structure
and optical studies are presented. X-ray diffraction analysis evidently indicates that
the fully amorphous system was prepared. Coexistence of trigonal BO 3 and tetrahedral
BO4 units was evidenced by Raman and FT-IR spectroscopy. The electronic states of
Dy 3+ ions in oxychloroborate glass were determined from the absorption and excitation
spectra. Luminescence spectra registered in the visible spectral region correspond to
4 F9/2 – 6 H J/2 (J = 11, 13, 15) transitions of Dy 3+ . Decay curve for 4 F 9/2 state of Dy 3+ is
nearly single exponential and luminescence lifetime is close to 0.42 ms. The systematic
studies indicate that multicomponent oxychloroborate glasses containing Dy 3+ are
promising solid-state materials for yellow/blue luminescence.
Acknowledgements – The author would like to thank Prof. W. Ryba-Romanowski for helpful discussion,
Dr. G. Dominiak-Dzik for absorption measurements, Dr. M. Mączka for Raman and FT-IR measurements
and Dr. T. Goryczka for X-ray diffraction measurements. The Ministry of Science and Higher Education
supported this work under the grant No. N N507 3617 33.
References
[1] JAYASANKAR C.K., RUKMINI E., Spectroscopic investigations of Dy 3+ ions in borosulphate glasses,
Physica B: Condensed Matter 240(3), 1997, pp. 273–288.
[2] TANABE S., KANG J., HANADA T., SOGA N., Yellow/blue luminescences of Dy 3+ -doped borate glasses
and their anomalous temperature variations, Journal of Non-Crystalline Solids 239(1–3), 1998,
pp. 170–175.
[3] BABU P., JAYASANKAR C.K., Spectroscopic properties of Dy 3+ ions in lithium borate and lithium
fluoroborate glasses, Optical Materials 15(1), 2000, pp. 65–79.
[4] SRIVASTAVA P., RAI S.B., RAI D.K., Optical properties of Dy 3+ doped calibo glass on addition of
lead oxide, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 59(14), 2003,
pp. 3303–33111.
[5] JAYASANKAR C.K., VENKATRAMU V., SURENDRA BABU S., BABU P., Luminescence properties of Dy 3+
ions in a variety of borate and fluoroborate glasses containing lithium, zinc, and lead, Journal of
Alloys and Compounds 374(1–2), 2004, pp. 22–26.

374 J. PISARSKA
[6] MAHATO K.K., RAI A., RAI S.B., Optical properties of Dy 3+ doped in oxyfluoroborate glass,
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 61(3), 2005, pp. 431–436.
[7] JAYASIMHADRI M., MOORTHY L.R., KOJIMA K., YAMAMOTO K., WADA N., WADA N., Optical properties
of Dy 3+ ions in alkali tellurofluorophosphate glasses for laser materials, Journal of Physics D:
Applied Physics 39(4), 2006, p. 635.
[8] ZHONGCHAO DUAN, JUNJIE ZHANG, LILI HU, Spectroscopic properties and Judd–Ofelt theory analysis
of Dy 3+ doped oxyfluoride silicate glass, Journal of Applied Physics 101(4), 2007, p. 043110.
[9] LAKSHMINARAYANA G., VIDYA SAGAR R., BUDDHUDU S., Emission analysis of Dy 3+ and Pr 3+ :Bi 2 O 3 –
–ZnF 2–B 2O 3–Li 2O–Na 2O glasses, Physica B: Condensed Matter 403(1), 2008, pp. 81–86.
[10] PRAVEENA R., VIJAYA R., JAYASANKAR C.K., Photoluminescence and energy transfer studies of
Dy 3+ -doped fluorophosphate glasses, Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy 70(3), 2008, pp. 577–586.
[11] PIRAMIDOWICZ R., KLIMCZAK M., MALINOWSKI M., Short-wavelength emission analysis in Dy:ZBLAN
glasses, Optical Materials 30(5), 2008, pp. 707–710.
[12] DWIVEDI Y., RAI S.B., Spectroscopic study of Dy 3+ and Dy 3+ /Yb 3+ ions co-doped in barium
fluoroborate glass, Optical Materials 31(10), 2009, pp. 1472–1477.
[13] SURENDRA BABU S., BABU P., JAYASANKAR C.K., TRÖSTER TH., SIEVERS W., WORTMANN G., Optical
properties of Dy 3+ -doped phosphate and fluorophosphate glasses, Optical Materials 31(4), 2009,
pp. 624–631.
[14] BABU P., KYOUNG HYUK JANG, EUN SIK KIM, LIANG SHI, HYO JIN SEO, RIVERA-LÓPEZ F.,
RODRÍGUEZ-MENDOZA U.R., LAVÍN V., VIJAYA R., JAYASANKAR C.K., RAMA MOORTHY L., Spectral
investigations on Dy 3+ -doped transparent oxyfluoride glasses and nanocrystalline glass ceramics,
Journal of Applied Physics 105(1), 2009, p. 013516.
[15] BASAVAPOORNIMA CH., JAYASANKAR C.K., CHANDRACHOODAN P.P., Luminescence and laser
transition studies of Dy 3+ :K–Mg–Al fluorophosphate glasses, Physica B: Condensed Matter 404(2),
2009, pp. 235–242.
[16] SHIQING XU, DAWEI FANG, ZAIXUAN ZHANG, ZHONGHONG JIANG, Effect of OH – on upconversion
luminescence of Er 3+ -doped oxyhalide tellurite glasses, Journal of Solid State Chemistry 178(6),
2005, pp. 2159–2162.
[17] SUN H., ZHANG L., WEN L., LIAO M., ZHANG J., HU L., DAI S., JIANG Z., Effect of PbCl 2 addition on
structure, OH – content, and upconversion luminescence in Yb 3+ /Er 3+ -codoped germanate glasses,
Applied Physics B: Lasers and Optics 80(7), 2005, pp. 881–888.
[18] PRADEESH K., OTON C.J., AGOTIYA V.K., RAGHAVENDRA M., VIJAYA PRAKASH G., Optical properties
of Er 3+ doped alkali chlorophosphate glasses for optical amplifiers, Optical Materials 31(2), 2008,
pp. 155–160.
[19] PISARSKA J., Novel oxychloroborate glasses containing neodymium ions: Synthesis, structure and
luminescent properties, Journal of Molecular Structure 887(1–3), 2008, pp. 201–204.
[20] SOUZA FILHO A.G., MENDES FILHO J., MELO F.E.A., CUSTODIO M.C.C., LEBULLENGER R.,
HERNANDES A.C., Optical properties of Sm 3+ doped lead fluoroborate glasses, Journal of Physics
and Chemistry of Solids 61(9), 2000, pp. 1535–1542.
[21] HONGTAO SUN, JUNJIE YANG, LIYAN ZHANG, JUNJIE ZHANG, LILI HU, ZHONGHONG JIANG, Composition
dependent frequency upconversion luminescence in Er 3+ -doped oxychloride germanate glasses,
Solid State Communications 133(12), 2005, pp. 753–757.
[22] SINHA S.P., Complexes of the Rare Earth, Pergamon Press, Oxford, 1966.
[23] CARNALL W.T., FIELDS P.R., RAJNAK K., Electronic energy levels of the trivalent lanthanide aquo
ions. IV. Eu 3+ , Journal of Chemical Physics 49(10), 1968, pp. 4450–4455.
[24] LAKSHMINARAYANA G., BUDDHUDU S., Spectral analysis of Sm 3+ and Dy 3+ : B 2O 3–ZnO–PbO
glasses, Physica B: Condensed Matter 373(1), 2006, pp. 100–106.
Received November 12, 2009
in revised form March 23, 2010

Optica Applicata, Vol. XL, No. 2, 2010
Thermal treatment effect on dynamics
of luminescent states in oxyfluoride
glass-ceramics doped with Pr 3+ and Tb 3+
GRAŻYNA DOMINIAK-DZIK 1 , BARBARA KLIMESZ 2* , WITOLD RYBA-ROMANOWSKI 1
1Institute of Low Temperature and Structure Research, Polish Academy of Sciences,
ul. Okólna 2, 50-395 Wrocław, Poland
2 Department of Physics, Opole University of Technology,
ul. Mikołajczyka 5, 45-271 Opole, Poland
* Corresponding author: b.klimesz@po.opole.pl
The 50GeO 2 –(50–x–y)PbO–yPbF 2 –xLnF 3 glass single doped with Pr 3+ and Tb 3+ ions was
studied. The composition of the material was modified by varying the content of both PbF 2 ( y =5,
10, 15 mol%) and LnF 3 (x = 0.2 and 2 mol%). The differential thermal analysis (DTA) of
as-melted samples was used to determine thermal characteristics. Optical techniques and kinetics
measurements were used to monitor the effect of thermal treatment on spectroscopic properties
and dynamics of luminescent states of optically-active ions in amorphous and two-phase systems.
It was found that non-exponential decays of praseodymium luminescence in as-melted material
become exponential or nearly exponential with corresponding longer lifetimes in thermally-treated
samples. This effect was not so strong in the Tb 3+ -doped glass. The influence of the PbF 2 content
on luminescence dynamics was studied for samples doped with 2 mol% of Pr 3+ . It was observed
that the increase of PbF 2 content leads to lengthening of luminescence lifetime, e.g., the 1 D 2 lifetime
increases from 4.1 to 45 μs in 5 and 15 mol% of PbF 2 as-melted samples, respectively.
Keywords: oxyfluoride glasses, differential thermal analysis (DTA), thermal treatment, optical
properties, luminescence dynamics, lifetimes.
1. Introduction
Rare earth doped oxyfluoride glass-ceramics combines physicochemical properties of
oxide host with profitable optical properties of fluoride crystals. Compared with
precursor material the glass-ceramics offers fluoride environment of rare earth sites
with low phonon energy. It has been found that part of rare earth ions is incorporated
into crystalline phase after ceramming process. In glass-ceramics containing PbF 2
or PbF 2 –CdF 2 the crystalline precipitates were identified as Ln:PbF 2 [1–3] and

376 G. DOMINIAK-DZIK, B. KLIMESZ, W. RYBA-ROMANOWSKI
Ln:Pb x Cd 2–x F 2 [4, 5] cubic phase, respectively. It is common knowledge that oxide
hosts have high energy of phonons. Their frequencies vary from host to host and in
silicate and germanate amount to 1000–1100 and 800–970 cm –1 , respectively.
Fluoride matrices are characterised by maximal phonon energy of 500–600 cm –1 . In
this context, polycrystalline fluoride phase in glass-ceramics offers lower
non-radiative transition probabilities and longer lifetimes of luminescent levels.
The ease and low cost of fabrication are additional advantages of oxyfluoride glass
ceramics.
The majority of glass ceramics with PbF 2 reports deal with Er 3+ [2,3,6] or Tm 3+
[1, 7, 8] due to practical importance of the near infrared laser transitions for
telecommunication and fiber amplifiers. Luminescence properties of the Pr 3+
crystalline precipitates in silicate [4, 5, 9] or germanate [7, 8] glasses have been
reported too, however, the knowledge of Tb 3+ luminescence properties in glass and
glass-ceramics is rather poor.
The trivalent praseodymium is an attractive optical activator owing to the presence
of several metastable states (e.g., 3 P 0 , 1 D 2 and 1 G 4 ) offering the possibility of the visible
emission for laser action. Terbium-activated hosts are known as good emitters of green
light.
In our investigations, a special attempt was made at using kinetics technique to
find changes of the ligand environmental around Pr 3+ and Tb 3+ in lead germanate glass
after heat-treatment process.
2. Experimental procedure
Precursor glasses with the molar composition of 50GeO 2 –(50–y–x)PbO–yPbF 2 –
–xPr(Tb)F 3 (y = 5, 10, 15 mol% and x = 0.2, 2 mol%) were fabricated. Starting
batches were thoroughly mixed in dry box, put in a covered platinum crucible and
melted at 1000 °C for 20 minutes in normal atmosphere. The liquefied material was
poured into preheated cooper form and pressed with preheated plate.
The differential thermal analysis (DTA) measurements were performed using
a NETZSCH differential scanning calorimeter DSC 404/3/F with Pt/PtRh DSC
measuring head and platinum sample pans. The measurements were carried out at
a heating rate of 10 °C per minute. Powder diffractograms were recorded in the 2Θ
range of 10–60° by a Siemens D-5000 diffractometer (Ni-filtered Cu K α radiation,
0.02 deg/s scanning rate). Emission spectra were carried out in the visible and infrared
spectral range. Samples were excited by a 458 or 488 nm line of an argon laser.
Luminescence decay curves were recorded following a short pulse excitation provided
by a Continuum Model Surelite optical parametric oscillator (OPO) pumped by a third
harmonic of a Nd:YAG laser. Resulting luminescence signal was filtered using a Zeiss
model GDM-1000 monochromator, detected by a Hamamatsu R928 photomultiplier
and recorded with a Tektronix TDS 3052 oscilloscope. All measurements were carried
out at room temperature. Heat-treatment processes were performed during five hours
at two extreme temperatures; 360 °C (slightly above the glass transition temperature

Thermal treatment effect on dynamics of luminescent states ... 377
of 5%PbF 2 –2%Pr(Tb)F 3 ) and 395 °C (close to the beginning of the β-PbF 2
crystallisation band). Refractive indexes of the glass matrix were measured by us
at several wavelengths in the visible using a prism method [7]. Its value is 1.65 at
λ = 643.8 nm.
3. Results and discussion
The DTA curves of the 50GeO 2 –(45–x)PbO–5PbF 2 –xPr(Tb)F 3 (x = 0.2 and 2 mol%)
are presented in Fig. 1. The glass transition temperature T g of as-melted samples with
low concentration of Pr 3+ or Tb 3+ is 340 ± 2 °C. The increase of dopant contents shifts
T g to 350 ± 1 °C. The crystallisation temperatures of the oxide glassy hosts T c are given
in Fig. 1. The DTA curve of 50GeO 2 –43PbO–5PbF 2 –2PrF 3 exhibits an additional
exothermic peak located between the T g and T c (T β = 415 °C in maximum)
corresponding to the β-PbF 2 crystallisation. However, this exothermic effect is not
observed in low concentrated systems.
Fig. 1. DTA curves of GeO 2 –PbO–5PbF 2 –xPr(Tb)F 3 recorded for as-melted (solid lines) and heated
at 360 °C (dash lines) samples; x = 0.2 and 2 mol%.
The hello patterns, characteristic of the amorphous states were observed in
the X-ray powder diffractograms acquired from precursor samples. Contrary to
GeO 2 –PbO–PbF 2 doped with Er 3+ [2, 3] or Tm 3+ [7], no crystalline peaks appeared
in the XRD spectrum of the samples studied after heat treatment at 360 °C and 395 °C
for 5 hours. However, a large number of crystalline peaks, attributed to PbF 2, PbGe 3O 7
and GeO 2 were recorded in 5%PbF 2 –2%PrF 3 heated at 395 °C for 15 hours [8].
Emission of the 5%PbF 2 –2%PrF 3 as-melted glass, presented in Fig. 2a,
corresponds to transitions only from the 3 P 0 level. However, luminescence originating
also from 1 D 2 was observed in spectrum with 0.2%PrF 3 . A contribution of the 1 D 2

378 G. DOMINIAK-DZIK, B. KLIMESZ, W. RYBA-ROMANOWSKI
a b
Fig. 2. Emission spectra of Pr 3+ and Tb ions acquired at room temperature from as-melted samples
under 458 and 488 nm excitation, respectively. In the inset: part of luminescence observed for sample
with 0.2PrF 3 .
luminescence appeared as a wing at the shorter wavelength side of the band at 615 nm
(see the inset). Such a result indicates that concentration quenching plays the role in
the depopulation of the 1 D 2 state.
Emission of GeO 2 –PbO–5PbF 2 doped with 2%TbF 3 (Fig. 2b) exhibits a strong
green luminescence at 543 nm and a significantly weaker yellow emission around
587 and 622 nm. A green luminescence corresponding to the 5 D 4 → 7 F 5 transition
dominates emission spectrum. The distribution of the 5 D 4 → 7 F J (5,4,3) luminescence
intensity is in good agreement with emission of 30PbO–70PbF 2 –xTb 3+ glasses
(x = 0.5 and 2 wt%), reported in [10]. A very weak luminescence related to 5 D 3 is not
presented here.
Decay curves of the 3 P 0 and 1 D 2 luminescence of Pr 3+ , acquired from heat-treated
samples with 2 mol% of PrF 3 and different PbF 2 content are presented in Fig. 3. They
are compared with luminescence decays of as-melted glasses. The thermal treatment
does not change exponential time dependences of the 3 P 0 luminescence but affects
lifetimes. The 3 P 0 lifetime increases from 5.2 μs in 5%PbF 2 –2%PrF 3 as-melted to
8.1 μs in the sample heated at 395 °C/5 hours. A similar effect is observed in
the 10%PbF 2 –2%PrF 3 sample. However, the increase of PbF 2 to 15 mol% does not
influence the lifetime significantly.
A more spectacular lifetime rise is observed for the 1 D 2 luminescence level; from
4 μs (as-melted) to 109 μs (heated) in 5%PbF 2 –2%PrF 3 and from 7 μs (as-melted) to
100 μs (heated) in 10%PbF 2 –2%PrF 3 . Moreover, the controlled heat-treatment
profitably affects the character of the 1 D 2 decays; non-exponential decays in precursor
samples become exponential or near exponential in cerammed material. The increase
of PbF 2 content in as-melted sample lengthens the lifetime to 45 μs, which may
indicate that part of Pr 3+ is in fluoride environment. Thus, the increase of lifetime in
heated sample is relatively smaller.

Thermal treatment effect on dynamics of luminescent states ... 379
a
b
c
Fig. 3. Effect of the PbF 2 content on the 3 P 0 (a, b, c) and 1 D 2 (d, e, f) luminescence decay curves in
the xPbF 2 –2%PrF 3 (x = 5, 10, 15 mol%) samples heated at 395 °C for over 5 hours. Circles in (a, d)
represent decay curve acquired from the 5%PbF 2–2%PrF 3 glass cerammed at 360 °C.
The luminescence dynamics of the 5 D 3 and 5 D 4 levels of terbium was investigated
as a function of dopant concentration for both as-melted and heat-treated samples.
Luminescence decay curves of the 5 D 3 level are presented in Fig. 4.
Decay curves are strongly non-exponential even for low concentrated glass
indicating the contribution of non-radiative energy transfer. Thus, the mean lifetime
τ mean , defined as [11]:
τ mean
∫ I0
It ()dt
=
-----------------------
where I 0 is the initial intensity, was determined. The 5 D 3 lifetimes of as-melted samples
are 168 and 70 μs for 5PbF 2 –0.2TbF 3 and 5PbF 2 –2TbF 3 , respectively and
insignificantly rise under heat-treatment process. In contrast to the 5 D 3 luminescence,
the 5 D 4 decay curves of as-melted and heat-treated samples follow a single exponential
dependence with τ ~ 1.7 ms. This value is close to those observed in other Tb-doped
systems [12, 13].
Decay curves of the 1 D 2 state of Pr 3+ and 5 D 3 state of Tb 3+ in as-melted glasses
follow a strong non-exponential dependence characteristic of disordered glassy
systems. Generally, the excited state relaxation is governed by the sum of radiative
d
e
f

380 G. DOMINIAK-DZIK, B. KLIMESZ, W. RYBA-ROMANOWSKI
a
b
c
Fig. 4. Effect of concentration quenching of the 5 D 3 luminescence in 5%PbF 2 –xTbF 3 (x =0.2 and
2 mol%) (a) and the influence of heat treatment at 360 °C on decay curves (b, c).
probability, multiphonon emission probability and ion–ion interaction probability. In
this material the decay by multiphonon emission is relatively small due to the large
energy gaps between luminescent states and their next lower levels and relatively low
host frequencies of about 800 cm –1 corresponding to Ge–O stretching vibrations of
the GeO 4 tetrahedral structural units [14, 15]. Hence, ion–ion interactions play
important role. As in other Pr 3+ and Tb 3+ systems investigated [4, 16–18] both the 1 D 2
and 5 D 3 are affected much more strongly by ion–ion interactions than the 3 P 0 and 5 D 4
ones. So, in 5PbF 2 –xPrF 3 unheated glass the 1 D 2 lifetime is reduced from 96 μs [7] to
4 μs for x = 0.2 and 2 mol%, respectively, whereas the 3 P 0 time constant changes
from 18 μs [7] to 5 μs, only. A non-exponential character of the 5 D 3 decay profile of
5PbF 2 –0.2TbF 3 indicates that Tb 3+ –Tb 3+ interactions are not negligible even for
a low concentrated sample. These concentration variations of the 1 D 2 and 5 D 3
luminescence decays have been related to non-radiative energy transfer by
cross-relaxation of ( 1 D 2 , 3 H 4 ) → ( 1 G 4 , 3 F 3, 4 ) and ( 5 D 3 , 7 F 6 ) → ( 5 D 4 , 7 F 0 ) within
the Pr 3+ and Tb 3+ energy level schemes, respectively.
Praseodymium decay profiles recorded with heat-treated samples approach single
or nearly single exponential time dependences with longer time constants. A single
exponential decay is consistent with luminescent ions residing in more ordered phase
in which site-to-site variations are less significant than in disordered glassy host. It
should be noticed that the 1 D 2 luminescence dynamics is very sensitive to changes of

Thermal treatment effect on dynamics of luminescent states ... 381
praseodymium environment. Kinetics results imply that observed luminescence is
emitted by Pr 3+ ions incorporated into crystalline fluoride precipitates embedded into
into oxide glass matrix. Thus, dopant ions reside fluoride sites with lower phonon
energy, which results in excited state dynamics. The concentration of Pr 3+ in
crystalline precipitates is drastically higher than in as-melted sample due to preferential
segregation of ions in nanocrystals [19]. In highly doped systems, the ion–ion
interaction brings about an excitation energy migration and/or concentration
quenching by cross-relaxation. If the cross-relaxation rate is higher than migration
energy rate the luminescence decay curve is no longer exponential (Figs. 3d, 3e, 3f).
A more exponential character of the 3 P 0 decays (Figs. 3a, 3b, 3c) indicates that
luminescence is quenched mainly by migration of excitation energy. Time constants
of luminescence decays increased after heat treatment but the degree of these changes
is different for different emitting levels and glass composition. An explanation for this
is that each lifetime recorded is a result of trade-off between the effect of structural
changes that lengthens the lifetime and the effect of the increase of the Pr 3+
concentration in crystalline species, which makes the lifetime shorter. Such
luminescence decay behaviours of other Ln 3+ -doped glass-ceramics are reported in
literature [2, 4, 8, 19–21].
4. Conclusions
Based on the results presented in the paper we can conclude that heat-treatment
process influences the kinetics of luminescent levels. It was found that thermal
treatment leads to an increase of luminescence lifetimes. This effect was clearly seen
for the 1 D 2 level which is highly sensitive to ligand environment around dopant ion
and to non-radiative energy transfer by cross-relaxation (like the 5 D 3 terbium level).
Strongly non-exponential luminescence decay curves of 1 D 2 in as-melted glasses
became near-exponential in heated samples and lifetimes increased from a few to about
100 μs. Such a result indicates the presence of the crystalline fluoride phase in being
in oxide host. It follows from the 5 D 3 kinetics of Tb 3+ in heat-treated samples that
terbium ions are less efficient nucleating agents than Pr 3+ in this material. The reason
is not obvious and further investigation is necessary to explain this phenomenon.
References
[1] HIRAO K., TANAKA K., MAKITA M., SOGA N., Preparation and optical properties of transparent
glass-ceramics containing β-PbF 2:Tm 3+ , Journal of Applied Physics 78(5), 1995, pp. 3445–3450.
[2] MORTIER M., AUZEL F., Rare-earth doped transparent glass-ceramics with high cross-sections,
Journal of Non-Crystalline Solids 256–257, 1999, pp. 361–365.
[3] MORTIER M., PATRIARCHE G., Structural characterisation of transparent oxyfluoride glass-ceramics,
Journal of Materials Science 35(19), 2000, pp. 4849–4856.
[4] TICK P.A., BORRELLI N.F., CORNELIUS L.K., NEWHOUSE M.A., Transparent glass ceramics for 1300 nm
amplifier applications, Journal of Applied Physics 78(11),1995, pp. 6367–6374.
[5] QUIMBY R.S., TICK P.A., BORRELLI N.F., CORNELIUS L.K., Quantum efficiency of Pr 3+ doped
transparent glass ceramics, Journal of Applied Physics 83(3), 1998, pp. 1649–1653.

382 G. DOMINIAK-DZIK, B. KLIMESZ, W. RYBA-ROMANOWSKI
[6] KUKKONEN L.L., REANEY I.M., FURNISS D., PELLATT M.G., SEDDON A.B., Nucleation and
crystallisation of transparent, erbium III-doped, oxyfluoride glass-ceramics, Journal of
Non-Crystalline Solids 290(1), 2001, pp. 25–31.
[7] KLIMESZ B., DOMINIAK-DZIK G., SOLARZ P., ŻELECHOWER M., RYBA-ROMANOWSKI W., Optical study
of GeO 2 –PbO–PbF 2 oxyfluoride glass singly doped with Pr 3+ , Nd 3+ , Sm 3+ and Eu 3+ , Journal of
Alloys and Compounds 403(1–2), 2005, pp. 76–85.
[8] RYBA-ROMANOWSKI W., DOMINIAK-DZIK G., SOLARZ P., KLIMESZ B., ŻELECHOWER M., Effect of
thermal treatment on luminescence and VUV-to-visible conversion in oxyfluoride glass singly doped
with praseodymium and thulium, Journal of Non-Crystalline Solids 345–346, 2004, pp. 391–395.
[9] GOUTALAND F., JANDER P., BROCKLESBY W.S., GUOJUN DAI, Crystallisation effects on rare earth
dopants in oxyfluoride glass ceramics, Optical Materials 22(4), 2003, pp. 383–390.
[10] NACHIMUTHU P., JAGANNTHAN R., Tb 3+ fluorescence as a probe of cluster formation in lead
oxyfluoride glasses, Journal of Non-Crystalline Solids 183(1–2), 1995, pp. 208–211.
[11] RYBA-ROMANOWSKI W., BERKOWSKI M., VIANA B., ASCHEHOUG P., Relaxation dynamics of excited
states of Tm 3+ in SrGdGa 3O 7 crystals activated with Tm 3+ and Tb 3+ , Applied Physics B 64(5),
1997, pp. 525–529.
[12] SAISUDHA M.B., RAMAKRISHNA J., Effect of host glass on the optical absorption properties of Nd 3+ ,
Sm 3+ , and Dy 3+ in lead borate glasses, Physical Review B 53(10), 1999, pp. 6186–6196.
[13] AMARANATH G., BUDDHUDU S., BRYANT F.J., Spectroscopic properties of Tb 3+ -doped fluoride
glasses, Journal of Non-Crystalline Solids 122(1), 1990, pp. 66–73.
[14] CANALE J.E., CONDRATE SR. R.A., NASSAU K., CORNILSEN B.C., Characterization of various glasses
in the binary PbO–GeO 2 and Bi 2 O 3 –GeO 2 systems, Journal of the Canadian Ceramic Society 55,
1986, pp. 50–56.
[15] WACHTLER M., SPEGHINI A., PIGORINI S., ROLLI R., BETTINELLI M., Phonon sidebands and vibrational
properties of Eu 3+ doped lead germanate glasses, Journal of Non-Crystalline Solids 217(1), 1997,
pp. 111–114.
[16] BALDA R., FERNÁNDEZ J., DE PABLOS A., FDEZ-NAVARRO J.M., Spectroscopic properties of Pr 3+ ions
in lead germanate glass, Journal of Physics: Condensed Matter 11(38), 1999, pp. 7411–7421.
[17] PISARSKI W.A., PISARSKA J., DOMINIAK-DZIK G., RYBA-ROMANOWSKI W., Visible and infrared
spectroscopy of Pr 3+ and Tm 3+ ions in lead borate glasses, Journal of Physics: Condensed Matter
16(34), 2004, pp. 6171–6184.
[18] TONOOKA K., KAMATA N., YAMADA K., MATSUMOTO K., MARUYAMA F., A non-linear analysis of
energy transfer in highly Tb 3+ -doped glasses, Journal of Luminescence 50(3), 1991, pp. 139–151.
[19] MORTIER M., GOLDNER P., CHATEAU C., GENOTELLE M., Erbium doped glass-ceramics: concentration
effect on crystal structure and energy transfer between active ions, Journal of Alloys and
Compounds 323–324, 2001, pp. 245–249.
[20] MELTZER R.S., YEN W.M., ZHENG H., FEOFILOV S.P., DEJNEKA M.J., TISSUE B., YUAN H.B., Effect of
the matrix on the radiative lifetimes of rare earth doped nanoparticles embedded in matrices,
Journal of Luminescence 94–95, 2001, 217–220.
[21] HAYASHI H., TANABE S., HANADA T., 1.4 μm band emission properties of Tm 3+ ions in transparent
glass ceramics containing PbF 2 nanocrystals for S-band amplifier, Journal of Applied Physics 89(2),
2001, pp. 1041–1045.
Received November 12, 2009

Optica Applicata, Vol. XL, No. 2, 2010
Hybrid materials doped with lithium ions
ELŻBIETA ŻELAZOWSKA 1* , EWA RYSIAKIEWICZ-PASEK 2
1 Institute of Glass, Ceramics, Refractory and Construction Materials – The Glass Branch in Cracow,
ul. Lipowa 3, 30-702 Kraków, Poland
2 Institute of Physics, Wrocław University of Technology, Wybrzeże Wyspiańskiego 27,
50-370 Wrocław, Poland
* Corresponding author: ezelazowska@isic.krakow.pl
Sol–gel derived lithium-ion conducting organic–inorganic hybrid materials have been synthesized
from tetraethyl orthosilicate (TEOS), propylene glycol, ethylene glycol dimethacrylate, poly(vinyl
alcohol), vinyl acetate, ethyl acetoacetate, poly(methyl methacrylate), propylene carbonate
and some other precursors and solvents. The mass fraction of the organic additions in the gels and
the level of the lithium salt doping (LiClO 4 ) were ~40 mass% and 0.01%, respectively.
The morphological and structural properties of the gels were investigated by a scanning electron
microscope equipped with energy dispersive X-ray spectroscopy (SEM/EDX), X-ray diffraction
(XRD), and Fourier-transform infrared spectroscopy (FTIR) and 29 Si MAS Nuclear Magnetic
Resonance ( 29 Si MAS NMR). The hybrid gels obtained were amorphous and colourless transparent
or slightly opalescent, with the room temperature ionic conductivities of the order of 10 –3 Scm –1 .
The results of FTIR spectroscopy and 29 Si MAS NMR investigations have revealed strong
influence of the organic modification, resulting in the direct chemical bonding between organic
and inorganic components of the gels. The WO 3 -based electrochromic cells with the hybrids
obtained being applied as the electrolytes were able to be reversibly coloured and bleached in
the optical transmittance range of ~58% to 5% at around 550 nm.
Keywords: organic–inorganic hybrids, sol–gel, lithium electrolyte, ionic conductivity.
1. Introduction
Solid materials with relatively high ionic conductivities at ambient temperatures have
potentially a wide range of practical applications in the solid-state rechargeable
batteries [1] and advanced electrochemical devices, such as electrochromic displays,
variable reflectance mirrors or smart windows [2, 3]. In the last years, intensive
development has been observed in the use of sol–gel process for preparing
the organically modified silanes (ormosils) [4, 5]. Amorphous organic–inorganic
hybrid materials, which are synthesized through relatively easy and low cost sol–gel
route and have the potential of being used in integrated optics and solid electrolyte
(ormolyte) applications have recently attracted a great deal of research attention [6, 7].
Many organic compounds have been proposed as components of the sol–gel
derived hybrid electrolytes, including polyacrylonitrile (PAN), poly(ethylene oxide)

384 E. ŻELAZOWSKA, E. RYSIAKIEWICZ-PASEK
(PEO), poly(tetramethylene oxide) (PTMO), poly(methyl methacrylate) (PMMA),
polyethylene glycol (PEG), polypropylene glycol (PPG), poly(vinylidene fluoride)
(PVDF), some network polymers prepared by cross-linking reactions, and mixtures of
polymers from these two groups [8–11].
Among the possible organic additions, polyether polymers have been studied
extensively due to their favourable feature of being miscible with many kinds of liquid
electrolytes for lithium batteries, [9] and [12]. CHAKER et al. [7] have reported on
siloxane-poly-(propylene oxide) (PPO, with 2000 and 4000 g/mol molecular weight)
based hybrid electrolytes doped with sodium perchlorate (NaClO 4), obtained by
the sol–gel method and exhibiting the ionic conductivity of 8.9×10 –4 Scm –1 at room
temperature. DAHMOUCHE et al. [13] and DE SOUZA et al. [14] have investigated lithium
ion-conducting ormolytes with ionic conductivities higher than 10 –4 Sm –1 at room
temperature. They have found that in the hybrids prepared by sol–gel process from
the mixture of tetraethyl orthosilicate (TEOS), polyethylene glycol (PEG), and lithium
salt (LiClO 4), the organic and inorganic parts were not chemically bonded, while
the chemical bonding has been revealed in the hybrid electrolytes obtained from
a mixture of 3-isocyanatopropyltriethoxysilane, O,O'-bis-(2-aminopropyl)-polyethylene
glycol or O,O'-bis-(2-aminopropyl)-polypropylene glycol, and lithium salt.
Due to appropriate doping and controlling of a molecular structure by organic
modification to enable fast proton and/or lithium ion conduction, organic–inorganic
hybrid materials have proved to be a remarkable family of amorphous solid state
electrolytes for promising practical applications. On the other hand, the ionic
conductivity of the hybrid electrolytes has been found to be strongly dependent on
the morphology and microstructure [9, 15, 16].
2. Experiment
2.1. Materials for hybrid synthesis
The hybrid materials for electrolytes have been synthesized from the tetraethyl
orthosilicate (TEOS, [Si(OC 2 H 5 ) 4 ]), propylene glycol (propane-1,2-diol; PG),
ethylene glycol dimethacrylate (C 10 H 14 O 4 , EGDMA), poly(vinyl alcohol) (ethenol,
T a b l e 1. Components of the starting solutions.
Sample Components
A
B
C
TEOS, PG, VAM, PMMA,
PC, CH2Cl2, ethanol
TEOS, PG, EGDMA, PVA,
PMMA VAM, EAA, CH2Cl2 ,
methanol, ethanol
TEOS, PG, PVA, VAM,
EGDMA, PC, methanol, ethanol
Lithium salt/solvent/
fraction
LiClO 4/ethanol/0.01
LiClO 4 /ethanol//0.01
LiClO 4/PC/0.01
Appearance,
remarks
colourless,
transparent
colourless,
slightly opalescent
colourless,
transparent

Hybrid materials doped with lithium ions 385
PVA, M w ≈ 72000), vinyl acetate (ethenyl acetate; VAM), ethyl acetoacetate (ethyl
3-oxobutanoate; EAA), poly(methyl methacrylate) (poly(methyl 2-methylpropenoate),
PMMA, M w ≈ 120000), propylene carbonate (4-methyl-1,3-dioxolan-2-one, C 4H 6O 3,
PC), dichloromethane (CH 2 Cl 2 ), ethanol and methanol, precursors and solvents.
Components (at least of reagent grade, Merck and Aldrich) of the starting solutions
for hybrids under investigation are listed in Tab. 1.
Mass fractions of the organic compounds were calculated on ~40 mass% in
the gels. The level of the lithium salt doping (LiClO 4 in solution with PC or ethanol)
was ~0.01 for all the gels synthesized.
2.2. Experimental procedure
2.2.1. Sol–gel procedure
Silica components of the gels under investigation were prepared by mixing TEOS
[Si(OC2H5) 4] (0.09 mol for each hybrid gel) and distilled water with the stoichiometric
molar ratio of TEOS:H2O = 1:4. As a catalyst, 36.6% HCl was added drop by drop,
up to pH = 2. Solutions of PMMA or PVA (1.5 g and/or 1 g, respectively) in organic
solvents (dichloromethane, methanol and ethanol) were prepared under stirring for at
least 3 h at a temperature of 45±5 °C. Solutions of TEOS, after stirring for 1 h, were
mixed with solutions of the PMMA or PVA. Then, under the continuous stirring, PG
and VAM (6 ml and 15 ml, respectively) per each gel and the other organic compounds
(0.08 mol of EGDMA, and/or PC and EAA in the weigh amounts equal to that of VAM
addition) were added one by one. The resulting mixtures after being stirred for ~1 h
were poured into the plastic dishes. The gelation process occurred within several hours
to 1 day. The hybrid gels were aged at ambient temperature for 2 weeks and then heated
in an electric oven for 3 h at a temperature of 105 °C.
2.2.2. Spray pyrolysis coating procedure for thin metal oxide electrochromic electrodes
The spectral and current–voltage characteristics have been obtained for a WO 3 –V 2 O 5
thin film electrochromic system. The layers of the sol–gel derived lithium ion doped
organic–inorganic hybrid materials under investigation were applied as the solid
electrolytes with the aim to determine their potential to be useful for room-temperature
electrochemical applications. Electrochromic devices consisted of: a transparent
conducting layer (SnO 2 :F)/a cathodic, active electrochromic layer (WO 3 )/an ion
conducting layer (hybrid electrolyte)/an anodic counter electrode layer (NiO)/
a transparent conducting layer (SnO 2 :F), which were prepared for this study as
the symmetric multilayer structures of a smart window arrangement.
Thin electrochromic films of tungsten oxide and vanadium oxide for an active
and a counter electrode, respectively, were obtained by a spray pyrolysis method, at
the substrate temperature of about 680 °C and 670 °C, respectively. The transparent
electrode substrates were soda-lime glass plates (25×50×4 mm 3 ) coated with fluorine
doped tin oxide (SnO 2 :F, K-Glass, Pilkington). The substrates to be coated were
carefully washed with a detergent solution, etched in a 4% aqueous solution of
hydrofluoric acid for 5 min, and then rinsed with distilled water and ethanol.

386 E. ŻELAZOWSKA, E. RYSIAKIEWICZ-PASEK
Tungsten (VI) oxide acetylacetonate WO(VI)(C 5 H 7 O 2 ) 4 and vanadyl
acetylacetonate (VO(IV)(C 5 H 7 O 2 ) 2 , bis(2,4-pentanedionato)vanadium(IV) oxide) in
solution with dichloromethane, were used as precursors of the metal oxide
electrochromic films. Detailed procedures were used for thin metal oxide films and
preparation of electrochromic cells followed that described in [17]. The thickness of
the films obtained when measured with a “Talystep” microprofilometer (Rank Taylor
Hobson Ltd., Great Britain), was about 120 nm and 150 nm for WO 3 and V 2 O 5 ,
respectively.
2.3. Instruments and measurements
The obtained hybrid materials and metal oxide films were characterized for
morphology by scanning electron microscopy equipped with energy dispersive
X-ray spectroscopy (SEM/EDX, JEOL JSM 5400 with LINK An 10/5, NOVA
NANOSEM-FEI). Fourier transform infrared spectroscopy (Bio-Rad FTS-60VM
FTIR spectrometer, KBr technique), nuclear magnetic resonance 29 Si MAS NMR
(NMR spectrometer at the magnetic field 7.05 T) and X-ray diffraction (XRD 7, Seifert
diffractometer) were used for examination of microstructure of the hybrids obtained
in this work. Spectral characteristics of the WO 3 -based thin film electrochromic cells
under investigation in the coloured and bleached states have been obtained by
applying a DC voltage of ±(1.4–1.8) V between a WO 3 /SnO 2 :F active electrode and
a V 2 O 5 /SnO 2 :F counter electrode, being registered with a Jasco V-570 spectrophotometer.
The spectral and current–voltage characteristics of the electrochromic
cells with hybrid electrolytes were observed at ± polarized DC potential of
±(1.4–3.5) V applied through a laboratory-made potentiostat/galvanostat. The AC
conductivity measurements were performed by using an Alpha N dielectric analyser
(Novocontrol) in the frequency range of 7.32×10 –2 Hz–3×10 6 Hz at room
temperature. The measurements were carried out in the specially constructed sample
cells with the platinum plate electrodes pressed against the sample surface. The area
of the contact was about 0.5 cm 2 .
3. Results and discussion
3.1. Structural characterization
3.1.1. XRD and SEM/EDX results
The appearance of the gels after heat treatment is described in Tab. 1. All the gels
obtained have revealed an amorphous structure under XRD examination. The XRD
pattern, typical of hybrids under investigation, is shown in Fig. 1.
Typical SEM images (surface view and fractured surface, at a magnification of
50000×) of the WO 3, V 2O 5 thin films obtained in this work for the electrochromic
electrodes and of the hybrids A, B and C applied as electrolytes in the electrochromic
cells of the WO 3 –V 2 O 5 system are shown in Figs. 2a–2c and 2d–2f, respectively.

Hybrid materials doped with lithium ions 387
Fig. 1. XRD pattern of the hybrid A, typical of the hybrids under investigation.
The EDX results typical of the organic–inorganic hybrid gels under investigation
(for gel C, synthesized from: TEOS, PG, PVA, VAM, EGDMA, PC, LiClO 4 , methanol,
ethanol) are presented in Fig. 3.
The scanning electron microscopy coupled with X-ray energy dispersive
spectroscopy (SEM/EDX) in agreement with the XRD investigation results have
revealed the obtained metal oxide films to be porous and polycrystalline with
uniformly distributed nano-sized crystallites. The amorphous and significantly porous
morphology has been observed for the sol–gel derived hybrid electrolytes A, B and
a b c
d e f
Fig. 2. SEM images of thin films of WO 3 (a), V 2 O 5 (b – surface view, c – fractured surface) and hybrid
gels: A (d), B (e), C (f), at a magnification of 50000×.

388 E. ŻELAZOWSKA, E. RYSIAKIEWICZ-PASEK
Fig. 3. EDX spectrum of a micro-area surface registered at a magnification of 5000× for hybrid gel C
synthesized from TEOS, PG, EGDMA, PVA (M w ≈ 72000), VAM, PC, LiClO 4 and organic solvents.
especially C (Figs. 2d–2f, respectively) and such a thin microstructure can be seen as
advantageously available for a diffusion of alkali ions.
3.1.2. 29 Si MAS NMR and FTIR spectroscopy results
29 Si MAS NMR spectra and calculated results of the hybrid gels after heat treatment
at 105 °C are shown in Fig. 4 and Tab. 2, respectively.
29 Si MAS NMR spectra of the hybrid electrolytes exhibit peak profiles with
different amounts of the Q 4 , Q 3 and Q 2 structural units corresponding to the silicon Si
in coordination of 4, 3 or 2 in respect to the bridging oxygen atoms. The analysis of
these spectra was based on the numerical values of the parameter A1 equal to the ratio
of Q 4 /Q 3 and parameter A2 equal to the ratio of Q 4 /Q 2 calculated from the relative
fractions of the peak area, corresponding to the appropriate Q species, where Q 4 value
Q 1
Q 2 Q 3
Fig. 4. 29 Si MAS NMR spectra for organic–inorganic hybrid electrolytes under investigation A, B
and C (the Q 4, Q 3 and Q 2 peaks are corresponding to the structural units corresponding to the silicon Si
in coordination 4, 3 or 2).

Hybrid materials doped with lithium ions 389
T a b l e 2. Isotropic chemical shifts (δ, ppm), line widths (half width at half maximum (hwhm), ppm)
and relative fraction (%) of Q n units in the hybrid materials.
Sample
Q 2
–δ, hwhm [ppm];
relative share [%]
Q 3
–δ, hwhm [ppm];
relative share [%]
Q 4
–δ, hwhm [ppm];
relative share [%]
A1 = -------- A2 = --------
A –92.4 (5.7) 7 –101.6 (7.1) 40 –110.8 (8.5) 50 1.25 7.14
B –93.0 (9.0) 12 –101.7 (7.0) 41 –110.8 (8.6) 47 1.15 3.92
C –91.7 (5.5) 8 –101.5 (6.2) 48 –110.3 (7.9) 44 0.92 5.50
at approximately –109 ppm corresponds to [SiO 4 ] tetrahedrons. The higher the A1 and
A2 values, the higher the poly-condensation degree of the silicon-oxygen network.
The observed chemical shifts were referenced to the signal of tetramethyl silane
(TMS).
The NMR measurements (Tab. 2), with a good agreement with results of
SEM/EDX, indicated the poly-condensation of the inorganic network to be relatively
less developed for hybrids B and C, with the (PG, EGDMA, PVA, PMMA, VAM,
EAA) or (PG, PVA, VAM, EGDMA, PC) organic additives, respectively, than that of
hybrid A, prepared with organic part containing PG, VAM, PMMA and PC.
Additionally, the time of gelation as short as about 5–6 h and an enormous increase
in the viscosity of the gels, especially just before the end of gelation process were
observed for all the hybrids under investigation. A similar effect was reported by
BOONSTRA et al. [18], among others, and it can be ascribed to the poly-condensation
of inorganic structural units overlapped with cross-linking process. The course of
condensation, as observed for all the hybrid gels under investigation, seems to be
associated with cross-linking polymerization of the organic and inorganic groups
connected with formation of the cross-linked chains of particles, especially due to
the presence of the carboxylic groups originated from acrylic acid derivatives.
The cross-linking effect of the carboxylic groups on a surface polymerization and
grown of the primary created particles has already been reported [19, 20].
FTIR spectra of the sol–gel derived hybrids obtained in this work are shown in
Fig. 5.
In the FTIR spectra of the sol–gel derived hybrid gels synthesized in this work
and investigated after the heat treatment at a temperature of 105 °C, the observed
broad absorption bands at around 3456–3435 cm –1 are assigned to stretching
vibrations of OH – groups originated from residual water and those from the organic
components (PVA, VAM) [23, 24]. The situation of these bands corresponds to
differing organic additions in the hybrids. Additionally, in the IR spectra of the gels
before the heat treatment, residual absorption signals from asymmetric stretching
vibrations ν as of the CH 2 groups and C–Hx bonds of aliphatic organic groups, were
observed in a range of about 2980–2880 cm –1 [5, 23].
The disappearance of signals from these groups as well as those at around
1460–1390 cm –1 corresponding to vibrations of the bonds in organic parts
Q 4
Q 3
Q 4
Q 2

390 E. ŻELAZOWSKA, E. RYSIAKIEWICZ-PASEK
Fig. 5. FTIR spectra of hybrid gels A, B and C,
heated at a temperature of 105 °C.
(COH- deformation, ν s (–COO – ), δ as (CH 3 ) groups) after heating at 105 °C, can be
ascribed to the incorporation of the organics, resulting in organic–inorganic bonding
and formation of a hybrid structure of the gels.
The bands located at around 1640 cm –1 are characteristic of adsorbed water
(H–O–H), while those at around 1784 cm –1 correspond to the stretching vibrations of
the C=O bonds and can be assigned to the etheric oxygen groups –C(=)–O– originated
from the carboxylic acid derivative (PMMA) and/or from acetic acid esters (VAM,
EAA) [11, 23]. In the case of hybrids under investigation, the absorption bands related
to C=O double bond vibrations are relatively weak. It can be supposed that in all
the hybrids obtained, and especially, gels A and B, there have occurred both
the organic–inorganic polymerization and a cross-linking process [19].
Three fundamental bands of the origin of Si–O vibrations, at about 1090 cm –1
(1087 cm –1 for gel C and 1086 cm –1 for gels A and B), 800 cm –1 and 460 cm –1 were
found in the FTIR spectra of all the gels under investigation. The first two correspond
to asymmetric and symmetric Si–O stretching vibrations, respectively, and the last
one to the O–Si–O bending vibrations. The presence of these bands, and especially
the bands at about 800 cm –1 , is the evidence of a considerable degree of polymerization
of the silica fragments into network due to the formation of oxygen bridges between
SiO 4 tetrahedrons. The large absorption band in a range of 1250 cm –1 –1000 cm –1 with
the dominating vibration mode at about 1087 cm –1 (ν as Si–O) seems to be overlapping
other vibration modes. A shoulder on the dominating vibration mode at around

Hybrid materials doped with lithium ions 391
1200 cm –1 can be assigned to the C–O stretching vibration and there in a region at
around 1110–1000 cm –1 the vibrations from Si–O–C can be overlapped [21, 24].
The absorption band for C–O bonds overlapped with Si–O vibrations band
without splitting the main absorption band at around 1087 cm –1 can be ascribed to
the conversion of the C–OH bonds in PVA and VAM to C–O–Si bonds, responsible
for the cross-linking of the organic parts to silica and due to a hybrid structure of
the gels [4].
Besides these bands, in the spectra of the gels under investigation, the absorption
peaks located at around 950 cm –1 correspond to νas Si–OH stretching vibrations
[21, 22]. Additionally, in the region at around 960 cm –1 the absorption corresponding
to the vibrations of the hydrogen bonding (δ (COH)) can overlap that of the stretching
vibrations of the non-bridging oxygen atoms, e.g., Si–OH [23].
The relatively weak bands at around 556–558 cm –1 corresponding to absorption
of lithium in LiClO4 and bonded to organics, are observed in the FTIR spectra of
all the hybrid electrolytes obtained [23]. Additionally, in the spectrum of hybrid
electrolyte C, besides the lithium bonded to organics, the peak from at
628 cm –1 can be observed, indicating the presence of the free lithium ions [25].
The FTIR data are in a good agreement with SEM/EDX and 29 Si MAS NMR data,
and from this it was concluded that the degree of the inorganic poly-condensation in
the gel A is higher than that of the gel B, and especially, gel C.
3.2. Electrochemical evaluation
–
ClO4 3.2.1. AC conductivity and cycling voltammetry
Figure 6 shows room temperature conductivities of hybrids A and C as a function of
frequency ranging from about 7.32×10 –2 Hz to 3×10 6 Hz.
AC conductivities of the order of 10 –3 Scm –1 , when measured at room temperature
have been typical values of the hybrid electrolytes investigated.
The conductivities of hybrids A and B proved to have almost the same dependence
of conductivity on the frequency. The best value of ionic conductivity of about
6.8×10 –3 Scm –1 was noticed for the hybrid electrolyte C, with ethylene glycol
Fig. 6. Conductivities of hybrids A and C as
a function of frequency at room temperature.

392 E. ŻELAZOWSKA, E. RYSIAKIEWICZ-PASEK
dimethacrylate (EGDMA), polyvinyl alcohol (PVA), vinyl acetate (VAM), and
propylene carbonate (PC) organic additives used as the gel precursors. The conductivities
of hybrids A and B, which were prepared with addition of PMMA, propylene
glycol (PG) and VAM, have proved to be a little lower than that of hybrid C and almost
equal to each other, although these gels differ in the content of such organic additives
as PG, EGDMA, PVA or EAA. The main difference in composition of the hybrids
under investigation is the content of PMMA in gels A and B, when the acrylic acid
derivatives are known for their cross-linking ability [20, 26]. On the other hand, it is
well known that the cross-linking density affects the flexibility of the polymer matrix:
the lower the cross-linking density, the more flexible the polymer matrix becomes [27].
The decrease in ionic conductivity with an increase of the content of polymer additives
in the gel matrix is related to the increase in the cross-linking density, resulteing in
a decrease of the flexibility of the hybrid matrix, and consequently, the mobility of
ionic charge carriers decreases.
Apart from the high conductivity, electrochemical stability is an important
characteristic of electrolytes for recent advanced applications. All the organic–inorganic
hybrid materials obtained in this work were examined as electrolytes for the symmetric
electrochemical cells of WO 3 –V 2 O 5 thin film system with an electrochromic window
arrangement.
The cyclic voltammetry (CV) results obtained for an electrochromic cell of
the WO 3 –V 2 O 5 thin film system with hybrid electrolyte B under a potential signal
of a rectangular shape applied by means of a potentiostat-galvanostat, typical of
the materials under investigation, are shown in Fig. 7.
The cyclic voltammogram presented in Fig. 7b was recorded at a sweep rate of
50 mV/s and with potentials ranging from –3.0 to 3.0 V after about 10 3 colouring–
–bleaching cycles.
a b
Fig. 7. Typical current response (a) and cyclic voltammogram (b) for thin film tungsten oxide–vanadium
oxide electrochromic cell with organic–inorganic hybrid electrolyte B, cycled at a voltage of ±3.0 V
(cycled area: 4 cm 2 ; scan rate 50 mV/s).

Hybrid materials doped with lithium ions 393
The CV course has been observed to stay established after a few initial cycles.
The electrochromic films exhibit two distinct reduction-oxidation peaks at the low
voltage values, which may be associated with redox couple in the V 2O 5 film and two
weakly distinguishable peaks which can be attributed to lithium ions intercalation/
deintercalation in the WO 3 film. The shape of the CV curve is typical of the diffusion
controlled and a highly reversible lithium intercalation/deintercalation process and
well corresponds to the symmetric current response of the cell (Fig. 7a), indicating
hybrid materials under investigation to be a sufficient host for reversible intercalation/
deintercalation of lithium ions. On the other hand, the colouring–bleaching cycles of
the WO 3 film have been performed very fast and associated with sharp colour changes.
Such a behaviour of the WO 3 film seems to be attributed to the nano-sized
polycrystalline morphology to be favourable to the colouring efficiency enhancement
due to the probable participation of the surface and pore bonded protons.
3.2.2. Transmission characteristics
Figure 8 shows typical UV/VIS/NIR spectral transmittance characteristics of
a WO 3 –V 2 O 5 symmetric thin film electrochromic system of an electrochromic
window arrangement with a WO 3 layer for the active electrode and a V 2 O 5 layer for
the complementary counter electrode. Electrochromic layers were coated onto glass
with the electro-conductive films of fluorine (F) doped SnO 2 , and laminated with
hybrid C employed as an electrolyte.
The spectral measurements conducted after up to 30 colouring–bleaching cycles
were performed at potential values ranging from ±1.4 to ±1.8 V. The presented data
Fig. 8. Typical spectral transmittance characteristics for a WO 3–V 2O 5 thin film system of an electrochromic
window arrangement, coloured and bleached under ±1.8 V polarized DC voltage, with a layer
of hybrid gel as electrolyte (C: synthesized from TEOS, PG, PVA, PC, VAM, EGDMA, LiClO 4,
dichloromethane and ethanol, precursors and solvents). The electrochromic layers are coated onto
the sheets of glass with electro-conductive transparent electrodes (SnO 2 :F); the labels W, V, W–V,
correspond to the electrodes of WO 3, V 2O 5 and WO 3–V 2O 5 cell in a bleached (b) and coloured state (c),
respectively.

394 E. ŻELAZOWSKA, E. RYSIAKIEWICZ-PASEK
were obtained both in the coloured and bleached states under a ±1.8 V polarized DC
voltage.
The thin film coating structure of the electrochemical cell used for CV and spectral
transmittance examination corresponds to a system in which lithium ions are
intercalated and deintercalated in tungsten oxide and vanadium oxide layers according
to the electrochemical reactions (1) and (2), respectively:
WO 3 + xe – + xLi + ↔ Li x WO 3
Li x V 2 O 5 ↔ V 2 O 5 + ye – + yLi + (2)
The vanadium pentoxide displays both cathodic and anodic colouration, but it is
applied mainly for ion storage counter electrodes because of a change in optical
spectrum not as large as that of the WO 3 [28]. In a bleached state the amorphous V 2 O 5
layer is yellow and after lithium insertion it becomes blue-green due to the absorption
band at around 450 nm, typical of intervalence transfers between V 4+ and V 5+ [29].
In crystalline V 2 O 5 the insertion of Li + follows the reaction (2) and results in a colour
change from yellow to blue (Fig. 8, V/c) [30].
In the electrochromic systems under investigation, the insertion of lithium ions
changes the transmission in the visible range (at a wavelength of 550 nm) from about
58% to about 5% or 40% when the WO 3 and V 2 O 5 electrochromic electrodes are in
a coloured state, respectively (Fig. 8). All the hybrid gels obtained in this work, when
applied as the electrolytes in a WO 3 –V 2 O 5 electrochromic system have proved to be
able to be reversibly coloured and bleached in a short time of less than 2 s and
with significant changes in the optical transmittance, with modulation from about 60%
to 5%.
The transmittance characteristics in the VIS/NIR spectral range presented in Fig. 8,
in a good agreement with the SEM observations have proved to be characteristic of
polycrystalline non-stoichiometric thin films of tungsten oxide and vanadium
pentoxide with spectral reflective properties connected with Drude’s free-electron
modulation in NIR in a bleached and coloured state, respectively [31, 32].
4. Conclusions
Sol–gel derived, amorphous Li-ion conductive organic–inorganic hybrid materials
with the ionic conductivities of about (6.2–6.8)×10 –3 Scm –1 at room temperature and
containing ~40% of the organic additives were obtained using tetraethyl orthosilicate
TEOS, propylene glycol, ethylene glycol dimethacrylate, poly(vinyl alcohol), vinyl
acetate, ethyl acetoacetate, poly(methyl methacrylate), propylene carbonate, lithium
perchlorate and organic solvents. Direct chemical bonding between the inorganic and
organic parts have been revealed from FTIR and 29 Si MAS NMR spectra. The polycondensation
process overlapped with cross-linking polymerization has been
observed, especially in the hybrids containing PMMA. The room temperature
(1)

Hybrid materials doped with lithium ions 395
conductivity of all the hybrids under investigation is almost linear in the frequency
range of about 50 Hz to 3.5×10 5 Hz. The symmetric situation and shape of cathodic
and anodic peaks for active- and counter-electrode due to ion intercalation and
deintercalation, respectively, indicate materials under investigation to be kinetically
favoured insertion hosts. On the other hand, relatively sharp peaks at the highest values
of the voltage applied makes the association of lithium and proton conductance
possible, due to protons bonded with surface pores of the nano-sized polycrystalline
structure of the hybrids. All the hybrid materials obtained in this work have proved to
be electrochemically effective in reversible electrochromic reactions depending on
reversible intercalation–deintercalation of the lithium ions, which makes them
prospective as electrolytes for ambient temperature electrochemical and optoelectronic
applications.
References
[1] KONO M., HAYASHI E., NISHIURA M., WATANABE M., Chemical and electrochemical characterization
of polymer gel electrolytes based on poly(alkylene oxide) macromonomer for application to lithium
batteries, Journal of The Electrochemical Society 147(7), 2000, pp. 2517–2524.
[2] GLÄSER H.J., Large Area Glass Coating, Von Ardenne Anlagentechnik GMBH, Dresden 2000,
pp. 377–393.
[3] GRANQVIST C.G., AVENDAÑO E., AZENS A., Electrochromic coatings and devices: survey of some
recent advances, Thin Solid Films 442(1–2), 2003, pp. 201–211.
[4] PEREIRA A.P.V., VASCONCELOS W.L., ORÉFICE R.L., Novel multicomponent silicate–poly(vinyl
alcohol) hybrids with controlled reactivity, Journal of Non-Crystalline Solids 273(1–3), 2000,
pp. 180–185.
[5] JITIANU A., BRITCHI A., DELEANU C., BADESCU V., ZAHARESCU M., Comparative study of the sol–gel
processes starting with different substituted Si-alkoxides, Journal of Non-Crystalline Solids 319(3),
2003, pp. 263–279.
[6] ATKINS G.R., KROLIKOWSKA R.M., SAMOC A., Optical properties of an ormosil system comprising
methyl- and phenyl- substituted silica, Journal of Non-Crystalline Solids 265(3), 2000,
pp. 210–220.
[7] CHAKER J.A., DAHMOUCHE K., SANTILLI C.V., PULCINELLI S.H., BRIOIS V., FLANK A.-M.,
JUDENSTEIN P., Siloxane-polypropyleneoxide hybrid ormolytes: structure-ionic conductivity
relationships, Journal of Non-Crystalline Solids 304(1–3), 2002, pp. 109–115.
[8] KONO M., HAYASHI E., WATANABE M., Preparation, mechanical properties, and electrochemical
characterization of polymer gel electrolytes prepared from poly(alkylene oxide) macromonomers,
Journal of The Electrochemical Society 146(5), 1999, pp.1626–1632.
[9] NAKAJIMA H., NOMURA S., SUGIMOTOT., NISHIKAWA S., HONMA I., High temperature proton
conducting organic/inorganic nanohybrids for polymer electrolyte membrane, Journal of
The Electrochemical Society 149(8), 2002, pp. A953–A959.
[10] SONG J.Y., WANG Y.Y., WAN C.C., Conductivity study of porous plasticized polymer electrolytes
based on poly(vinylidene fluoride) – A comparison with polypropylene separators, Journal of
The Electrochemical Society 147(9), 2000, pp. 3219–3225.
[11] SAMAR KUMAR MEDDA, DEBTOSH KUNDU, GOUTAM DE, Inorganic–organic hybrid coatings on
polycarbonate: Spectroscopic studies on the simultaneous polimerizations of methacrylate and silica
networks, Journal of Non-Crystalline Solids 318(1–2), 2003, pp. 149–156.
[12] POINSIGNON C., Polymer electrolytes, Materials Science and Engineering: B 3(1–2), 1989, pp. 31–37.

396 E. ŻELAZOWSKA, E. RYSIAKIEWICZ-PASEK
[13] DAHMOUCHE K., SANTILLI C.V., DA SILVA M., RIBEIRO C.A., PULCINELLI S.H., CRAIEVICH A.F.,
Silica-PEG hybrid electrolytes: structure and properties, Journal of Non-Crystalline Solids
247(1–3), 1999, pp. 108–113.
[14] DE SOUZA P.H., BIANCHI R.F., DAHMOUCHE K., JUDEINSTEIN P., ROBERTO M. FARIA R.M.,
BONAGAMBA T.J., Solid-state NMR, ionic conductivity, and thermal studies of lithium-
-doped siloxane–poly(propylene glycol) organic–inorganic nanocomposites, Chemistry of
Materials 13(10), 2001, pp. 3685–3692.
[15] YONG-IL PARK, MASAYUKI NAGAI, Proton-conducting properties of inorganic-organic nanocomposites,
proton-exchange nanocomposite membranes based on 3-glycidoxypropyltrimethoxysilane and
tetraethylorthosilicate, Journal of The Electrochemical Society 148(6), 2001, pp. A616–A623.
[16] HUNT A., Statistical and percolation effects on ionic conduction in amorphous systems, Journal of
Non-Crystalline Solids 175(1), 1994, pp. 59–70.
[17] ŻELAZOWSKA E., ZIEMBA B., LACHMAN W., Counter electrodes for WO 3 -based electrochromic
coatings, Optica Applicata 30(4), 2000, pp. 663–670.
[18] BOONSTRA A.H., MEEUWSEN T.P.M., BAKEN J.M.E., ABEN G.V.A., A two-step silica sol–gel process
investigated with static and dynamic light-scattering measurements, Journal of Non-Crystalline
Solids 109(2–3), 1989, pp. 153–163.
[19] DOO-HYUN LEE, JIN-WOONG KIM, KYUNG-DO SUH, Monodisperse micron-sized polymethylmethacrylate
particles having a crosslinked network structure, Journal of Materials Science 35(24),
2000, pp. 6181–6188.
[20] SHUXUE ZHOU, LIMIN WU, WEIDIAN SHEN, GUANGXIN GU, Study on the morphology and tribological
properties of acrylic based polyurethane/fumed silica composite coatings, Journal of Materials
Science 39(5), 2004, pp. 1593–1600.
[21] PRIMEAU N., VAUTEY C., LANGLET M., The effect of thermal annealing on aerosol-gel deposited SiO 2
films: a FTIR deconvolution study, Thin Solid Films 310(1–2), 1997, pp. 47–56.
[22] YING J.Y., BENZIGER J.B., NAVROTSKY A., Structural evolution of alkoxide silica gels to glass: effect
of catalyst pH, Journal of the American Ceramic Society 76(10), 1993, pp. 2571–2582.
[23] GÜNZLER H., GREMLICH H.-U., IR Spectroscopy: An Introduction, Wiley-VCH Verlag GmbH,
Weinheim, 2002, pp. 189–246.
[24] PARASHAR V.K., RAMAN V., BAHL O.P., Sol–gel preparation of silica gel monoliths, Journal of
Non-Crystalline Solids 201(1–2), 1996, pp. 150–152.
[25] MUNRO B., Ion-conducting properties of SiO 2 gels containing lithium salt, Glass Science and
Technology – Glastechnische Berichte 68(4), 1995, pp. 123–132.
[26] KYOUNG-HEE LEE, KI-HO KIM, HONG S. LIM, Studies on a new series of cross-linked polymer
electrolytes for a lithium secondary battery, Journal of The Electrochemical Society 148(10),
2001, pp. A1148–A1152.
[27] EISENBERG A., Physical Properties of Polymers, 2nd Ed., American Chemical Society, Washington
DC, 1993, p. 88.
[28] DONNADIEU A., Electrochromic materials, Materials Science and Engineering: B 3(1–2), 1989,
pp. 185–195.
[29] ÖZER N., Electrochemical properties of sol–gel deposited vanadium pentoxide films, Thin Solid
Films 305(1–2), 1997, pp. 80–87.
[30] COGAN S.F., NGUYEN N.M., PERROTTI S.J., RAUH R.D., Optical properties of electrochromic
vanadium pentoxide, Journal of Applied Physics 66(3), 1989, pp. 1333–1337.
[31] ASHRIT P.V., BADER G., TRUONG V.V., Electrochromic properties of nanocrystalline tungsten oxide
thin films, Thin Solid Films 320(2), 1998, pp. 324–328.
[32] COGAN S.F., PLANTE T.D., PARKER M.A., RAUH R.D., Electrochromic solar attenuation in crystalline
and amorphous Li xWO 3, Solar Energy Materials 14(3–5), 1985, pp. 185–193.
Received November 12, 2009
in revised form January 4, 2010

Optica Applicata, Vol. XL, No. 2, 2010
Optical properties of small silver particles
embedded in soda-lime silica glasses
MARIA SUSZYŃSKA * , TERESA MORAWSKA-KOWAL, LUDWINA KRAJCZYK
Institute of Low Temperature and Structure Research, Polish Academy of Sciences,
ul. Okólna 2, 50-950 Wrocław, Poland
* Corresponding author: Maria Suszynska@int.pan.wroc.pl
The optical characteristics of silver nanoparticles embedded in a surface layer of commercial soda
lime silica glass have been analysed. Additional results were obtained by the transmission electron
microscopy observations and the selective area electron diffraction patterns. In this report, we
have shown the effect of deviation from the spherical shape and non-homogeneous distribution on
the optical characteristics of the Ag nanocrystals embedded in the dielectric matrix under study.
Keywords: soda-lime silica glass, ion exchange, silver nanoparticles, optical absorption, transmission
electron microscopy.
1. Introduction
Embedding silver-clusters of nanometer dimensions in a dielectric matrix, e.g.,
the oxide glasses, provides a simple way to study the linear and nonlinear optical
properties of the systems thus composed [1]. The main feature of the linear optical
response of these new materials is the collective excitation of the free conduction band
electrons, known as the surface plasmon resonance (SPR), and observed in the visible
region of the optical spectra [1]. In addition to the basic interest, the presence of
a quantum-size behaviour has attracted much attention in view of the potential photonic
applications of the systems mentioned [2, 3].
In the present communication, we report on the optical response of Ag-clusters
embedded in a soda-lime silica (SLS) glass. This study extends our previous
works reporting on the optical, mechanical and dielectric characteristics of the same
system [4–6]. Because of the results obtained recently for the copper-doped SLS
glass [7], special attention was paid to changes of the shape of matrix droplets as well
as to the shape and size of the metal nanoparticles during the thermal treatment which
follows the Ag/Na ion exchange process.

398 M. SUSZYŃSKA, T. MORAWSKA-KOWAL, L. KRAJCZYK
2. Experimental part
The main constituents of the SLS glass were (mole percent): SiO 2 (73.5), Na 2 O (13.8),
CaO (6.5), MgO (4.5), and Fe 2O 3 (0.15) that contains about 50% of divalent iron; this
composition corresponds to the miscibility gap in the SiO 2 –Na 2 O system [8].
For ion exchange, the sample (about two millimetres thick) was kept at
a temperature T ex for a time t ex in a molten mixture of NaNO 3 and AgNO 3. After
exchange, the samples were annealed at 873 K either for 0.5 or 4 h in the ambient
air. The Table gives the concentration c of AgNO 3 , the parameters T ex and t ex as well
as values of the penetration depths (pd) of metallic silver obtained after the thermal
treatment. Values of pd 0.5 and pd 4 were determined by microspectrophotometric
measurements, cf. [5, 9].
T a b l e. Parameters of the ion exchange process and the silver penetration depths for specimens
annealed at 873 K for 0.5 and 4 h.
Sample c [%] T ex [K] t ex [h] pd 0.5 [μm] pd 4 [μm]
FAg1 0.5 673 2 130 250
FAg2 2 673 2 180 380
FAg3 0.5 603 310 250 490
FAg4 2 603 310 330 595
The optical absorption (OA) spectra were recorded in the range between 250 and
600 nm using a Varian (Cary 5) spectrophotometer; all measurements were performed
at 294 K.
Microstructural data were obtained by means of a transmission electron microscope
(TEM; PHILIPS-CM20) operating at 200 kV and providing a 24 nm point-to-point
resolution. Two types of replica (extraction and carbon-shadowed) were prepared from
surfaces normal to the exchanged one. The selected area electron diffraction pattern
(SAEDP) evidenced the presence of crystalline species.
3. Results and discussion
3.1. TEM observations and SAED performances
A typical TEM image of the doped SLS glass is shown in Fig. 1 for the sample FAg2.
The crystalline nature of nanoparticles is revealed by the SAED, cf. the inset of
Figs. 1a and 1b (left-hand side). The detected diffraction rings with reflections
from the {111} and {200} type planes correspond to the fcc structure of metallic
silver. Figures 1a and 1b (right-hand side) shows the matrix morphology for the same
specimens.
It is evident that after a short annealing time, the silver nanoparticles are mostly
spherical in shape, their size ranging between 2 and 10 nm. With increasing
annealing time, coalescence of adjacent nanocrystals is facilitated and a marked

Optical properties of small silver particles embedded in soda-lime silica glasses 399
Fig. 1. TEM-micrographs of the ion exchange sample FAg2 after annealing at 873 K for 0.5 h (a) and
4h (b).
deviation from the spherical shape of the Ag-particles is observed. The phase separated
droplets, present yet in the glass-matrix, behave qualitatively in the same way, i.e.,
they change their size and shape along with the thermal treatment.
It should be stressed that the variation of the shape of metal nanocrystallites with
size is often overlooked and a simplistic description of the optical behaviour based on
spherical particles is assumed [10–13]. On the other hand, the altered matrix
morphology, not considered up to now, has been tentatively related with the formation
of mixed sodium-silver silicates, similar to the case of copper-doped SLS glass [7].
3.2. Optical absorption data
Figures 2a–2c shows the OA-characteristics of spectra obtained for annealed
specimens, and the last picture gives values of the Ag-particle diameters versus their
penetration depth.
It was detected that the spectra exhibited a shift of the absorption-edge in the near-
-UV-region (not shown here) towards lower energies, and the spectral features of
the UV-Ag-absorption were affected by the UV-absorption of the glass-matrix.
The occurence of the SPR absorbance is attributed to the interband transitions
which dominate UV-vis region. The blue and red shift (for different depths of each
sample) of the band position λ is accompanied by changes of the absorbance A and of
the full-width half-maximum of the absorption peak δ1/2. These changes are strongly
dependent upon the annealing time, cf. Figs. 2a–2c.
The behaviour of the SPR absorption peak corresponds well with the size of
the Ag-particles which are changing not only with the exchange parameters but also
with the penetration depth characteristic of the thermal treatment.
a
b

400 M. SUSZYŃSKA, T. MORAWSKA-KOWAL, L. KRAJCZYK
a b
c
Fig. 2. OA-characteristics of the FAg2 specimen annealed for 4 h at 873 K (a–c), and the size of
the created silver particles (d). All data are shown as a function of the silver penetration depth.
The formation of mixed silver-alkali ion silicates at a given stage of the production
is probably responsible for the complex character of the depth-dependences of 2R,
A, λ and δ 1/2 shown in the present communication.
Several attempts have been made to model the OA spectra of dielectrics doped
with metal nanoparticles by taking into account the effect of their size [1]. The effect
of shape, which also modifies the optical properties and the effective dielectric
constant, has drawn lesser attention; for instance, the effective medium theory
introduced by MAXWELL-GARNETT [12] and BRUGGEMAN [13] considered the spherical
and ellipsoidal shapes only. Unfortunately, the complex character of our results cannot
at present be explained on the basis of the aforementioned models. It seems that more
experimental work is necessary, especially with respect to the nucleation and growth
of the matrix occlusions and the metal nanoparticles, as well.
4. Conclusions
We have reported changes of the half-width, intensity, and shift of the position of
the plasmon resonance absorption peak with increasing size of the Ag-particles
embedded in the SLS glass matrix.
d

Optical properties of small silver particles embedded in soda-lime silica glasses 401
The following conclusions have been drawn:
1. The substitution of Na by Ag-ions cannot be described by a simple replacement
reaction; one has to take into account some structural rearrangements during the ion
exchange well below the glass-transformation temperature;
2. The effect of size, shape and distribution of the silver nanoparticles upon
the optical absorption of a composite material is more complicated than anticipated
theoretically on the basis of the free metal nanoparticles;
3. A combination of the ion exchange process with thermal treatments is a proper
technique for obtaining waveguiding structures with Ag-metallic-aggregates.
Acknowledgements – The authors wish to thank Dr. K.-J. Berg from the MLU in Halle/Saale (Germany)
for making the microspectrophotometric measurements possible.
References
[1] KREIBIG U., VOLLMER M., Optical Properties of Metal Clusters, Springer, Berlin, 1995.
[2] HACHE F., RICARD D., FLYTZANIS C., KREIBIG U., The optical Kerr effect in small metal particles and
metal colloids: The case of gold, Applied Physics A 47(4), 1988, pp. 347–357.
[3] RAMASWAMY R.V., SRIVASTAVA R., Ion-exchanged glass waveguides: A review, Journal of Lightwave
Technology 6(6), 1988, pp. 984–1000.
[4] CAPELLETTI R., COISSON R.,VAN HOI P., MORA C., SUSZYNSKA M., VEDDA A., Thermally stimulated
depolarisation currents of quartz and mixed alkali silicate glasses, 8th International Symposium on
Electrets (ISE 8), 1994, pp. 511–516.
[5] BERG K., CAPELLETTI R., KRAJCZYK L., SUSZYNSKA M., Optical and electrical characterization of
silver nanoparticles in soda lime silicate glasses, 9th International Symposium on Electrets (ISE 9),
1996, pp. 378–383.
[6] SUSZYNSKA M., SZMIDA M., GRAU P., Mechanical characteristics of mixed soda-lime silicate glasses,
Materials Science and Engineering A 319–321, 2001, pp. 702–705.
[7] SUSZYNSKA M., SZMIDA M., CIZMAN A., Structure and hardness of the copper-doped soda-lime silica
glass, 2009, accepted for publication in J. Phys. (c).
[8] PORAI-KOSHITS E.A., AVERJANOV V.I., Primary and secondary phase separation of sodium silicate
glasses, Journal of Non-Crystalline Solids 1(1), 1968, pp. 29–38.
[9] BERG K.-J., BERGER A., HOFMEISTER H., Small silver particles in glass surface layers produced by
sodium-silver ion exchange – their concentration and size depth profile, Zeitschrift für Physik D:
Atoms, Molecules and Clusters 20(1–4), 1991, pp. 309–311.
[10] STEUBING W., Über die optischen Eigenschaften kolloidaler Goldlösungen, Annalen der
Physik 331(7), 1908, pp. 329–371.
[11] KREIBIG U., Electronic properties of small silver particles: the optical constants and their
temperature dependence, Journal of Physics F: Metal Physics 4(7), 1974, pp. 999–1014.
[12] MAXWELL-GARNETT J.C., Colours in metal glasses and in metallic films, Philosophical Transactions
of the Royal Society A 203, 1904, pp. 385–420.
[13] BRUGGEMAN D.A.G., Berechnung verschiedener physikalischer Konstanten von heterogenen
Substanzen. I. Dielektrizitätskonstanten und Leitfähigkeiten der Mischkörper aus isotropen
Substanzen, Annalen der Physik, Leipzig 416(7), 1935, pp. 636–664.
Received November 12, 2009
in revised form January 6, 2010

Optica Applicata, Vol. XL, No. 2, 2010
Biocompatible glass composite system –
some physical-mechanical properties
of the glass composite matrix system
BARBARA STANIEWICZ-BRUDNIK 1* , MAŁGORZATA LEKKA 2 ,
LUCYNA JAWORSKA 1 , WŁODZIMIERZ WILK 1
1 Institute of Advanced Manufacturing Technology, Wrocławska 37a, 30-011Kraków, Poland
2 Institute of Nuclear Physics PAN, Radzikowskiego 152, 31-342 Kraków, Poland
* Corresponding author: bbrudnik@ios.krakow.pl
In this work there are discussed the physical-mechanical properties of the glass CaO–SiO 2–P 2O 5–
–Na 2 O system (FB3) assigned for the glass composite matrix system using the following research
methods: spectral chemical analysis (XRF), S BET specific surface area analysis, XRD investigation,
observation with a scanning electron microscope (SEM), wettability of the submicrocrystalline
sintered corundum (ssc) by the glass system, microhardness test and DTA measurement. It was
found that theoretical oxide chemical composition was close to that obtained from the spectral
chemical analysis (XRF), the prolongated high energetic milling of the glass system did not have
any significant influence on the specific surface area of grains (from 0.9159 m 2 /g after 5-hour
milling to 1.9241 m 2 /g after 20-hour milling process only), in comparison to the specific surface
area of the ssc, wettability investigation of the submicrocrystalline sintered corundum by the glass
FB3 system showed the value of contact angle (θ < 45°), and the microhardness value of
about 6 GPa. On the basis of DTA results the sintering temperature of bioglass composite with
the strengthening phase from the submicrocrystalline sintered corundum was determined and,
using the previous experience, the way of producing composite was proposed. The calculation of
the thermodynamic stability of the glass system-strengthening phase by VCS algorithm showed
the presence of 4–5 solid compounds. The results of the fibroblast (cell line CCL 110,
Promochem LG) preliminary culture investigation on the bioglass composite substrate were
positive. The best results were obtained in the case of the biocomposite with the smallest amount
of strengthening phase.
Keywords: glass of CaO–SiO 2 –P 2 O 5 –Na 2 O system, submicrocrystalline sintered corundum, bioglass
composite, XRF, XRD, DTA, contact angle, VCS algorithm, fibroblast culture.
1. Introduction
Glassy biocompatible composites form a new generation of ceramic materials for use
in tissue engineering [1–5]. Inorganic, polymer and hybrid biomaterial substrates
can form two- or three-dimensional scaffolds on which cells (e.g., fibroblasts) are

404 B. STANIEWICZ-BRUDNIK et al.
planted and bred in vitro and subsequently this material-cell product is implanted.
The fundamental criteria for suitability of the substrates have been thus formulated
[4, 6–8]:
– The substrate should contain interconnected pores of such sizes that would favor
integration of the cells, and subsequently tissues and their vascularity.
– They should have appropriate chemical properties of bioactivity and non-toxicity
which favor the attachment of cells to the substrate, their differentiation and
multiplication. Also, mechanical properties similar to the natural ones are required,
specifically, resistance to stretching and twisting, hardness and Young’s modulus.
– They must not produce unwanted reactions such as inflammation.
– They should be easily produced in various shapes and sizes.
Taking account of all these requirements, substrate materials were synthesized,
including biocompatible glassy composites. Glassy composites, comprising properties
of their constituent materials, allow the attainment of unique properties, such as:
high mechanical strength, resistance to fracture, high biocompatibility and bioactivity.
The biological activity of glasses and glass-ceramics depends on their chemical
composition and results from the specific nature of the glassy substance contained
[8–11].
The ability of bioactive glasses and glass-ceramic implants to bond to bone tissue
forms the subject of numerous investigations involving in vitro observations of
changes on the material surface caused by solutions simulating human blood plasma
(SBF). It was shown that for materials such as Bioglass, Ceravital, and glass-ceramics,
hydroxylapatite Cerabone, bonding with the living bone material starts by
the formation of a surface layer enriched in calcium and phosphorus, which forms
a hydroxyapatite containing a carbonate molecule with a deformed structure, similar
to that of bone apatite [3, 7, 12, 13].
2. Subject and research methodology
The research aims at a glass matrix composite from the glass of CaO–SiO 2 –P 2 O 5 –
–Na 2 O system and the bioglass composite with the strengthening phase of
submicrocrystalline sintered corundum added with the amounts of 10, 20, and 30 vol%
designed for the substrate of human skin fibroblast culture.
The glass of CaO–SiO 2 –P 2 O 5 –Na 2 O system (FB3) was obtained by traditional
method (heat treatment and fritting process) from previously precisly mixed raw
materials.
Further, the glass system powder was subjected to the high energetic milling for
5, 10, 15, 20 hours in the Fritsch type milling grinder in the weight proportion of balls
to grains 10:1 and the addition of water as a sliding substance. The glass samples after
specific time (5, 10, 15, 20 hours) were removed from the chamber and subjected to
further research procedures.
The measurement of the specific surface area S BET was done using the special
multifunctional apparatus of ASAP2010 of Micrometrix. The specific surface area

Biocompatible glass composite system ... 405
S BET was determined by the physical adsorption of nitrogen at nitrogen’s liquefaction
temperature (77 K) with the Brunauer–Emmett–Teller equation.
The specific density measurements of the glass FB3 system were done in the helium
picometer of Accu Pyc 330.The average grain size based on the specific density and
specific surface area data was calculated using the following equation:
2r =
6
----------------------
SBET ρ
where: 2r – diameter of the grains, S BET – specific surface area of grains, ρ – specific
density of the glass FB3 system.
The obtained glass powder was subjected to spectral analysis by XRF method.
The X-ray investigation was carried out on the X’Pert diffractometer of Panalytical
Company using the Cu lamp in the 2θ angle range of 10–90°.
Microscopic observation of the glass system and bioglass composite was carried
out on the scanning electron microscope of the Joel Company of JSM6460 LV at low
vacuum and accelerating voltage of 20 kV at magnifications of 10, 100, 1000.
DTA investigation of the glass FB3 system was carried out using the Derivatograph
1500 D apparatus by heating the sample in the platinum crucible with 10 °C/min speed
to 1000 °C in the air atmosphere.
The wettability investigation of the submicrocrystalline sintered corundum
substrate by the glass FB3 system was carried out under the high temperature
microscope of MHO2 Leitz–Watzler type by the sessile-drop method in the air
atmosphere.
Microhardness test was performed using the FM7 detector under a 100 g loading.
On the basis of DTA of the glass FB3 system investigation the sintering temperature
of glass matrix composite system with strengthening phase was carried out and using
the previous experience the way of obtaining the bioglass composite was proposed.
Thermodynamic stability of the glass FB3 system-strengthening phase (10, 20,
30 vol% of submicrocrystalline sintered corundum) was calculated using VCS
algorithm.
On the samples of the bioglass composite (φ 10×4 mm), after proper preparation
of surface area (quasi-polished section) and sterilization (12 hours in a 70% alcohol
solution and 2 hours of exposure of each side of the sample to UV lamp), fibroblasts
from human skin (cell line No CCL 110, Promochem LG) were cultured in DMEM
medium (Dulbecco’s Modified Eagle Medium, Sigma) containing 5% of fetal bovine
serum and a 1% mixture solution of antibiotics (streptomycin, neomycin and
penicillin). The results of investigation are discussed below.
3. Results and discussion
The glass of the CaO–SiO 2 –P 2 O 5 –Na 2 O system (FB3) obtained by fritting process
at a temperature of 1350 °C was characterized by low viscosity, absence of gas bubble
and milk-amber color (Fig. 1).

406 B. STANIEWICZ-BRUDNIK et al.
a b
Fig. 1. The scanning electron microscope images of the glass CaO–SiO 2 –P 2 O 5 –Na 2 O (FB3) system
after fritting process; magnified 15× (a), magnified 200× (b).
a b
Fig. 2. The scanning electron microscope images of the glass CaO–SiO 2 –P 2 O 5 –Na 2 O (FB3). FB3 glass
system after 5-hour milling (a), FB3 glass system after 20-hour milling (b).
The glass powder was milled for 5, 10, 15, 20 hours (Fig. 2) in the Fritsch planetar
ball grinder. It was found that prolongated high energetic milling of glass FB3 system
did not have a significant influence on the increase of specific surface area of the glass
FB3 system (S BET 0.9159 m 2 /g after 5-hour milling, 1.9241 m 2 /g after 20-hour milling)
in comparison to the specific surface area changes of the submicrocrystalline sintered
corundum (0.1 m 2 /g for unmilled sample and 16.4 m 2 /g after 30-hour milling). This
can be explained by the specific structure of the glass FB3 system and big cohesive
interactions.
Because of this fact the granulometric analysis of grains was difficult to perform.
The calculations of average grains size from the equation showed that the grain size
of the glass FB3 system was decreased 2.5 times only (Tab. l).
The density of the glass FB3 system was determined by the helium method at
the AccuPyc 330 picometer and had the value of 2.6554 g/cm 3 .
Microhardness test was done using the FM7 detector under a 100 g loading. In
Tab. 2 and Fig. 3, the results of microhardness of the glass FB3 system (about 6 GPa)
are presented.

Biocompatible glass composite system ... 407
T a b l e 1. The results of specific surface area and average grain size after prolongated high energetic
milling of the glass FB3 system.
Milling time [h] Specific surface area [m 2 /g] Average grain size [μm]
5 0.9159 2.47
10 0.9553 2.36
15 1.1964 1.89
20 1.9241 1.17
T a b l e 2. The microhardness measurement of glass FB3 system.
Sample HV HVav
Standard deviation
of single measurement
Average
standard deviation
Uncertainty of HVav
for t(α = 0.005, n–1 = 4)
[–] [–] [–] [–] +/– %
FB3 560 568 8.4 3.7 10.4 1.8
Fig. 3. The microhardness indents of the glass FB3
system.
To fulfill the requirements of the XRF apparatus assigned for spectral chemical
analysis, the glass powder milled for 10 hours was used. The method, which is simple
and cheap, allowed the chemical oxide composition to be precisely determined
(Tab. 3). The obtained values of spectral chemical oxide composition were close to
those of the theoretical calculations.
The X-ray investigation showed absolutely amorphic structure with increasing
the background in the low angle range.
T a b l e 3. Chemical oxide compositions of glass system, spectral chemical analysis [wt%].
Oxide composition
of glass system
Calculated
composition
CaO 19.200 19.0
SiO 2 54.145 52.9
P 2 O 5 5.912 5.23
Na 2 O 20.706 20.0
Additives < 0.37 < 2.67
Spectral chemical
analysis

408 B. STANIEWICZ-BRUDNIK et al.
a b c
Fig. 4. The wettability of submicrocrystalline sintered corundum by glass FB3 system: 101 °C (a),
958 °C (b), 1010 °C (c), θ < 45°.
The wettability investigation of submicrocrystalline sintered corundum substrate
by the glass FB3 system showed that contact angle was proper and low at elevated
temperature (θ < 45°, Fig. 4).
The DTA research (Fig. 5) allowed determination of the vitrification temperature
(T g = 525.2 °C) and dilatometric point temperature (T d = 711.9 °C). On the basis of
the above investigation the sinter temperature of bioglass composite with the strengthening
phase was initially estimated.
Fig. 5. DTA of the glass CaO–SiO 2 –P 2 O 5 –Na 2 O (FB3) system.
A production technology comprising cold pressing and traditional heat treatment
or cold pressing, isostatic densification and traditional heat treatment was
developed.
The theoretical calculation of the thermodynamic stability of the glass FB3 systemstrengthening
phase with the submicrocrystalline sintered corundum (ssc-amount of
10, 20, 30 vol%) was carried out by the VCS algorithm (Tab. 4).
Using the VCS algorithm, theoretical calculations were made of the thermodynamic
stability of the system FB3 glass – 10, 20 and 30 vol% submicrocrystalline
sintered corundum strengthening phase. It was found that amongst some 100
possible compounds, probably stable are 4–5 compounds in the solid phase (Tab. 4).
From both hypotheses it follows that, for all of the three types of composite present,

Biocompatible glass composite system ... 409
T a b l e 4. The thermodynamic stability of bioglass composites with additives of ssc – VCS algorithm
calculation.
Glass FB3 system (90 vol%) + ssc (10 vol%)
Temperature 570 570 590 590
Assumption I II I II
Na 2 SiO 3 2.868 2.868 2.868 2.868
CaSiO 3 4.104 4.104 4.104 4.104
Ca 3(PO 4) 2 0.786 0.786 0.786 0.786
NaAlSiO 4 6.59 6.59 6.59 6.59
NaAlSi 3 O 8 1.148 1.148 1.148 1.148
Glass FB3 system (80 vol%) + ssc (20 vol%)
Temperature 570 570 590 590
Assumption I II I II
Ca 3(PO 4) 2 0.698 0.698 0.698 0.698
NaAlSiO 4 11.975 11.975 11.975 11.975
Ca 2 Al 2 SiO 7 0.241 0.241 0.241 0.241
Ca 3Al 2Si 3O 12 0.965 0.965 0.965 0.965
Glass FB3 system (70 vol%) + ssc (30 vol%)
Temperature 570 570 590 590
Assumption I II I II
Al 2 O 3 4.554 4.554 4.554 4.554
Ca 3 (PO 4 ) 2 0.611 0.611 0.611 0.611
CaAl 4O 7 0.448 0.448 0.448 0.448
NaAlSiO 4 10.478 10.478 10.478 10.478
Ca 3 Al 2 Si 3 O 12 0.914 0.914 0.914 0.914
a b
c
Fig. 6. The microscopic image of haematoxylin
stained fibroblast (violet) cultured for 14 days on
a surface of bioglass composite with: 10 vol% (a),
20 vol% (b), 30 vol% (c) of the submicrocrystalline
sintered corundum additives, magnified 6×.

410 B. STANIEWICZ-BRUDNIK et al.
there are the following compounds: NaAlSiO 4 solid state and Ca 3 (PO 4 ) 2 in the liquid
state.
Practical verification of the presence of these compounds in the biocomposites will
be made by X-ray methods in the next stage of the work.
The fibroblasts from human skin (cell line No CCL 110, Promochem LG) were
cultured, after the appropriate surface preparation, on the three variants of bioglass
samples (φ 10×4 mm). After 14 days of growth, the cells were fixed using cold
acetone (4 °C) for 10 minutes and stained with haematoxylin to visualize cell
nucleolus. The optical microscope images showed the largest number of fibroblast
cells to be present on the surface of the sintered composite containing 10 vol% of
submicrocrystalline corundum. A felt-like layer of fibroblasts was established, which,
during the cleaning process, was not separated from the surface. With increasing
amount of the strengthening phase, submicrocrystalline sintered corundum (20%,
30%), the number of the cultured fibroblast cells decreased (Fig. 6). This observation
will be possible to explain after examination of the surface topography (roughness,
open and closed porosity) of the sintered glassy biocomposites.
4. Resume
The glass of CaO–SiO 2 –P 2 O 5 –Na 2 O system (FB3) has proper physical-mechanical
properties (microhardness – 6 GPa, contact angle to submicrocrystalline sintered
corundum substrate θ < 45°) and biocompatibility (the fibroblast culture results)
which fulfill the application criteria for biocomposites.
The theoretical oxide chemical composition of the glass system was the same as
that resulting from the spectral chemical analysis (XRD) taking into consideration
volatility of phosphates at a 10% level.
It was found that prolongated high energetic milling of glass system, did not have
any significant influence on the specific surface area of grains (from 0.9159 m 2 /g
after 5-hour milling, to 1.9241 m 2 /g after 20-hour milling process) and decrease of
the average value of grains (from 2.47 μm to 1.17 μm).
The wettability (wetting) investigation of the submicrocrystalline sintered
corundum by the glass system showed the value of contact angle (θ

Biocompatible glass composite system ... 411
5. Conclusions
On the basis of the research work performed it can be concluded that:
– The proposed glass of the CaO–SiO 2–P 2O 5–Na 2O system (FB3) fulfills
the application criteria for glass matrix composite because of the proper physical-
-mechanical properties (microhardness, wettability of submicrocrystalline sintered
corundum, temperature stability) and biocompatibility (the fibroblast culture results).
– Verification of the thermodynamic stability of compounds calculated by VCS
algorithm based on XRD and DTA investigation is necessary.
– Investigation of the influence of the way of producing bioglass composite (cold
sintering and traditional heat treatment or cold sintering with isostatic densification
and traditional heat treatment) on the topography of the surface area (roughness,
porosity) is necessary.
Acknowledgement – This work was supported by the Polish Ministry of Science and Higher Education
under the statutory grant DS 3683.
References
[1] JAEGERMANN Z., ŚLÓSARCZYK A., Gęsta i porowata bioceramika korundowa w zastosowaniach
medycznych, Uczelniane Wydawnictwo Naukowo-Dydaktyczne AGH, Kraków, 2007 (in Polish).
[2] JAEGERMANN Z., Porowata bioceramika korundowa, PhD Thesis, AGH, Kraków, 2005 (in Polish).
[3] BŁAŻEWICZ S., STOCH L., Biomateriały, [In] Biocybernetyka i Inżynieria Biomedyczna, Vol. 4,
Akademicka Oficyna Wydawnicza, Exit, Warszawa, 2003 (in Polish).
[4] SACHLOS E., CZERNUSZKA J.T., Making tissue engineering scaffolds work. Review: The application
of solid freeform fabrication technology to the production of tissue engineering scaffolds, European
Cells and Materials, No. 5, 2003, pp. 29–40.
[5] HENCH L.L., Biomaterials: a forecast for the future, Biomaterials 19(16), 1998, pp. 1419–1423.
[6] ŚLÓSARCZYK A., RAPACZ-KMITA A., Bioaktywne ceramiczne materiały kompozytowe, Materiały
Ceramiczne 56(4), 2004, pp. 144–149 (in Polish).
[7] CHEN Q.Z., EFTHYMIOU A., SALIH V., BOCCACINI A.R., Bioglass-derived glass-ceramic scaffolds:
Study of cell proliferation and scaffold degradation in vitro, Journal of Biomedical Materials
Research Part A 84(4), 2008, pp. 1049–1060.
[8] KRAJEWSKI A., RAVAGLIOLI A., Bioceramics and biological glasses, [In] Integrated Biomaterials
Science, Springer US, 2002.
[9] NIŻANKOWSKI CZ., Manufacturing sintered corundum abradants, Archives of Civil and Mechanical
Engineering 2(2), 2002, pp. 53–64.
[10] SZARSKA S., STANIEWICZ-BRUDNIK B., LEKKA M., The effect of the size of the substrate grain made
of submicrocrystalline sintered corundum on the bioglass composite structure and certain physico-
-mechanical properties of the bioglass, Optica Applicata 38(1), 2008, pp. 251–258.
[11] PUTTINI S., LEKKA M., DORCHIES O.M., SAUGY D., INCITTI T., RUEGG U.T., BOZZONI I., KULIK A.J.,
MERMOD N., Gene-mediated restoration of normal myofiber elasticity in dystrophic muscles,
Molecular Therapy 17(1), 2009, pp. 19–25.
[12] JAEGERMANN Z., MICHAŁOWSKI S., KARAŚ J., CHROŚCICKA A., LEWANDOWSKA-SZUMIEŁ M.,
Porowate nośniki korundowe do zastosowania w inżynierii tkankowej, Szkło i Ceramika 57(4), 2006,
pp. 16–20 (in Polish).

412 B. STANIEWICZ-BRUDNIK et al.
[13] LEKKA M., LEIDLER P., Applicability of AFM in cancer detection, Nature Nanotechnology 4(2), 2009,
p. 72.
[14] VITALE BROVARONE C., VERNÉ E., APPENDINO P., Macroporous bioactive glasse-ceramic scaffolds
for tissue engineering, Journal of Materials Science: Materials in Medicine 17(11), 2006,
pp. 1069–1078.
Received November 12, 2009
in revised form March 26, 2010

Optica Applicata, Vol. XL, No. 2, 2010
Synthesis and optical spectroscopy
of the Eu- and Pr-doped glasses
with SrO–2B 2 O 3 composition
BOHDAN PADLYAK 1, 2* , MAREK GRINBERG 3 , BENEDYKT KUKLIŃSKI 3 , YURIY OSELEDCHIK 4 ,
OLEKSANDR SMYRNOV 2 , DMITRIY KUDRYAVTCEV 4 , ANDREW PROSVIRNIN 4
1 Institute of Physical Optics, Sector of Spectroscopy,
23 Dragomanov St., 79-005 Lviv, Ukraine
2University of Zielona Góra, Institute of Physics, Division of Spectroscopy of Functional Materials,
4a Szafrana St., 65-516 Zielona Góra, Poland
3University of Gdańsk, Institute of Experimental Physics, Condensed Matter Spectroscopy Division,
57 Wita Stwosza St., 80-952 Gdańsk, Poland
4 Zaporizhya State Engineering Academy, Department of Physics,
226 Lenin Ave., 69-006 Zaporizhya, Ukraine
* Corresponding author: B.Padlyak@proton.if.uz.zgora.pl; bohdan@mail.lviv.ua
A series of Eu- and Pr-doped glasses with SrO–2B 2 O 3 (or SrB 4 O 7 ) composition were obtained
and their spectroscopic properties were investigated. The SrB 4O 7 polycrystalline compounds were
synthesised at T = 1300 K using high purity strontium carbonate (SrCO 3) and boric acid (H 3BO 3).
The Eu and Pr impurities were added to SrB 4 O 7 compounds as Eu 2 O 3 (amount: 0.167 at.%) and
Pr 2O 3 (amounts: 0.05 and 0.25 at.%) oxides. The glass samples of high chemical purity and optical
quality were obtained from corresponding polycrystalline compounds in the air atmosphere in
platinum crucibles according to standard glass technology. Optical absorption, luminescence
excitation and emission spectra of the Eu- and Pr-doped glasses with SrO–2B 2O 3 composition
were investigated in the spectral range 300–800 nm at temperatures of 293 and 85 K. On the basis
of optical spectra obtained and electron paramagnetic resonance (EPR) data analysis it is shown
that Eu and Pr impurities are incorporated into the SrO–2B 2O 3 glass network as Eu 3+ (4f 6 , 7 F 0)
and Pr 3+ (4f 2 , 3 H 4) ions, exclusively. All the observed transitions of the Eu 3+ and Pr 3+ centres in
absorption and luminescence spectra were identified. The luminescence kinetics of Eu 3+ and Pr 3+
centres were investigated and analysed. The decay constants for main emission transitions in all
samples investigated were obtained at room temperature. Peculiarities of incorporating the Eu 3+
and Pr 3+ activator ions in the glass with SrO–2B 2 O 3 composition and their optical spectra are
discussed in comparison with rare-earth doped polycrystalline compounds and single crystals with
the same (SrB 4O 7) composition and other borate glasses.
Keywords: borate glasses and crystals, Eu 3+ centre, Pr 3+ centre, optical absorption, luminescence, decay
kinetics, local structure.

414 B. PADLYAK et al.
1. Introduction
The strontium tetraborate crystalline compounds (SrB 4 O 7 ) are perspective nonlinear
optical and luminescent materials due to their excellent mechanical and optical
properties, such as high hardness, non-hygroscopy, high SHG (second harmonic
generation) coefficient, high transparency in a wide spectral range (135–3200 nm)
and high optical damage threshold [1–3]. The polycrystalline SrB 4 O 7 compounds can
be obtained by solid state reaction synthesis and corresponding single crystals of high
optical quality can be obtained using Kyropoulos and Czochralski methods [1, 2].
Practically, all borate compounds, including tetraborates, can be obtained in both
crystalline and glassy forms. From technological point of view the glassy (or vitreous)
compounds are more perspective in comparison with corresponding single crystals,
because glass synthesis technology is relatively cheap. But spectroscopic studies of
the electron and local structure of luminescence centres in oxide glasses are more
complicated and require adequate spectroscopic and structural data for their crystalline
analogies [4, 5].
During the last decade intensive luminescence investigations of the rare-earth
doped crystalline strontium tetraborates, obtained by solid-state synthesis,
Czochralski, and Kyropoulos methods have been carried out [6–18]. The results prove
the materials under study to be perspective for use as commercial phosphors. In
particular, optical and luminescence properties of the Eu- and Pr-doped SrB 4 O 7
crystalline compounds were investigated in [6–14] and [15], respectively. Nonlinear
optical properties of the SrB 4 O 7 single crystals were investigated in [14, 19, 20].
The SrB 4 O 7 crystalline and glassy compounds also exhibit thermoluminescence (TL)
and were investigated by different authors [21–24] as perspective materials for solid
state dosimetry.
For the first time the crystal structure of SrB 4 O 7 was reported in [25] and described
in detail in [26]. The SrB 4 O 7 crystals belong to the rhombic system (space group
Pnm2 1 ) and their lattice is formed by fourfold-coordinated boron–oxygen complexes
(tetrahedrons) [25, 26]. The Sr atoms are stabilising in the SrB 4 O 7 crystal lattice in
sites with coordination number to oxygen N = 9. The presence of BO 4 tetrahedrons
only in the SrB 4 O 7 lattice (while in other borate compounds, for example, in
the Li 2 B 4 O 7 crystal, the polyanions are formed by both boron–oxygen tetrahedrons
and boron–oxygen triangles [27]) provides the stabilisation of rare-earth ions, e.g.,
Eu, Sm, Yb, Pr, etc., in divalent state even if the compound is synthesised in the air
[6, 7, 9–14]. This allows obtaining broad emission and luminescence excitation bands
of divalent ions caused by interconfiguration f–d transitions in the UV–VIS spectral
region. It is generally acknowledged that rare-earth ions are incorporated in divalent
state into the lattice of oxide compounds synthesised in the vacuum or in the inert
atmosphere. From the analysis of reference data [6–18] we can conclude that
the rare-earth doping of SrB 4 O 7 crystals obtained in the air leads to incorporation of
rare-earth ions into their lattice, generally, in a divalent state. Only several papers
[8–12] report luminescence properties of the Eu 3+ ions in SrB 4 O 7 :Eu crystalline

Synthesis and optical spectroscopy of the Eu- and Pr-doped glasses ... 415
compounds, obtained in the air. The mechanism of incorporation of divalent rare-earth
ions into the strontium borate polycrystalline compounds (SrB 4 O 7 , SrB 6 O 10 , etc.),
obtained by solid-state synthesis in the air was discussed in [28–30]. Luminescence
properties of the Pr-doped SrB 4 O 7 crystalline compounds were investigated in [15].
In this paper, it is shown that the Pr impurities are incorporated into the SrB 4 O 7 lattice
as Pr 2+ ions. Emission lines at 216, 237, 225, 253, 271, 340, 396, and 400 nm in [15]
were assigned to the Pr 2+ transitions from 1 S 0 state to 3 H 4 , 3 H 6 , 3 F 2 , 3 F 4 , 1 G 4 , 1 D 2 , 1 I 6 ,
and 3 P 2,1,0 states, respectively.
For the first time the results of optical and EPR investigations of Eu- and Pr-doped
glasses with SrO–2B 2 O 3 (or SrB 4 O 7 ) composition were reported by us in [31]. But up
to now, optical spectra and peculiarities of incorporation of Eu and Pr impurities in
the glass with SrO–2B 2O 3 composition have not been systematically investigated nor
published. This work presents synthesis peculiarities and systematic investigations of
optical and luminescence properties of the SrO–2B 2 O 3 glasses doped with Eu and Pr.
Local symmetry and structure of the luminescence centres are discussed. The results
are compared to the ones obtained for corresponding crystalline compounds.
2. Experimental details
2.1. Synthesis and characterisation of the SrB4O7 polycrystalline compounds
and glasses
The SrB4O7 polycrystalline compounds were obtained by solid state reaction synthesis
at T = 700–900 °C in the air, using a resistance furnace. The high purity strontium
carbonate (SrCO3 ) and boric acid (H3BO3 ) in the proportion corresponding to SrB4O7 composition were used as starting materials. For the purpose of compensating
evaporation during the solid state reaction an extra charge of H3BO3 in amount of
2 mol% was added. The Eu and Pr impurities were added to the starting composition
as Eu2O3 (amount: 0.167 at.%) and Pr2O3 (amounts: 0.05 and 0.25 at.%) compounds.
All chemicals used for sample synthesis are characterised by special purity (99.5 wt%)
and were purchased in Krasnyj khimik (Saint-Petersburg, Russia). The synthesis
process of SrB4O7 polycrystalline compounds included the following technological
operations: mixing of the starting materials, slow heating (2–3 h) to 200–250 °C,
heating (3–4 h) up to 850–900 °C, keeping at this temperature for 2–3 h and cooling
together with the furnace. Chemical composition of the compounds obtained was
controlled by the X-ray phase analysis.
The Eu- and Pr-doped glasses with SrO–2B2O3 composition of high chemical
purity and optical quality were obtained in the air atmosphere by melting
the pre-synthesised SrB4O7 :Eu and SrB4O7 :Pr compounds in platinum crucibles
according to technology developed by the authors. Synthesised polycrystalline
compounds were heated up to melting temperature 1030–1050 °C, mixed by platinum
stirrer and held (2 h) at melting temperature to achieve the complete homogenisation
and remove any gas bubbles and other centres of crystallisation, then poured into
a corundum cylindrical form (20 mm in diameter, 20 mm in length) and fast cooled.

416 B. PADLYAK et al.
Finally, glasses were annealed at 400 °C during 3–4 h. The obtained glasses were
almost uncoloured and characterised by high optical quality and chemical purity.
Samples for optical measurements were cut and polished to obtain an approximate size
of 5×4×2 mm 3 .
2.2. Experimental methods and equipment
The optical absorption spectra of the Eu- and Pr-doped glasses were registered at room
temperature on a Specord M-40 (Carl Zeiss Jena) spectrophotometer.
The EPR spectra of non-controlled and rare-earth paramagnetic impurities in
the glasses obtained were registered at room and liquid helium temperatures using
modernised commercial X-band spectrometer of SE/X-2544 type (RADIOPAN,
Poznań, Poland), operating in the high-frequency (100 kHz) modulation mode of
magnetic field.
Photoluminescence (excitation and emission) spectra were obtained at
temperatures of 300 and 85 K upon frontal excitation and observation of the sample
emission using equipment built in the Condensed Matter Spectroscopy Division
(Institute of Experimental Physics, Gdańsk University, Poland). The emission spectra
were corrected for spectral sensitivity of the equipment. A Hanovia xenon lamp
(power: 1000 W) was used as excitation source. The wavelengths required for
excitation and observation were selected using an SPM-2 prismatic monochromator
(Carl Zeiss Jena) with stepping motors driven by a computer and photomultipliers used
in the detection circuit and working in analog or photon counter regime. In the latter
case, they sent data to computer via a digital boxcar system. A Hamamatsu R 928
photomultiplier was used as a detector.
The luminescence decays were measured using equipment described in detail
in [32]. As excitation source the EKSPLA (Vilnius, Lithuania) laser system was used,
which consisted of Nd:YAG pulsed laser (model PL 2143A/SS) and parametric optical
generator (model PG 401/SH). The detection part consisted of the 2501S spectrograph
(Bruker Optics, USA) and the C4334-01 streak camera (Hamamatsu, Japan).
3. Results and discussion
3.1. The Eu3+ centres in glasses with SrO–2B2O3 composition
The Eu impurity in the oxide compounds can be revealed as Eu3+ (4f 6 , 7F0 ) and Eu2+ (4f 7 , 8 S7/2 ) ions with characteristic optical absorption and luminescence spectra.
The Eu2+ paramagnetic ions can also be registered by EPR technique. In the Eu-doped
glasses with SrO–2B2O3 composition the Eu2+ EPR spectrum was not observed
either at room or liquid nitrogen temperatures. Thus, the Eu impurity is incorporated
into the SrO–2B 2O3 glass network as Eu 3+ ions.
In all SrO–2B2O3 glass samples doped with Eu there were observed optical
absorption and luminescence spectra, characteristic of Eu3+ ions, caused by f–f
transitions. The optical absorption spectrum of the Eu-doped SrO–2B2O3 glass
registered in the spectral range 230–800 nm at room temperature consists of several

Synthesis and optical spectroscopy of the Eu- and Pr-doped glasses ... 417
Fig. 1. Optical absorption (a) and luminescence excitation (b) spectra of the Eu-doped (Eu 2 O 3 content:
0.167 at.%) glass with SrO–2B 2 O 3 composition, registered at room temperature.
characteristic weak absorption bands (Fig. 1, spectrum a). In accordance with the Eu 3+
energy level diagram all observed absorption bands were assigned to the following
transitions and groups of transitions: 7 F0, 1 → 5 I 5 , 7 F 0 → 3 H4, 6, 7 F 0 → 5 D 4 , 5 L 8 ,
7 F0 → 5 G 4–6 , 7 F0, 1 → 5 L 6, 7 , 5 G2, 3 , 7 F0 → 5 D 3 , 7 F0 → 5 D 2 , 7 F0, 1 → 5 D 1 ,
7 F0, 1 → 5 D 0 (Fig. 1, spectrum a). The intense broad absorption band with pronounced
maximum near 300 nm was assigned to the O 2– → Eu 3+ charge transfer band (Fig. 1,
spectrum a). One can notice that some absorption bands are only weakly revealed
in the absorption spectrum (Fig. 1, spectrum a), but are easily observed in
the luminescence excitation spectrum (Fig. 1, spectrum b). The luminescence
excitation bands show good correlation with corresponding absorption bands (Fig. 1,
spectra a and b). In the optical absorption spectrum of Eu-doped SrO–2B 2 O 3 glasses,
no bands related to Eu 2+ ions were observed, which confirms incorporation of Eu
impurity into the glass as Eu 3+ ions, exclusively.
The luminescence spectra of Eu 3+ centres (Fig. 2) were registered at temperatures
of 293 and 85 K under excitation with λ exc = 395 nm that corresponds to the 7 F 0, 1 →
→ 5 L 6, 7 , 5 G 2, 3 band in absorption and luminescence excitation spectra (Fig. 1,
spectra a and b). In the luminescence spectrum at T = 293 K five emission bands,
characteristic of Eu 3+ ions, in the spectral range 570–730 nm are observed. These
bands belong to the 5 D 0 → 7 F J (J = 0–4) transitions and are identified in Fig. 2.
The absence of emission from higher 5 D J levels can be related to multiphonon or
cross-relaxation processes, caused by a relatively high concentration of Eu 3+ centres
in the glass network.
The linewidth and resolution of the Eu 3+ absorption and luminescence bands
(Figs. 1 and 2) remained practically unchanged as the temperature decreased to 85 K.
This is an evidence of the inhomogeneous broadening of spectral lines, caused by
disorder of the local environment around Eu 3+ centres. The luminescence excitation
and emission spectra of Eu 3+ ions in the SrB 4O 7 powdered polycrystals (Figs. 3a

418 B. PADLYAK et al.
Fig. 2. Luminescence spectra of Eu 3+ centres in the Eu-doped (Eu 2 O 3 content: 0.167 at.%) glass with
SrO–2B 2O 3 composition, registered under excitation with λ exc = 395 nm at temperatures of 293 and 85 K.
Fig. 3. The luminescence excitation (T =293K, λ obs =692nm) (a) and emission (T =293K and
T =85K, λ exc = 280 nm) (b) spectra of the Eu 3+ centres in the SrB 4 O 7 :Eu (Eu 2 O 3 content: 0.167 at.%)
polycrystalline powder.
a
b

Synthesis and optical spectroscopy of the Eu- and Pr-doped glasses ... 419
and 3b, respectively) are characterised by narrower and better resolved bands in
comparison with the corresponding spectra in the glasses with SrO–2B 2 O 3
composition, registered under the same experimental conditions (Figs. 1 and 2).
The number and relative intensities of the Eu 3+ emission lines ( 5 D 0 → 7 F J transitions)
are defined by the number of crystallographically non-equivalent centres and their
local symmetry in the crystal lattice or glass network [33]. Because of the fact that
the most intense emission band of the Eu 3+ luminescence spectra in the SrO–2B 2 O 3
glass corresponds to the 5 D 0 → 7 F2 structurally-sensitive electric dipole transition
(Fig. 2), one can suppose that the Eu 3+ centres occupy structural sites without inversion
symmetry (non-centrosymmetric sites) [33]. In the luminescence spectra of
SrB 4 O 7 :Eu 3+ polycrystalline compounds the Eu 3+ centres are localised in the sites with
inversion symmetry (centrosymmetric sites), because the most intense bands
correspond to the 5 D 0 → 7 F 4 electric and 5 D 0 → 7 F 1 magnetic dipole transitions
(Fig. 3b). Based on the results obtained and the SrB 4 O 7 crystal structure analysis we
can suppose that the Eu 3+ ions occupy Sr 2+ sites in the crystal and glass with the same
composition. In the real glass network the coordination number to oxygen (N) is
smaller than that in the corresponding real crystal one (for ideal SrB 4 O 7 crystal
N = 9) [26, 27], because it is characteristic of the glass structure in which the number
of oxygen vacancies is larger. Based on this result, we can explain the localisation
of Eu 3+ ions in the centrosymmetric Sr-sites of the SrB 4 O 7 crystal lattice and
non-centrosymmetric Sr-sites in the corresponding glass network.
The luminescence decay curves of Eu 3+ centres for the 5 D 0 → 7 F 2 emission
transition registered under excitation at λ exc = 280 nm and T = 300 K in the narrow
and wide (whole) emission band ranges are presented in Figs. 4a and 4b, respectively.
Decay curves for glass in the Δλ = 607–627 nm (Fig. 4a) and whole band (Fig. 4b)
ranges were described in the framework of a single exponential model with close
lifetime values: τ 1 = 1.82 ms and τ 1 = 1.97 ms, respectively. At the same time, decay
curves for the polycrystalline compound in the Δλ = 586–596 nm (Fig. 4a) and whole
band (Fig. 4b) ranges were satisfactorily fitted with double exponential decay with
lifetimes τ 1 =1.76ms, τ 2 = 0.48 ms and τ 1 =2.02ms, τ 2 = 0.56 ms, respectively.
The τ 1 values for glasses and polycrystalline samples are very similar and can be
assigned to the same centres, whereas the τ 2 values are considerably (approximately
4 times) lower than those of τ 1 . The longer (τ 1 ) values are characteristic of Eu 3+
luminescence centres in other oxide glasses and crystals including borate compounds
and belong to isolated Eu 3+ centres in glassy and polycrystalline samples. Because
the observed optical spectra show only one type of Eu 3+ centres in the SrB 4 O 7 :Eu glass
network, according to [34, 35] we can suppose that the centres with shorter lifetime
values belong to the Eu 3+ –Eu 3+ exchange-coupled pairs or small exchange-coupled
Eu 3+ clusters.
The results presented above correlate with spectroscopic data for SrB 4O 7
crystalline compounds [8–12] and other Eu-doped borates obtained in the air, in
particular for glasses with 4SrO–7B 2 O 3 (or Sr 4 B 14 O 25 ) composition [36]. On the other
hand, in [6, 7, 13–18] it was shown that the europium impurity can be stabilised in

420 B. PADLYAK et al.
Fig. 4. Luminescence decay curves of the Eu 3+ centres for 5 D 0 → 7 F 2 emission transition in the narrow (a)
and whole (b) bands, registered in the SrB 4O 7:Eu glass (curves a) and corresponding polycrystalline
powder (curves b) under excitation with λ exc =280nm at T = 300 K. Solid lines – results of fitting.
the SrB 4 O 7 crystalline compounds in divalent (Eu 2+ ) state during synthesis in the air
atmosphere. In [13], authors reported on the preparation of a system containing (RE) 2+
ions (RE = Sm, Eu) in the SrB 4 O 7 crystalline matrix by ceramic, Pechini, and
combustion methods using reduction of (RE) 3+ to (RE) 2+ ions in the air. The emission
spectra of the SrB 4 O 7 :Eu 2+ system prepared by combustion and Pechini methods are
characterised by a broadband assigned to the 4f 6 5d–4f 7 interconfiguration transition.
The SrB 4O7:RE compounds prepared by combustion method present emission bands
from (RE) 3+ ions as intense as that arising from (RE) 2+ , suggesting that the preparation
route is not efficient for (RE) 3+ → (RE) 2+ reduction [13].
3.2. The Pr 3+ centres in glasses with SrO–2B 2 O 3 composition
The Pr impurity in the oxide compounds can be revealed as Pr 3+ (4f 2 , 3 H 4 ) and
Pr 2+ (4f 3 , 4 I 9/2) ions with characteristic optical absorption and luminescence spectra.
The paramagnetic Pr 2+ ions can be registered also by EPR technique. In the Pr-doped
a
b

Synthesis and optical spectroscopy of the Eu- and Pr-doped glasses ... 421
Fig. 5. Optical absorption (curve a) and luminescence excitation (curve b) spectra of the Pr-doped (Pr 2O 3
content: 0.25 at.%) glass with SrO–2B 2 O 3 composition, registered at room temperature.
glass with SrO–2B 2 O 3 composition the Pr 2+ EPR spectrum was not observed even
at liquid helium temperatures. Thus, the praseodymium impurity is incorporated into
the SrO–2B 2 O 3 glass network as Pr 3+ ions, exclusively.
The optical absorption spectrum of the Pr-doped glass with SrO–2B 2 O 3
composition in the spectral range 250–800 nm at room temperature consists of
four characteristic absorption bands. According to rare-earth energy level diagram
the observed bands were assigned to appropriate f–f electronic transitions of the Pr 3+
ions from the 3 H 4 ground state to the 1 D 2 , 3 P 0 , 3 P 1 , 3 P 2 excited states (Fig. 5,
spectrum a).
In the luminescence excitation spectrum of the SrO–2B 2 O 3 glass doped with Pr
(Pr 2 O 3 content: 0.25 at.%) one can observe three resolved bands in the spectral range
550–280 nm, which correspond to the 3 H 4 → 3 P 0 , 3 H 4 → 3 P 1 , 3 H 4 → 3 P 2 transitions
(Fig. 5, spectrum b). The Pr 3+ luminescence excitation bands show good correlation
with corresponding absorption bands (Fig. 5, spectra a and b). It should be noted that
the resolution of Pr 3+ optical absorption and luminescence excitation bands in the glass
containing 0.25 at.% of Pr 2 O 3 is lower than that in the glass containing 0.05 at.% of
Pr 2 O 3 . This is related to homogeneous broadening of spectral lines, which depends on
centres concentration and temperature.
The luminescence spectrum of Pr 3+ centres (Fig. 6) was registered at temperatures
of 293 and 85 K under excitation with λ exc = 450 nm that corresponds to the 3 H 4 → 3 P 1
transition in the absorption and luminescence excitation spectra (Fig. 5, spectra a
and b). In the Pr 3+ luminescence spectrum at temperatures of 293 and 85 K there were
observed an intense broad complex emission band, peaking near 600 nm, which
corresponds to the 3 P 0 → 3 F 2 , 3 H 6 and 3 P 0 → 3 H 4 transitions, and weak emission bands,
peaking near 450, 690, and 800 nm, which corresponds to the 3 P 0 → 3 H 4 , 3 P 0 → 3 F 3 ,
3 P0 → 3 F 4 transitions (Fig. 6). The luminescence spectra of the SrO–2B 2O 3 glasses
which contained 0.05 and 0.25 at.% of Pr 2 O 3 are similar and characterised by

422 B. PADLYAK et al.
Fig. 6. The luminescence spectrum of the Pr 3+ centres in the Pr-doped (Pr 2 O 3 content: 0.25 at.%) glass
with SrO–2B 2O 3 composition, registered under excitation with λ exc = 450 nm at temperatures of 293
and 85 K.
practically the same resolution at temperatures of 293 and 85 K. The linewidth and
resolution of the Pr 3+ absorption, luminescence excitation and emission bands in
the glass samples with the same Pr 3+ content practically did not change with
temperature decreasing to 85 K, which is an evidence of the inhomogeneous
broadening of spectral lines, caused by disorder of the local structure of Pr 3+ centres.
The results of investigation of luminescence kinetics for Pr 3+ centres in
the SrO–2B 2 O 3 glass containing 0.05 and 0.25 at.% of Pr 2 O 3 are presented in Fig. 7.
Luminescence kinetics of the Pr 3+ centres for the whole emission band corresponding
to the 1 D 2 → 3 H 4 transition is satisfactorily described by a two-exponential model
with decay constants τ 1 = 32.92 μs and τ 2 =16.2μs for glass containing 0.05 at.% of
Fig. 7. Luminescence decay curves of the Pr 3+ centres for 1 D 2 → 3 H 4 transition (λ max =599nm),
registered under excitation with λ exc = 450 nm at T = 300 K in the SrB 4 O 7 glasses containing 0.05 at.%
(curve a) and 0.25 at.% (curve b) of Pr 2O 3. Solid lines – results of fitting.

Synthesis and optical spectroscopy of the Eu- and Pr-doped glasses ... 423
Fig. 8. A fragment of SrB 4 O 7 single crystal ideal structure. A unit cell is shown by lines. The B1 and B2
atoms have coordination numbers to oxygen N =3 and N = 4, respectively. The Sr atoms stabilising in
the framework have coordination number to oxygen N =9.
Pr 2 O 3 and τ 1 = 27.49 μs and τ 2 = 11.3 μs for glass containing 0.25 at.% of Pr 2 O 3 .
According to [34, 35] and the data analysis we can suppose that longer lifetimes
correspond to isolated Pr 3+ centres and shorter lifetimes correspond to the Pr 3+ –Pr 3+
pair centres in the SrB 4 O 7 glass network.
The results obtained do not correlate with the results published in [15], where
the incorporation of Pr impurity ions in divalent state into the SrB 4 O 7 crystal lattice is
described. On the other hand, the results of optical spectroscopy of SrO–2B 2 O 3
glasses doped with Pr show good correlation with the optical spectroscopy of
the Pr-doped glass and crystal with 4SrO–7B 2 O 3 (or Sr 4 B 14 O 25 ) composition that
shows the presence of Pr 3+ luminescence centres exclusively in the glass network [36]
and crystal lattice [37, 38].
Based on structural [25–27] and optical spectroscopy data for Eu 3+ in the SrB 4 O 7
crystal [8–12] and SrO–2B 2 O 3 glass (see Section 3.1) as well as for Pr 3+ in
the Sr 4 B 14 O 25 crystal [37, 38] and 4SrO–7B 2 O 3 glass [36] we confirm incorporation
of trivalent rare-earth ions (Eu 3+ , Pr 3+ , etc.) into the Sr-sites (Fig. 8) with coordination
number to oxygen N = 8 for real crystalline and N = 7 for real glassy compounds.
4. Conclusions
The Eu- and Pr-doped borate glasses of high optical quality and chemical purity with
the SrO–2B 2 O 3 basic composition were synthesised in the air according to technology
conditions, developed by the authors. On the basis of optical absorption and
luminescence spectra analysis it was shown that the Eu and Pr impurities are
incorporated into the SrO–2B2O 3 glass network in trivalent state, exclusively and form

424 B. PADLYAK et al.
the Eu 3+ (4f 6 , 7 F 0 ) and Pr 3+ (4f 2 , 3 H 4 ) luminescence centres. All transitions of
the Eu 3+ and Pr 3+ centres, observed in the UV–VIS optical spectra are identified.
Peculiarities of absorption and luminescence spectra as well as luminescence kinetics
of the Eu 3+ and Pr 3+ centres in the glass with SrO–2B 2 O 3 composition were analysed
in comparison with their crystalline analogs and other borate glasses. In particular, it
was shown that the Eu 3+ and Pr 3+ optical absorption and luminescence spectra in the
SrB 4 O 7 and Sr 4 B 14 O 25 crystalline and glassy compounds are very similar, which is an
evidence of the same local structure for rare-earth luminescence centres in strontium
borate glasses with different compositions and their crystalline analogs. Luminescence
kinetics of the SrB 4 O 7 :Eu compounds shows only isolated Eu 3+ centres in the glass
network, whereas it is the Eu 3+ isolated and Eu 3+ –Eu 3+ pair centres that are
characteristic of SrB 4O 7 crystal lattice. Luminescence kinetics of the SrB 4O 7:Pr glass
with 0.05 and 0.25 at.% Pr 2 O 3 content shows the presence of the Pr 3+ isolated and
Pr 3+ –Pr 3+ pair centres in the glass network.
On the basis of reference data and analysis of the results it was confirmed that
the Eu 3+ , Pr 3+ and other trivalent rare-earth ions in the structure of SrB 4 O 7 compounds
are localised in one type of structural positions according to RE 3+ → Sr 2+ heterovalent
substitution with coordination number to oxygen N = 8 for SrB 4 O 7 real crystal and
N = 7 for real glass with the same composition. The multisite character of the Eu 3+ and
Pr 3+ luminescence in the strontium borate glasses can be explained by compositional
(or substitutional) disorder and continual disturbance of short-range order that leads
to statistical distribution of local crystal field parameters for luminescence centres and
is revealed in the inhomogeneous broadening of spectral lines.
Acknowledgements – This work was supported by the Ministry of Education and Science of Ukraine
(scientific research project No. 0109U001063) and University of Zielona Góra (Poland).
References
[1] OSELEDCHIK YU.S., PROSVIRNIN A.L., STARSHENKO V.V., OSADCHUK V.V., PISAREVSKY A.I.,
BELOKRYS S.P., KOROL A.S., SVITANKO N.V., SELEVICH A.F., KRIKUNOV S.A., Crystal growth and
properties of strontium tetraborate, Journal of Crystal Growth 135(1–2), 1994, pp. 373–376.
[2] FENG PAN, GUANGQIU SHEN, RUJI WANG, XIAOQING WANG, DEZHONG SHEN, Growth, characterization
and nonlinear optical properties of SrB 4 O 7 crystals, Journal of Crystal Growth 241(1–2), 2002,
pp. 108–114.
[3] MICHAIL P., HULLIGER J., SCHNIEPER M., BILL H., SrB 4O 7:Sm 2+ : crystal chemistry, Czochralski growth
and optical hole burning, Journal of Materials Chemistry 10(4), 2000, pp. 987–991.
[4] PADLYAK B.V., KUKLIŃSKI B., GRINBERG M., Synthesis, structure and spectroscopic properties of
CaO–Ga 2O 3–GeO 2 glasses, Physics and Chemistry of Glasses 43C, 2002, pp. 392–397.
[5] PADLYAK B.V., RYBA-ROMANOWSKI W., LISIECKI R., Optical spectroscopy and local structure of Er 3+
luminescence centres in CaO–Ga 2O 3–GeO 2 glasses, Journal of Non-Crystalline Solids 354(35–39),
2008, pp. 4249–4255.
[6] MACHIDA K., ADACHI G., SHIOKAWA J., Luminescence properties of Eu(II)-borates and Eu 2+ -activated
Sr-borates, Journal of Luminescence 21(1), 1979, pp. 101–109.
[7] MEIJERINK A., NUYTEN J., BLASSE G., Luminescence and energy migration in (Sr, Eu)B 4O 7, a system
with a 4f 7 –4f 6 5d crossover in the excited state, Journal of Luminescence 44(1–2), 1989, pp. 19–31.

Synthesis and optical spectroscopy of the Eu- and Pr-doped glasses ... 425
[8] ZHIWU PEI, QIANG SU, SHANHUA LI, Investigation on the luminescence properties of Dy 3+ and Eu 3+
in alkaline-earth borates, Journal of Luminescence 50(2), 1991, pp. 123–126.
[9] ZHIWU PEI, QIANG SU, JIYU ZHANG, The valence change from RE 3+ to RE 2+ (RE ≡ Eu, Sm, Yb)
in SrB 4 O 7 :RE prepared in air and the spectral properties of RE 2+ , Journal of Alloys and
Compounds 198(1–2), 1993, pp. 51–53.
[10] YONG GAO, CHUNSHAN SHI, YING WU, Luminescence properties of SrB 4O 7:Eu,Tb phosphors,
Materials Research Bulletin 31(5), 1996, pp. 439–444.
[11] HYO JIN SEO, BYUNG KEE MOON, BEANG JU KIM, JEONG BAE KIM, TAIJU TSUBOI, Optical
properties of europium ions in SrB 2O 4 crystal, Journal of Physics: Condensed Matter 11(39), 1999,
pp. 7635–7643.
[12] MACHIDA K., UEDA D., INOUE S., ADACHI G., Reversible valence change of the europium ion doped
in alkaline-earth tetraborates, Chemistry Letters 28(8), 1999, pp.785–786.
[13] STEFANI R., MAIA A.D., TEOTONIO E.E.S., MONTEIRO M.A.F., FELINTO M.C.F.C., BRITO H.F.,
Photoluminescent behavior of SrB 4 O 7 :RE 2+ (RE = Sm and Eu) prepared by Pechini, combustion
and ceramic methods, Journal of Solid State Chemistry 179(4), 2006, pp. 1086–1092.
[14] ALEKSANDROVSKY A.S., MALAKHOVSKII A.V., ZABLUDA V.N., ZAITSEV A.I., ZAMKOV A.V., Optical
and magneto-optical spectra of europium-doped strontium tetraborate single crystals, Journal of
Physics and Chemistry of Solids 67(8), 2006 pp. 1908–1912.
[15] VAN DER KOLK E., DARENBOS P., VAN EIJK C.W.E., Vacuum ultraviolet excitation of 1 S 0 and
3 P0 emission of Pr 2+ in Sr 0.7 La 0.3 Al 1.7 Mg 0.3 O 19 and SrB 4 O 7 , Journal of Physics: Condensed
Matter 13(23), 2001, pp. 5471–5486.
[16] SCHIPPER W.J., MEIJERINK A., BLASSE G., The luminescence of Tm 2+ in strontium tetraborate, Journal
of Luminescence 62(2), 1994, pp. 55–59.
[17] QINGHUA ZENG, ZHIWU PEI, SHUBING WANG, QIANG SU, SHAOZHE LU, The luminescent properties of
Sm 2+ in strontium tetraborates (SrB 4 O 7 :Sm 2+ ), Journal of Physics and Chemistry of Solids 60(4),
1999, pp. 515–520.
[18] JING GOU, YUHUA WANG, FENG LI, The luminescence properties of Dy 3+ -activated SrB 4O 7 under
VUV excitation, Journal of Luminescence 128(5–6), 2008, pp. 728–731.
[19] OSELEDCHIK YU.S., PROSVIRNIN A.L., PISAREVSKIY A.I., STARSHENKO V.V., OSADCHUK V.V.,
BELOKRYS S.P., SVITANKO N.V., KOROL A.S., KRIKUNOV S.A., SELEVICH A.F., New nonlinear optical
crystals: strontium and lead tetraborates, Optical Materials 4(6), 1995, pp. 669–674.
[20] PETROV V., NOACK F., SHEN D., PAN’ F., SHEN G., WANG X., KOMATSU R., ALEX V., Application
of the nonlinear crystal SrB 4O 7 for ultrafast diagnostics converting to wavelengths as short as
125 nm, Optics Letters 29(4), 2004, pp. 373–375.
[21] SANTIAGO M., LAVAT A., CASELLI E., LESTER M., PERISINOTTI L.J., DE FIGUEREIDO A. K., SPANO F.,
ORTEGA F., Thermoluminescence of strontium tetraborate, Physica Status Solidi (a) 167(1), 1998,
pp. 233–236.
[22] SANTIAGO M., GRASSELI C., CASELLI E., LESTER M., LAVAT A., SPANO F., Thermoluminescence of
SrB 4O 7:Dy, Physica Status Solidi (a) 185(2), 2001, pp. 285–289.
[23] DUBOVIK M.F., KORSHIKOVA T.I., OSELEDCHIK YU.S., PARKHOMENKO S.V., PROSVIRNIN A.L.,
SVITANKO N.V., TOLMACHEV A.V., YAVETSKY R.P., Thermostimulated luminescence of SrB 4O 7 single
crystals and glasses, Functional Materials 12(4), 2005, pp. 685–688.
[24] LAVAT A., GRASELLI C., SANTIAGO M., POMARICO J., CASELLI E., Influence of the preparation route
on the optical properties of dosimetric phosphors based on rare-earth doped polycrystalline
strontium borates, Crystal Research and Technology 39(10), 2004, pp. 840–848.
[25] KROGH-MOE J., On the structure of boron oxide and alkali borate glasses, Physics and Chemistry
of Glasses 1(1), 1960, pp. 26–31.
[26] PERLOFF A., BLOCK S., The crystal structure of the strontium and lead tetraborates, SrO.2B 2O 3 and
PbO.2B 2 O 3 , Acta Crystallographica 20(2), 1966, pp. 274–279.
[27] KROGH-MOE J., Refinement of the crystal structure of lithium diborate, Li 2O.2B 2O 3, Acta
Crystallographica Section B 24(2), 1968, pp. 179–181.

426 B. PADLYAK et al.
[28] ZHIWU PEI, QINGHUA ZENG, QIANG SU, The application and a substitution defect model for
Eu 3+ → Eu 2+ reduction in non-reducing atmospheres in borates containing BO 4 anion groups,
Journal of Physics and Chemistry of Solids 61(1), 2000, pp. 9–12.
[29] YAVETSKIY R.P., DOLZHENKOVA E.F., TOLMACHEV A.V., PARKHOMENKO S.V., BAUMER V.N.,
PROSVIRNIN A.L., Radiation defects in SrB 4 O 7 :Eu 2+ crystals, Journal of Alloys and
Compounds 441(1–2), 2007, pp. 202–205.
[30] QINGHUA ZENG, ZHIWU PEI, SHUBING WANG, QIANG SU, The reduction of Eu 3+ in SrB 6 O 10 prepared
in air and the luminescence of SrB 6 O 10 :Eu, Journal of Alloys and Compounds 275–277, 1998,
pp. 238–241.
[31] PADLYAK B., GRINBERG M., KUKLIŃSKI B., OSELEDCHIK YU., SMIRNOV A., KUDRYAVTCEV D.,
PROSVIRNIN A., Synthesis and optical spectra of the Eu- and Pr-doped glasses with SrO–2B 2 O 3
composition, [In] The Second International Workshop on Advanced Spectroscopy and Optical
Materials, 13–17 July 2008, Gdańsk (Poland): Institute of Experimental Physics, University of
Gdańsk, 2008, p. 8-O-1.
[32] KUBICKI A.A., BOJARSKI P., GRINBERG M., SADOWNIK M., KUKLIŃSKI B., Time-resolved streak camera
system with solid state laser and optical parametric generator in different spectroscopic
applications, Optics Communications 263(2), 2006, pp. 275–280.
[33] SVIRIDOV D.T., SVIRIDOVA R.K., SMIRNOV YU.F., Optical spectra of transition metal ions in crystals
(Opticheskie spektry ionov perekhodnych metallov v kristallakh), Moskwa, Nauka, 1976, p. 267
(in Russian).
[34] RONDA C.R., AMREIN T., Evidence for exchange-induced luminescence in Zn 2SiO 4:Mn, Journal of
Luminescence 69(5–6), 1996, pp. 245–248.
[35] VINK A.P., DE BRUIN M.A., ROKE S., PEIJZEL P.S., MEIJERINK A., Luminescence of exchange coupled
pairs of transition metal ions, Journal of the Electrochemical Society 148(7), 2001, pp. E313–E320.
[36] KUDRJAVTCEV D.P., OSELEDCHIK YU.S., PROSVIRNIN A.L., SVITANKO N.V., The spectroscopy of
4SrO·7B 2O 3:RE 3+ (RE = Eu 3+ , Pr 3+ , Nd 3+ ) glasses, Ukrainian Journal of Physical Optics 4(2),
2003, pp. 83–89.
[37] KUDRJAVTCEV D.P., OSELEDCHIK YU.S., PROSVIRNIN A.L., SVITANKO N.V., PETROV V.V.,
The luminescence of the praseodymium-doped strontium borate Sr 4B 14O 25:Pr 3+ , Ukrainian Journal
of Physical Optics 3(2), 2002, pp. 155–160.
[38] KUDRJAVTCEV D.P., OSELEDCHIK YU.S., PROSVIRNIN A.L., SVITANKO N.V., The spectral-generation
properties of Sr 4B 14O 25:Pr 3+ crystal, Ukrainian Journal of Physics 48(1), 2003, pp. 11–16.
Received November 12, 2009
in revised form December 30, 2009

Optica Applicata, Vol. XL, No. 2, 2010
Optical spectra and luminescence kinetics
of the Sm 3+ and Yb 3+ centres
in the lithium tetraborate glasses
BOHDAN PADLYAK 1, 2* , WITOLD RYBA-ROMANOWSKI 3 , RADOSŁAW LISIECKI 3 ,
VOLODYMYR ADAMIV 1 , YAROSLAV BURAK 1 , IHOR TESLYUK 1 ,
AGNIESZKA BANASZAK-PIECHOWSKA 4
1 Institute of Physical Optics, 23 Dragomanov St., 79-005 Lviv, Ukraine
2 University of Zielona Góra, Institute of Physics, Division of Spectroscopy of Functional Materials,
4a Szafrana St., 65-516 Zielona Góra, Poland
3 Institute of Low Temperatures and Structure Research, Polish Academy of Sciences,
2 Okólna St., 50-422 Wrocław, Poland
4 Kazimierz Wielki University in Bydgoszcz, Institute of Physics,
11 Weyssenhoff Sq., 85-072 Bydgoszcz, Poland
* Corresponding author: B.Padlyak@proton.if.uz.zgora.pl; bohdan@mail.lviv.ua
Optical absorption, luminescence excitation, and emission spectra as well as luminescence
kinetics of the Sm- and Yb-doped glasses with lithium tetraborate (Li 2B 4O 7) composition were
investigated and analysed. The Sm- and Yb-doped lithium tetraborate glasses of high optical
quality were obtained in air from corresponding polycrystalline compounds according to standard
glass synthesis technology. The Sm and Yb impurities were added to the Li 2B 4O 7 compound in
the form of Sm 2 O 3 and Yb 2 O 3 oxides in amount of 0.4 mol%. Using optical and electron
paramagnetic resonance spectroscopy it was shown that the Sm and Yb impurities are incorporated
into the lithium tetraborate glass network as Sm 3+ (4f 5 , 6 H 5/2) and Yb 3+ (4f 13 , 2 F 7/2) ions,
exclusively. All of the observed transitions in the absorption and luminescence spectra of
Sm 3+ and Yb 3+ centres were identified. The luminescence kinetics of the Sm 3+ and Yb 3+ centres
in the Li 2B 4O 7 glass are characterised by a single exponential decay. Decay constants for the main
emission transitions of the Sm 3+ and Yb 3+ centres in the lithium tetraborate glass were obtained
at T = 300 K. Incorporation peculiarities and optical spectra of Sm 3+ and Yb 3+ ions in the lithium
tetraborate glass have been discussed in comparison with other borate glasses and crystals.
Keywords: borate glasses, Sm 3+ centre, Yb 3+ centre, optical absorption, luminescence, decay kinetics,
local structure.
1. Introduction
The borate, in particular tetraborate crystals, are characterised by extremely high
radiation stability [1, 2] and high transparency in the wide spectral range from vacuum

428 B. PADLYAK et al.
ultraviolet (VUV) to far infrared (IR). The rare-earth ions, such as Eu 3+ , Er 3+ , Tm 3+ ,
Sm 3+ , Yb 3+ , etc., show high luminescence efficiency in a variety of host materials with
emission in a wide spectral range, in particular the Sm 3+ and Yb 3+ ions give a red and
IR characteristic emission bands [3, 4], respectively. Therefore, the rare-earth activator
ions are widely used in different luminescent materials [3, 4], including borate crystals
and glasses [5, 6].
In connection with their attractive spectroscopic and luminescence properties,
the undoped and doped borate crystals and glasses are promising materials for different
technical applications: scintillators and tissue-equivalent materials for thermoluminescence
(TL) dosimeters [7, 8], γ and neutron detectors [9, 10], lasers [11] and second
harmonic generation media [12]. Obtaining tetraborate single crystals is technologically
difficult, time-consuming and, consequently, very expensive. Besides, very low
crystal growth rate and high viscosity of the melt lead to problems with doping,
particularly with the rare-earth doping of tetraborate crystals. Therefore, from
the technological point of view the glassy (or vitreous) tetraborate compounds are most
perspective in comparison with their crystalline analogies. On the other hand, the study
of electron and local structure of the luminescence centres in complex oxide glasses
is an interesting problem of quantum electronics and solid state physics. Thus,
synthesis and spectroscopic investigations of rare-earth doped tetraborate crystals and
glasses are fundamental as far as real-life applications are concerned.
Methods of optical and electron paramagnetic resonance (EPR) spectroscopy allow
investigating the electron and local structure of the impurity luminescence and
paramagnetic centres in crystals and glasses. For interpretation of optical and EPR
spectra in complex glasses need corresponding spectroscopic and structural data for
their crystalline analogies [13, 14]. Practically all borate compounds, including
tetraborates, can be obtained in both crystalline and glassy states. Therefore, borates
are good candidates for studying the electron and local structure of luminescence and
paramagnetic centres in them.
In [10, 15–17], optical and spectroscopic properties of doped lithium tetraborate
crystals and glasses, obtained in air, were investigated and perspectives of their
applications for scintillators in neutron detectors, TL dosimeters and laser media were
considered. In [10, 15, 16] it was shown by means of optical spectroscopy that
the rare-earth impurities, particularly Sm and Yb, are incorporated into the Li 2 B 4 O 7
glass and crystal structure, in general, as trivalent ions, which are characterised by high
efficient luminescence at room temperature. In [16], by EPR spectroscopy it was
shown that the Yb impurity is incorporated into the Li 2 B 4 O 7 glass and crystal as
Yb 3+ ions, located in the Li + and, probably B 3+ or interstitial sites of the structure.
Optical spectroscopy shows the presence of Yb 2+ centres in the γ-irradiated Li 2 B 4 O 7
crystal [16]. According to [17], no Yb 3+ bands were observed in optical absorption
spectra of the “as-grown” in air Li 2B 4O 7:Yb crystals and absorption bands, peaked
near 198, 234, and 280 nm in these crystals were assigned to Yb 2+ centres. In lithium

Optical spectra and luminescence kinetics of the Sm 3+ and Yb 3+ centres ... 429
borate glasses, there were also observed the Yb 2+ centres with characteristic broad
absorption band near UV region and emission in the 520–540 nm spectral range [10].
As we can see from the above referenced data, optical and luminescence
properties of the Sm- and Yb-doped glasses with Li 2 B 4 O 7 composition have not been
systematically investigated up to now and electron and local structure of Sm and Yb
luminescence centres in them have not been finally established. The present paper
reports the synthesis and optical spectroscopy of the Li 2 B 4 O 7 glasses, doped by
Sm and Yb. The electron and local structure of Sm and Yb luminescence centres in
the lithium tetraborate glass and crystal have been discussed based on referenced
structural and spectroscopic data and the results obtained.
2. Glass synthesis, characterisation, and experimental equipment
The Sm- and Yb-doped glasses with lithium tetraborate (Li 2B 4O 7) compositions were
obtained in air from corresponding polycrystalline compounds according to standard
glass technology. For solid state synthesis of the Li 2 B 4 O 7 polycrystalline compounds
there were used the Li 2 CO 3 carbonate and boric acid (H 3 BO 3 ) of high chemical purity
(99.999%). The Sm and Yb impurities were added into the Li 2 B 4 O 7 composition in
the form of Sm 2 O 3 and Yb 2 O 3 oxide compounds in the amount of 0.4 mol%.
The Sm- and Yb-doped lithium tetraborate glasses were obtained by fast cooling of
the corresponding melt, heated more than 100 K above the melting temperature
(T melt = 1190 K) for exceeding the glass transition point.
Our undoped lithium tetraborate glasses are characterised by high transparency in
the 330–2500 nm spectral range (Fig. 1a). According to [10], undoped lithium borate
glasses are transparent in the 281–2760 nm region, whereas nominally-pure Li 2 B 4 O 7
single crystals reveal high transparency in a very wide (167–3200 nm) spectral
range [17]. The Sm- and Yb-doped glass samples obtained are almost uncoloured and
characterised by high optical quality. In Sm- and Yb-doped glasses with Li 2 B 4 O 7
composition, characteristic optical spectra were observed, which are presented in
Figs. 1–7 and discussed in Section 3.
The non-controlled and rare-earth paramagnetic impurities in the glasses obtained
were registered by EPR technique with the use of modernised commercial X-band
spectrometers of the SE/X-2013 and SE/X-2544 types (RADIOPAN, Poznań, Poland),
operating in the high-frequency (100 kHz) modulation mode of magnetic field at room
and liquid helium temperatures. The microwave frequency was measured with the help
of the Hewlett–Packard microwave frequency counter of the 5350 B type and DPPH
g-marker (g = 2.0036±0.0001). Practically, in all undoped and rare-earth doped
glasses with Li 2 B 4 O 7 composition, two characteristic EPR signals were observed,
with g eff = 4.29±0.01 and g eff = 2.00±0.01. The integral intensity of the signal with
g ≅ 4.29 is more than 100 times greater than that of g ≅ 2.00. According to [18, 19]
both observed EPR signals were assigned to the Fe 3+ (3d 5 , 6 S 5/2 ) non-controlled

430 B. PADLYAK et al.
Fig. 1. Optical absorption spectra of the undoped (a) and Sm-doped (Sm 2O 3 content – 0.4 mol%) (b)
glasses with Li 2 B 4 O 7 composition, recorded at T =300K.
impurity ions in octahedral and/or tetrahedral sites of the glass network. Weak
EPR signals of the non-controlled Mn 2+ (3d 5 , 6 S 5/2 ) ions, characteristic of glassy
state [18, 19] were also observed in Sm- and Yb-doped samples.
Optical absorption spectra were recorded with a Varian spectrophotometer
(model 5E UV-VIS-NIR). Luminescence and excitation spectra were acquired with
a Dongwoo (model DM711) scanning system consisting of an excitation monochromator
with 150 mm focal length and emission monochromator having a 750 mm focal
length equipped with a photomultiplier and an InGaAs detector. Spectral response of
the whole emission system was calibrated in the 400–800 nm spectral region against
reference source. The Yb 3+ emission spectra were measured using a 1m GDM 1000
double grating monochromator with a spectral bandwidth of 2 cm –1 and detected by
a photomultiplier with S-20 or S-1 spectral response. The resulting signal was analysed
by a Stanford (model SRS 250) boxcar integrator and stored in a personal computer.
Decay curves were recorded with a Tektronix (model TDS 3052) digital oscilloscope.
Excitation was provided by a Continuum Surelite I Optical Parametric Oscillator
a
b

Optical spectra and luminescence kinetics of the Sm 3+ and Yb 3+ centres ... 431
(OPO) pumped by a third harmonic of an Nd:YAG laser and the emitted light was
filtered using a GDM grating monochromator (focal length – 1000 mm). All optical
measurements were performed at room temperature.
3. Results and discussion
3.1. The Sm3+ centres in the Li2B4O7 glass
The Sm impurity in oxide crystals and glasses reveals Sm3+ (4f 5 , 6H5/2 ) and Sm2+ (4f 6 , 7 F0) ions with characteristic optical absorption, luminescence and EPR spectra.
In the obtained Li2B4O7 :Sm glasses only Sm3+ optical and EPR spectra were observed.
This result correlates with the previous referenced data for Li2B4O7 :Sm glass and
corresponding crystal [10, 15].
Optical absorption spectra of the Li2B4O7 :Sm glasses in the visible spectral range,
registered at room temperature consist of several very weak absorption bands (Fig. 1b).
In the luminescence excitation spectrum of the Li2B4O7:Sm glass (Fig. 2) at room
temperature there were also observed several weakly-resolved bands that correspond
to Sm3+ optical absorption transitions (Fig. 1b). In accordance with energy levels
diagram and referenced data [20, 21], the observed weak absorption and luminescence
excitation bands centred about 345, 362, 377, 405, 421, 463, 476, 490 nm were
assigned to appropriate electronic f–f transitions within Sm3+ ion from 6H5/2 ground state to the following terms of excited states: 3 H7/2 , 4 F9/2 , 4 D3/2 , 4 G7/2 , 6 P5/2 ,
4F5/2 , 4I11/2 , and 4I9/2, respectively (Fig. 1b and Fig. 2). One can notice that bands
corresponding to the 6H5/2 → 3H7/2 and 6H5/2 → 4F9/2 transitions of the Sm3+ centres
were not well revealed in the optical absorption (Fig. 1b), but clearly observed in
the luminescence excitation spectrum (Fig. 2). The intense absorption below 350 nm
(Fig. 1b) may result from the O2– → Sm3+ charge transfer band [22] and fundamental
Fig. 2. The luminescence excitation spectrum of Sm 3+ centres in the Li 2 B 4 O 7 :Sm glass, monitored at
λ mon = 599 nm and T =300K.

432 B. PADLYAK et al.
Fig. 3. The luminescence spectrum of Sm 3+ centres in the Li 2 B 4 O 7 :Sm glass, obtained under excitation
with λ exc = 475 nm and recorded at T = 300 K.
absorption of the Li 2 B 4 O 7 glass host (Fig. 1a). Thus, the Sm impurity is incorporated
into the Li 2 B 4 O 7 :Sm glass network as Sm 3+ ions, exclusively, because characteristic
optical absorption and luminescence excitation spectra of Sm 2+ [21] ions were not
observed.
Under excitation of the Li 2 B 4 O 7 :Sm glass with λ exc = 475 nm that corresponds to
6 H5/2 → 4 I 11/2 luminescence excitation transition (Fig. 2) at room temperature there
were observed intense characteristic reddish-orange emission bands originating from
4 G5/2 → 6 H J (J = 5/2, 7/2, 9/2) transitions of the Sm 3+ ions (Fig. 3). In crystalline
compounds, each Sm 3+ emission band corresponds to 4 G 5/2 → 6 H J transitions in
the luminescence spectrum, and is split to several separate components, which
practically are unresolved in the Li 2 B 4 O 7 glass (Fig. 3). Thus, from the emission
spectrum (Fig. 3) we can see only one type of the Sm 3+ centres in the Li 2 B 4 O 7 :Sm
glass network with complex unresolved emission bands.
The observed optical absorption and luminescence spectra of the Sm 3+ ions in
the Li 2 B 4 O 7 :Sm glass are similar to those obtained earlier for the Sm 3+ ions in
lithium tetraborate glasses [10, 15] and other borate glasses with different
compositions [22–24]. The linewidth and resolution of the Sm 3+ optical absorption
and luminescence bands in Li 2 B 4 O 7 :Sm glasses were practically not changed at
lowering temperature up to liquid nitrogen, which is the evidence of their
inhomogeneous broadening. The inhomogeneous broadening of spectral lines is
characteristic of luminescence centres in glasses and is related to disordering of
the local neighbourhood around centres in a glass network.
The luminescence decay curve of Sm 3+ centres in the Li 2 B 4 O 7 :Sm glass for
the most intense emission band corresponds to the 4 G 5/2 → 6 H 7/2 transition
(λ max = 599 nm) and was registered at T = 300 K (Fig. 4). The observed decay curve
has been satisfactorily fitted by a single exponential model with lifetime value

Optical spectra and luminescence kinetics of the Sm 3+ and Yb 3+ centres ... 433
Fig. 4. The luminescence decay curve of Sm 3+ centres for 4 G 5/2 → 6 H 7/2 transition (λ max =599nm),
registered at T = 300 K. Solid line – result of a single exponential fit.
τ = 2.6 ms in the 4 G 5/2 emitting level (Fig. 4) that corresponds to one type of Sm 3+
centres in the Li 2 B 4 O 7 :Sm glass network. One can notice that the obtained lifetime
value is characteristic of 4 G 5/2 level of the Sm 3+ luminescence centres and close to
Sm 3+ lifetimes in other complex oxide glasses [25], particularly in borate glasses with
different compositions [22–24]. The local structure of Sm 3+ luminescence centres in
the Li 2 B 4 O 7 :Sm crystal and glass is considered and discussed in Section 3.3.
3.2. The Yb 3+ centres in the Li 2 B 4 O 7 glass
The Yb impurity can be incorporated in oxide crystals and glasses as Yb 3+ (4f 13 , 2 F 7/2 )
and Yb 2+ (4f 14 , 1 S 1 ) ions with characteristic optical absorption, luminescence and EPR
spectra. In the investigated glasses with Li 2 B 4 O 7 :Yb composition only Yb 3+ optical
and EPR spectra were observed. This result shows good agreement with previous
referenced data for Yb-doped lithium tetraborate (Li 2 B 4 O 7 :Yb) glass [15, 16], but does
not correlate with results obtained for Yb-doped lithium borate glasses [10] and
Li 2 B 4 O 7 :Yb crystals [17], which show the presence of Yb 2+ centres, exclusively.
Room temperature optical absorption and luminescence spectra of the Li 2 B 4 O 7 :Yb
glass show spectra typical of Yb 3+ (Figs. 5 and 6). The absorption spectrum
consists of a strong peak centred at 970 nm and an unstructured broadband restricted
from 875 to 1100 nm associated with the 2 F 7/2 → 2 F 5/2 transition within the Yb 3+ ions
electronic f–f levels (Fig. 5). The 2 F 5/2 excited level is separated from the 2 F 7/2
ground level by about 10000 cm –1 . Therefore, under resonant photoexcitation of
the Li 2 B 4 O 7 :Yb glass with λ exc = 970 nm (10700 cm –1 ) that corresponds to
2 F7/2 → 2 F 5/2 absorption transition (Fig. 5) there was observed a characteristic
emission spectrum of Yb 3+ centres, which consists of unresolved zero-line peak at
970 nm and broadband in the 950–1020 nm spectral range ( 2 F 5/2 → 2 F7/2 transition)
(Fig. 6). The observed absorption and emission spectra show one type of Yb 3+ centres
in the Li 2B 4O 7:Yb glass network.
The observed optical absorption and emission spectra of Yb 3+ ions in
the Li 2 B 4 O 7 :Yb glass (Figs. 5 and 6) are very similar to corresponding Yb 3+ optical

434 B. PADLYAK et al.
spectra, observed in other borate glasses [26, 27] and disordered borate crystals with
different compositions [28, 29]. The linewidth and resolution of the Yb 3+ optical
absorption and emission bands in the Li 2B 4O 7:Yb glass did not practically change
with temperature decreasing to that of liquid nitrogen, which is the evidence of
their inhomogeneous broadening characteristic of luminescence centres in disordered
hosts.
The luminescence decay curve of Yb 3+ centres in the Li 2 B 4 O 7 :Yb glass for
2 F5/2 → 2 F 7/2 emission transition (λ max = 970 nm) is satisfactorily described in
the framework of a single exponential decay with lifetime τ =484μs in the 2 F 5/2 level
at T = 300 K (Fig. 7). One can notice that the obtained lifetime value is similar to
the Yb 3+ lifetimes in borate glasses and crystals with different compositions [26, 27]
Fig. 5. The optical absorption spectrum of the Li 2B 4O 7:Yb glass, containing 0.4 mol% of Yb 2O 3,
recorded at T =300K.
Fig. 6. The luminescence spectrum of Yb 3+ centres in the Li 2 B 4 O 7 :Yb glass, obtained under excitation
with λ exc =970nm (ν = 10700 cm –1 ) and recorded at T =300K.

Optical spectra and luminescence kinetics of the Sm 3+ and Yb 3+ centres ... 435
Fig. 7. The luminescence decay curve of Yb 3+ centres for 2 F 5/2 → 2 F 7/2 transition (λ max =970nm),
registered at T = 300 K. Solid line – result of a single exponential fit.
and other oxide glasses [30, 31]. Particularly, in [30] it was shown that the Yb 3+ decay
time strongly depends on Yb concentration and luminescence kinetics can be described
by a double exponential model with slow (190–1250 μs) and fast (6–300 μs) decay
times, which was assigned to the Yb 3+ isolated and Yb 3+ –Yb 3+ pair centres,
respectively. Thus, the luminescence kinetics of Li 2 B 4 O 7 :Yb 3+ glasses shows one type
of isolated Yb 3+ centres in the glass network. The local structure of Yb 3+ luminescence
centres in the Li 2 B 4 O 7 :Yb crystal and glass is considered in Section 3.3.
3.3. The local structure of Sm 3+ and Yb 3+ centres in the Li 2 B 4 O 7 crystal and glass
Let us consider the incorporation peculiarities and local structure of the Sm 3+ and Yb 3+
luminescence centres in the Li 2 B 4 O 7 crystal and corresponding glass with the same
(Li 2 O–2B 2 O 3 ) composition. The Li 2 B 4 O 7 crystal belongs to a 4mm point group and
I4 1 cd (C 4v ) space group of tetragonal symmetry (a = b =9.479Å, c = 10.286 Å).
The B 3+ ions occupy threefold- and fourfold-coordinated sites with average B 3+ –O 2–
bonds equal to 1.373 and 1.477 Å, respectively [32]. According to [32], the Li + ions
are located in the fourfold-coordinated distorted tetrahedra with Li + –O 2– distances in
the range 1.97–2.14 Å. The numbers of nearest oxygen anions (coordination number
to oxygen N ) with the Li + –O 2– distances equal to 2.63, 2.85, and 2.88 Å are 5, 6, and
7, respectively [32]. The statistical distribution of Li + –O 2– distances for different
coordination numbers (N = 4–7) leads to so-called “positional disorder” in
the Li 2B 4O 7 crystal lattice. Based on the crystal structure data we can suppose that
trivalent rare-earth impurity ions, RE 3+ , in the Li 2 B 4 O7 crystal occupy Li + sites of
the lattice due to extremely small ionic radius of the B 3+ ions (0.23 Å). So, the Sm 3+
and Yb 3+ ions are expected to incorporate in Li + sites of the Li 2B 4O 7 crystal lattice,
because the Li + , Sm 3+ , and Yb 3+ ionic radii are close and approximately equal to 0.76,
0.958, and 0.868 Å, respectively. Owing to positional disorder, the RE 3+ luminescence
centres in Li + sites of the Li 2B 4O 7 lattice are characterised by slightly different
spectroscopic parameters and the weak inhomogeneous broadening of spectral lines.

436 B. PADLYAK et al.
The local environment of Sm 3+ and Yb 3+ centres in the Li 2 B 4 O 7 glass network also
consists of O 2– anions with statistically-distributed structural parameters (RE 3+ –O 2–
interatomic distances and coordination numbers) in the first coordination shell
(positional disorder) that is revealed in the inhomogeneous broadening of the optical
absorption and luminescence bands. Additionally, a glass network is characterised by
continual disturbance of the short-range order that destroys middle- and long-range
order. This glassy-like disorder in the second (cationic) coordination sphere around
the luminescence centres leads to the additional inhomogeneous broadening of
spectral lines. As a result, the Sm 3+ and Yb 3+ optical spectra in glasses with Li 2B 4O 7
composition are characterised by strong inhomogeneous broadening. Because the local
structures of oxide crystals and corresponding glasses with the same composition are
very similar [13, 14, 33] we can suppose that the Sm 3+ and Yb 3+ centres are also
located in Li + sites of the Li 2 O–2B 2 O 3 glass network. This suggestion needs
confirmation by the direct EXAFS (extended X-ray absorption fine structure)
investigation of Sm and Yb impurity L 3-edge in the crystal and glass with Li 2B 4O 7
composition that will be a subject of future work.
4. Conclusions
The Sm- and Yb-doped lithium tetraborate glasses (Li 2 B 4 O 7 :Sm and Li 2 B 4 O 7 :Yb) of
high optical quality and chemical purity were obtained by standard glass synthesis in
air according to technology developed by the authors. On the basis of optical
spectroscopy data analysis we have shown the following:
1. The samarium and ytterbium impurities are incorporated into the Li 2 B 4 O 7 glass
network as Sm 3+ (4f 3 , 4 I 9/2 ) and Yb 3+ (4f 13 , 2 F 7/2 ) ions, exclusively, and form
the Sm 3+ and Yb 3+ luminescence centres with characteristic optical absorption and
luminescence spectra.
2. All the observed UV–VIS–IR transitions of the Sm 3+ and Yb 3+ centres in optical
absorption and luminescence spectra have been identified. Optical spectra of the Sm 3+
and Yb 3+ centres in the Li 2 B 4 O 7 glass network are quite similar to the Sm 3+ and Yb 3+
optical spectra, observed in other complex borate glasses and disordered crystals and
are characterised by inhomogeneous broadening of spectral lines.
3. The luminescence kinetics of the Sm 3+ centres for the 4 G 5/2 → 6 H 7/2 transition
(λ max = 599 nm) in the Li 2 B 4 O 7 :Sm glass containing 0.4 mol% of Sm is satisfactorily
described by a single exponential decay with lifetime τ = 2.6 ms at T =300K that is
typical of the 4 G 5/2 level of Sm 3+ centres in other borate glasses.
4. The luminescence kinetics of the Yb 3+ centres for 2 F 5/2 → 2 F 7/2 transition
(λ max = 970 nm) in the Li 2B 4O 7:Yb glass containing 0.4 mol% of Yb is satisfactorily
described by a single exponential decay with τ =484μs at T = 300 K that correlates
with corresponding data for Yb 3+ centres in other borate glasses.
5. It was supposed that the Sm 3+ and Yb 3+ luminescence centres are localised
in the Li + sites, coordinated by O 2– positionally-disordered anions in the Li 2 B 4 O 7
glass network that is also characteristic of crystals with the same composition and

Optical spectra and luminescence kinetics of the Sm 3+ and Yb 3+ centres ... 437
other borate glasses and disordered crystals. The multisite character of the Sm 3+ and
Yb 3+ luminescence centres in the glass and crystal with Li 2 B 4 O 7 is related to
the presence of Li + sites in their structure with different coordination numbers
(N = 4–7) and statistically-distributed RE 3+ –O 2– distances (positional disorder),
which leads to distribution of Sm 3+ and Yb 3+ spectroscopic parameters and is revealed
in the inhomogeneous broadening of their spectral lines.
Acknowledgements – This work was supported by the Ministry of Education and Science of Ukraine
(scientific research project No. 0109U001063) and University of Zielona Góra (Poland).
References
[1] BURAK YA.V., PADLYAK B.V., SHEVEL V.M., Radiation-induced centers in the Li 2 B 4 O 7 single
crystals, Nuclear Instruments and Methods in Physics Research Section B 191(1–4), 2002,
pp. 633–637.
[2] BURAK YA.V., PADLYAK B.V., SHEVEL V.M., Neutron-induced defects in the lithium tetraborate
single crystals, Radiation Effects and Defects in Solids 157(6–12), 2002, pp. 1101–1109.
[3] YEN W., SHIONOYA S. [Eds.], Phosphor Handbook, CRC Press, New York, 1999.
[4] BLASSE G., GRABMAIER B.C., Luminescent Materials, Springer Verlag, Berlin, 1994.
[5] DIAZ A., KESZLER D.A., Red, green, and blue Eu 2+ luminescence in solid-state borates: A structure-
-property relationship, Materials Research Bulletin 31(2), 1996, pp. 147–151.
[6] DUBOVIK M.F., TOLMACHEV A.V., GRINYOV B.V., GRIN’ L.A., DOLZHENKOVA E.F.,
DOBROTVORSKAYA M.V., Luminescence and radiation-induced defects in Li 2 B 4 O 7 :Eu single crystals,
Semiconductor Physics, Quantum Electronics and Optoelectronics 3(3), 2000, pp. 420–422.
[7] SANTIAGO M., LESTER M., CASELLI E., LAVAT A., GES A., SPANO F., KESSLER C., Thermoluminescence
of sodium borate compounds containing copper, Journal of Materials Science Letters 17(15), 1998,
pp. 1293–1296.
[8] CAN N., KARALI T., TOWNSEND P.D., YILDIZ F., TL and EPR studies of Cu, Ag and P doped Li 2 B 4 O 7
phosphor, Journal of Physics D: Applied Physics 39(10), 2006, pp. 2038–2043.
[9] ISHII M., KUWANO Y., ASABA S., ASAI T., KAWAMURA M., SENGUTTUVAN N., HAYASHI T., KOBOYASHI M.,
NIKL M., HOSOYA S., SAKAI K., ADACHI T., OKU T., SHIMIZU H.M., Luminescence of doped lithium
tetraborate single crystals and glass, Radiation Measurements 38(4–6), 2004, pp. 571–574.
[10] ZADNEPROWSKI B.I., EREMIN N.V., PASKHALOV A.A., New inorganic scintillators on the basis of LBO
glass for neutron registration, Functional Materials 12(2), 2005, pp. 261–268.
[11] SASAKI T., MORI Y., YOSHIMURA M., YAP Y.K., KAMIMURA T., Recent development of nonlinear
optical borate crystals: key materials for generation of visible and UV light, Materials Science and
Engineering R: Reports 30(1–2), 2000, pp. 1–54.
[12] GHOTBI M., EBRAHIM-ZADEH M., Optical second harmonic generation properties of BiB 3O 6, Optics
Express 12(24), 2004, pp. 6002–6019.
[13] PADLYAK B.V., KUKLIŃSKI B., GRINBERG M., Synthesis, structure and spectroscopic properties of
CaO–Ga 2O 3–GeO 2 glasses, Physics and Chemistry of Glasses 43C, 2002, pp. 392–397.
[14] PADLYAK B.V., RYBA-ROMANOWSKI W., LISIECKI R., Optical spectroscopy and local structure of Er 3+
luminescence centres in CaO–Ga 2 O 3 –GeO 2 glasses, Journal of Non-Crystalline Solids 354(35–39),
2008, pp. 4249–4255.
[15] RZYSKI B.M., MORATO S.P., Luminescence studies of rare-earth doped lithium tetraborate, Nuclear
Instruments and Methods 175(1), 1980, pp. 62–64.
[16] KACZMAREK S.M., PODGÓRSKA D., BERKOWSKI M., Multivalent state of Mn and Yb ions in Li 2B 4O 7
single crystals and glasses, Abstracts of Polish-French-Israeli Symposium “Spectroscopy of Modern
Materials in Physics and Biology”, September 27–30, 2004, Będlewo (near Poznań), Poland, p. 64.

438 B. PADLYAK et al.
[17] PODGÓRSKA D., KACZMAREK S.M., DROZDOWSKI W., BERKOWSKI M., WORSZTYNOWICZ A., Growth
and optical properties of Li 2 B 4 O 7 single crystals pure and doped with Yb, Co and Mn ions for
nonlinear applications, Acta Physica Polonica A 107(3), 2005, pp. 507–518.
[18] GRISCOM D.L., Electron spin resonance in glasses, Journal of Non-Crystalline Solids 40(1–3), 1980,
pp. 211–272.
[19] BRODBECK C.M., BUKREY R.R., Model calculations for the coordination of Fe 3+ and Mn 2+ ions in
oxide glasses, Physical Review B 24(5), 1981, pp. 2334–2342.
[20] CARNALL W.T., FIELDS P.R., RAJNAK K., Electronic Energy levels in the trivalent lantanide aquo
ions. I. Pr 3+ , Nd 3+ , Pm 3+ , Sm 3+ , Dy 3+ , Ho 3+ , Er 3+ , and Tm 3+ , Journal of Chemical Physics 49(10),
1968, pp. 4424–4442.
[21] STEFANI R., MAIA A.D., TEOTONIO E.E.S., MONTEIRO M.A.F., FELINTO M.C.F.C., BRITO H.F.,
Photoluminescent behavior of SrB 4O 7:RE 2+ (RE = Sm and Eu) prepared by Pechini, combustion
and ceramic methods, Journal of Solid State Chemistry 179(4), 2006, pp. 1086–1092.
[22] LIN H., YANG D.L., LIU G.S., MA T.C., ZHAI B., AN Q.D., YU J.Y., WANG X.J., LIU X.R., PUN E.Y.B.,
Optical absorption and photoluminescence in Sm 3+ - and Eu 3+ -doped rare-earth borate glasses,
Journal of Luminescence 113(1–2), 2005, pp. 121–128.
[23] JAYASANKAR C.K., BABU P., Optical properties of Sm 3+ ions in lithium borate and lithium
fluoroborate glasses, Journal of Alloys and Compounds 307(1–2), 2000, pp. 82–95.
[24] SOUZA FILHO A.G., FREIRE P.T.C., GUEDES I., MELO F.E.A., MENDES FILHO J., CUSTÓDIO M.C.C.,
LEBULLENGER R., HERNANDES A.C., High-pressure dependence of Sm 3+ emission in PbO–PbF 2 –
–B 2O 3 glasses, Journal of Materials Science Letters 19(2), 2000, pp. 135–137.
[25] SAISUDHA M.B., RAMAKRISHNA J., Effect of host glass on the optical absorption properties of Nd 3+ ,
Sm 3+ , and Dy 3+ in lead borate glasses, Phys. Rev. B 53(), 1995, pp. 6186–6196.
[26] KASSAB L.R.P., TATUMI S.H., MORAIS A.S., COURROL L.C., WETTER N.U., SALVADOR V.L.R.,
Spectroscopic properties of lead fluoroborate glasses doped with ytterbium, Optics Express 8(10),
2001, pp. 585–589.
[27] YUJIN CHEN, YIDONG HUANG, ZUNDU LUO, Spectroscopic properties of Yb 3+ in bismuth borate
glasses, Chemical Physics Letters 382(3–4), 2003, pp. 481–488.
[28] VIVIEN D., GEORGES P., Crystal growth, optical spectroscopy and laser experiments on new
Yb 3+ -doped borates and silicates, Optical Materials 22(2), 2003, pp. 81–83.
[29] ROMERO J.J., JOHANNSEN J., MOND M., PETERMANN K., HUBER G., HEUMANN E., Continuous-wave
laser action of Yb 3+ -doped lanthanum scandium borate, Applied Physics B: Lasers and Optics 80(2),
2005, pp. 159–163.
[30] BURSHTEIN Z., KALISKY Y., LEVY S.Z., LE BOULANGER P., ROTMAN S., Impurity local phonon
nonradiative quenching of Yb 3+ fluorescence in ytterbium-doped silicate glasses, IEEE Journal of
Quantum Electronics 36(8), 2000, pp. 1000–1007.
[31] GUONIAN WANG, SHIXUN DAI, JUNJIE ZHANG, SHIQING XU, LILI HU, ZHONGHONG JIANG, Effect of F –
ions on emission cross-section and fluorescence lifetime of Yb 3+ -doped tellurite glasses, Journal of
Non-Crystalline Solids 351(24–26), 2005, pp. 2147–2151.
[32] KROGH-MOE J., Refinement of the crystal structure of lithium diborate, Li 2 O.2B 2 O 3 , Acta
Crystallographica Section B 24(2), 1968, pp. 179–181.
[33] WITKOWSKA A., PADLYAK B., RYBICKI J., Influence of the rare-earth impurities on the Ge and Ga
local structure in the Ca 3 Ga 2 Ge 3 O 12 glass, Journal of Non-Crystalline Solids 352(40–41), 2006,
pp. 4346–4350.
Received November 12, 2009
in revised form December 13, 2009

Optica Applicata, Vol. XL, No. 2, 2010
The influence of nanocrystallization process
on thermal and optical parameter
in oxyfluoride glasses
JANUSZ JAGLARZ 1* , MANUELA REBEN 2
1 Cracow University of Technology, Institute of Physics,
ul. Podchorążych 1, 30-084 Kraków, Poland
2 AGH – University of Science and Technology, Faculty of Materials Science and Ceramics,
al. Mickiewicza 30, 30-059 Kraków, Poland
* Corresponding author: pujaglar@cyfronet.pl
The influence of nanocrystallization process in oxyfluoride glasses Na 2O–Al 2O 3–SiO 2–
–LaF 3 – NaF doped with rare earth (RE) ions on their thermal and optical properties is
studied. The thermal characteristics of oxyfluoride glasses (OG) with Tm 3+ , Yb 3+ are presented.
The effect of the glass crystallization on thermal stability of the glass and crystallizing phases
formed upon heat treatment is investigated by DTA/DSC and XRD methods. It has been found
that the effect of nanocrystallization of LaF 3 and incorporation of RE elements in formed upon
heat treatment nanocrystallites depends on the kind of rare earth elements and is determined by
factors of crystallochemical nature and requires adequate proportions between the components
forming glass structure.
The ellipsometric investigations are performed by M2000 spectroscopic ellipsometer. These
measurements allowed us to determine dispersion of refractive indices in the range 190–1700 nm
and depolarization coefficients. The influence of nanocrystallization process on refractive indices
is discussed.
Keywords: oxyfluoride glasses, rare earth elements, thermal and optical properties.
1. Introduction
In recent years, an increasing interest has been devoted to rare earth doped oxyfluoride
glasses, particulary oxyfluoride transparent glass ceramic, because of their potential
use for making optical devices, such as solid lasers and optical amplifiers, transparent
host materials based on rare earth (RE) ions [1]. Among numerous host materials,
transparent oxyfluoride glass ceramics, which combine the advantages of the excellent
optical properties of fluoride and high chemical and thermal stability of oxide, have
attracted a great deal of attention [2]. An RE doped LaF 3 single crystal, characterized

440 J. JAGLARZ, M. REBEN
by the low phonon energy and large transfer coefficient between the RE ions, has been
revealed to be a suitable host to achieve laser and up-conversion. It is well known that
up-conversion is difficult to generate in conventional oxide glasses due to their high
phonon energies, corresponding to the stretching vibrations of the oxide glass network
former. But oxide glasses might be much better for practical applications because of
their high thermal stability, chemical durability and not complicated fabrication [3].
Rare earth ions are preferentially incorporated into crystalline phases with small
phonon energies of 350 cm –1 . Consequently, excited-state lifetimes and optical
absorption cross-sections of the doped RE ions become substantially larger in them
than in vitreous environments [4]. The glass host matrices are based on silicates with
mechanically and chemically desirable characteristics. The lanthanum trifluoride LaF 3
is a classical host for studying thermal and optical properties of the trivalent RE ions.
1.1. Spectroscopic ellipsometry measurements
Ellipsometry technique uses light of known polarization incident on a surface under
study and detects the polarization state of the reflected light [5].
Spectroscopic ellipsometry (SE) data can be acquired from ultraviolet to near
infrared. SE determines two angles Ψ and Δ, with:
rp rs ρ tanΨ
--------- e iΔ
= =
where r p and r s are complex Fresnel reflection coefficients for p and s polarizations,
respectively, and Δ is a phase shift between both polarized waves. The fundamental
ellipsometry equation (1) allows determination of thickness of a film and the spectral
dependences of optical constants (i.e., the refractive index n and extinction
coefficient k). Ellipsometric measurements also permit determination of the depth
profile and surface roughness, as has been done in this work. In each spectral range,
different properties of materials are studied. However, the data must be analyzed to
obtain useful information.
An optical model representing the assumed physical geometry and microstructure
is developed, and Fresnel reflection coefficients calculated, allowing predictions of
Ψ and Δ to compare with measured values. Model parameters, such as n, k and
roughness σ, vary in regression until the comparator function, such as mean square
error, is minimized. The resulting parameters are the “best fit” values of n, k, and σ.
1.2. Experimental details
For each batch, the starting materials of high purity were fully mixed and melted in
a covered platinum crucibles in an electric furnace at the temperature range from
1400 to 1450 °C in air. The melts were poured out onto a steel plate forming a layer
thickness of 2 to 5 mm and then cast into a brass mould followed by annealing at
a temperature of 100 °C below the glass transition temperature determined by
differential scanning calorimetry (DSC) to relinquish the inner stress. The following
(1)

The influence of nanocrystallization process ... 441
T a b l e 1. Composition of the rare earth doped oxyfluoride glasses.
Composition [mol%]
Glass No. SiO2 Al2O3 Na2O LaF3NaF Tm2O3 Yb2O3 O 42.55 31.32 10.08 14.50 1.55 – –
O1 36.56 26.89 9.33 25.32 1.81 0.09 –
O2 36.56 26.89 9.33 25.32 1.81 – 0.09
O3 36.57 26.89 9.33 25.32 1.82 0.03 0.03
raw materials were used to prepare the batches: SiO 2 , Al 2 O 3 , Na 2 CO 3 , LaF 3 , NaF,
Tm 2O 3 and Yb 2O 3. The compositions of the glasses are listed in Tab. 1.
The crystallization ability of the glasses obtained was determined by DTA/DSC
measurements conducted on the Perkin–Elmer DTA-7 System operating in heat
flux DSC mode. The samples (60 mg) were heated in platinum crucibles at a rate
10 °C/min in dry nitrogen atmosphere to the temperature 1000 °C. All glasses
revealing the effect of ceramization process were selected for further thermal
treatment. To obtain the ceramming effect the glasses were heated 20 min at
a temperature of the maximum of the exothermal peak. The transparent glassy samples
with 2–5 mm in thickness so produced were then cut into square coupons of about
1cm 2 , and heated to the ceramming temperature at a rate of 10 °C/min, held for 10 min,
then cooled down to room temperature naturally to obtain transparent glass ceramics.
1.3. Ellipsometric study
The spectroscopic measurements of Ψ and Δ for the layers presented were performed
with the use of Woollam M2000 spectroscopic ellipsometer in spectral range form
190 to 1700 nm. The samples were measured for two angles of incidence (60°, 65°).
To analyze the data, we combined all angular spectra and we fitted all data
simultaneously. The data have been analyzed using CompleteEASE 3.65 software.
Also, the depolarization coefficient versus light wavelength has been determined.
2. Experimental results
The DTA and DSC thermal analysis are sensitive to changes in the chemical
composition of the glass and they are very easy methods to determine the characteristic
temperature of glasses. From DTA/DSC curves the vitreous state transformation
(glass transition temperature T g), crystallization temperature T cryst, as well as
the thermal effect accompanying them can be determined. In the course of cooling or
heating the glass demonstrates the phenomenon of jump-like change of the molar
heat C p similarly to the phase transition of the 2-nd order according to Ehrenfest’s
thermodynamic classification. The change in the value of C p accompanying the glassy
state transition (ΔC p ), determined from the DSC curves is related to the degree of
rearrangement of the glass structure connected with this transition and depends on
the strength of modified bonds with the components of the glass network.

442 J. JAGLARZ, M. REBEN
Figure 1 shows the DSC curve of an as-prepared oxyfluoride glass doped with
0.09 mol% of Tm 2 O 3 and Yb 2 O 3 , respectively. The DSC curve shows a glass transition
temperature T g and exothermal effects, one just above T g temperature which is
connected with ceramming process and the second one which occurs in higher
temperatures. These exothermal effects indicate the same crystallization phases but
the first crystallization effect is connected with crystallization of LaF 3 as a nanocrystallite
and the second one with crystallization of LaF 3 but in micro-sizes. The thermal
stability factor ΔT has been frequently used as a rough estimate of the glass stability.
To achieve a large working range of temperature during sample fiber drawing, it is
desirable for a glass host to have ΔT as large as possible.
Fig. 1. DTA/DSC curves of rare earth
doped oxyfluoride glasses.
From Table 2, it could be observed that the values of T g , T ceram , T cryst , and ΔT of
O1, O2 glass increased evidently compared to reference glass samples O. From
DTA/DSC curves of O1, O2, O3 glass it can be seen that the kind of rare earth ions
has a great influence on ceramming process. The maximum of ceramming temperatures
increases with addition of Tm 3+ and Yb 3+ ions. Simultaneously, the enthalpy
(ΔH cer ) of this process becomes reduced. This is the evidence of an increasing
ability of the glass for ceramization, manifested by a decreasing value of the thermal
stability index of the glass ΔT 2 . Simultaneously, the glass transition temperature is
T a b l e 2. Thermal characteristics of rare earth doped oxyfluoride glasses (ΔT 1 = T max.cer – T g,
ΔT 2 = T max.cryst – T g ).
Glass
No.
T g
[°C]
ΔC p
[Jg –1 °C –1 ]
T max. cer
[°C]
ΔH cer
[Jg –1 ]
1-st stage of
crystal.
(ceram.)
T max.cryst
[°C]
ΔH cryst
[Jg –1 ]
ΔT 1
[°C]
O 576 0.810 664 18.04 LaF 3 908 41.15 88 332
O1 593 0.491 671 53.25 LaF 3 953 69.59 78 360
O2 592 0.251 668 21.61 LaF 3 933 78.85 76 341
O3 560 0.252 657 19.69 LaF 3 959 159.34 97 399
ΔT 2
[°C]

The influence of nanocrystallization process ... 443
shifted towards higher temperatures with addition of RE ions compared to glass O
without RE. The addition of Tm 3+ and Yb 3+ ions causes the reduction of the specific
heat (ΔC p) accompanying the glass transition region, which may be the evidence of
an increased flexibility of the glass network.
The XRD measurements were performed on as-prepared glass and its corresponding
glass-ceramic. The XRD pattern for as-prepared glass presented in Fig. 2, does not
show diffraction peaks, indicating its amorphous structure by nature. But in Fig. 3a,
the mild diffraction peaks for sample O1 heat treated at 671 °C for 10 min have
appeared. The marked peaks are matched with the diffraction peaks of crystalline LaF 3
reported earlier [2, 4, 6]. From XRD studies one can see in the case of glass O1 doped
with Tm 3+ ions that the heat treatment of this glass in the ceramming temperature
671 °C for 10 min causes appearance of very weak diffraction peaks of crystalline
LaF 3 . In the case of glass O2, the addition of Yb 3+ ions causes appearance of very
well visible diffraction peaks of crystalline LaF 3 , when the glass is heat treated at
the maximum ceramization temperature of 668 °C for 10 min (Fig. 3b).
Fig. 2. XRD pattern for the host matrix glass prepared.
a b
Fig. 3. XRD pattern of glasses O1, O2 after cerammization process; O1, 671 °C, 10 min (a), O2, 668 °C,
10 min (b).

444 J. JAGLARZ, M. REBEN
Fig. 4. Spectral dependence of ellipsometric angles measured for O1 (a) and O2 (b) samples, respectively.
The spectral dependence of ellipsometric angles for samples O1 and O2 is shown
in Fig. 4. In the same figure, the values of Ψ and Δ generated using the fitting Cauchy
model are given.
The Cauchy model describes dispersion relations for n and k indices namely:
B C
n( λ)
= A + ---------- + ----------
k( λ)
ke β
=
λ 2
λ 4
⎛ hc
----------- – E ⎞
⎝ bandedge
λ
⎠
where A, B, C and β are constant terms. The k and E bandegde are the fit parameters
which describe Urbach’s tail absorption and allow the shape of dispersion of extinction
T a b l e 3. Values of parameters determined from ellipsometric measurements.
Sample no. A B×10 –4 C×10 –4 k×10 –4
Roughness [nm] n at 633 nm
O1 1.306±0.017 2.21±0.3 1.77±0.16 3.4±0.2 4.19±0.29 1.312
O2 1.366±0.018 28.7±0.2 1.40±0.10 7.1±0.5 1.13±0.10 1.374
a
b
(2)
(3)

The influence of nanocrystallization process ... 445
a b
Fig. 5. Cauchy dispersion dependences for refraction indices n (a) and extinction coefficients k (b).
Fig. 6. Degree of depolarization of reflected radiation
from O1 and O2 samples versus wavelength.
coefficient to be determined. The values of these fit parameters for O1 and O2 samples
are presented in Tab. 3. Figure 5 shows the n and k dispersive relations in spectral
range from 190 to 1700 nm for the samples under study. Ellipsometric results
allow surface roughness to be determined. In the samples investigated we assumed
the appearance of the surface roughness which can be described using the Bruggeman
effective medium approximation (EMA) [7]. This approximation uses a 50:50 mixture
of the material and air on the sample surface to get optical constants that approximate
the effect of the surface roughness. The obtained values of σ are presented in column 6
of Tab. 3.
The oxyfluoride glasses (OG) doped with Tm ions exhibits lower optical
parameters than the one with Yt ions. Generally, the OG host matrix shows higher
refractive index in UV–VIS0–NIR range than rare earth doped glass.
Additionally, for the samples under investigation the depolarization coefficients [8]
(ratio of incoherent part to the total reflected radiation) have been determined. The results
of depolarization state of reflected radiation of the samples are showed in Fig. 6.
The reflected light beam may consist of two or more components with well defined
polarization states. Yet, the resultant total beam does not exhibit a single well
defined polarization state. There is so in the case of a nonuniform film, or transparent

446 J. JAGLARZ, M. REBEN
substrate exhibiting back reflection effects as is for the glass samples [9]. However
the depolarization coefficient of reflected beam is much bigger than other mentioned
effect. This is because of depolarizing light in the bulk of OG glasses.
3. Conclusions
Stable glasses could be prepared in a relatively large composition domain of the NaF–
–LaF 3 system. Unfortunately, the effect of LaF 3 crystallization as the only
nanocrystalline phase, which is indispensable from the optoelectronics point of view,
is strongly dependent on the rare earth content with respect to the kind of those ions.
The thermal properties of rare earth (RE) ion doped glass depend strongly on local
environment of RE, and therefore differences in the DTA/DSC curves are expected
if they are placed in a glassy or in a crystalline surrounding of the glass ceramic.
The advantages of oxyfluoride glass ceramic are that the rare earth ions would be
incorporated selectively into the fluoride crystalline phase LaF 3 after crystallization,
and these materials possess good transparency due to the much smaller size of
precipitated crystals than the wavelength of visible light. The thermal stability factor
ΔT has been frequently used as a rough estimate of the glass stability.
The index of refraction of oxyfluoride glasses is low (~1.4) in visible range.
RE ions lower the refractive index of oxyfluoride host matrix. The doping of RE ions
causes change in coefficients n and k. The Yt ions doped to modify optical constants
enter the host matrix much more than the same quantity of Tb ions.
The depolarization of reflected beam results from light scattering in the bulk and
backscattering from the bottom surface of OG wafer. Depolarized light comes mainly
from scattering on nanocrystals appearing in the host matrix. The presence of RE ions
enhance nanocrystallization in OG glasses.
Reference
[1] ZHONGCHAO DUAN, JUNJIE ZHANG, WEIDONG XIANG, HONGTAO SUN, LILI HU, Multicolor
upconversion of Er 3+ /Tm 3+ /Yb 3+ doped oxyfluoride glass ceramics, Materials Letters 61(11–12),
2007, pp. 2200–2203.
[2] REBEN M., WACŁAWSKA I., Structure and nanocrystallization of SiO 2–Al 2O 3–Na 2O–LaF 3,
Proceedings of the XXI ICG Strasbourg, 2007.
[3] PAN Z., JAMES K., CUI Y., BURGER A., CHEREPY N., PAYNE S.A., MU R., MORGAN S.H., Terbium-
-activated lithium–lanthanum–aluminosilicate oxyfluoride scintillating glass and glass-ceramic,
Nuclear Instruments and Methods in Physics Research A 594(2), 2008, pp. 215–219.
[4] REBEN M., WACŁAWSKA I., PALUSZKIEWICZ C., ŚRODA M., Thermal and structural studies of
nanocrystallization of oxyfluoride glasses, Journal of Thermal Analysis and Calorimetry 88(1), 2007,
pp. 285–289.
[5] AZZAM R.M.A., BASHARA N.M., Ellipsometry and Polarized Light, Nord Holland, 1987.
[6] ŚRODA M., WACŁAWSKA I., STOCH L., REBEN M., DTA/DSC study of nanocrystallization in oxyfluoride
glasses, Journal of Thermal Analysis and Calorimetry 77(1), 2004, pp. 193–200.

The influence of nanocrystallization process ... 447
[7] BRUGGEMAN D.A.G., Berechnung verschiedener physikalischer konstanten von heterogenen
substanzen, Annalen der Physik (Leipzig) B 24, 1935, pp. 636–674.
[8] JELLISON G.E., Spectroscopic ellipsometry data analysis: measured versus calculated quantities,
Thin Solid Films 313–314, 1998, pp. 33–39.
[9] CompleteEasy Data Analysis Manual, J.A. Woolam Co., Inc., 2008.
Received November 12, 2009
in revised form January 10, 2010

Optica Applicata, Vol. XL, No. 2, 2010
Stabilized detection scheme of surface acoustic waves
by Michelson interferometer
OLEH MOKRYY 1, 2* , VOLODYMYR KOSHOVYY 1 , IGOR ROMANYSHYN 1 , ROMAN SHARAMAGA 1
1
Karpenko Physico-Mechanical Institute of the National Academy of Science of Ukraine,
Lviv, 79601, Ukraine
2 Lviv Politechnic National University, Department of Photonics, 79013 Lviv, Ukraine
* Corresponding author: mokomo@lviv.farlep.net
A new detection scheme of surface acoustic waves by Michelson interferometer has been proposed.
A substantial advantage of this scheme lies in its being stabilized against vibration and independent
sensitivity of the width of an optical beam. These effects were achieved by creating an interference
field on the surface of a photodetector. The measurement scheme proposed was analyzed by means
of a numerical modeling method. Experiments confirming the fact of the sensitivity of the proposed
detection scheme being independent of vibration and width of optical beam have also been made.
Keywords: surface acoustic wave, Michelson interferometer, noncontact detection.
1. Introduction
Surface acoustic waves (SAW) are used for determining the space distribution of
the elastic properties of coated materials, composite structures, materials that have
sustained surface modifications. These materials are important for the aircraft industry,
medicine and other applications. Laser ultrasound methods have been used for
the excitation and detection of SAW in recent years. These methods are successful
because they are noncontact and have a high space and time resolution. We consider
the problem of detection of SAW using Michelson interferometer. This is a detection
method of a sample surface displacement due to the acoustic wave [1–3]. It is quite
easy to use and allows high sensitivity to be obtained. The sensitivity of Michelson
interferometer is equal to zero when the optical path difference equals 0.5λ N,
where λ is the optical wavelength and N is an integer. Temperature drifts and
vibrations can result in the change of optical path difference of several micrometers,
thus seriously complicating an interferometer operation. Therefore, there is a problem
of stabilization of Michelson interferometer against vibration. This problem is typical
of other interferometers, too. The active and passive methods are used for
stabilization of interferometers. The changing path length is stabilized by displacement
of an interferometer mirror or electro-optic cell [1, 4]. The feedback signal is used
in these methods. Another method is based on the quadrature dual interferometer. In

450 O. MOKRYY et al.
this method, two interference signals with a π/2 shift phase are detected by
two photodetectors [1]. However, all these require an essential complication of
construction. We proposed a new stabilization scheme for detecting SAW by
Michelson interferometer. A distinctive feature of this setup is that the interference
pattern is formed on the surface of a photodetector in the form of space periodic fringes.
The sensitivity of the Michelson interferometer depends on the optical beam
size [5]. When the optical beam size is proportional to the wavelength of SAW
the sensitivity is small because different parts of the optical beam have a different
optical path. In this case, the intensity of one part of interference field is increased and
the intensity of another part of interference field is decreased, therefore the full signal
has been compensated. The measurement scheme which we proposed is free from that
defect. The sensitivity of this scheme is independent of the optical beam size, when
the optical beam size is larger than certain value. This effect is possible due to
the existing interference fringes with the width corresponding to the SAW length. This
conclusion is confirmed by a numerical simulation and experiment.
2. Detection scheme of surface acoustic waves
A general scheme of the measurement setup is presented in Fig. 1. This setup differs
a little from the classical setup of Michelson interferometer. Optical beams reflected
from the sample and from the interferometer mirror interact and an interference
pattern is formed. The intensity of interference field is registered by a photodetector.
The displacement of the sample surface changes the optical path difference and
correspondingly changes the intensity of interference field. A distinctive feature of
the measurement setup proposed is that there is a certain angle between interfering
beams. This angle appears as a result of the inclination of interferometer mirror
(Fig. 1). The presence of an angle between interfering beams results in appearance of
the spatial periodically modulated interference pattern. Thus, the interference field
on the surface of the sensitive area of the photodetector is formed as a result of action
of two factors: the angle between interference beams and modulation of phase shift
between these beams due to propagation of SAW through a sample.
Laser
Photodetector
Mirror
Sample
Interference field
Fig. 1. A scheme illustrating detection
of SAW by Michelson interferometer.

Stabilized detection scheme of surface acoustic waves ... 451
Both these factors result in forming a spatially-periodic interference pattern.
The first factor made a static interference field, the second factor forms a dynamic
interference field. However, the interference pattern created due to SAW is not visible
because the shift of the sample surface caused by the acoustic wave is of the order of
a few nanometers. The photodetector registers an integral change of intensity which
is defined by both contributions in the interference pattern. The sensitivity of this
scheme is independent of the change of path difference. On the other hand, sensitivity
of the measurement scheme depend on the length of SAW Λ and the width of
fringes L. The condition when sensitivity is maximum is defined by numerical
simulation.
3. Numerical model of Michelson interferometer
In this paper, we consider the case where magnitude of SAW wavelength is about
millimeter or few nanometers. These conditions correspond to conditions of using
SAW in nondestructive testing.
For analysing the performance of Michelson interferometer the approach of
geometrical optics has been used. The one-dimensional case is considered. The surface
of the sample is taken as a mirror surface. The interference of optical waves with
the same polarization and intensity is considered. In such a case the intensity of
interference field is expressed by [6, 7]:
I = I1+ I2 + 2 I1I 2 cosδ
where I 1 and I 2 are the intensities of beams reflected from the mirror and from
the sample, respectively, and δ is the phase difference between them.
It has been taken into account that optical beams have Gaussian distribution of
intensity which is given by:
I1, 2
=
1
--------------------x
I0 2π a
2 ⎛ ⎞
exp⎜–
------------- ⎟
⎝ ⎠
2a 2
Axis x is the axis on the plane of the photodetector, ( 1 ⁄ 2πa)I0is the maximal
intensity in the centre of the optical beam, a is the parameter of distribution.
Expression (2) is normalized. The magnitude of full power of optical beam is
independent of parameter a, which is convenient for numerical simulation.
The phase difference δ appears for a variety of reasons and, in general, it is different
at various points of the interference field. First of all, δ is defined as the difference d
of distance to the mirror and the sample. Correspondingly, it is possible to write:
δ 1
=
2π
----------- 2d
λ
(1)
(2)
(3)

452 O. MOKRYY et al.
In the case where one beam is parallel to the axis of the interferometer and
the other one is inclined under a small angle β to this axis, the phase change between
them is described by the expression [6]:
δ 2
=
2π
----------- x sinβ
λ
Thus, the periodic interference fringes are formed having a width L = λ/sinβ.
A particular feature of using Michelson interferometer for detection of the SAW
is that the surface of the sample through which a wave propagates is displaced under
the action of SAW. We considered the case where the frequency range of SAW is from
a few MHz to tens of MHz (the wavelength ranges from less than a millimeter to a few
millimeters) and its amplitude has value of a few nanometers. The minimal wavelength
of SAW is 0.2 mm in the area considered. Since the magnitude of SAW amplitude is
accepted as 1 nm, then the inclination of the surface is less than 2×10 –5 radian. This
magnitude is small and it can be assumed that the angle spectrum of the reflected
optical wave is equal to the angle spectrum of the falling optical wave. The front of
the reflected wave changes by a double value of surface displacement under the action
of SAW. The space distribution of change of the front reflected wave corresponds to
the space distribution displacement of the sample surfaces.
The phase shift between optical waves, caused by the SAW, will take the form:
δ 3
=
2π
2π
----------- 2h sin ⎛ωt+ ----------- x ⎞
λ ⎝ Λ ⎠
where ω is the frequency of SAW and Λ is the length of SAW, h is the amplitude
of SAW.
Taking into account Eqs. (1)–(5) the distribution of intensity in plane of
interference pattern can be written as follows:
⎧ 2π
I I1I2 2 I1I 2 ----------- 2d xsinβ 2h ⎛ 2π
ωt + ---------- x⎞
⎫
= + + cos⎨
+ + sin
λ
⎝ Λ ⎠ ⎬
⎩ ⎭
For recording a signal the photodetector is placed in the interference field (Fig. 1).
Photocurrent is proportional to the total intensity of incident light on the photodetector
∫∫
s
i =
g Idx s is the area of interference field on photodetector, which was determined through
the diaphragm size, g is the coefficient of proportionality.
(4)
(5)
(6)
(7)

Stabilized detection scheme of surface acoustic waves ... 453
When describing the measurement setup for registration of SAW the parameter V,
i.e., which is sensitivity, is used:
V
=
Δi
----------------------------hg
Id x
∫∫
s
where Δi is the AC amplitude of the photodetector current.
A change in the magnitude of length difference produces modulation of
the photocurrent. The depth modulation is:
Δimax – Δimin
G =
--------------------------------------
Δimax + Δimin
Δi max and Δi min are maximum and minimum AC amplitudes of the photodetector
current determined when the optical path difference is changed by the value λ/2.
The distribution of intensity in the interference field is determined by the numerical
calculation. The interference field is in the plane of photodiode. The plane of
photodiode is divided into small elements and we accept that the optical intensity is
constant in each respective element. The intensity in one element is calculated by
Eq. (6). The total intensity is calculated as the sum of the intensities in all elements.
The photocurrent is proportional to the total intensity. The photocurrent is
calculated for the different moments of time during the period of SAW. The amplitude
of photocurrent is determined this way and correspondingly its dependence on
the different parameters is calculated.
4. Numerical experiment
Equations (6)–(9) allow us to analyze the sensitivity of Michelson interferometer and
to optimize parameters of the detecting scheme. The dependence of sensitivity V versus
optical beam size r and width L of interference fringes is considered.
For numerical modeling the following values of parameters were taken: a =1.5mm,
ω = 6.28×10 6 Hz, λ =0.6μm. A displacement h of the surface of the sample under
the action of the SAW was taken sufficiently smaller than the optical wavelength and
was equal to 1 nm, and this magnitude of displacement corresponds to the power of
a few mW/cm [8].
A change of a few millimeters in length difference of the interferometer arms was
considered in calculations. The wavelength of SAW is 1 mm.
The results of the numerical simulation are presented in Figs. 2–4. The sensitivity
dependence of the optical beam width is shown in Fig. 2. This figure presents the case
where the width of the interference fringes is infinity. The sensitivity is maximum
(8)
(9)

454 O. MOKRYY et al.
Fig. 2. Sensitivity versus width of optical beam.
Fig. 3. Sensitivity versus distance difference,
r = 0.1 mm.
under condition of the width of the optical beam being small. This principle is well
known and therefore small width of the optical beam is used in this scheme of
the detection of SAW. The change of sensitivity due to the path difference of optical
beams is shown in Fig. 3. The Michelson interferometer sensitivity is minimal when
the distance difference is 2d = Nλ/2. This dependence illustrates the need for
stabilization of the path difference.
The sensitivity dependence of the optical beam width and the change of path
difference is shown in Fig. 4. The difference distance d is presented as a sum of
the constant part d 0 and variable part Δd. The cases when d 0 =0.1mm (see
Figs. 4a–4c) and d 0 = 2 mm (see Figs. 4d–4f) are presented. As can be seen from
the graphs there exists a strong dependence of sensitivity on magnitude Δd.
The sensitivity changes in accordance with sinusoidal law from maximal value to
zero. When the optical beam width increases the dependence sensitivity of the change
in path difference decreases for all the cases presented in Fig. 4. Under condition of
Λ = L (Figs. 4b and 4e) the sensitivity approximates a constant magnitude but for
Λ > L (see Figs. 4a, 4d) and Λ < L (see Figs. 4c, 4f) the sensitivity decreases to zero.
The results of numerical simulation show that sensitivity is independent of the optical
beam width when the latter is great.
The obtained results of numerical simulation agree with the known experimental
data and show new possibilities for detection of SAW. In the traditional scheme of
Michelson interferometer the optical beam width is much less than the wavelength

Stabilized detection scheme of surface acoustic waves ... 455
a b c
d
Fig. 4. Simulated sensitivity versus width of beam r and change of distance difference Δd. L = 0.4 mm,
d 0 = 0.1 mm (a), L = 1 mm, d 0 = 0.1 mm (b), L = 1.4 mm, d 0 = 0.1 mm (c), L = 0.4 mm, d 0 = 2 mm (d);
L = 1 mm, d 0 = 2 mm (e); L = 1.4 mm, d 0 = 2 mm (f); Λ = 1 mm.
of SAW. This case is shown in the area graphs where value r is small. The sensitivity
is greatly dependent on path difference. Instability of the path difference magnitude
of 0.1 μm can considerably change the sensitivity. Therefore, it is necessary to stabilize
the interferometer against vibration. On the other hand, the numerical simulation
shows that sensitivity is independent of the change of the path difference in the case
of great optical beam width and it is maximum under condition of Λ = L (Figs. 4b, 4e).
Exactly such geometry is used in the proposed scheme of detection of SAW, which is
independent of the change of path difference and is stabilized against vibration.
5. Experimental research
e
For verification of the results of numerical modeling a setup has been constructed in
which the proposed scheme of detection of SAW is realized. The sensitivity depending
on the size of the optical beam is investigated.
A schematic layout of the setup is shown in Fig. 5. The geometry in which
the interfering beams are forming some angle between themselves due to inclination
of a mirror is used. On the surface of the sample the SAW with frequency of 2.5 MHz
generated by prismatic piezoelectric transducer is propagated. The acoustic pulse has
duration of 50–100 μs. A He-Ne laser with output radiation wavelength of 632.8 nm
is used. The interferometer mirror has been fixed on a piezoelectric washer to which
f

456 O. MOKRYY et al.
Laser
f = 46 kHz
Photodetector
Diaphragm
Generator Pulse generator
Fig. 5. Scheme of the experimental setup.
Amplifier Oscilloscope
SAW
transducers
f = 2.5 MHz
Mirror on piezoelectric washer
a sinusoidal signal with frequency of 46 kHz is supplied. It is the resonance
frequency of the piezoelectric washer. Under the action of this signal the mirror
oscillates, which causes a change of distance difference d. An oscillation of mirror
simulates vibrations and allows us to study experimentally their influence on
the sensitivity of the measurement setup. The oscillation swing of the mirror is a few
hundred nanometers. A signal which is supplied to the interferometer mirror and
a pulse of the SAW are synchronized with each other. An interference pattern is
registered by the photodetector and the signal is observed on the oscilloscope.
The signal is amplified by the band-pass amplifier. The setup also uses a diaphragm
which allows changing of the width of the beam which falls onto the photodetector.
The whole interfering field falls at the photodiode.
A glass plate is used as a specimen. The measured velocity of SAW is 3300 m/s
and the wavelength is 1.32 mm. The result of the experiment is presented in Fig. 6.
The sensitivity is maximum and changes very little with an increase in the size of optic
Fig. 6. Sensitivity versus width of optical beam. The wavelength of SAW is 1.32 mm. The starting optical
path is different for L = 1.0 mm, L = 1.32 mm and L = 1.6 mm.

Stabilized detection scheme of surface acoustic waves ... 457
beam r beginning from r ≈ 0.5 mm under condition of L = Λ. Otherwise, the sensitivity
decreases when the optic beam size is increased. These results of the experiment agree
with the results of the numerical calculation (Fig. 4).
The proposed scheme of measurement is stabilized against the change in path
difference, too. The oscillograms of signals received at the registration of pulses of
SAW at vibrations of the interferometer mirror are shown in Fig. 7. In this case,
the scheme for which L = Λ is used. The shape of the signal shows that the swing of
the mirror vibration is greater than λ/4 (see Fig. 7a). The depth modulation decreases
when the optical beam size increases. The amplitudes of the mirror vibration in both
cases are equal. The shape of the signal (see Fig. 7b) shows that the sensitivity is less
dependent on the change of path difference. The depth of modulation decreases to
0.07 when the width of optical beam increases to 1 millimeter. This result tells us that
the proposed scheme of detection of SAW is stabilized against vibration.
6. Conclusions
A scheme for detecting SAW using Michelson interferometer in which the sensitivity
does not depend on the change of length difference of interferometer arms has been
proposed. The sensitivity is also independent of the change of optical beam size.
The numerical simulation and experimental investigation of this scheme have been
made. The proposed scheme of SAW may be used under conditions of vibration and
temperature drifts.
References
a b
Fig. 7. Photocurrent at vibration of the interferometer mirror. Amplitude of the vibration larger than
λ/4, r = 0.1 mm (a), r = 1 mm (b).
[1] WAGNER J.W., Optical detection of ultrasound in Physical Acoustics: Ultrasonic Measurement
Methods, R.N. Thurston, A.D. Pierce [Eds.], V. XIX. Academic Press, Boston, SanDiego, New York,
London, Sydney, Tokyo, Toronto, 1990, pp. 201–265.
[2] KNUUTTILA J.V., TIKKA P.T., SALOMAA M.M., Scanning Michelson interferometer for imaging surface
acoustic wave fields, Optics Letters 25(9), 2000, pp. 613–615.
[3] PRADA C., BALOGUN O., MURRAY T.W., Laser-based ultrasonic generation and detection of
zero-group velocity Lamb waves in thin plates, Applied Physics Letters 87(19), 2005, p. 194109.
[4] REIBOLD R., MOLKENSTRUCK W., Laser interferometric measurement and computerized evaluation of
ultrasonic displacements, Acustica 49(3), 1981, pp. 205–211.

458 O. MOKRYY et al.
[5] GOLLWITZER A., HAUGG S., FISCHERAUER G., An auto-focusing approach for a dynamic quadrature
interferometer, Proceeding of the Conference Opto 2009, May 26–28, 2009, Nurnberg, pp. 29–34.
[6] VEST C.M., Holographic Interferometry, John Wiley & Sons, New York, 1979.
[7] ANGELSKY O.V., MAKSIMYAK A.P., MAKSIMYAK P.P., HANSON S.G., Optical correlation diagnostics
of rough surfaces with large surface inhomogeneities, Optics Express 14(16), 2006, pp. 7299–7311.
[8] GULYAEV YU.V., PLESSKII V.P., Propagation of acoustic surface waves in periodic structures, Soviet
Physics Uspekhi 32(1), 1989, pp. 51–74.
Received June 21, 2009
in revised form October 14, 2009

Optica Applicata, Vol. XL, No. 2, 2010
Optical correlation technique
for cement particle size measurements
MYKHAYLO P. GORSKY * , PETER P. MAKSIMYAK, ANDREW P. MAKSIMYAK
Correlation Optic Department, Chernivtsi National University, 2 Kotsybunska St., Chernivtsi, Ukraine
* Corresponding author: misha@itf.cv.ua
Optical correlation technique of determining the cement particle size distribution is described. It
is based on transverse coherent function measurement using a polarization transverse shearing
interferometer. The proposed technique of data processing decreases the dependence of the result
on interferometer noise, emission source intensity fluctuations and difference of refractive index
magnitudes of different cement particles. The technique allows fast and reliable determination of
the size distribution function of cement particles.
Keywords: transverse coherence, polarization interferometer, cement, size distribution function.
1. Introduction
The size distribution function of particles is an important characteristic of cement.
Different kinds and brands of cement differ by particle sizes. For physical and
mathematical modelling of different processes, which occur during specific hydration
and studying its mechanical, optical and other properties, it is necessary to know
the size distribution function of particles. Cement particle size distribution
measurements are taken by different methods, such as electrical zone sensing,
sedimentation, scanning electron microscopy [1–5]. But these methods are too
complicated and are not widely used. A standard procedure consists in measuring
the weight of the remains on the sieve during consecutive screening from the biggest
mesh aperture to the smallest one. Laser light diffraction method [5] is also used.
For determination of cement particle size we suggest using optical correlation
technique [6, 7].
Cement is a complicated mixture of particles with different sizes and forms, which
by 95–97% consists of oxides CaO, SiO 2, Al 2O 3 and Fe 2O 3. These compounds
constitute minerals, the main of which are [1–4]:
– tricalcium silicate (alite), 3CaO·SiO 2 , 40–65%;
– dicalcium silicate (belite), 2CaO·SiO 2, 15–45%;
– tricalcium aluminate, 3CaO·Al 2 O 3 , 4–12%;

460 M.P. GORSKY, P.P. MAKSIMYAK, A.P. MAKSIMYAK
– tetracalcium alumoferrite, 4CaO·Al 2 O 3 ·Fe 2 O 3 ,12–25%;
– gypsum.
The size of a particle with complex shape could be determined by the maximum
linear dimension or by the spherical particle diameter with equivalent volume. As is
known, optical properties are mathematically calculated only for spherical, cylindrical
and spheroid forms [8, 9]. For practical use, in calculations of specific cement optical
properties, it is convenient to approximate particles by spherical form [10]. This
approximation is used in laser radiation diffraction method [5]. But the distribution
found essentially depends on incoming parameters for calculation. One of these
parameters is the magnitude of relative refractive index. The refractive index of
cements is complex m = n + iχ, but its real and imaginary parts are found within
the intervals of n = 1.5–1.7, χ = 0.003–1 [1–5]. As cement is a mixture of particles
with different chemical composition, each particle could have its own refractive
index magnitude. In the case of measurement of laser radiation diffraction on
isolated particles, consideration of this peculiarity is quite complicated. Usually, some
refractive index is set for all particles, which causes distortion of results.
It has been shown in papers [6, 7] that it is possible to determine sizes and
concentration of particles from the transverse coherent function of a particle’s image.
However, this technique needs high measurement accuracy of coherence function, and
samples must provide only single scattering (distances between particles have to
exceed maximum particle size). Often in practice, these conditions are hard to provide.
We suggest the technique of processing and approximation of experimental results,
which decreases the obtained particle size distribution function dependence on
concentration and spread in refractive index magnitudes.
2. Coherence function calculation
Under light scattering on large particles, particle images are projected into observation
plane. It is easy to analyze particle images using the transverse coherence function:
Γ⊥( ρ)
= ψ⊥ ρ +
( ) Γ X
where ψ⊥( ρ)
– transverse coherence function of particle images giving the data on
particle size distribution; Γ X – constant component describing non-scattered radiation
intensity. Experimentally, the coherence function of a field is determined in transverse
shearing interferometer. The transverse coherence function magnitudes for certain
transversal shares are determined from interference pattern visibility. For scalar optical
fields visibility is found as:
Imax – Imin V =
------------------------------
Imax + Imin where I max and I min – maximum and minimum magnitudes of intensity, respectively.
(1)
(2)

Optical correlation technique for cement particle size measurements 461
d
ρ
Fig. 1. Image overlay for spherical particle with diameter
d and transverse displacement ρ.
Let us find the transversal coherence function of spherical particle’s image with
diameter d. The correlation of particle images for transversal displacement in
interferometer leg ρ can be defined by overlapped zone square of particle image
(Fig. 1):
sr( d, ρ)
=
d 2
-----------
2
acos
ρ ρ
------- ------- d
d 2
2 ρ 2
– –
Overlapped square normalization of particle images gives us the correlation
function of image particle. Let us denote the radiant flux through a unit area by dI.
The particle image overlaps radiant flux in the beam. Then, in interference maximum,
the radiant flux at the observation plane behind the particle image would be the result
of beam interference with zero phase difference, and the total radiant flux would be
equal to 4dI. Radiant flux in particle image area outside the overlapped image zone
would be equal to dI. The flux in overlapped zone is zero. Particle image zone square,
outside the overlapped zone, equals 2[d 2 π/4 – s r (d, ρ)]. If the observation zone square
is larger than the particle image square by ρ s times, then the observation zone square,
without particle images, is determined as: ρ s (d 2 π/4) – 2[d 2 π/4 – s r (d, ρ)] – s r (d, ρ).
Then, the maximum intensity for displacement ρ and particle diameter d could be
written as:
Imax( ρ, d, ρs) 2 ρ
dI d acos-------- d
d
2 π⎛ 3
ρs – ------ ⎞ ρ d
⎝ 2 ⎠
2 ρ 2
+ – – , ρ ≤ d
dI d 2 ⎧
⎪
⎪
=
⎨
⎪
3
⎪ ⋅ π ⎛ρs– ------- ⎞ ,
ρ > d
⎩
⎝ 2 ⎠
where ρ s – the ratio of the observation field square to the particle image square. In
interference minimum, the observation field would be the result of beam interference
with phase difference π, so that the radiant flux outside the particle images and in
overlapped image zone equals zero. The radiant flux in not overlapped zones of particle
(3)
(4)

462 M.P. GORSKY, P.P. MAKSIMYAK, A.P. MAKSIMYAK
images is also equal to dI. Then, the minimum intensity in the transverse shearing
interferometer for displacement ρ and particle diameter d is:
Imin( ρ, d )
=
d
dI
2 π
------------ ρ d
2
2 ρ 2 2 ρ
+ – – d acos-------- , ρ ≤ d
d
dI d 2 ⎧
⎪
⎪
⎨
⎪
⎪
π
------------ , ρ > d
⎩ 2
Then, the transverse coherence function through the extreme magnitudes of
intensity is:
Γ⊥( ρ, d, ρs) Imax – Imin = ------------------------------ =
Imax + Imin d 2 π( ρs – 2)
2ρ d 2 ρ 2 2 ρ
– – + 2d acos------d d 2 ⎧
⎪
⎪---------------------------------------------------------------------------------------------------------------,
ρ ≤ d
⎪
= ⎨
π( ρs – 1)
⎪
⎪ ρs – 2
-------------------
⎪
, ρ > d
ρs – 1
⎩
For the ensemble of particles with different sizes and the corresponding size
distribution p(d ), the transverse coherence function is defined as:
total
Γ ⊥ ρ, ρs
∞
∫
( ) =
pd ( )Γ⊥( ρ, d, ρs)dd 0
Determination of the distribution function from these equations is very
complicated. But, if we know the function p(d ), we could find its parameters using
the least-squares method [11].
If an analytical form of function p(d ) is known, then determination of its
parameters is done by the following algorithm. From experimental data, by extreme
magnitudes of intensity, the transverse coherence function magnitudes are determined
for certain transverse shifts as interference pattern visibility. Then, using the least-
-squares method and Eq. (7), the best approximation is found, from which distributive
parameters and value ρ s could be determined, which gives us particle concentration.
3. Measuring technique with polarization transverse
shearing interferometer
For measuring the field’s transverse coherence function, we use a polarization
interferometer arrangement (Fig. 2). It consists of two identical wedges 3 and 4
(5)
(6)
(7)

Optical correlation technique for cement particle size measurements 463
Fig. 2. Beam paths in interferometer.
forming a plane-parallel plate, which are placed between crossed polarizers 1 and 5.
The main optical axes of wedges 3 and 4 are parallel and form 45° angles with plane
of polarization of polarizers 1 and 5. Sample 2 is placed between polarizer 1 and
wedge 3.
In Figure 2, the ordinary “o” and extraordinary “e” beam paths are shown. Space
division of the beams occurs on a way out from the first wedge 3. At normal incoming
beam incidence on the surface of wedge 3, refraction angles of ordinary ψ o and
extraordinary ψ e beams could be written as:
sinψ
o
sinψ
e
=
=
no ---------- sinϕ
n
ne ---------- sinϕ
n
where ϕ – incident angle, which is equal to prism angle; n o and n e – refractive indices
of ordinary and extraordinary beams, respectively; n – refractive index of a surrounding
medium.
Transverse displacement between beams ρ is assigned by the distance between
wedges h and depends on wedge angle and birefringence of the wedge. From
the geometry of Fig. 1 one gets:
ρ = h ⎛tanψ o – tanψ
⎞
e cosϕ = ah
(9)
⎝ ⎠
As one can see, ρ is linearly dependent only on h (parameters ϕ, ψo, ψe are constant
for specific scheme realization). So, for transverse displacement determination it is
necessary to know the dependence ρ = f (h) =ah.
In the scheme of Fig. 2, transverse displacement ρ is accompanied by longitudinal
one, ρ || , determined from the equation:
ρ ||
⎛ 1 1 ⎞
= ⎜------------------ – ----------------- ⎟ – ne( tanψ o – tanψ
e)
sinϕ
h =
bh
⎝ cos cos ⎠
ψ o
ψ e
(8)
(10)

464 M.P. GORSKY, P.P. MAKSIMYAK, A.P. MAKSIMYAK
Longitudinal displacement between the beams in an interferometer causes
modulation of the field intensity, whose dependence, while changing the distance
between the wedges from zero to a defined value, is represented in Fig. 3. As
longitudinal displacement between beams is linearly bound with transverse one, it is
convenient to calibrate transverse displacement with the extreme magnitudes of
total field intensity for longitudinal displacements (Fig. 3). The distance between
the extrema (maximum and minimum) amounts to λ/2. Such a calibration could be
provided in case of substantial scale excess of longitudinal field modulation over
transverse modulation scale. So, even for irregular changes of the distance between
wedges (Fig. 3), the magnitude of transverse displacement is known by extrema of
the total field intensity at the output of an interferometer. In our experiment,
the distance between neighbouring extrema corresponded to transverse displacement
by 3.36 μm.
4. Experiment
Fig. 3. Intensity changes measured vs. longitudinal
displacements of interferometer wedges.
For the least-squares method implementation, it is necessary to know function p(d ).
The analytic function p(d ) is not known. That is why in order to find this function
we have investigated the images of cement particle samples. The samples consisted of
Fig. 4. Microscopic images of cement particles.

Optical correlation technique for cement particle size measurements 465
dry cement particles uniformly distributed on a glass plate surface. These samples were
later used for measurements in transversal shearing interferometer.
An example of microscopic images of cement particles is shown in Fig. 4. In order
to find the analytical view of function p(d ) for cement, we have analyzed microscopic
sample images. Calculated from images the quantities of cement particles, in
corresponding size interval are best approximated by Rayleigh distribution (Fig. 5):
pr( d, σ )
=
d
---------d
2 ⎛ ⎞
exp⎜–
--------------- ⎟
⎝ ⎠
σ 2
2σ 2
Fig. 5. Calculated dependence of the quantities
of cement particles vs. size (bar graph) and
Rayleigh distribution approximation (line).
where σ – the most probable magnitude of particle diameter.
For measurement purposes we need to obtain images of cement particles. We use
an optical scheme shown in Fig. 6. The beam from laser 1, through inverse telescopic
system 2, illuminates sample 3. Images of cement particles 3, through polarization
interferometer 4, using a microobjective 5, are projected on a photodetector 6. Signal
from a photodetector is recorded by computer 7.
Fig. 6. Experimental optical scheme: 1 – laser, 2 – inverse telescopic system with diaphragm, 3 – sample,
4 – polarization interferometer, 5 – microobjective, 6 – photodetector, 7 – computer.
Measurement precision was controlled each time by a microscope. Measurements
were performed for samples with high and low concentration of cement particles.
Typical experimental dependences of intensity obtained from measurement using
interferometer are shown in Fig. 7.
(11)

466 M.P. GORSKY, P.P. MAKSIMYAK, A.P. MAKSIMYAK
a b
Fig. 7. Experimental dependence of intensity on longitudinal displacement of wedges for high (a) and
low (b) concentration of particles.
Finding the extreme magnitudes of the distribution function parameters was
based on condition of the minimum mean square deviation of theoretical magnitudes
of the transversal coherence function from the observed ones (Fig. 8). For optical
scheme defect correction we made some control measurements on interferometer
without a sample. In ideal case, the coherence function value Γ ⊥ for interferometer has
to be equal to 1, independently of the transversal displacement. But optical scheme
defects cause interferometer noise, which we use for normalization of the obtained
experimental magnitudes of the coherence function.
a b
Fig. 8. Experimentally obtained magnitudes of coherence function (dots) and theoretical graph following
the least-squares method (line), for samples with large (a) and small (b) concentration of particles.
Original experimental data processing provides the particle size distribution
measurement with error less than 10% for each measurement in comparison with
microscopical results.
Each experimental measurement provides information about distribution of
particles, which are found at the observation plane. That is why, in order to receive
the data on complete cement particle size distribution on a sample, we made
measurements in different parts of the sample. The analysis of microscopical cement
sample images shows that in different parts of the sample, the most probable particle

Optical correlation technique for cement particle size measurements 467
T a b l e 1. Experimental data for samples with high concentration.
No. σ [μm] ρ s
1 5.3 4.0
2 6.1 4.0
3 6.1 3.7
4 4.1 3.7
5 6.1 3.7
6 5.6 3.7
7 6.0 3.7
8 7.0 3.8
9 6.7 4.0
10 4.8 3.7
T a b l e 2. Experimental data for samples with low concentration.
No. σ [μm] ρ s
1 5.8 18.4
2 6.3 18.3
3 5.4 16.4
4 6.7 17.4
5 4.1 18.9
6 5.9 17.7
7 5.8 17.4
8 10.6 16.6
9 7.9 16.0
10 4.9 15.7
size varies from 4 to 8 μm. This limit was an assessment criterion of reliability for
the result obtained by one measurement for our samples.
There were 10 measurements performed on samples with high and 10 with low
concentration. Distributive parameters and parameter ρ s were found from the experimental
data obtained. The results are given in Tabs. 1 and 2, respectively.
According to statistics rules, measurement results in limited quantity are
described by Student’s distribution. The interval with certain confidence level is
defined as [11]:
x ± Δ(D, P, N) (12)
where sample standard deviation D:
D =
1
----------------- ( xn – x )
N – 1
2
∑
n

468 M.P. GORSKY, P.P. MAKSIMYAK, A.P. MAKSIMYAK
average value x:
x =
and P – confidence level, N – number of measurements, x n – result of the n-th
measurement. For P =0.95 and N = 10, the spread in the values is defined as:
Δ(D, 0.95, 10) = 2.262 D (13)
Processing of obtained results gives us such confidence intervals with confidence
level P = 0.95: for samples with high concentration σ = 3.9–7.7 μm, and for samples
with low concentration σ = 3.7–9.0 μm.
5. Conclusions
As can be seen from experimental results and calculations, confidence intervals for
samples with high concentration of particles are found in reliable limits. For samples
with low concentration confidence intervals slightly overstep the reliable limits. So,
upon further decreasing of cement particles concentration, reliable determination of
distribution for samples with low concentration is complicated. Spread in calculated
values of distributive parameter σ arises from irregularity of particle distribution in
different parts of the sample. Average experimental values of the most probable
cement particle size σ =5.6μm for samples with high and σ =6.3μm for samples
with low concentration of particles correspond to values obtained for this cement by
sieve method.
Experimental technique for determination of particle size distribution function
used by us weakly depends on spread in refractive index values of separate particles,
contary to the laser diffraction method. Calculation technique developed by us
decreases calculated coherent function dependence on interferometer noise, emission
source intensity fluctuations and different cement particles overlapping image effect.
The technique described allows the cement particle size distribution function to be
found fast and with high reliability.
References
1
-------- xn N ∑
n
[1] GORSKIY V.F., Plugging Materials and Solutions – Handbook, Oblpoligrafvydav, Chernivtsi, 2006,
p. 524 (in Ukrainian).
[2] LEE F.M., The Chemistry of Cement and Concrete, 3rd Ed., Chemical Publishing Company, 1971.
[3] RAMACHANDRAN V.S., BEAUDOIN J.J., Handbook of Analytical Techniques in Concrete Science and
Technology, National Research Council of Canada, Ottawa, Canada, 2001.
[4] BULATOV A.I., DANYUSHEVSKIY V.S., Plugging Materials Reference Manual, Nadra, Moscow, 1987,
p. 280 (in Russian).

Optical correlation technique for cement particle size measurements 469
[5] FERRARIS C.F., HACKLEY V.A., AVILES A.I., Measurement of particle size distribution in portland
cement powder: Analysis of ASTM round robin studies, Journal of Cement, Concrete and
Aggregates (CCA) 26(2), 2004, p. CCA11920.
[6] ANGELSKY O.V., MAKSIMYAK P.P., Optical correlation method for studying disperse media, Applied
Optics 32(30), 1993, pp. 6137–6141.
[7] MAKSIMYAK P.P., ANGELSKY O.V., An optical correlation method for measuring particle size and
concentration, Proceedings of IC Mechatronics 2000, Warsaw, Poland, pp. 466–468.
[8] ISHIMARU A., Wave Propagation and Scattering in Random Media, Vol. 1, 2, Academic Press,
New York, 1978.
[9] BORN M., WOLF E., Principles of Optics, New York, Cambridge University Press, 1999.
[10] GORSKY M.P., MAKSIMYAK P.P., MAKSIMYAK A.P., Studies of light backscattering at concrete during
its hydration, Ukrainian Journal of Physical Optics 10(3), 2009, pp. 134–149.
[11] KORN G.A., KORN T.M., Mathematical Handbook for Scientists and Engineers, McGraw-Hill, New
York, 1987.
Received July 10, 2009
in revised form December 21, 2009

Optica Applicata, Vol. XL, No. 2, 2010
Investigation and analysis of time response
in Geiger mode avalanche photodiode
M. DEHGHAN 1 , V. AHMADI 2* , E. DARABI 3
1 Department of Electrical Engineering Islamic Azad University,
Science and Research Branch, Tehran, Iran
2 Department of Electrical Engineering, Tarbiat Modares University, Tehran, Iran
3Department of Plasma Physic Research Center, Islamic Azad University,
Science and Research Branch, Tehran, Iran
* Corresponding author: v_ahmadi@modares.ac.ir
Statistical properties of the impulse response of avalanche photodiode (APDs) are determined.
The model is based on recurrence equations. These equations are solved numerically to calculate
the mean current impulse response and standard deviation as a function of time. In this paper, we
investigate the effects of parameters such as ionization coefficient-multiplication thickness
product (α w), dead space, excess noise factor, mole fraction, temperature on the mean current
impulse response of APD in the Geiger mode.
Keywords: avalanche photodiode, Geiger mode, time response.
1. Introduction
Avalanche photodiodes (APDs) are known as detectors in long-haul fiber optic
systems and Geiger mode applications due to their advantage of high internal gain
generated by avalanche multiplication [1, 2]. According to the local-field avalanche
theory, both the multiplication noise and the gain-bandwidth product of APDs are
determined by the ratio of the electron and hole ionization coefficients of the semiconductor
in the multiplication region. Since this ratio is a material property, for a given
electric field, efforts to improve the APD performance have focused on optimizing
the electric field profile and characterizing new materials. APDs can be operated in
Geiger mode to count single photons. In this mode the APD is biased above its
breakdown voltage. When the reverse bias voltage of a p-n junction is raised above
the breakdown voltage, even a single carrier can trigger an avalanche process, leading
to a measurable current. The absorption of photon in the depletion layer initiates
the avalanche breakdown, which can be easily detected. After breakdown, the current
is quenched and the diode is recharged to allow the detection of new photon. Silicon

472 M. DEHGHAN, V. AHMADI, E. DARABI
p-n junctions reverse biased above the breakdown voltage are usually called single
photon avalanche diodes (SPADs).
Geiger mode APDs (GM-APDs) are excellent devices for detecting weak optical
signals. Because of their excellent time resolution, they are often used for photon
timing measurements. Recent advances in GM-APDs have made these devices
promising candidates for detectors in photon-counting receivers. Today, SPADs are
profitably used in various applications such as time-resolved spectroscopy, chemistry,
physics, and biology [3], fluid velocimetry [4], laser ranging [5], optical time-domain
reflectometry [6], single molecule detection [7, 8]. Several works have been done as
regarding calculation and analysis of impulse response and quantum detection
efficiency of GM-APD [9, 10], but to the best of our knowledge the effects of
ionization coefficient-multiplication thickness product (α w), temperature, mole
fraction, and dead space have not been demonstrated yet. In this paper, we study
these characteristics of GM-APD. This paper is organized as follows. In Section 2,
a modified model to calculate the mean impulse response and standard deviation by
solving the recurrence equations is presented. In Section 3, the model is applied to
SPADs and effects of α w, dead space, velocity and ionization coefficients on the mean
impulse response are discussed. Finally, conclusions are presented in Section 4.
2. Theory of model
We consider an APD with a multiplication region of width w. A parent photo-electron
is injected into the multiplication region at x = 0 with a fixed velocity v e under
the effect of an electric field. After traveling a fixed dead space d e , in the x-direction,
the electron becomes capable of impact ionizing with an ionization coefficient α.
Upon ionization, an electron–hole pair is generated, so that the parent electron is
replaced by two electrons and a hole. The hole travels in the (–x)-direction and becomes
capable of impact ionizing with an impact ionization coefficient β only after traveling
a dead space d h . This avalanche of ionization events continues until all carriers exit
the multiplication region. In the case of multiplication with a fixed dead space d e ,
the probability density function (pdf) of carriers vs. time τ and distance ξ is given by
he( ξ, τ)
hh( ξ, τ)
⎧
⎪
= ⎨
ξ
α – α( ξ – de) δ⎛τ– -------- ⎞
⎪
,
⎝ v ⎠
⎩
e
0, ξ ≤ de exp ξ > de
⎧
⎪
=
⎨
ξ
β – β( ξ – dh) δ⎛τ– --------- ⎞
⎪
,
⎝ v ⎠
⎩
h
0, ξ ≤ dh exp ξ > dh
(1)
(2)

Investigation and analysis of time response in Geiger mode avalanche photodiode 473
where d e and d h are the electron and hole dead spaces, respectively, v e and v h are
the velocity of the electrons and holes, respectively; α and β are the ionization rates
for electrons and holes, respectively, that are often modeled by standard equation
[11, 12]
⎛ Ec ⎞
α ( E ) , β ( E ) A ⎜---------- ⎟
⎝ E ⎠
m
= exp –
were A, E c and m are the parameters taken from [13, 14]. With integration of this
distribution function over the total time, the position dependent ionization pdf is
given as
he( h)
ξ
∞
∫
( ) = he( h)
( ξ, τ)dτ
0
The recurrence equation for electron and hole mean current impulse response are
given by [15]
〈 Ie( z, t)
〉 = Pe( z, t)
〈 Ie( z, t)
〉 +
+
min( w – z,
vet )
〈 Ih( z, t)
〉 = Ph( z, t)
〈 Ih( z, t)
〉 +
+
∫
0
min( w – z,
vht )
∫
0
⎛ ξ
+ t – -------- ⎞
ξ
〈 〉 〈 I ⎛
⎝ ⎠ h z + ξ,
t – -------- ⎞〉
⎝ ⎠
2 Ie z ξ,
2 Ih z ξ,
where the first terms on the right-hand side of these equations represent the contributions
from the injected, primary currents 〈 Ie( h)
( z, t)
〉 . The probabilities that the injected
carriers avoid ionizing before exiting the multiplication region before time t is given by
min( w – z,
vet )
( ) = 1 –
he ξ
Pe z, t
min( w – z,
vht )
( ) =
1 –
hh ξ
Ph z, t
∫
0
∫
0
v e
+ he ξ
ve ⎛ ξ
+ t – -------- ⎞
ξ
〈 〉 〈 I ⎛
⎝ ⎠ e z + ξ,
t – -------- ⎞〉
⎝ ⎠
( )dξ
( )dξ
v h
+ hh ξ
vh (3)
(4)
( )dξ
(5)
( )dξ
(6)
(7)
(8)

474 M. DEHGHAN, V. AHMADI, E. DARABI
The initial current from electrons and holes can be calculated as
Ie0( z, t)
Ih0( z, t)
=
=
w – z
⎧ 0, t > ----------------
⎪
ve ⎨
⎪
qve w – z
-----------, t ≤ ----------------
⎩ w
Standard deviation of the impulse response can be determined by developing
recurrent expressions for the second order statistics of Ie (z, t), Ih (z, t) using the same
technique as that for the mean currents. The second moment of the impulse response
i2( z, t)
I can be computed by
2 = 〈 ( z, t)
〉
And the standard deviation of I(z, t) can then be obtained using [16]
3. Results and discussion
v e
w – z
⎧ 0, t > ----------------
⎪
vh ⎨
⎪
qvh w – z
----------- , t ≤ ----------------
⎩ w
v h
2 2
2
〈 I e(
z, t)
〉 = Pe( z, t)
〈 I e0(
z, t)
〉 + dξ 2 〈 Ie ( z + ξ,
t – τ ) 〉 +
〈 ( + t – τ ) 〉 2 2
+ + 〈 ( z + ξ,
t – τ ) 〉 +
2 Ie z ξ,
w – z
∫
0
+ 4 〈 Ih ( z + ξ,
t – τ ) 〉 × 〈 Ie ( z + ξ,
t – τ ) 〉 × he ξ, τ
2 2
2
〈 I h(
z, t)
〉 = Ph( z, t)
〈 I h0(
z, t)
〉 + dξ 2 〈 Ih ( z + ξ,
t – τ ) 〉 +
z
∫
0
2 〈 Ih ( z + ξ,
t – τ ) 〉 2 2
+ + 〈 ( z + ξ,
t – τ ) 〉 +
One of the important parameters in the APDs is the value of ionization coefficient-
-multiplication thickness product (α w), where α is the electron ionization coefficient
t
∫
0
I h
I e
0
t
∫
( )dτ
+ 4 〈 Ih ( z + ξ,
t – τ ) 〉 × 〈 Ie ( z + ξ,
t – τ ) 〉 × hh ξ, τ
σ ( z, t)
i2( z, t)
i 2 =
– ( z, t)
( )dτ
(9)
(10)
(11)
(12)
(13)

Investigation and analysis of time response in Geiger mode avalanche photodiode 475
Fig. 1. Dimensionless mean current impulse response for different values of α w with v h = v e =10 5 m/s,
w = 100 nm, d/w = 0.1, k =1.
Fig. 2. Dimensionless mean impulse response for different values of d/w and with α w =2,
v h = v e =10 5 m/s, w = 100 nm, k =1.
and w is the thickness of multiplication region. With changing the value of α w,
APD can operate in the Geiger or analogue mode. For smaller values of α w, the APD
operates in analogue mode. In Figure 1, the effect of α w on the mean current impulse
response in Geiger mode, considering the dead space effect is shown which is
normalized to the injected primary current qv e /w. According to this figure we find
that with an increase of α w, the value of impulse response increases with higher rate.
In Figure 2, the effect of dead space on impulse response is studied. In this
figure, the impulse response without dead space effect (d/w = 0) and with dead space
(d/w = 0.05 and 0.1) are shown. We find that the presence of dead space results in
a reduction of the impulse response for all the times. According to this figure, the rate
of response in APD decreases for higher values of dead space.
In Figure 3, the mean current impulse responses for different values of k (k = β/α)
are shown. We find that the rate of response in APD increases with k.
Figure 4 shows the mean current impulse response for different ratios of carrier
velocities. With an increase of the ratio v h/v e, the peak of current and therefore,
the rate of response in APD are increased.

476 M. DEHGHAN, V. AHMADI, E. DARABI
Fig. 3. Dimensionless mean impulse response for different values of k with α w = 2.5, v h = v e =10 5 m/s,
w = 100 nm, d/w =0.1.
Fig. 4. Dimensionless mean impulse response for different values of v h /v e with α w = 2.5, w =100nm,
d/w = 0.1, k =1.
Multiplication noise strongly depends on the carrier injection into the multiplication
region. The noise becomes small when photogenerated electrons are selectively
injected into the multiplication region which has a large electron ionization rate α in
comparison with that of holes. The photoabsorption in the multiplication region causes
contamination by the hole injection which accompanies an increase of the multiplication
noise. Transparency of the multiplication region is therefore essential to get low noise
performance. In Figure 5, dimensionless standard deviation for different values of k
is shown. According to this figure, the excess noise increases with k.
It is well known that the fluctuation of temperature changes the ionization
coefficient parameters. With an increase of temperature, the value of ionization
coefficient is decreased. In Figure 6, we compare the mean current impulse response
for different values of temperature with w = 100 nm, d/w = 0.1, k =1, v h /v e =1.
According to this figure, we find that with an increase of temperature the peak of mean
current impulse response and the rate of response decrease. Meanwhile, we have better
Geiger mode characteristics at lower temperature.
In Figure 7, we study the effect of changing the mole fraction on the mean current
impulse response. For each of the four materials (Al 0.6Ga 0.4As, Al 0.3Ga 0.7As,

Investigation and analysis of time response in Geiger mode avalanche photodiode 477
Al 0.15 Ga 0.85 As and GaAs) we are able to find a single set of parameters (A, E c and m)
that satisfy the exponential model presented in Eq. (3) independent of the multiplication
region width. With a constant value of multiplication width, we have a larger value of
ionization coefficient-multiplication thickness product (α w) with an increase of Al
Fig. 5. Dimensionless standard deviation for different values of k with α w = 2.5, w = 100 nm, d/w =0.1,
v h /v e =1.
Fig. 6. Mean current impulse response for w =100nm with d/w = 0.1, k =1, v h/v e =1 at T =200K,
250 K and 290 K.
Fig. 7. Effect of mole fraction variation on the mean current impulse response for w =100nm, d/w =0.1,
k =1, v h/v e =1.

478 M. DEHGHAN, V. AHMADI, E. DARABI
mole fraction and finally the peak of mean current impulse response increases and
APD has a good performance in the Geiger mode.
4. Conclusions
In this paper, using a model based on recurrence equations, we investigated the effects
of several parameters such as α w, dead space, excess noise factor, velocity on
the mean and standard deviation of impulse response time of avalanche photodiode
in Geiger mode. We found that with an increase of α w, ratio v h /v e and k, the peak of
the mean current impulse response in the Geiger mode is increased. We also studied
the effect of temperature and mole fraction on the Geiger mode characteristics of APD,
and we showed that for better operation, lower temperature and higher value of Al
mole fraction in Al xGa 1–xAs-APD must be chosen.
References
[1] CHEE HING TAN, DAVID J.P.R., PLIMMER S.A., REES G.J., TOZER R.C., GREY R., Low multiplication
noise thin Al 0.6Ga 0.4 As avalanche photodiodes, IEEE Transactions on Electron Devices 48(7), 2001,
pp. 1310–1317.
[2] CAMPBELL J.C., Recent advances in telecommunications avalanche photodiodes, Journal of
Lightwave Technology 25(1), 2007, pp. 109–121.
[3] LOUIS T.A., RIPAMONTI G., LACAITA A., Photoluminescence lifetime microscope spectrometer based
on time-correlated single-photon counting with an avalanche diode detector, Review of Scientific
Instruments 61(1), 1990, pp. 11–22.
[4] CUMMINS H.Z., PIKE E.R., Photon Correlation Spectroscopy and Velocimetry, Plenum, New York,
1977.
[5] VEILLET C. [Ed.], 7th International Workshop on Laser Ranging Instrumentation, OCA/CERGA,
Matera, Italy, October 2–8, 1989.
[6] BETHEA C.G., LEVINE B.F., COVA S., RIPAMONTI G., High-resolution and high-sensitivity optical-
-time-domain reflectometer, Optics Letters 13(3), 1988, pp. 233–235.
[7] LI-QIANG LI, DAVIS L.M., Single photon avalanche diodes for single molecule detection, Review of
Scientific Instruments 64(6), 1993, pp. 1524–1529.
[8] SPINELLI A., DAVIS L.M., DAUTET H., Single photon avalanche diode for high count rate applications,
[In] Proc. 1995 OSA Ann. Mtg., Portland, OR, September 10–15, 1995.
[9] GROVES C., TAN C.H., DAVID J.P.R., REES G.J., HAYAT M.M., Exponential time response in analogue
and Geiger mode avalanche photodiodes, IEEE Transactions on Electron Devices 52(7), 2005,
pp. 1527–1534.
[10] MAZZILLO M., PIAZZA A., CONDORELLI G., SANFILIPPO D., FALLICA G., BILLOTTA S., BELLUSO M.,
BONANNO G., COSENTINO L., PAPPALARDO A., FINOCCHIARO P., Quantum detection efficiency in Geiger
mode avalanche photodiodes, IEEE Transactions on Nuclear Science 55(6), 2008, pp. 3620–3625.
[11] MOLL J.L., MEYER N., Secondary multiplication in silicon, Solid-State Electronics 3(2), 1961,
pp. 155–158.
[12] SALEH M.A., HAYAT M.M., SALEH B.E.A., TEICH M.C., Dead-space based theory correctly predicts
excess noise factor for thin GaAs and AlGaAs avalanche photodiodes, IEEE Transactions on
Electron Devices 47(3), 2000, pp. 625–633.
[13] PLIMMER S.A., DAVID J.P.R., GREY R., REES G.J., Avalanche multiplication in Al x Ga 1–x As (x = 0
to 0.60), IEEE Transactions on Electron Devices 47(5), 2000, pp. 1089–1097.

Investigation and analysis of time response in Geiger mode avalanche photodiode 479
[14] GROVES C., CHIA C.K., TOZER R.C., DAVID J.P.R., REES G.J., Avalanche noise characteristics of
single Al x Ga 1–x As (0.3 < x < 0.6)–GaAs heterojunction APDs, IEEE Journal of Quantum
Electronics 41(1), 2005, pp. 70–75.
[15] TAN C.H., HAMBLETON P.J., DAVID J.P.R., TOZER R.C., REES G.J., Calculation of APD impulse
response using a space- and time-dependent ionization probability distribution function, Journal
of Lightwave Technology 21(1), 2003, pp. 155–159.
[16] HAYAT M.M., SALEH B.E.A., Statistical properties of the impulse response function of double-carrier
multiplication avalanche photodiodes including the effect of dead space, Journal of Lightwave
Technology 10(10), 1992, pp. 1415–1425.
Received April 21, 2009
in revised form June 18, 2009

Optica Applicata, Vol. XL, No. 2, 2010
Higher-order space charge field effects
on the self-deflection of bright screening
spatial solitons in two-photon
photorefractive crystals
QICHANG JIANG * , YANLI SU, XUANMANG JI
Department of Physics and Electronic Engineering, Yuncheng University, Yuncheng, 044000, China
* Corresponding authors: jiangsir009@163.com
We investigate the effects of higher-order space charge field on the self-deflection of bright
screening spatial solitons due to two-photon photorefractive effects by a numerical method
under steady-state conditions. The expression for an induced space charge electric field
including higher-order space charge field terms is obtained. Numerical results indicate that bright
screening solitons undergo self-deflection process during propagation, and the solitons always
bend in the opposite direction of the c axis of the crystal. The self-deflection of bright screening
solitons can experience considerable increase especially in the regime of high bias field strengths.
Relevant examples are provided.
Keywords: non-linear optics, two-photon photorefractive effect, bright screening spatial solitons,
self-deflection.
1. Introduction
During the last decade, the optical spatial solitons based on photorefractive effect have
attracted much interest, for these photorefractive spatial solitons can be formed at low
light intensity and are potentially useful for all-optical switching, beam steering, and
optical interconnects. At present, three types of steady-state scalar solitons (screening
solitons [1–3], photovoltaic solitons [4–7] and screening-photovoltaic solitons [8–10])
have been predicted theoretically and found experimentally.
The diffusion process introduces an asymmetric tilt in the light-induced photorefractive
waveguide, which results in the self-deflection process of solitons [1].
Self-deflection was firstly found in bright screening solitons in bias photorefractive
crystals [11, 12]. The self-deflection process was explained theoretically with first-
-order diffusion effect taken into account [13]. However, experimental results have
shown that self-deflection can exceed the deflection predicted by theory, especially in
the regime of high bias field strengths. To account for this discrepancy, SINGH et al. [14]
investigated the effects that arise from the higher-order space charge field terms on

482 Q. JIANG, Y. SU, X. JI
the evolution of bright screening solitons. Recently, LIU and HAO [15] and
ZHANG et al. [16–18] investigated the higher-order space charge field effects on
the evolution of bright screening-photovoltaic soliton, bright photovoltaic soliton, dark
screening soliton, and dark photovoltaic soliton.
All of the above-mentioned solitons result from the single-photon photorefractive
effect. Recently, CASTRO-CAMUS and MAGANA [19] provided a model of the two-photon
photorefractive effect. Later, screening solitons [20], photovoltaic solitons [21] and
screening-photovoltaic solitons [22] in two-photon photorefractive crystals have
been predicted. On the other hand, incoherently coupled bright–bright, dark–dark,
bright–dark, and grey–grey soliton pairs have been predicted [23–26] that result from
the two-photon photorefractive effect. In this paper, we investigate the higher-order
space charge field effects on the self-deflection of bright screening spatial solitons in
two-photon photorefractive crystals through an approach similar to that presented in
[14–18]. The induced space charge field in which these higher-order terms are
included is obtained, a dynamical evolution equation is derived in which the effects
that arise from these higher-order terms are considered. Our results show that bright
screening solitons due to two-photon photorefractive effect possess a self-deflection
procedure during propagation in the opposite direction of the crystal’s c axis on
the base of the first-order diffusion terms. Taking into account the higher-order
space charge field, numerical results further indicate that the value of the spatial shift
that is due to the first-order diffusion term alone is always smaller than that due to
both the first-order diffusion term and the higher-order space charge field terms
acting together. This behavior is similar to that of bright screening solitons due to
single-photon photorefractive effect.
2. Theoretical model
We start with considering an optical beam that propagates in a biased photorefractive
crystal with the two-photon photorefractive effect along the z axis and is permitted to
diffract only along the x direction. The crystal is proposed here to be SBN:60 with its
optical c axis along the x coordinate and is illuminated by the gating beam. Moreover,
let us assume that the optical beam is linearly polarized along the x direction. As usual,
we express the optical field of the incident beam in terms of slowly varying envelope φ,
xˆ
i.e., E = φ (x, z)exp(ikz), where k = k 0 n e =(2π/λ 0 )n e , n e is the unperturbed
extraordinary index of refraction, and λ 0 is the free-space wavelength. Under these
conditions the optical beam satisfies the following envelope evolution equation:
iφ z
3
k0n er33Esc
1
+ ---------- φxx – -------------------------------φ =
0
2k
2
where φ z = ∂φ/∂z, φ xx = ∂ 2 φ/∂x 2 , r 33 is the electro-optic coefficient, E sc = E sc x is
the space charge field in the crystals. Following Ref. [20], the space charge field in
Eq. (1) can be obtained from the set of rate, current, and Poisson’s equations proposed
(1)

Higher-order space charge field effects ... 483
by CASTRO-CAMUS and MAGANA [19] to describe the two-photon photorefractive effect.
In the steady-state and under a strong bias field condition such that the photovoltaic
field can be neglected, or in a non-photovoltaic crystal, these equations are [19, 20]:
( ) N N + ( – ) γ1n 1N + – γ nN + – = 0
s 1 I 1
+ β1 ( s1I 1 + β1) N N + ( – ) γ2nn ( 01 – n1) γ1n 1N +
+ + – – ( s2 I2 + β2)n1= 0
( s2 I2 + β2)n1 1
-----e
∂J
--------- γ nN
∂x
+
+ – – γ2nn ( 01 – n1) = 0
∂Esc ε0ε r --------------- eN
∂x
+ = ( – n – n1 – NA) J eμnEsc eD ∂n
= + -----------
∂x
∂J
--------- = 0 or J = const
∂x
where N is the donor density, N + is the ionized density, N A is the acceptor or trap
density, and n is the density of the electrons in the condition band (CB); n 1 is the density
of the electron in the intermediate state; n 01 is the density of traps in the intermediate
state; s 1 and s 2 are cross section; β 1 and β 2 are the thermoionization probability
constants for the transitions of the value band (VB) to the allowed intermediate
levels (IL) and IL-CB, respectively. γ 1 , γ 2 and γ 3 are the recombination factors of
the CB-VB, IL-VB, and CB-IL transitions, respectively; D is the diffusion coefficient;
μ and e are the electron mobility and charge, respectively; ε 0 and ε r are the vacuum
and relative dielectric constants, respectively; J is the current density; I 1 is the intensity
of the gating beam, which can be considered as a constant; I 2 is the intensity of
the soliton beam. According to Poynting’s theorem, I 2 can be expressed in terms
of the φ, that is, I 2 =(n e /2η 0 )|φ | 2 where η 0 =(μ 0 /ε 0 ) 1/2 . One can neglect the term
(n 01 – n 1)

484 Q. JIANG, Y. SU, X. JI
Under the approximation n, n 1

Higher-order space charge field effects ... 485
Under strong bias conditions E0 will be large enough, and therefore the drift
component of the current in the medium will be dominant and moreover in typical
ε0ε r
photorefractive crystals the dimensionless quantity --------------

486 Q. JIANG, Y. SU, X. JI
Substituting Eq. (16) into Eq. (1), and adopting the following dimensionless
coordinates and variables: s = x/x0 , ξ = z/(k ), U =(2η0I2d /ne ) –1/2 2 x0 φ, x0 is an arbitrary
spatial width. Under these conditions, the following dynamical evolution equation can
be obtained
1
1 + ρ
iUξ ------ Uss β ---------------------------σ
1
2 1 + σ + ρ
1 U 2
⎛ ⎞ σ U
– ⎜ + ----------------------- ⎟Uδ
⎝ + ⎠
2
( )s
1 U 2 ( + + σ ) 1 U 2
+ + ------------------------------------------------------------------ U +
( + )
( 1 + ρ)
δ 1
2 σ 1 σ U 2
( + + ) U 2
( )s
( 1 + ρ + σ)
2 1 U 2
( + ) 3
( 1 + ρ)σU
------------------------------------------------------------------------------------ U δ 2
2
( )s
( 1 + ρ + σ)
1 U 2
( + ) 3
+ – ------------------------------------------------------------- U +
( 1 + ρ)σU
δ 3
2
( )ss
( 1 + ρ + σ)
1 U 2
( + ) 2
+ ------------------------------------------------------------- U = 0
4 4
where r33 ⁄ 2 , = r33 ⁄ 2 ( ⁄ ) , δ1 = βE0τ, β ( k0 x0) δ2 =2βτκ, δ3 = βτκ, , , , ,
ρ = I2∞ /I2d . In Equation (18), the term δ represents the first-order diffusion process
whereas δ1 , δ2 , δ3 are higher-order space charge field effects.
By considering only the drift nonlinearity (i.e., β term) and by entirely neglecting
all the δ perturbations, for bright screening solitons (ρ = 0), from Eq. (18) we have
2 = ( ne )E0δ( k0x 0)
2 ( ne ) KBT ex0 ε0ε r
τ ------------eNA
1
---------
D KBT ∂U ∂
= κ = ------------- = -------------- Uξ = ------------ Uss x0 μ x0 ex0 ∂ξ
2 U
∂s 2
= --------------
1 β
iU ------U -----------------σ
ξ ss 1
2 1 + σ
1 U 2
⎛ ⎞
+ – ⎜ + ------------------------ ⎟U=
0
⎝ + ⎠
The fundamental bright screening solitary solution can be derived from Eq. (19)
by expressing the beam envelope U in the usual fashion: U = r 1/2 y(s)exp(ivξ ). Here,
v represents a nonlinear shift of the propagation constant, y(s) is a normalized real
function bounded between 0 ≤ y(s) ≤ 1. By integrating Eq. (19) under the boundary
conditions: y(0) = 1, y· ( 0)
= 0, y(s → ±∞) = 0, we found that [19]
⎛ 2βσ ⎞
⎜------------------ ⎟
⎝ 1 + σ ⎠
1 2 ⁄
s
=
±
1
∫
y
1 2
r ⁄ dy˜
1 ry˜ 2
ln( + ) y˜ 2
----------------------------------------------------------------------------------
1 ⁄ 2
– ln(
1 + r)
The bright solitary beam profile can be obtained from Eq. (20) by a simple
numerical integration.
2
(18)
(19)
(20)

Higher-order space charge field effects ... 487
3. The self-deflection of bright screening solitons
due to two-photon photorefractive effects
3.1. The self-deflection on base of the first-order diffusion terms
We will now investigate the first-order diffusion effects on the evolution of bright
screening solitons due to two-photon photorefractive effects. By assuming solitary
wave solutions as input beam profiles, we solve Eq. (18) numerically ignoring all
the higher-order space charge field terms δ 1 , δ 2 , δ 3 by using a finite-difference method.
As an example, let us consider SBN:60 a crystal with following parameters [14]:
γ 33 = 237×10 –12 m/V, N A =4×10 16 cm –3 , ε r = 880, λ 0 =0.5μm, x 0 =25μm, E 0 =
=1×10 5 V/m, r = 10. We find that β = 34.5, δ = 0.35. By numerically solving Eq. (18),
we obtain the intensity profile evolution of the bright screening in the two-photon
photorefractive crystal as shown in Fig. 1a. The evolution of the spatial shift on
a b
Fig. 1. Intensity profile evolution (a) and the corresponding evolution (b) of the spatial shift under
the influence of δ.
the base of the first-order diffusion terms, denoted by Δs, which is defined as
the distance between s = 0 and the position of the beam centre at ξ, is shown in Fig. 1b.
The results show that the bright screening solitons experience approximately adiabatic
self-deflection in the opposite direction of the c axis of the crystal and the spatial
shift moves on an approximately parabolic trajectory. Its behavior is similar to bright
screening solitons based on single-photon photorefractive effects [14].
3.2. The self-deflection on base of the higher-order space charge field
Now, we investigate the effects that arise from the higher-order terms δ 1 , δ 2 , δ 3 on
the bright screening solitons. The parameters of the crystal being taken as above, we
find moreover that δ 1 = 0.168, δ 2 = 0.0035, δ 3 = 0.0017. It is obvious that the terms
δ 2 and δ 3 are much smaller than δ and δ 1 , so we neglect the effects of δ 2 and δ 3 .
Figure 2 compares the spatial shift due to δ alone to that obtained with δ and δ 1 acting
together at different strengths of applied electric field, i.e., E 0 =10 5 V/m,
E 0 =2×10 5 V/m, and E 0 =5×10 5 V/m. The solid curves denote the dynamic evolutions

488 Q. JIANG, Y. SU, X. JI
Fig. 2. Comparison of spatial shift obtained by considering the δ alone and the δ and δ 1 together at
different applied electric fields.
of spatial shift on base of the first-order diffusion term for various bias fields and
the dashed curves denote the dynamic evolutions of spatial shift in various bias fields
when δ and δ 1 act together. It is quite clear from the figure that at low bias fields
the process is dominated by first-order diffusion effects whereas at high bias one needs
to account for δ 1 term, and the value of the spatial shift that is due to δ alone is always
smaller than that of δ and δ 1 acting together. This behavior is similar to that of bright
screening solitons based on the single-photon photorefractive effects [14].
4. Conclusions
The effects of higher-order space charge field terms on the self-deflection of bright
screening solitons for two-photon photorefractive model have been investigated by
a numerical method. We have obtained an expression for the induced space charge
field in which higher-order space charge field terms are involved. Numerical results
indicate that the higher-order space charge field terms result in a considerable increase
in the self-deflection of bright screening solitons especially in the high bias field
strengths. That is, the value of the spatial shift that is due to both the first-order
diffusion term and the higher-order space charge field terms acting together is always
larger than that due to the first-order diffusion term alone.
Acknowledgements – This work was supported by the Science and Technology Development Foundation
of Higher Education of Shanxi Province, China (Grant No. 200611042).
References
[1] SEGEV M., VALLEY G.C., CROSIGNANI B., DIPORTO P., YARIV A., Steady-state spatial screening solitons
in photorefractive materials with external applied field, Physical Review Letters 73(24), 1994,
pp. 3211–3214.
[2] CHRISTODOULIDES D.N., CARVALHO M.I., Bright, dark and gray spatial soliton states in photorefractive
media, Journal of the Optical Society of America B 12(9),1995, pp. 1628–1633.

Higher-order space charge field effects ... 489
[3] SHIH M.F., SEGEV M., VALLEY G.C., SALAMO G., CROSIGNANI B., DIPORTO P., Observation of
two-dimensional steady-state photorefractive screening solitons, Electronics Letters 31(10), 1995,
pp. 826–827.
[4] VALLEY G.C., SEGEV M., CROSIGNANI B., YARIV A., FEJER M.M., BASHAW M.C., Dark and bright
photovoltaic spatial solitons, Physical Review A 50(6), 1994, pp. R4457–R4460.
[5] TAYA M., BASHAW M.C., FEJER M.M., SEGEV M., VALLEY G.C., Observation of dark photovoltaic
spatial solitons, Physical Review A 52(4), 1995, pp. 3095–3100.
[6] SHE W.L, LEE K.K, LEE W.K., Observation of two-dimensional bright photovoltaic spatial solitons,
Physical Review Letters 83(16), 1999, pp. 3182–3185.
[7] SHE W.L., XU C.C., GUO B., LEE W.K., Formation of photovoltaic bright spatial soliton in
photorefractive LiNbO 3 crystal by a defocused laser beam induced by a background laser beam,
Journal of the Optical Society of America B 23(10), 2006, pp. 2121–2126.
[8] LIU J.S., LU K.Q., Spatial solitaire wave in biased photovoltaic photorefractive crystals, Acta
Physica Sinica 47(9), 1998, pp. 1509–1514.
[9] LIU J.S., LU K.Q., Screening-photovoltaic spatial solitons in biased photovoltaic–photorefractive
crystals and their self-deflection, Journal of the Optical Society of America B 16(4), 1999,
pp. 550–555.
[10] FAZIO E., RENZI F., RINALDI R., BERTOLOTTI M., CHAUVET M., RAMADAN W., PETRIS A., VLAD V.I.,
Screening-photovoltaic bright solitons in lithium niobate and associated single-mode waveguides,
Applied Physics Letters 85(12), 2004, pp. 2193–2195.
[11] SHIH M.F., LEACH P., SEGEV M., GARRETT M.H., SALAMO G., VALLEY G.C., Two-dimensional steady-
-state photorefractive screening solitons, Optics Letters 21(5), 1996, pp. 324–326.
[12] PETTER J., WEILNAU C., DENZ C., STEPKEN A., KAISER F., Self-bending of photorefractive solitons,
Optics Communications 170(4–6), 1999, pp. 291–297.
[13] CARVALHO M.I., SINGH S.R., CHRISTODOULIDES D.N., Self-deflection of steady-state bright spatial
solitons in biased photorefractive crystals, Optics Communications 120(5–6), 1995, pp. 311–315.
[14] SINGH S.R., CARVALHO M.I., CHRISTODOULIDES D.N., Higher-order space charge field effects on
the evolution of spatial solitons in biased photorefractive crystals, Optics Communications
130(4–6), 1996, pp. 288–294.
[15] LIU J.S., HAO Z.H., Higher-order space-charge field effects on the self-deflection of bright screening
photovoltaic spatial solitons, Journal of the Optical Society of America B 19(3), 2002, pp. 513–521.
[16] ZHANG G.Y., LIU J.S., LIU S.X., ZHANG H.L., WANG C., The self-deflection of photovoltaic bright
spatial solitons on the basis of higher-order space-charge field, Journal of Optics A: Pure and
Applied Optics 8(5), 2006, pp. 442–449.
[17] ZHANG G.Y., LIU J.S., LIU S.X., WANG C., ZHANG H.L., Self-deflection of dark screening spatial
solitons based on higher-order space charge field, Chinese Physics Letters 24(2), 2007,
pp. 442–445.
[18] ZHANG G.Y., LIU J.S., ZHANG H.L., WANG C., LIU S.X., Higher-order space-charge field effects on
the self-deflection of photovoltaic dark spatial solitons, Optik 118(9), 2007, pp. 440–444.
[19] CASTRO-CAMUS E., MAGANA L.F., Prediction of the physical response for the two-photon
photorefractive effect, Optics Letters 28(13), 2003, pp. 1129–1131.
[20] CHUNFENG HOU, YANBO PEI, ZHONGXIANG ZHOU, XIUDONG SUN, Spatial solitons in two-photon
photorefractive media, Physical Review A 71(5), 2005, p. 053817.
[21] CHUNFENG HOU, YU ZHANG, YONGYUAN JIANG, YANBO PEI, Photovoltaic solitons in two-photon
photorefractive materials under open-circuit conditions, Optics Communications 273(2), 2007,
pp. 544–548.
[22] ZHANG G.Y., LIU J.S., Screening-photovoltaic spatial solitons in biased two-photon photovoltaic
photorefractive crystals, Journal of the Optical Society of America B 26(1), 2009, pp. 113–120.
[23] ZHANG Y., HOU C.F., SUN X.D., Incoherently coupled spatial soliton pairs in two-photon
photorefractive media, Acta Physica Sinica 56(6), 2007, pp. 3261–3265.

490 Q. JIANG, Y. SU, X. JI
[24] LU K.Q., ZHAO W., YANG Y.L., YANG Y., ZHANG M., RUPP R.A., FALLY M., ZHANG Y., XU J.,
One-dimensional incoherently coupled grey solitons in two-photon photorefractive media,
Applied Physics B 87(3), 2007, pp. 469–473.
[25] SRIVASTAVA S., KONAR S., Two-component coupled photovoltaic soliton pair in two-photon
photorefractive materials under open circuit conditions, Optics and Laser Technology 41(4),
2009, pp. 419–423.
[26] ZHANG Y., HOU C.F., WANG F., SUN X.D., Incoherently coupled grey–grey spatial soliton pairs due
to two-photon photorefractive media, Optik 119(14), 2008, pp. 700–704.
Received July 4, 2009
in revised form December 7, 2009

Optica Applicata, Vol. XL, No. 2, 2010
Extraordinary optical transmission
by interference of diffracted wavelets
RAJ KUMAR
Central Scientific Instruments Organisation, Chandigarh-160030, India
Present affiliation: Institute for Plasma Research, Gandhinagar-382 428, India;
e-mail: raj_csio@yahoo.com
The phenomenon of extraordinary optical transmission is drawing much attention of researchers
because of its potential applications in diverse emerging areas. In the present work, experimental
observations on diffraction-Lloyd-mirror interferometer are reported, where two diffracted
wavefronts are superimposed using Lloyd’s mirror. These observations provide direct
experimental evidence in support of the idea that one of the main reasons of enhanced transmission
through subwavelength apertures is the coherent superposition of diffracted wavelets originating
from diffractive scattering at the apertures.
Keywords: extraordinary optical transmission, diffraction.
1. Introduction
The discovery of extraordinary optical transmission [1] through subwavelength
apertures gave rise to an explosion of experimental and theoretical research in this
direction. This research is motivated by both the brilliance and fundamental character
of this phenomenon and because of its tremendous potential applications in the newly
emerging areas such as subwavelength optics, opto-electronic devices, wavelength-
-tunable filters, optical modulators [2–5]. Although the photon tunneling effect has
long been well known, the attenuation of evanescent waves, involved in the photon-
-tunneling process, shows that this phenomenon is not the actual source of extraordinary
optical transmission. Several other mechanisms such as excitation of delocalized
surface plasmon Bloch modes, interference between incident and surface waves and
localized coupling between adjacent structures, waveguide resonances, etc., have been
proposed as the possible origins of this phenomenon [2–10]. It is well known that to
excite surface plasmon polaritons a transverse-magnetic (TM) polarized light, i.e.,
the magnetic field parallel to the slits, should be incident on the subwavelength
apertures [1–5, 11] because the surface plasmon polaritons have a TM wave-like
character. Recently it has been demonstrated that the extraordinary transmission is
independent of polarization of incident light [12] and can also be achieved with

492 R. KUMAR
transverse-electric (TE) polarized light. Besides it has been reported that enhanced
transmission can also be observed in marginally metallic Cr [13] and the non-metallic
tungsten hole arrays [14]. These observations show that extraordinary transmission is
also possible without exciting the surface plasmon polaritons. It is also argued that
the quoted enhancement factor of 1000 for optical transmission through subwavelength
hole arrays is misleading, and that in fact placing a hole in an array leads to
enhancement of its transmission coefficient by a factor of 7 at most at selected
wavelengths [15]. Those authors have suggested that enhanced transmission is due to
interference of light incident on the aperture and the composite diffracted evanescent
wave. Recently, another model is reported that says that enhancement and suppression
in transmission is due to constructive and destructive interference of diffracted waves
generated by the subwavelength apertures, and classical as well as quantum mechanical
theory of this process has been developed [16, 17].
In the present paper, based on the newly reported concept of superposition of
boundary diffraction waves using a Lloyd’s mirror [18, 19], we present experimental
observations which support the above idea. We have used for the first time the physical
appealing boundary diffraction wave theory [20, 21] to explain the phenomenon of
extraordinary optical transmission. These investigations indicate that apart from
other possible processes, mutual interference of diffracted waves originating from
diffractive scattering at the apertures is the main source for enhanced transmission
through subwavelength apertures.
2. Experimental details
Experimental arrangement of the setup proposed is schematically shown in Fig. 1.
A photograph of the experimental setup is shown in Fig. 2a, and Fig. 2b shows a close
view of the arrangement of knife-edge and Lloyd’s mirror used to generate interference
fringes due to superposition of diffracted waves. A transverse electric (vertical)
polarized He-Ne laser L (Coherent Inc. Model No. 31-2140-000, 35 mW output at
632.8 nm) is expanded and spatially filtered using spatial filtering (SF) assembly.
A telescopic system of lenses L 1 and L 2 is used to generate the diffraction limited focus
spot S. A knife-edge K (good quality razor blade) is positioned vertically in proximity
of the focus such that a single diffraction fringe covers the field of view, as shown in
Fig. 1. Schematic experimental arrangement of diffraction Lloyd’s mirror interferometer.

Extraordinary optical transmission ... 493
L 2
L 1
Knife-edge and
Lloyd’s mirror
Spatial filtering
assembly
λ/2 plate
Fig. 2. Photograph of the experimental arrangement of diffraction Lloyd’s mirror interferometer (a) and
close view of the knife-edge and Lloyd’s mirror arrangement (b).
Fig. 3. At this position knife-edge diffracts light from the Airy disk [22] and
thereby diffracted light has maximum amplitude. In order to demonstrate that two
diffracted wavefronts could interfere, a Lloyd’s mirror M (20 mm×50 mm×1 mm,
SiO 2 protected front surface silver coated, reflectivity ~94%) is positioned near
the knife-edge. Lloyd’s mirror and the knife-edge were mounted on precise translation
stages for fine control. A λ/2 plate with its axis making an angle of 45° with the vertical
was used in the thin beam to change the state of polarization of initially vertically
polarized light into horizontally polarized light. Experimental results have been
captured with a Canon S-50 Power Shot digital camera with 1024×768 pixel resolution
settings.
3. Results and discussion
a b
Lloyd’s mirror
Knife-edge
It is well known that in a conventional Lloyd’s mirror interferometer a geometrical
wavefront in divided into two parts which are subsequently superimposed to generate
Laser beam
Fig. 3. A typical photograph of knife-edge diffraction
pattern where single diffraction fringe covers the field
of view.

494 R. KUMAR
Fig. 4. Schematic representation of diffraction from a knife-edge.
the interference fringes. In our case the Lloyd’s mirror configuration is used on
a diffracted wavefront (known as boundary diffraction wave), generated by diffraction
of geometrical light at the knife-edge, to generate equi-spaced and straight interference
fringes analogous to those obtained with a conventional Lloyd’s mirror interferometer.
Formation of these fringes due to superposition of two diffracted wavefronts can
be explained with the physically appealing boundary diffraction wave theory [20, 21]
which relates diffraction to the true cause of its origin, i.e., existence of the boundary
of diffracting aperture. According to this theory the diffracted field in the observation
plane at point P is given by
where
and
U(P) = U g (P) + U d (P) (1)
U g ( P)
U d ( P)
=
=
⎧
⎪
⎨
⎪
⎩
A
-------- exp( jkR)
when P is in the direct beam
R
A
----------
4π
0 when P is in geometrical shadow
∫
Σ
exp jk( r + s)
cos(
n, s)
----------------------------------------- ------------------------------------ sin( r, dl ) dl
rs 1 + cos(
s, r)
where R is the distance from source to the point of observation P; s is the distance
between point P and a typical point Q situated on the illuminated boundary Σ of
knife-edge K and r is the distance from source to point Q (Fig. 4). Here, dl is
an infinitesimal element situated on Σ, n is a unit vector outward normal to the plane
of diffracting aperture and j = . Here, U g –
1 propagates according to the laws of
geometrical optics and is known as the geometrical wave while U d is generated
from every point of the illuminated boundary of the diffracting element and is called
the boundary diffraction wave. The geometrical wave and the boundary diffraction
wave are shown in Fig. 1 by solid and dotted lines, respectively. The intensity
distribution due to superposition of two boundary diffraction waves and a geometrical
wave at the observation plane may be represented as:
I(P) = (U g + U d1 + U d2 ) (U g + U d1 + U d2 ) * (4)
(2)
(3)

Extraordinary optical transmission ... 495
where U d1 is the boundary diffraction wave starting from illuminated part of
the knife-edge; U d2 is the boundary diffraction wave starting from mirror image
of the knife-edge which works as a virtual source for this wave. It is known that
the amplitude of boundary diffraction wave is maximum near the geometrically
illuminated to geometrically shadowed transition boundary where its value is approximately
equal to half of the incident light [20]. For subwavelength apertures the spacing
between the edges is small and thus amplitude of interfering beams is maximum
~U g /2. Solving Eq. (4) and taking U d1 = U d2 = U g /2 for the case of subwavelength
apertures, gives
IP ( ) = I0 3
------ + 2cosψ cosφ
+
2
1
2
------ cos(
2ψ )
where I 0 represents intensity of the geometrical wave impinging on the aperture, φ is
the phase difference between the geometrical wave and the two boundary diffraction
waves, and ψ represents phase difference between the two boundary diffraction
waves reaching the observation point P. The fringes generated due to interference of
two boundary diffraction waves are superimposed on the geometrical wave present
in observation plane as background light, as demonstrated in reference [19].
The fringe width of these fringes formed due to interference of two boundary
diffraction waves is given by
β ∼
λ D
-----------a
where λ is the wavelength of light used, D is the distance between the plane of
the two-point sources (knife-edge and its virtual image) and the observation plane OP,
and a is the distance between two-point sources. Equation (6) shows that the fringe
width β could become infinite when distance between the two-point sources
approaches zero. Experimentally, change in the fringe width was observed by changing
the distance between the knife-edge and Lloyd’s mirror, and two interferograms with
different fringe widths obtained using this system are shown in Fig. 5. These fringes
a b
Fig. 5. Photographs of experimental results showing interferograms of different fringe widths obtained
by superposition of two boundary diffraction waves using a Lloyd’s mirror.
(5)
(6)

496 R. KUMAR
a b
Fig. 6. Photographs of experimental results showing interferograms with different polarization states
of the incident laser beam; with vertical polarization (a) and with horizontal polarization (b).
are shown to reach an infinite fringe mode condition for the case of mirror-edge
diffraction, where mirror-edge diffracts light and mirror surface folds it back [23, 24].
This variation of fringe width with distance between the knife-edge and Lloyd’s mirror
confirms that the illuminated part of the diffracting aperture acts as a real source
of light wherefrom boundary diffraction wave originates. In order to see the effect of
polarization of the incident beam on these fringes the polarization of the beam was
changed from vertical to horizontal one using a λ/2 plate, and interference fringes
obtained with these polarization states are shown in Fig. 6 (with vertically
polarized – 6a and with horizontally polarized light – 6b). These photographs show
that formation of these fringes is independent of the state of polarization of incident
beam and the intensity ratio for these fringes was also found to be the same, i.e.,
I/I 0 ~ 3.7. These observations on polarization effect on fringe formation are in
agreement with the results reported in reference [12] on extraordinary transmission
of light through slit apertures.
It is known that one can achieve infinite fringe width condition only when two
sources of light (knife-edge and its virtual image in our case) overlap each other or
physically speaking, when distance between them is of the order of subwavelength.
Thus the infinite fringe width condition is easily satisfied for the case of subwavelength
apertures. As this is interference pattern of two waves originating from diffractive
scattering at the apertures one would get a peak in the transmitted intensity when two
interfering boundary diffraction waves are in phase with each other (constructive
interference) and a valley will be detected when these interfering beams are out of
phase (destructive interference). In the infinite fringe mode condition (bright field)
all the three waves will travel along the same line and the same optical paths, i.e.,
φ = ψ = 0 which means a is of the order of subwavelength. In this situation, it
becomes obvious from Eq. (5) that I =4I 0, i.e., light transmitted through a single
subwavelength slit is four times more intense than light incident on the slit.
Experimental measurements in our setup give a ratio of I/I 0 ~ 3.7. It may be noted
that the theoretically calculated value of intensity I/I 0 = 4 is valid only for the case of

Extraordinary optical transmission ... 497
subwavelength apertures and the peak intensity will reduce with increase in slit
width due to sharp decrease in amplitude of boundary diffraction wave away from
the geometrically illuminated to geometrically shadowed transition boundary. Here
we have considered a single diffraction only but, actually, the process of multiple
diffractions in the slit (as explained by KELLER [25]) will take place, which could
further increase the intensity of the transmitted beam. Due to subwavelength nature of
the apertures, for the macroscopic point of view, the diffraction originates from
the aperture as a whole entity and thus the transmitted light can be termed as originating
from the process of diffractive scattering from the aperture.
In the case of a slit or hole arrays the transmission is determined by coherent
addition of fields from all the diffracting apertures. The dependence of the fringe
width on the ratio λ/a shows that infinite fringe mode condition will be obtained at
different values of wavelengths for different slit widths. The infinite fringe mode
maximum occurs when the interfering beams starting from edges of the apertures are
in phase, i.e., path difference between them is a multiple of the wavelength of incident
light. For an array of, say, N slits, each slit having width a and period d, there will be
total N waves of intensity given by Eq. (5) produced by these N independent slits. For
such a system of slits KUKHLEVSKY [16] has demonstrated that in the transmitted
spectrum intensity peaks will be observed at wavelengths that satisfy the condition
λ n = d/n, where n = 1, 2, 3, etc., which is applicable for the present case also.
The dependence on wavelength of the transmitted intensity for such a system is
presented in Fig. 1 of reference [16]. Likewise, if the slit width is varied the wavelength
corresponding to peak value will also be changed due to the condition of constructive
interference of light waves. Further it may be noted that in the case of subwavelength
slits the phases of the boundary diffracted waves from the apertures have nearly
the same phase and thus adds constructively resulting an enhancement in the peak
value of transmitted light that depends on the phases and amplitudes of the interfering
beams where intensity scales as the number of light sources squared, i.e., I N ~ N 2 I 1
(I 1 is the intensity from a single slit) regardless of periodicity, which is a requirement
for enhancement using equivalent circuit theory [26] and excitation of surface
plasmons [1–5]. It may be noted that for large N experimental results may differ
from the theoretical dependence of peak intensity as N 2 I 1 . In addition to the process
of interference of diffracted wavelets transmitted intensity can further be enhanced
due to additional energy that could also be channeled through the slit by excitation of
surface polaritons at periodic structures for resonant condition.
4. Conclusions
The phenomenon of extraordinary transmission through subwavelength apertures has
been discussed in the light of experimental observations on the diffraction Lloyd’s
mirror interferometer and is explained using the boundary diffraction wave theory. It
has been shown that for the case of subwavelength apertures our observations strongly

498 R. KUMAR
support the recently reported model of far-field multiple-beam interference [16, 17],
which requires that in the case of subwavelength apertures the mutual constructive
interference of these diffracted waves, originating from diffractive scattering at
the apertures, is the main source for enhanced transmission.
Acknowledgements – The author thanks Dr. Sushil Kumar Kaura for helpful discussions and
Mr. D.P. Chhachhia for help in performing the experiments at Central Scientific Instruments Organisation,
Chandigarh (India).
References
[1] EBBESEN T.W., LEZEC H.J., GHAEMI H.F., THIO T., WOLFF P.A., Extraordinary optical transmission
through sub-wavelength hole arrays, Nature 391, 1998, pp. 667–669.
[2] BARNES W.L., DEREUX A., EBBESEN T.W., Surface plasmon subwavelength optics, Nature 424,
2003, pp. 824–830.
[3] ENGHETA N., Circuits with light at nanoscales: Optical nanocircuits inspired by metamaterials,
Science 317(5845), 2007, pp. 1698–1702.
[4] GENET C., EBBESEN T.W., Light in tiny holes, Nature 445, 2007, pp. 39–46.
[5] GARCÍA DE ABAJO F.J., Light scattering by particle and hole arrays, Reviews of Modern
Physics 79(4), 2007, pp. 1267–1290.
[6] POPOV E., NEVIÈRE M., ENOCH S., REINISCH R., Theory of light transmission through subwavelength
periodic hole arrays, Physical Review B 62(23), 2000, pp. 16100–16108.
[7] GARCÍA-VIDAL F.J., LEZEC H.J., EBBESEN T.W., MARTÍN-MORENO L., Multiple paths to enhance
optical transmission through a single subwavelength slit, Physical Review Letters 90(21), 2003,
p. 213901.
[8] LIU H., LALANNE P., Microscopic theory of the extraordinary optical transmission, Nature 452,
2008, pp. 728–731.
[9] PACIFICI D., LEZEC H.J., ATWATER H.A., WEINER J., Quantitative determination of optical
transmission through subwavelength slit arrays in Ag films: Role of surface wave interference
and local coupling between adjacent slits, Physical Review B 77(11), 2008, p. 115411.
[10] PACIFICI D., LEZEC H.J., SWEATLOCK L.A., WALTERS R.J., ATWATER H.A., Universal optical
transmission features in periodic and quasiperiodic hole arrays, Optics Express 16(12), 2008,
pp. 9222–9238.
[11] PORTO J.A., GARCÍA-VIDAL F.J., PENDRY J.B., Transmission resonances on metallic gratings with
very narrow slits, Physical Review Letters 83(14), 1999, pp. 2845–2848.
[12] LU Y., CHO M.H., LEE Y.P., RHEE J.Y., Polarization-independent extraordinary optical
transmission in one-dimensional metallic gratings with broad slits, Applied Physics Letters 93(6),
2008, p. 061102.
[13] THIO T., GHAEMI H.F., LEZEC H.J., WOLFF P.A., EBBESEN T.W., Surface-plasmon-enhanced
transmission through hole arrays in Cr films, Journal of the Optical Society of America B 16(10),
1999, pp. 1743–1748.
[14] SARRAZIN M., VIGNERON J.-P., Optical properties of tungsten thin films perforated with
a bidimensional array of subwavelength holes, Physical Review E 68(1), 2003, p. 016603.
[15] LEZEC H.J., THIO T., Diffracted evanescent wave model for enhanced and suppressed optical
transmission through subwavelength hole arrays, Optics Express 12(16), 2004, pp. 3629–3651.
[16] KUKHLEVSKY S.V., Enhanced transmission of light through subwavelength nanoapertures by
far-field multiple-beam interference, Physical Review A 78(2), 2008, p. 023826.

Extraordinary optical transmission ... 499
[17] KUKHLEVSKY S.V., Interference-induced enhancement of intensity and energy of a quantum
optical field by a subwavelength array of coherent light sources, Applied Physics B 93(1), 2008,
pp. 145–150.
[18] KUMAR R., KAURA S.K., CHHACHHIA D.P., AGGARWAL A.K., Direct visualization of Young’s boundary
diffraction wave, Optics Communications 276(1), 2007, pp. 54–57.
[19] KUMAR R., Structure of boundary diffraction wave revisited, Applied Physics B 90(3–4), 2008,
pp. 379–382.
[20] RUBINOWICZ A., Thomas Young and the theory of diffraction, Nature 180, 1957, pp. 160–162.
[21] BORN M., WOLF E., Principles of Optics, 6th Edition, Pergamon Press, Oxford, 1993, pp. 449–453.
[22] KUMAR R., KAURA S.K., CHHACHHIA D.P., MOHAN D., AGGARWAL A.K., Comparative study of
different schlieren diffracting elements, Pramana – Journal of Physics 70(1), 2008, pp. 121–129.
[23] KUMAR R., CHHACHHIA D.P., AGGARWAL A.K., Folding mirror schlieren diffraction interferometer,
Applied Optics 45(26), 2006, pp. 6708–6711.
[24] KUMAR R., Interference and diffraction effects in folding mirror schlieren diffraction interferometer,
Applied Physics B 93(2–3), 2008, pp. 415–420.
[25] KELLER J.B., Diffraction by an aperture, Journal of Applied Physics 28(4), 1957, pp. 426–444.
[26] MARQUÈS R., MESA F., JELINEK L., MEDINA F., Analytical theory of extraordinary transmission
through metallic diffraction screens perforated by small holes, Optics Express 17(7), 2009,
pp. 5571–5579.
Received April 13, 2009
in revised form August 21, 2009

Optica Applicata, Vol. XL, No. 2, 2010
A polynomial approach for reflection,
transmission, and ellipsometric parameters
by isotropic stratified media
TAHER EL-AGEZ 1 , SOFYAN TAYA 1* , AHMED EL TAYYAN 2
1 Physics Department, Islamic University of Gaza, Gaza, Palestine
2 Physics Department, Al Azhar University, Gaza, Palestine
* Corresponding author: staya@iugaza.edu.ps
A polynomial approach for the calculation of the reflectance, the transmittance, and
the ellipsometric parameters of a stratified isotropic planar structure is presented. We show
that these parameters can be written in a very simple and compact form using the so-called
elementary symmetric functions that are extensively used in the mathematical theory of
polynomials. This approach is applied to quarter-wave Bragg reflectors. The numerical results
reveal an exact match with the well known matrix formalism.
Keywords: ellipsometry, reflectance, transmittance, ellipsometric parameters, quarter-wave Bragg
reflectors, stratified planar structure.
1. Introduction
Ellipsometry offers a precise technique for measuring thin film properties. Advanced
ellipsometers have shown an excellent sensitivity for monitoring the growth of optical
films during film deposition. DRUDE [1] was the first to build an ellipsometer even
before the word “ellipsometry” was coined in 1954. In the aftermath, the equipment
built by Drude received little attention for decades until the 1970’s, ellipsometry
received an increasing interest and a considerable number of papers on ellipsometry
have been published [2–5].
Ellipsometry measures the changes in the state of polarization of light upon
reflection or transmission from a sample. It has a number of advantages over traditional
intensity reflection and transmission measurements. Some of these advantages lie in
that it measures an intensity ratio and therefore it is less affected by intensity
instabilities of the light source. It also measures at least two parameters at each
wavelength.

502 T. EL-AGEZ, S. TAYA, A. EL TAYYAN
The ellipsometric results are usually presented in terms of two parameters ψ and
Δ given by
ρ = tan(
ψ)
exp(
iΔ)
=
where r p and r s are the complex Fresnel reflection coefficients for p- and s-polarized
light, respectively.
This paper addresses the use of a polynomial approach for the study of reflectance,
transmittance, and ellipsometric parameters ψ and Δ for any number of isotropic
multilayer structures. Some examples of these structures are ITO on glass, SiO 2 on
silicon, and HfO 2 on silicon. We first present the conventional matrix method, then
we introduce the so-called elementary symmetric functions used in the mathematical
theory of polynomials to write the reflection and transmission coefficients in a simple
and compact form.
2. Matrix representation for the reflection
and transmission coefficients
r p
---------
r s
Consider the case where a beam of light is incident on a multilayer structure of (N +1)
isotropic media, as shown in Fig. 1. The j-th medium has d j and n j as a thickness and
a refractive index, respectively. The j-th interface located at z j separates the two media
of refractive indices n j and n j+1 .
(1)
Fig. 1. A structure of (N + 1) stratified planar
media.

A polynomial approach for reflection, transmission, and ellipsometric parameters ... 503
In general, the total field can be written as
Ez ( )
E + ( z)
E – ⎛ ⎞
= ⎜ ⎟
⎜ ⎟
⎝ ( z)
⎠
where E + (z) and E – (z) denote the complex amplitudes of the forward and the backward-
-traveling plane waves at an arbitrary plane z. If we consider the fields at two different
planes parallel to the interfaces, then the fields E 1 and E N are related by a transformation
matrix [M ] according to the following equation [6]
+
⎛E⎞ ⎛
1 M
⎜ ⎟ 11 M ⎞⎛E⎞ 12 N
= ⎜ ⎟⎜
⎟
⎜ – ⎟ ⎜
⎝E M
1 ⎠ 21 M ⎟⎜
– ⎟
⎝ 22 ⎠⎝EN⎠
+
–
For the last interface we have EN = 0.
So, the reflection and transmission
coefficients of the whole system are given by
–
E1 rN = ------------
+
E1 +
EN tN = ------------
+
E1 =
=
M21 --------------
M11 1
--------------
M11 ⎫
⎪
⎪
⎬
⎪
⎪
⎭
(4)
The Fresnel reflection and transmission coefficients r j, j+1 and t j, j+1 at the j, j +1
interface for s- and p-polarizations are given by [6]
s nj cosθ j – nj + 1 cosθ
j + 1
rj, j + 1 =
nj cosθ j + nj + 1 cosθ
j + 1
--------------------------------------------------------------
cos
--------------------------------------------------------------
s 2nj θj tj, j + 1 =
nj cos θj + nj + 1 cos θj + 1
p nj + 1 cosθ j – nj cosθ
j + 1
rj, j + 1 =
nj + 1 cosθ j + nj cosθ
j + 1
--------------------------------------------------------------
cos
p 2nj θj tj, j + 1 = --------------------------------------------------------nj
+ 1 cosθ j + nj cosθ
j + 1
The matrix [M ] can be expressed as the product of interface matrices and
α
layer matrices. The matrix [ rj ]
of the j-th interface located at the plane zj between
(2)
(3)
(5)
(6)
(7)
(8)

504 T. EL-AGEZ, S. TAYA, A. EL TAYYAN
two layers of refractive indices n j and n j+1 relates the fields on both sides of
the interface, i.e.,
E α α α
( zj – ε ) = rj E ( zj + ε )
where α stands for p in p-polarization and for s in s-polarization, and ε is an infinitely
small distance. The interface matrix is given by
r j α
=
1
----------------- 1 rj j + 1
α
tj, j + 1
α 1
rj, j + 1
The propagation of the fields across the same layer with refractive index n j between
two interfaces located at z j –1 and z j = z j –1 + d j is given by the matrix [φ j], i.e.,
where the matrix [φ j ] is given by
and ϕj = k o n j d j cos(θ j ), with k o being the free space wave number.
The M-matrix of such a system can be written as the product
3. Polynomial approach
α
,
E α ( zj – 1 + ε ) [ φ j]E
α = ( zj – ε )
φ j
α
MN e iϕj 0
0 e iϕ ⎛ ⎞
= ⎜ ⎟
⎜ – ⎟ j
⎝ ⎠
=
φ 1 r 1 α φ 2 r 2 α … φ N r N α
The interface and layer matrices have the following commutation relation [7, 8]
α
rj, j + 1
α
φj rj =
α
rj ( ϕj)
φj (9)
(10)
(11)
(12)
(13)
(14)
α
The matrix [ rj ( ϕj)
] is obtained by adding a phase term exp(±2iϕj ) to the element
in the matrix [ r α
j ] in Eq. (10), i.e.,
α
rj ( ϕj)
α
tj, j + 1
α
,
1
------------------ 1 rj j + 1
=
α
rj, j + 1e
2iϕ – j
1
e 2iϕ j
(15)

A polynomial approach for reflection, transmission, and ellipsometric parameters ... 505
It is more convenient to introduce the matrix
α
rj ϕ1 + ϕ2 + … + ϕj and to define
where the overbar on R denotes the change of ϕ j into –ϕ j . According to Eq. (16) and
Eq. (17) we can write a new matrix
The interesting feature of Eqs. (16) and (17) is the phase term exp(±2iϕj ) multiplied
α
by the element rj, j + 1 which means that each interface takes into account the entire
history of the wave due to all layers up to the j-th interface.
In view of the commutation relation given by Eqs. (14), (17) and (18) we can write
α
any product of [ rj ] and [ φj] matrices in such a form that all the layer matrices [ φj] are located to the right of all the interface matrices [ r α
j ] . Thus, Eq. (13) can be
rewritten as [7–9]
where
( )
=
1
-------------
α
tj, j + 1
α α
α
Rj ≡ Rj
, j + 1 rj, j + 1e
2i ϕ1 ϕ2 … ϕ – ( + + + j)
=
α α
α
Rj ≡ Rj, j + 1 rj, j + 1e
2i ϕ1 ϕ2 … ϕ ( + + + j)
=
α 1
-----------------α
tj, j + 1
1 Rj j + 1
=
α
1
R j
α
MN =
Rj, j + 1
α
1 rj, j + 1e
2i ϕ1 ϕ2 … ϕ ( + + + j)
α
rj, j + 1e
2i ϕ1 ϕ2 … ϕ – ( + + + j)
1
α
,
α α α α
R1 R2 R3 … RN
φ1 φ2 … φN = φ1 + φ2 + … + φN α
(16)
(17)
(18)
(19)
(20)
Let the product of the [ Rj ] matrices in Eq. (19) be given by a matrix [ DN ] , i.e.,
α
DN =
α α α
R1 R2 … RN
It has been shown [7–9] that the elements of the matrix [ DN ]
can be written using
a complex generalization of the symmetric functions of the mathematical theory of
polynomials [10, 11] as follows
⎭ ⎪⎬⎪⎫
φ1 + φ2 + … + φN α
α
(21)

506 T. EL-AGEZ, S. TAYA, A. EL TAYYAN
where
α
DN α, N
S0 α , N
S1 α , N
S2 α, N
S3 α , N
SP =
=
1
------------------------------
1
N
α
∏ tj, j + 1
j = 1
N
α
∑ Ri i = 1
⎛ α, N
S ⎞ ⎛ α, N
∑ ⎝ 2m
S ⎞
⎠ ∑ ⎝ 2m + 1⎠
m ≥ 0
∑
m ≥ 0
⎛ α, N
S ⎞
⎝ 2m + 1⎠
α α α
R2 … RN
= = R1 + + +
α α
Ri Rj ∑
1 ≤ i < j ≤ N
= =
α α α
Ri Rj Rk ∑
1 ≤ i < j < k ≤ N
α α
R1 R2
= =
=
m ≥ 0
⎛ α, N
S ⎞
⎝ 2m ⎠
(22)
(23a)
(23b)
(23c)
(23d)
(23e)
where P – terms in each sum. Equations (23) defines the elementary symmetric
α α α α
functions of the variables R1 , R2 , R3 , ..., RN .
At this point, we emphasize the following:
1. As mentioned above, the overbar in R denotes the change of ϕ j into –ϕ j;
2. S P is the sum of all possible products of P-terms Rj;
3. In each product term of Eqs. (23), the factors R and R appear alternatively with
the first factor being always R. This remark gives the meaning of R, that is, R when
the place of in the product is odd and R when the place of is even;
4. = 0 for P > N.
Now, we can write the M-matrix, given by Eq. (19), as
0
R 0
R 0
α , N SP M N
∑
m ≥ 0
α α α α
R3 … R1 RN
+ R1 + + +
α α α α α α α α
R3 R2 R4 … R2 RN … RN
– 1RN
+ R2 + + + + +
α α α α α α
R1 R2 R3 R1 R2 R4 …
α α α α α α
R2 RN … RN
– 2RN
– 1RN
+ R1 + +
α α α α 0 α
Ri Rj Rk R1
∑
…Rw 1 ≤ i < j < k < … < w ≤ N
α 1
= ------------------------------
N
α
∏ tj, j + 1
j = 1
+ + +
α, N i( ϕ
⎛S⎞ 1 + ϕ2 + … + ϕN) α, N i
∑ ⎝ 2m e ⎛S⎞ ⎠
∑ ⎝ 2m + 1 e
⎠
m ≥ 0
∑
m ≥ 0
( + + + )
α, N i ϕ
⎛S⎞ 1 ϕ2 … ϕN ⎝ 2m + 1 e
⎠
m ≥ 0
∑
m ≥ 0
α, N i
⎛S⎞ ⎝ 2m e
⎠
– ( ϕ1 + ϕ2 + … + ϕN) – ( ϕ1 + ϕ2 + … + ϕN) (24)

A polynomial approach for reflection, transmission, and ellipsometric parameters ... 507
Equation (24) enables us to write the overall reflection and transmission
coefficients of the isotropic planar stratified structure in the general form
α
rN t N
α
M21 -------------α
M11 = =
α 1
= --------------- =
α
M11 ∑
α , N
S 2m + 1
m ≥ 0
---------------------------------
⎛ α, N
S ⎞
⎝ 2m ⎠
∑
m ≥ 0
N
α
∏ tj, j + 1
j = 1
----------------------------------------------------------------------------α,
N i( ϕ
⎛S⎞ 1 + ϕ2 + … + ϕN) ⎝ 2m e
⎠
∑
m ≥ 0
Moreover, the ellipsometric parameters ψ and Δ are then given by
( ψ )e iΔ
tan
p
rN = ----------- =
s
rN p, N
S ⎛ s, N
∑ 2m + 1 S ⎞
∑ ⎝ 2m ⎠
m ≥ 0 m ≥ 0
---------------------------------------------------------------s,
N
S ⎛ p, N
2m + 1 S ⎞
⎝ 2m ⎠
∑
m ≥ 0
∑
m ≥ 0
4. Numerical applications and results
To demonstrate the validity of the polynomial approach we consider a planar
multilayer dielectric coating designed as a dielectric mirror. Dielectric mirrors (also
known as Bragg reflectors) have received an increasing interest due to their extremely
low losses at optical and infrared frequencies, as compared to ordinary metallic
mirrors. A dielectric mirror usually consists of identical alternating layers of high and
low refractive indices, as shown in Fig. 2. The optical thicknesses are typically chosen
(25)
(26)
(27)
Fig. 2. Five-layer quarter-wave Bragg reflector
(dielectric mirror).

508 T. EL-AGEZ, S. TAYA, A. EL TAYYAN
Fig. 3. Calculated reflectance of 3, 5, 7 quarter-wavelength layer Bragg reflectors at normal incidence in
the spectral range of 350–850 nm for the polynomial approach (points) and the matrix formulation
(solid lines).
to be quarter-wavelength long at some center wavelength λ o , that is, n H d H = n L d L =
= λ o /4, where n H and n L are the indices of refraction of the high- and low-index
layers, respectively, d H and d L are the thicknesses of the high- and low-index layers,
respectively. The standard arrangement is to have an odd number of layers, with
the high index layer being the first and last layer [12].
The numerical calculation is done for a system of (2K + 1) stack of quarter-
-wavelength layers where K = 1, 2, and 3. The design wavelength of the Bragg
reflectors (filter) is centered at 550 nm. The reflectance and the ellipsometric
parameters ψ and Δ were calculated using the well known matrix formulation [6] and
the model proposed. These calculations were performed for the systems under
consideration in the spectral range from 350 to 850 nm. The indices n H and n L
correspond to layers of TiO 2 and MgF 2 on a glass substrate. The optical parameters of
these layers were obtained from the handbook of optical constants of solids [13, 14].
The results are depicted in Figs. 3 and 4. The calculated overall reflectance of
3, 5, and 7 layer Bragg reflectors centered at λ o = 550 nm are plotted in Fig. 3.
The figure reveals an exact match between the polynomial and matrix formalisms.
The ellipsometric parameters ψ and Δ are depicted in Fig. 4 for the same reflectors
mentioned above. A complete agreement between the two approaches is obvious.
5. Conclusions
In this article, we have shown that the reflectance, transmittance, and the ellipsometric
parameters can be calculated for any stack of layers using a simple method utilizing
the elementary symmetric functions. This approach exhibits an excellent agreement

A polynomial approach for reflection, transmission, and ellipsometric parameters ... 509
Fig. 4. Calculated ψ (a) and Δ (b) of 3, 5, 7 quarter-wavelength layer Bragg reflectors at a 70° angle
of incidence in the spectral range of 350–850 nm for the polynomial approach (points) and the matrix
formulation (solid lines).
with the traditional matrix method for a system representing a dielectric mirror. We
believe that this method is much easier than the traditional matrix multiplication
method.
References
[1] DRUDE P., The Theory of Optics, Dover, New York, 1959.
[2] ASPNES D.E., THEETEN J.B., Optical properties of the interface between Si and its thermally
grown oxide, Physical Review Letters 43(14), 1979, pp. 1046–1050.
[3] IRENE E.A., Models for the oxidation of silicon, Critical Reviews in Solid State and Materials
Sciences 14(2), 1988, pp. 175–223.
[4] GONÇALVES D., IRENE E.A., Fundamentals and applications of spectroscopic ellipsometry, Quimica
Nova 25(5), 2002, pp. 794–800.
a
b

510 T. EL-AGEZ, S. TAYA, A. EL TAYYAN
[5] POSTAVA K., MAZIEWSKI A., YAMAGUCHI T., OSSIKOVSKI R., VISNOVSKY S., PISTORA J., Null ellipsometer
with phase modulation, Optics Express 12(24), 2004, pp. 6040–6045.
[6] AZZAM R., BASHARA N., Ellipsometry and Polarized Light, North-Holland, Amsterdam, 1977.
[7] VIGOUREUX J.M., Polynomial formulation of reflection and transmission by stratified structures,
Journal of the Optical Society of America A 8(11), 1991, pp. 1697–1701.
[8] GROSSEL PH., VIGOUREUX J.M., BAIDA F., Nonlocal approach to scattering in a one-dimensional
problem, Physical Review A 50(5), 1994, pp. 3627–3637.
[9] SHABAT M.M., TAYA S.A., A new matrix formulation for one-dimensional scattering in Dirac comb
(electromagnetic waves approach), Physica Scripta 67(2), 2003, pp. 147–152.
[10] WAERDEN B., Modern Algebra, Ungar, New York, 1966.
[11] LANG S., Algebra, Addison-Wesley, MA, 1965.
[12] ORFANIDIS S., Electromanetic Waves and Antennas, On-Line Textbook, Rutgers University;
http://www.ece.rutgers.edu/~orfanidi/ewa.
[13] PALIK E., Handbook of Optical Constants of Solids, Vol. 2, Academic Press, San Diego, CA, 1991.
[14] PALIK E., Handbook of Optical Constants of Solids, Vol. 1, Academic Press, San Diego, CA, 1998.
Received June 4, 2009
in revised form October 24, 2009

Optica Applicata, Vol. XL, No. 2, 2010
Optimization of a FBG-based filtering module
for a 40 Gb/s OSSB transmission system
MIGUEL V. DRUMMOND1* , ARTUR FERREIRA1, 2 , TIAGO SILVEIRA1, 2 ,
DANIEL FONSECA1, 2 , ROGÉRIO N. NOGUEIRA1, 2 1, 2
, PAULO MONTEIRO
1 Instituto de Telecomunicações, Campus Universitário de Santiago, 3810 Aveiro, Portugal
2 Nokia Siemens Networks Portugal, 2720-093 Amadora, Portugal
* Corresponding author: mvd@av.it.pt
We present the optimization of an optical filtering module (OFM) of a single-channel 40 Gb/s
transmission system with optical single-sideband modulation and alternate mark inversion
signaling. Sideband suppression and dispersion compensation are simultaneously performed by
the fiber Bragg grating (FBG) optical filtering through amplitude and phase response, respectively.
Different amounts of accumulated dispersion are compensated using an OFM based on optical
switches and chirped FBGs with different accumulated dispersion. Linear transmission simulations
to assess the OFM effectiveness yield a Q-factor penalty variation lower than 1 dB relative to
back-to-back considering a maximum accumulated dispersion of 20400 ps/nm. A transmission
distance of 1040 km of nonlinear standard single mode fiber is achieved with a Q-factor higher
than 7.
Keywords: optical single sideband (OSSB), alternate mark inversion (AMI), dispersion compensation
(DC), fiber Bragg gratings (FBG).
1. Introduction
The growing volume and bandwidth demand of data services is leading to an increasing
interest in ultradense wavelength division multiplexing (UDWDM) systems. The design
of cost effective UDWDM systems greatly depends on the use of appropriate modulation
formats. Such modulation formats enable high spectral efficiency, reduced signal
degradation caused by interchannel crosstalk, and enhanced tolerance to fiber group
velocity dispersion (GVD) [1]. Advanced modulation formats such as differential
quadrature phase shift keying (DQPSK) [2], duobinary [1] or vestigial sideband [3]
have been thoroughly investigated for use in such systems.
Optical single-sideband (OSSB) modulation has been proposed as a good candidate
for implementation in such systems [4]. The sideband suppression can be achieved
using one of two techniques: a phase-shift technique [4], or the use of a detuned optical

512 M.V. DRUMMOND et al.
filter (OF) [5]. In the first technique, sideband suppression is achieved by adding
the information signal and the Hilbert transform of the information signal. The Hilbert
transform is obtained using a quadrature filter. As ideal quadrature filters are extremely
difficult to implement, the main problem of this technique is the design of a device
that approximates the Hilbert transform and operates at high bit rates. In the second
technique, sideband suppression is achieved through detuned optical filtering. This
technique enables the use of high bit rates, as it requires a transmitter with simpler
electrical circuitry. Nevertheless, it has limitations. The use of pure intensity-modulated
(IM) signals with non-return-to-zero (NRZ) or return-to-zero (RZ) pulses, and limited
amplitude decay of feasible OFs result in reduced sideband suppression or carrier tone
filtering [6]. However, optical signals with poor spectral content around the carrier
frequency allow overcoming such disadvantage [6]. Alternate mark inversion (AMI)
signaling is a good candidate due to the poor spectral content near the optical carrier
and because it can be detected with conventional direct detectors [5]. An OSSB system
with AMI–RZ signaling presented remarkable tolerance to GVD and improved
tolerance to polarization mode dispersion relative to duobinary sideband in [5].
Moreover, OSSB–AMI–RZ systems with detuned optical filtering require simpler
transmitter and receiver than DQPSK systems [2].
Dispersion compensation (DC) is an important issue in high per-channel bit rate
systems. In optically routed networks, optical signals travel along different paths. As
each path has its own dispersion profile, the signal at the receiver may have different
values of accumulated dispersion on a short time scale. Therefore, the use of fast
adaptable DC devices is imperative. The combination of such devices with proper
dispersion maps results in better performance. Chirped FBGs can be used to perform
DC. In comparison to dispersion compensating fiber (DCF), CFBGs have lower losses
and insignificant nonlinear effects.
In this paper, the optimization of the optical filter module (OFM) of a 40 Gb/s
OSSB–AMI–RZ single-channel system is presented. Sideband suppression is
obtained by detuned filtering implemented by FBGs. The filter phase response is used
to perform DC. The presented system is similar to that given in [5]. However, in [5]
the filters are based on flat-top arrayed waveguide gratings (AWGs) and the DC is
achieved with DCFs and periodic dispersion maps.
The remainder of this paper is structured as follows. Section 2 presents
the description of the system setup and simulation parameters. In Section 3, the design
of the FBGs used in the system is described. Optimization of the filter parameters is
described in Section 4. Section 5 presents the linear and nonlinear transmission results.
Section 6 presents a test of the system DC scheme robustness. Section 7 states the main
conclusions of this work.
2. Setup description
A scheme of the system is shown in Fig. 1. The system is divided into three parts:
a transmitter (TX), a transmission link (TL) and a receiver (RX). The modulation of

Optimization of a FBG-based filtering module ... 513
Fig. 1. OSSB system setup.
the AMI–RZ optical signal is performed with a Mach–Zehnder modulator (MZM)
and a delay interferometer, as described in [7]. The deBruijn sequences with 2 12
symbols are used to generate the data pattern. The frequency response of the TX
electrical circuitry is modeled by a third-order Bessel filter with a –3-dB cutoff
frequency equal to the bitrate. The optical source is an ideal continuous wavelength
laser with an average power of 10 dBm. The MZM has insertion losses of 6 dB.
The optical PSK signal at the output of the MZM is amplified by an optical
amplifier (OA) that retrieves an average power of 18 dBm at its output. All the OAs
of the system have a noise figure of 6 dB. A delay of 12.5 ps is used in the delay
interferometer (DI) in order to obtain RZ pulses with a duty-cycle of 50%. The OFM
TX performs sideband suppression and DC. The variable optical attenuator (VOA)
sets the defined optimum power at the input of the TL.
The TL consists of one or more 80 km standard single mode fiber (SSMF) sections,
interleaved with OAs. The SSMF has a dispersion parameter of 17 ps/nm/km,
dispersion slope of 80 fs/(nm 2 km), nonlinearity coefficient of 1.32 W –1 km –1 and
attenuation coefficient of 0.2 dB/km. The OAs fully compensate the losses associated
to one fiber section.
At the RX, a second OFM is used to compensate the remaining accumulated
dispersion and perform noise filtering. The electrical part of the receiver is composed
of an ideal square-law detector and an electrical filter modeled by a third-order Bessel
filter with a –3-dB cutoff frequency of 28 GHz.
Figure 2 presents the OFM setup. Each device is composed by a five-port
circulator, three optical switches (OSs) and respective FBGs. The OSs select
the operating FBGs, depending on the TL length. The OFM is divided into three stages.
The first stage is performed by a 1×6 OS and respective FBGs, used to compensate
the accumulated dispersion of zero to five SSMF sections. If more accumulated
dispersion needs to be compensated, the second stage is used. This stage is performed

514 M.V. DRUMMOND et al.
Fig. 2. OFM scheme (b2b – back-to-back). Each CFBG compensates the accumulated dispersion of
the correspondent SSMF length.
by the 1×4 OS and respective FBGs. With these two stages an accumulated dispersion
of zero to ten sections can be compensated. The third stage is composed of a 1×2 OS
and a FBG with continuously adjustable group delay slope, as can be found in [8]. This
stage can be used to provide continuous tunability to the OFM. The mirrors presented
in Fig. 2 are used when the second and/or third stages are not needed. In this paper,
only the first two stages are considered, since continuous dispersion compensation is
not required. Although only one stage could be considered, this would result in having
many FBGs. On the other hand, too many stages would result in high insertion losses
due to the need of cascading several FBGs. Hence, employing three stages balances
such drawbacks.
In order to achieve maximum number of sections with DC performed solely by
the OFMs, each one compensates the same amount of accumulated dispersion, which
is half the total accumulated dispersion. Consequently, the accumulated dispersion of
twenty SSMF sections can be compensated. However, in this work, only zero to fifteen
sections are considered. The choice of this dispersion map is discussed in Section 6.
3. FBG design
Second-order super-Gaussian filters are commonly used in optical systems. Although
such filters are frequently implemented using AWGs, we use FBGs instead, due to
the simplicity of implementation and the possibility of having sideband suppression
and DC done in a single filter. Moreover, the design of FBGs with similar amplitude
response and different DC values can be easily accomplished. The transfer function
of the FBGs was obtained using the transfer matrix method [9].
As mentioned in Fig. 2, two different kinds of FBGs are considered: shaded-
-sinc [10], for transmission distances lower than 80 km; and linearly CFBGs [11] with

Optimization of a FBG-based filtering module ... 515
a b
c d e
Fig. 3. Normalized refractive index profile of shaded sinc (a) and Gaussian apodizations (b); and
frequency response of shaded sinc (c), CFBG 80 km (d); and CBFG 200 km (e). In graphics (c), (d)
and (e), the dashed curve is the amplitude response of an ideal super-Gaussian filter. RIV – refraction
index variation.
Gaussian apodization. These kinds of gratings differ in the apodization profile, as
depicted in Figs. 3a and 3b. Fourier theory is applicable to grating responses when
weak gratings (with reflectivity of approximately or less than 50%) are considered.
Therefore, a sinc-shaped refractive index profile should result in a square overall
reflection spectrum. Gratings with this refractive index profile have also proven to be
almost dispersion free. The apodization of this profile with a Gaussian function (also
called shading function) allows the control of the filter order without degrading
significantly the group delay response (Fig. 3c). To obtain a second order super-
-Gaussian filter, a Gaussian shading function with a full width at half maximum
(FWHM) of L/3.7 [9] is considered, where L is the grating length. Linearly CFBGs
are useful for DC. To obtain a second-order super-Gaussian response, a second-order
Gaussian profile with FWHM = L/3 is considered for all CFBGs. The adjustment of
the refraction index, chirp and length of the grating allows changing the filter’s
dispersion without altering significantly the amplitude response (Figs. 3d and 3e).
The losses associated to optical filtering in the TX and RX OFMs are less than 7
and 5 dB, respectively. The FBGs maximum group delay ripple is 10 ps.
4. SSB filter optimization
In this section, the performance criteria and TX filter optimization are presented. In
a first approach, the TX and RX OFM filtering is replaced by a single filter with

516 M.V. DRUMMOND et al.
a second-order super-Gaussian response, as such filters can be implemented with
FBGs.
Three different performance criteria are considered: –20 dB signal spectral
bandwidth (SBW); Q-factor penalty (ΔQ) and sideband suppression ratio (SSR).
The –20 dB SBW measurements are accomplished by finding the lowest spectral range
with 99% of the total power of the optical signal. The Q-factor penalty in decibels is
given by
ΔQ = 20log 10(Q ref) – 20log 10(Q OSSB) (1)
where Q OSSB and Q ref are the Q-factor of the OSSB and reference signals, respectively.
The reference signal is an unfiltered NRZ signal with an extinction ratio (ER) of 10 dB,
as considered in [12] for 40-Gb/s signals long-haul transmission. A semi-analytical
approach is employed to estimate Q-factor, where the signal waveform is obtained
using a numerical simulation, while the impact of optical noise is taken into account
analytically [13]. The SSR in decibels is
SSR = 10log 10 (P NSSB ) – 10log 10 (P SSB ) (2)
where P NSSB and P SSB are the optical powers of the non-suppressed and suppressed
sidebands, respectively. A signal with SSR less than 20 dB is considered vestigial
sideband, otherwise, it is considered SSB. The –20 dB SBW and SSR are measured at
the TX OF output.
The filter optimization has two main purposes: improving the robustness to fiber
dispersion and compacting the signal spectra [5]. Hence, the following criteria are used
to select the filter settings: i) the –20 dB SBW is minimized; ii) ΔQ is minimized, and
iii) the SSR is higher than 20 dB. Although the criteria chosen are similar to the ones
used in [5], the optimum filter settings obtained in that work cannot be used in
the system presented, as the AMI–RZ signal at the TX OF input has a duty cycle
of 50%.
The optimization of the filter bandwidth and detuning is performed in back-to-
-back, according to the scheme presented in Fig. 4. The bandwidth of the RX OF should
be high enough to enable reduced signal degradation and low enough in order to have
efficient noise filtering. Therefore, a bandwidth of 40 GHz is chosen. The RX OF has
equal detuning to the TX OF. At the RX OF output, an optical signal-to-noise ratio
(OSNR) of 22.0 dB is considered. This value remains constant in all tests along
Fig. 4. TX OF optimization scheme.

Optimization of a FBG-based filtering module ... 517
this section, and results in a Q-factor of 7 when the reference signal is used.
The optimization results are presented in Fig. 5. Following the performance criteria
described, a detuning of 24 GHz and a bandwidth of 35 GHz are considered. With
these parameters, a filtered signal with a –2.7 dB of Q-factor penalty, 31.6 GHz of
–20 dB SBW and 34.3 dB of SSR is obtained. Therefore, all FBGs were designed with
a detuning of 24 GHz. The FBGs of the first stages of the TX and RX OFMs have
a bandwidth of 35 and 40 GHz, respectively. The FBGs of the second stages must
have a larger bandwidth to avoid changing significantly the amplitude response of
combined filtering of first and second stages. Hence, the FBGs of the second stages
of the TX and RX OFMs have a bandwidth of 55 GHz.
5. Transmission simulations
a b c
Fig. 5. Q-factor penalty (a), –20 dB SBW (b), and SSR (c) for the TX OF bandwidths and detunings
considered.
After optimizing the TX and RX FBG settings each OFM, the DC effectiveness and
system performance are assessed.
The DC effectiveness is assessed with a linear transmission simulation.
The simulation scheme is similar to the one presented in Fig. 1. Linear lossless SSMF
sections are considered and an OSNR of 22.0 dB is set at the RX OFM output,
independently of the number of sections. Figure 6 presents ΔQ as a function of
the fiber length. The Q-factor penalty variation to the back-to-back case is lower than
1 dB, proving that the effectiveness of the optical DC does not change significantly
with the fiber length considered.
The nonlinear transmission simulation scheme is the one presented in Fig. 1.
The Q-factor as a function of the input power per section is presented in Fig. 7,

518 M.V. DRUMMOND et al.
Fig. 6. Q-factor penalty for the linear transmission simulation. Inset: eye patterns for 0 and 480 km
of linear SSMF.
Fig. 7. Q-factor as a function of the input power per section.
considering different number of sections. Figure 7 shows that thirteen sections of
SSMF are achieved with a Q-factor higher than 7, proving that the signal degradation
arises mainly from the noise accumulation and fiber nonlinear effects.
6. Dispersion compensation robustness
In this section, we investigate the robustness of the system to different dispersion maps
and small deviations in the DC. Thirteen sections and optimum input power per section
(0 dBm) are considered. Both OFMs compensate half of the total accumulated
Fig. 8. Q-factor as a function of dispersion map and RX OFM DC deviation.

Optimization of a FBG-based filtering module ... 519
dispersion. The dispersion variation is performed by two linear lossless fiber sections,
each one placed after the TX and RX OFMs. Figure 8 presents the Q-factor as
a function of the total DC performed at the TX and deviation of the DC performed at
the RX from the remaining DC. Considering optimum DC, a Q-factor variation of
1.2 dB is obtained for the dispersion maps considered, proving that the use of different
dispersion maps results in negligible penalties. However, DC variations from
the optimum value (dotted line) result in higher penalties. This attests the need for
small adjustments of the DC, enabled by the third stage of the OFMs.
7. Conclusions
A 40 Gb/s OSSB transmission system with AMI–RZ signaling format and optical DC
has been investigated. Sideband suppression and DC are both performed by optical
filtering, implemented with FBGs. A scheme based on FBG switching has been
proposed to perform DC for different SSMF lengths. Linear transmission simulation
yielded a Q-factor penalty variation to the back-to-back case lower than 1 dB
considering a maximum transmission distance of 1200 km. Nonlinear transmission
simulation achieved a Q-factor higher than 7 for 1040 km of SSMF using optimum
input power in each fiber section. Simulations with different dispersion maps yielded
a maximum Q-factor variation of 1.2 dB. The use of the DC scheme presented
with equal DC at the TX and RX has proven to be almost ideal. Moreover, the system
has proven to be robust to different dispersion maps. However, DC variations from
the optimum value result in significant penalties, proving the need for small
adjustments of the DC.
Acknowledgements – THRONE (PTDC/EEA-TEL/66840/2006) Fundação para a Ciência e a Tecnologia
(FCT) project is acknowledged. M.V. Drummond was supported by FCT under the SFRH/BD/40250/
2007 scholarship.
References
[1] WINZER P.J., ESSIAMBRE R.J., Advanced optical modulation formats, Proceedings of the IEEE 94(5),
2006, pp. 952–985.
[2] GRIFFIN R.A., CARTER A.C., Optical differential quadrature phase-shift key (oDQPSK) for high
capacity optical transmission, [In] Optical Fiber Communication Conference and Exhibit, OFC 2002,
pp. 367–368.
[3] SU Y., MOLLER L., RYF R., CHONGJIN XIE, XIANG LIU, Feasibility study of 0.8-b/s/Hz spectral efficiency
at 160 Gb/s using phase-correlated RZ signals with vestigial sideband filtering, IEEE Photonics
Technology Letters 16(5), 2004, pp. 1388–1390.
[4] FONSECA D., CARTAXO A.V.T., MONTEIRO P., Optical single-sideband transmitter for various
electrical signaling formats, Journal of Lightwave Technology 24(5), 2006, pp. 2059–2069.
[5] CHARRUA P.M.A., CARTAXO A.V.T., Performance analysis of AMI-RZ single-sideband signals in
40 Gbit/s transmission systems, IEE Proceedings – Optoelectronics 153(3), 2006, pp. 109–118.
[6] FONSECA D., CARTAXO A., MONTEIRO P., Comparison and optimisation of optical single sideband
transmitters, IET Optoelectronics 1(2), 2007, pp. 82–90.

520 M.V. DRUMMOND et al.
[7] WINZER P.J., GNAUCK A.H., RAYBON G., CHANDRASEKHAR S., SU Y., LEUTHOLD J., 40-Gb/s
return-to-zero alternate-mark-inversion (RZ-AMI) transmission over 2000 km, IEEE Photonics
Technology Letters 15(5), 2003, pp. 766–768.
[8] MATSUMOTO S., OHIRA T., TAKABAYASHI M., YOSHIARA K., SUGIHARA T., Tunable dispersion
equalizer with a divided thin-film heater for 40-Gb/s RZ transmissions, IEEE Photonics Technology
Letters 13(8), 2001, pp. 827–829.
[9] ERDOGAN T., Fiber grating spectra, Journal of Lightwave Technology 15(8), 1997, pp. 1277–1294.
[10] IBSEN M., DURKIN M.K., COLE M.J., LAMING R.I., Optimised square passband fibre Bragg grating
filter with in-band flat group delay response, Electronics Letters 34(8), 1998, pp. 800–802.
[11] JUNHEE KIM, JUNKYE BAE, YOUNG-GEUN HAN, SANG HYUCK KIM, JE-MYUNG JEONG, SANG BAE LEE,
Effectively tunable dispersion compensation based on chirped fiber Bragg gratings without central
wavelength shift, IEEE Photonics Technology Letters 16(3), 2004, pp. 849–851.
[12] International Telecommunication Union (ITU-T) Recommendation G.959.1, Optical Transport
Network Physical Layer Interfaces.
[13] REBOLA J.L., CARTAXO A.V.T., Gaussian approach for performance evaluation of optically
preamplified receivers with arbitrary optical and electrical filters, IEE Proceedings –
Optoelectronics 148(3), 2001, pp. 135–142.
Received November 6, 2009
in revised form January 6, 2010

Optica Applicata, Vol. XL, No. 2, 2010
Theoretical analysis of electro-optical characteristics
of the modified three cylindrical mirror analyzer
SZYMON KLEIN 1 , STANISŁAW KASZCZYSZYN 1 , ANDRZEJ GRZESZCZAK 1 , PIOTR KOŚCIELNIAK 2
1 Institute of Experimental Physics, University of Wrocław, Wrocław, Poland
2 Department of Electron Technology, Silesian University of Technology, Gliwice, Poland
In this paper, theoretical electro-optical characteristics of a modified cylindrical mirror analyzer
based on three coaxial cylindrical electrodes obtained with numerical calculations are presented.
It was shown, for the first time, that the image of a point source of electrons located on the analyzer
optical axis is in the form of a circle which does not depend on the entrance angle of electrons into
the analyzer within the range of angles α = 30°–40°. In particular, for the input angle α =36° and
dispersion Δα = ±3°, the relative energy resolution is equal to 0.01% at the analyzer constant
K = 1.97.
Keywords: cylindrical mirror analyzer, TCMA analyzer, Bashforth–Adams–Moulton method.
1. Introduction
The control of physicochemical properties of solid state surfaces in view of the various
applications stimulates the dynamic development of surface analytical methods, in
particular, methods of electron spectroscopy. In these methods the electron energy
analyzers play the most important role. Therefore, during the development of
the electron spectroscopic methods, new technical improvements of electron energy
analyzer having the best analytical parameters are of great demand.
The most important parameters of the electron energy analyzers are: energy
resolution, transmission coefficient, the input angle of electrons into the analyzer and
the speed of spectra registration. Moreover, in some types of analyzers the acceptance
angle also determines the sample–analyzer distance, which restricts a simultaneous
use of different surface analytical methods to control the same surface area.
In the conventional cylindrical mirror analyzer (CMA) [1] the distance between
the sample and analyzer is about 6–8 mm and remains the same also for the double
pass cylindrical mirror analyzer (DPCMA), because the same conditions of the second
order focusing have to be fulfilled [2, 3]. The relative energy resolution for both
analyzers can be increased only at the cost of decreasing the entrance slit in the inner
cylinder and transmission coefficient, at a constant sample–analyzer distance.

522 S. KLEIN et al.
In order to improve the energy resolution of a conventional CMA several
modifications were proposed. In paper [4], the results of theoretical analysis of
a modified CMA analyzer were presented, for which the additional third cylindrical
electrode with properly made slits was proposed between the external and internal
cylinders of the conventional CMA analyzer. After such modification for the set
transmission coefficient, the relative energy resolution (of the order of 0.1%) of
the CMA was evidently better than that of the conventional one. However, the distance
between the sample and the analyzer was taken in such a way that the entrance angle
of electrons was about α =40°.
In another modification of a conventional CMA analyzer proposed by
MENCHIKOV [5, 6], known as the three cylindrical mirror analyzer, three coaxial
cylindrical electrodes were also used in a configuration shown in Fig. 1. In these
papers, a perturbation theory analysis of the electro-optical properties of electron beam
in such a system was carried out and the possibility of existence of the third order
focusing conditions and relative energy resolution at the level of 0.01% was predicted.
In an earlier work [7], we presented the results of experimental investigations of
the electro-optical characteristics of the electron energy analyzer (TCMA) designed
and constructed on the basis of the theoretical prediction by MENCHIKOV [5, 6].
The analytical parameters obtained were very far from the theoretically predicted ones.
In this paper, we present the results of numerical calculations of electro-optical
characteristics of the TCMA working under axis-ring focusing conditions.
2. Fundamentals
The TCMA consists of three coaxial metal cylinders, as shown in Fig. 1. It works in
the regime of axis-ring focusing [6].
The sample and the central cylinder are grounded. The voltage applied between
the outer and inner cylinders creates the electrostatic field which separates the electrons
entering the analyzer.
The electrons emitted from the point source located on the analyzer axis, after
having passed the four slits in the central cylinder, are focused on a circle of radius r
Fig. 1. A simplified diagram of the three cylindrical mirror analyzer (TCMA), working in axis-ring
focusing mode, together with exemplary electron trajectories inside.

Theoretical analysis of electro-optical characteristics ... 523
close to the central cylinder. The calculation of electron trajectories was based on
the Bashforth–Adams–Moulton method implemented as ode113 function in the
MATLAB package.
Equations of the electron motion were integrated forward and backward
subsequently in order to control the numerical error of the trajectory coordinates
defined as the difference in coordinate r between the results of forward and backward
integration. The time step of the integration was chosen to keep this error at the level
better than 10 –6 m. Our calculations were performed for the energy of electrons E and
E±ΔE, where ΔE was equal to 0.1% E or to 0.01% E, respectively. For the above
mentioned energies, the trajectories of electrons were analyzed for the entrance angle
α in the range 30°–40°, and the constant value Δα =3°.
3. Results and discussion
As is shown in Fig. 1, and in particular in Fig. 2, the electron beams which differ in
energy by about ΔE are not only well focused, but also their focuses are well
separated.
Fig. 2. An enlarged area of electron trajectories in the region of their focusing into the ring, where
the input slit should be located. The focal length for α =36° and Δα = ±3° is marked on the horizontal axis.
The well-separated electron beams confirm that the energy resolution of the analyzer
is at least equal to ΔE.
A next feature of the analyzer is clearly visible in Fig. 3.
These dependences confirm that the separation of focuses is really equal to
ΔE = 0.1% E and ΔE = 0.01% E. Moreover, based on the analysis of the electron
trajectories for energy varying by ±ΔE one can conclude that, in a wide range of
input angles and analyzer constant K, the energy resolution is at the level 0.1%. For
the chosen values of K, one can obtain this value at the level 0.01% or even better
owing to the input angle in the range 30°–40°.

524 S. KLEIN et al.
Fig. 3. The relative energy resolution of the analyzer as a function of constant K (defined as the ratio
of pass energy to separation voltage), and entrance angle α.
Fig. 4. The analyzer constant K as a function of focal length for the entrance angles in the range 30°–40°.
Figure 4 shows the dependence of K on the distance between the focus and sample
for the chosen energy E and chosen values of entrance angle α.
It is clearly visible that all the curves are crossing at one joint point corresponding
to K = 1.97 and L = 11.5125. This means that the TCMA working in the regime of
axis-ring focusing is able to separate the electrons in a wide range of entrance angles.
This is well confirmed in Fig. 5, where the dependences of constant K of
the analyzer on radius r of an image, are presented.
It is clearly visible that for different electron entrance angles of the analyzer,
the crossing point of all the curves appears in a very narrow range of constant
K = 1.97, similarly as for Fig. 3.

Theoretical analysis of electro-optical characteristics ... 525
Thus, our analysis confirmed that, using the TCMA working in axis-ring focusing
mode, one can obtain well-resolved energy distribution curves of electrons in a wide
range of electron entrance angles of the analyzer without any change in position and
size of the analyzing slits, as well as without a change of the deflection potential on
the cylinders for the chosen relative energy resolution.
4. Conclusions
From the numerical calculation of electro-optical characteristics of the three
cylindrical mirror analyzer working in axis-ring focusing mode, one can conclude that:
– the modified analyzer can reach an extremely high energy resolution at the level
0.01%, or even better;
– this level of resolution is attainable also for a wide range of entrance angles of
electrons entering the analyzer, which is a unique achievement of this work;
– for the chosen resolution, the analyzing slit can be twice as large as that of
the conventional CMA analyzer;
– it can be interchanged with the conventional CMA without modification of both
the vacuum system and the electronics steering system.
Acknowledgements – This work was sponsored by the Institute of Experimental Physics, University of
Wrocław, within the research project GBW 2016/IFD/W 2008, as well as by the Institute of Physics,
Silesian University of Technology, Gliwice, within the research project BK/RMF1/2009. We thank
Dr. Stanisław Surma for valuable linguistic assistance.
References
Fig. 5. Constant K versus image radius r.
[1] GRZESZCZAK A., KASZCZYSZYN S., SIDORSKI Z., Home made cylindrical mirror analyzer (CMA):
construction and performance, Acta Universitatis Wratislaviensis 37, 1980, p. 351.
[2] AKSELA S., KARRAS M., PESSA M., SUONINEN E., Study of the electron optical properties of an electron
spectrograph with coaxial cylindrical electrodes, Review of Scientific Instruments 41(3), 1970,
p. 351.

526 S. KLEIN et al.
[3] KOVER A., VARGA D., CSERNY I., SZMOLA E., MORIK G., GULYAS L., TOKESI K., A distorted field
cylindrical mirror electron analyzer: II. Performances and application for studying ion–atom
collisions, Nuclear Instruments and Methods in Physics Research A 373(1), 1996, pp. 51–56.
[4] FRANZEN W., TAAFFE J., Theory of modified cylindrical mirror electron spectrometer free of third-
-order aberration, Journal of Physics E: Scientific Instruments 13(7), 1980, p. 719.
[5] MENCHIKOV K.A., Elektrostaticheskii analizator zariazhennykh chastits s tremia koaksialnymi
tsilindricheskimi elektrodami: I. Konstruktsia s tremia kaskadami sluchai tonkogo srednego elektroda
i fokusirovki tipa os’-os’, Journal of Technical Physics 51, 1981, p. 17 (in Russian).
[6] MENCHIKOV K.A., Elektrostaticheskii analizator zariazhennykh chastits s tremia koaksialnymi
tsilindricheskimi elektrodami: III. Konstruktsia s tremia kaskadami i fokusirovkoi obshchego vida
koltso-koltso, Journal of Technical Physics 52, 1982, p. 2245 (in Russian).
[7] KOŚCIELNIAK P., KASZCZYSZYN S., SZUBER J., A new type of electron energy analyzer based on three
coaxial cylindrical electrodes for Auger electron spectroscopy, Vacuum 63(1–2), 2001, pp. 361–366.
Received July 9, 2009
in revised form October 6, 2009

lnstructions for Authors
l. Papcrs wil l be considcrccl for publication in Optica Applicata i f thcy have not bccn prcviously
publishcd clscwhcrc. T hcy should clca l with original rcscarch in appliccl optics and may
conta in cxpcrimc nta l as wcll as theorctical rcsults. Ali papcrs will be subjcctccl to rcfcrcci ng.
2. Manuscripts s hould be typed in cloublc spacing o n one sidc of th c pagc on ly. Printcd
manuscripts shou lcl be scnt in duplicale to th e Ecl it orial Ofl'icc. We also acccpt elcetronie
submi ssion, prcferably in Word, txt or rtf format.
3. Thc mathcmatical formulne should be ty pcd and carc shoulcl be takcn that thc symbols casi ly
confusing (e.g., supc rscripts and subscripts) arc vcry clearly cli stinguishcd. formu lne shou lcl
be numbercel o n thc ri g ht-hancl sicie in rouncl parcnthcscs.
4. Each papcr s houlcl be prcccclccl by an nbstract of no more than 100 words. lt must includc thc
scopc o f t he research and principal finclings.
5. A li illustrations, drawings and photographs shoulcl be submitted o n scpm·ate shcets. E lcetron ie
submission as bmp o r tiff format with minimum resolution of 300 dpi is preferrcd. Aria! or
1-lclvctica fonts typc shoulcl be usccl (bolcl a nd italic are avoiclccl). Ali illustrations, inclucling
photog raphs, must havc thc figure numbcr, thc author's namc and the title of the art ic lc.
f-'i g urc caption s shou lcl be listcel on a scparate sheet at the end of th c manuscript.
6. Tablcs shoulcl be submittecl a lso on the separatc shccts, numbercel in Arabie numcrals, and
refcn·ccl to t he text. Thc s i ze o f a ta b l e m u st not be larger than A3 .
7. Rcfcrcnccs shoulcl be numbercel consccuti vely as thcy are citccl in thc tcxt and li stcel aftcr tcxt.
In thc li s t of rcferc nccs, the followin g information s ho ul cl be g ivcn:
a) autho r 's name and initials,
b) t h e lilie o f thc journal,
c) j ournal vo lume, year of issuc, and thc first pagc,
ci) i f a book is c it ecl: p ublisbing house, p lace, and year of issue.
8. T he authors rcceive one copy of the manuscript (with changes suggcstcd by thc Eclitor) for
thcir acccptancc and this copy scnt back to thc Ecli tor will be thc basis for a ll th c proofrcacling
macic by thc cclitorial s taff. Thc Ecli tors rcscrvc th e msc lvcs thc right to charge thc
autbo r for t he a lt crati ons in t he proof oth er than t h e correcti o n o f printcr's crrors.
9. Thc authors o f each articlc will rccc ivc 25 rcprints o f thcir papcr frcc o f charge.
10. T hc a utho r(s) o f thc papcr(s) submittccl to publication and publishccl in Optica Applicata agrcc
to cxc lus ivc transfer of thc cluc copyright to the publishcr.