Optical intensity analyses of Er3+:YAlO3 - PHYSICS & ASTRONOMY

Optical intensity analyses of Er 3+ :YAlO 3
Dhiraj K. Sardar, a Sreerenjini Chandrasekharan, Kelly L. Nash, and John B. Gruber
Department of Physics and Astronomy, University of Texas at San Antonio,
San Antonio, Texas 78249-0697, USA
Received 25 April 2008; accepted 9 May 2008; published online 17 July 2008
Analyses of the optical absorption and emission intensities are performed on Er3+ ions doped into
yttrium orthoaluminate YAlO3 to assess this material as a laser source. The Judd–Ofelt model is
applied to the room temperature absorption intensities of Er3+ in YAlO3 to obtain the
phenomenological intensity parameters: 2=1.0610−20 cm2 , 4=1.9610−20 cm2 , and 6 =1.4010−20 cm2 . The intensity parameters are used to determine the radiative decay rates and
branching ratios of the Er3+ transitions from the upper multiplet manifolds to the corresponding
lower-lying multiplet manifolds 2S+1 LJ of Er3+ in YAlO3. Using the radiative decay rates, radiative
lifetimes of 13 excited states have been determined. The room temperature fluorescence lifetime of
the Er3+ 4 S3/2→ 4 I15/2 transition is measured to be 0.43 ms. Values of emission cross section and
peak emission cross section have been obtained for the Er3+ 4 I13/2→ 4 I15/2 and 4 S3/2→ 4 I15/2 intermanifold transitions. The detailed structure observed in the manifold-to-manifold transitions
allows us to identify the Stark splitting of the individual manifolds. © 2008 American Institute of
Physics. DOI: 10.1063/1.2956331
I. INTRODUCTION
Trivalent erbium Er3+ 4f 11 has long been considered as
an optical activator or as a sensitizer in a large number of
midinfrared mid-IR solid-state laser host materials due to
its rich energy level structure. 1–14 Among the entire group of
rare-earth ions, the Er3+ ion has been investigated in detail
since intense green emission from Er3+ is observed in a number
of laser hosts. The first continuous-wave upconversion
laser was demonstrated in Er3+ doped into YAlO3. YAlO3 is
similar to yttrium aluminum garnet, but superior to yttrium
lithium fluoride in terms of hardness, thermal conductivity,
and optical properties. 15–17 It is known to be the second most
successful rare-earth laser host material with a band edge
between 0.3 and 5.8 m Ref. 18 and is considered to be
one of the most efficient laser hosts. When doped with erbium
ions, it could produce several upconversion laser emissions
between 510 nm and 2.7 m. 19
Yttrium orthoaluminate YAlO3 has the perovskite
structure, and it is often referred to as yttrium aluminum
perovskite. It exhibits orthorhombic symmetry having four
16
molecules per unit cell and space group D2h Pbnm. Trivalent
erbium Er3+ ions substitute the trivalent Y3+ ions on
entering the YAlO3 lattice, thereby requiring no charge compensation.
Since the point-group symmetry at these sites is
low C1h, radiative transitions between all levels of the 4f 11
electronic configuration of Er3+ are allowed. 20 The Er ions
occupy Cs site symmetry when doped into YAlO3. 21
In this study, we report an in-depth Judd–Ofelt JO
Refs. 22 and 23 analysis of Er3+ 4f 11 in YAlO3. The JO
analysis is performed on the room temperature absorption
intensities of the Er3+ 4f 11 ions in YAlO3. The room temperature
fluorescence lifetime of the 4 S3/2→ 4 I15/2 transition
a
Author to whom correspondence should be addressed: Electronic mail:
dsardar@utsa.edu.
JOURNAL OF APPLIED PHYSICS 104, 023102 2008
has been measured and compared with the radiative lifetime
as predicted by the JO model. The room temperature emission
cross section and peak emission cross section values for
the Er 3+ 4 I 13/2→ 4 I 15/2 and the 4 S 3/2→ 4 I 15/2 transitions have
been determined as well.
II. EXPERIMENTAL DETAILS
A. Materials
Single crystals of YAlO 3 containing Er 3+ 1.0 at. %
were grown using the Czochralski pulling method from the
melt in air using platinum crucibles. The crystals used in the
present study were obtained from Kokta of Bicron. Based on
a distribution coefficient that allows for 96% of the Er 3+ ions
to be incorporated into the crystal and based on the dopant
concentration in the melt, the ion concentration was determined
to be approximately 1.910 20 cm −3 in the crystal.
The spectroscopic sample was optically polished to flat parallel
faces and had dimensions of 342 mm 3 .
B. Absorption measurements
An upgraded Cary model 14R spectrophotometer controlled
by a desktop computer was used to acquire the room
temperature absorption spectra for Er 3+ :YAlO 3. The room
temperature absorption spectra covering the wavelength
range between 325 and 700 nm and between 725 and 1700
nm are shown in Figs. 1 and 2, respectively. The spectral
bandwidth was kept fixed at 0.1 nm over the entire wavelength
range to obtain an optimum signal-to-noise ratio.
C. Fluorescence and lifetime measurements
The room temperature fluorescence spectra for the
Er 3+ 4 I 13/2→ 4 I 15/2 transition ranging from 1420 to 1600 nm
and for the Er 3+ 4 S 3/2→ 4 I 15/2 transition ranging from 535 to
565 nm were taken by exciting the sample with the 514.5 nm
0021-8979/2008/1042/023102/8/$23.00 104, 023102-1
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023102-2 Sardar et al. J. Appl. Phys. 104, 023102 2008
FIG. 1. Room temperature absorption spectrum of Er 3+ in YAlO 3, ranging
from 325 to 700 nm.
line from a Spectra Physics argon ion laser model 2005.
The fluorescence from the sample was detected by a photomultiplier
tube attached to the entrance slit of a SPEX scanning
monochromator model 1250 M. The fluorescence
spectrum for 4 I 13/2→ 4 I 15/2 transition was taken using 600
grooves/mm grating blazed at 1.0 m, and the fluorescence
spectrum for the 4 S 3/2→ 4 I 15/2 transition was taken using
1200 grooves/mm reflection grating blazed at 0.5 m, and
the spectral resolution was 0.1 nm in all measurements. The
wavelength reproducibility of the monochromator is better
than 0.01 nm. A desktop computer was employed to control
the monochromator and to acquire and analyze the data in
both cases. The radiative lifetime was taken for the
Er 3+ 4 S 3/2→ 4 I 15/2 transition by pulsing the laser beam with a
chopper at 230 Hz. The fluorescence decay was analyzed
with a 560 MHz Tektronix oscilloscope model TDS 3054B
and found to be a single exponential. The fluorescence lifetime
of the Er 3+ 4 S 13/2→ 4 I 15/2 transition was determined to
be 0.43 ms.
FIG. 2. Room temperature absorption spectrum of Er 3+ in YAlO 3, ranging
from 725 to 1700 nm.
III. DATA ANALYSIS
A. JO analysis
Nine absorption bands corresponding to the manifolds
2
K15/2+ 4 G9/2+ 4 G11/2, 2 G19/2, 4 F3/2+ 4 F5/2, 4 F7/2, 2 H211/2 + 4 S3/2, 4 F9/2, 4 I9/2, 4 I11/2, and 4 I13/2 in the room temperature
absorption spectra shown in Figs. 1 and 2 were chosen to
determine the JO intensity parameters 2, 4, and 6 for the
corresponding Er3+ 4f 11 transitions in Er3+ :YAlO3. Many
researchers have applied the JO analysis to determine the
important spectroscopic and laser parameters. 24–31 Therefore,
we provide only a short synopsis appropriate to the analysis
of the Er3+ transitions in Er3+ :YAlO3. The measured line strengths SmeasJ→J of the chosen
bands are determined using the following expression:
3ch2J +1n
SmeasJ → J =
83 ¯e2 9 N n
0 2 +22, 1
where J and J represent the total angular momentum quantum
numbers of the initial and final manifold states, respectively;
N0 is the Er3+ ion concentration; ¯ is the mean wavelength
of the specific absorption band that corresponds to the
J→J transition; n is the refractive index RI, which is a
function of wavelength; =d is the integrated absorption
coefficient as a function of ; c is the speed of light;
and h is Planck’s constant. The factor 9/n 2 +22 in Eq. 1
represents the local field correction for the ion in the dielectric
medium.
The wavelength-dependent index of refraction n was determined
using Sellmeier’s dispersion equation,
n2 =1+ S2
2 2 . 2
− 0 For orthorhombic YAlO3, Morrison and Leavitt 18 provided
2
Sellmeier’s coefficients S and 0 for the a, b, and c crystallographic
axes as S=2.708 92, 2.677 92, and 2.634 68,
2 2 2 and 0=0.012 607 m , 0.012 282 m , and
0.011 592 m2 , respectively. Since our sample was not oriented,
the mean values of the Sellmeier’s coefficients were
used to determine the average refractive index as a function
of wavelength. The values of refractive indices obtained for
wavelengths of interest are given in Table I. These n values
are used to determine the absorption line strengths for the
chosen Er3+ transitions and are given in Table I.
The JO theory predicts that the absorption line strength
ScalcJ→J for electric-dipole transitions can be written in
the form
ScalcJ → J = tS,LJU t=2,4,6
tS,LJ2 , 3
where Ut is the doubly reduced matrix element of rank
tt=2,4,6 between the initial and terminal states characterized
by the quantum numbers S,L,J and S,L,J, respectively.
The values of the squared reduced matrix elements
for the chosen Er3+ transitions are obtained from Ref.
32. A least-squares fitting of Smeas to Scalc provides the three
JO parameters 2, 4, and 6 for Er3+ in YAlO3 host; these
values are given in Table II. The spectroscopic quality factor
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023102-3 Sardar et al. J. Appl. Phys. 104, 023102 2008
X= 4/ 6 for the Er 3+ :YAlO 3 laser material was determined
to be 1.40, which falls within the range of 1.06–3.37 reported
for Er 3+ in YAlO 3 from Refs. 32 and 33. Table II shows the
comparison of JO parameters obtained for Er 3+ doped into
YAlO 3. These JO parameters were used to recalculate the
transition line strengths of the absorption bands using Eq.
3. The measured and calculated absorption line strengths
are tabulated in Table I. The accuracy of fit between S meas
and S calc is given by the rms deviation squared S 2 and is
given in Table I.
The JO parameters can then be used to calculate the
radiative decay rates for transitions from the upper manifold
J to the corresponding lower-level manifolds J according
to Eq. 4,
64
AJ → J =
4e2 nn
3h2J +1 ¯ 3
2 +22 ScalcJ → J, 4
9
where S calc represents the line strength for the electric-dipole
transition from the upper multiplet manifold J to the corresponding
lower-lying multiplet manifolds J. The refractive
indices n in Eq. 4 are determined by using Eq. 2. The
radiative lifetime r for an excited state J is calculated by
r =
TABLE I. Values of refractive index, and measured and calculated absorption line strengths of Er 3+ transitions
in YAlO 3 at 300 K.
Transition from 4 I 15/2 ¯
nm
1
. 5
AJ → J
The fluorescence branching ratios, J→J, were determined
from the radiative decay rates by using the following
expression:
n S meas 10 −20 cm 2 S calc 10 −20 cm 2 S 2 10 −40 cm 4
4 I13/2 1513.51 1.92 2.3168 2.2513 0.0043
4 I11/2 971.43 1.45 0.5133 0.5829 0.0049
4 I9/2 787.93 1.31 0.2117 0.3535 0.0201
4 F9/2 651.18 1.22 1.6639 1.6953 0.0010
4 S3/2+ 2 H2 11/2 520.85 1.15 1.7332 2.0033 0.0730
4 F7/2 486.04 1.13 1.0765 1.1635 0.0076
4 F5/2+ 4 F 3/2 450.38 1.11 0.5823 0.4898 0.0086
2 G19/2 408.19 1.09 0.3150 0.3524 0.0014
4 G11/2+ 4 G 9/2+ 2 K 15/2 378.51 1.08 3.1588 2.9533 0.0422
TABLE II. JO parameters for Er 3+ doped in single crystal YAlO 3.
Sample 2
10 −20 cm 2
4
10 −20 cm 2
6
10 −20 cm 2
X= 4/ 6
1.06 1.96 1.40 1.40
YAlOb 0.91 0.70 0.56 1.24
b
YAlO3 1.06 2.63 0.78 3.37
c
YAlO3 0.95 0.58 0.55 1.06
YAlO 3 a
a This work.
b Reference 32.
c Reference 33.
J → J =
AJ → J
AJ → J = AJ → J r, 6
where the sum runs over all final manifold multiplets J. The
values of the radiative decay rates, the radiative lifetimes,
and the branching ratios for Er3+ transitions in Er3+ :YAlO3 are given in Table III.
The emission cross section for the 4 I13/2→ 4 I15/2 and the
4
S3/2→ 4 I15/2 transitions can be determined from the following
expression:
J,J;˜ = 2
8cn 2
J,J
g˜, 7
r
where is the central peak wavelength, J,J is the fluorescence
branching ratio from the upper manifold state J to
the lower manifold state J, r is the radiative lifetime of the
excited manifold state J, and g˜ is the line shape function.
The line shape function can be obtained from the fluorescence
spectrum using the following relation:
g˜ =
I˜
, 8
I˜d˜
where I˜ is the intensity at wave number ˜. According to
Eq. 8, the line shape function g˜ for the chosen transition
was determined by dividing the intensity I˜ by the integrated
area of the fluorescence spectral band.
The peak emission cross section for the 4 I 13/2→ 4 I 15/2
and the 4 S 3/2→ 4 I 15/2 transitions has been determined using
the following expression for a Gaussian line shape:
pY 1 → Z 1 =
2
p 4cn2 1/2 ln 2
AY1 → Z1, 9
where AY 1→Z 1 is the radiative transition rate from the
lowest Stark level Y 1 of the 4 I 13/2 manifold to the lowest
Stark level Z 1 of the 4 I 15/2 manifold, p is the wavelength at
the peak position of the emission band, n is the RI, c is the
speed of light, and v is the full width at half maximum
linewidth given in cm −1 .
The values for emission cross section and peak emission
cross section were determined to be 1.8210 −20 and 1.44
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023102-4 Sardar et al. J. Appl. Phys. 104, 023102 2008
TABLE III. Predicted line strengths, radiative lifetimes, and branching ratios of Er 3+ in YAlO 3 at 300 K.
Transition State Energy cm −1
nm
ed −20 2 Scal 10 cm rad ms J→J
4 I13/2→ 4 I 15/2 6 500 1 538.46 2.8914 3.53 1.0000
4 I11/2→ 4 I 13/2 3 600 2 777.78 1.7077 7.82 0.2580
4 I15/2 10 100 990.10 0.2192 0.7420
4 I9/2→ 4 I 11/2 2 150 4 651.16 0.0315 8.12 0.0013
4 I13/2 5 750 1 739.13 0.7170 0.5517
4 I15/2 12 250 816.33 0.0590 0.4470
4 F9/2→ 4 I 9/2 2 900 3 448.28 0.0185 0.59 0.0001
4 I11/2 5 050 1 980.20 2.3091 0.0868
4 I13/2 8 650 1 156.07 0.0545 0.0104
4 I15/2 15 150 660.07 0.8602 0.9027
4 S3/2→ 4 F 9/2 3 200 3 125.00 0.0010 1.06 0.0000
4 I9/2 6 100 1 639.34 0.1025 0.0308
4 I11/2 8 250 1 212.12 0.0077 0.0057
4 I13/2 11 850 843.88 0.1675 0.3756
4 I15/2 18 350 544.96 0.0683 0.9027
2 H211/2→ 4 S 3/2 800 12 500.00 0.0776 0.36 0.0000
4 F9/2 4 000 2 500.00 0.1408 0.0013
4 I9/2 6 900 1 449.28 0.1686 0.0083
4 I11/2 9 050 1 104.97 0.0407 0.0046
4 I13/2 12 650 790.51 0.0118 0.0036
4 I15/2 19 150 522.19 0.8844 0.9821
4 F7/2→ 2 H2 11/2 1 150 8 695.65 0.2420 0.26 0.0001
4 S3/2 1 950 5 128.21 0.0001 0.0000
4 F9/2 5 150 1 941.75 0.0028 0.0001
4 I9/2 8 050 1 242.24 0.2738 0.0232
4 I11/2 10 200 980.39 0.1696 0.0294
4 I13/2 13 800 724.64 0.2228 0.0970
4 I15/2 20 300 492.61 0.5909 0.8502
4 F5/2→ 4 F 7/2 1 650 6 060.61 0.0256 0.67 0.0001
2 H211/2 2 800 3 571.43 0.0533 0.0006
4 S3/2 3 600 2 777.78 0.0001 0.0000
4 F9/2 6 800 1 470.59 0.2930 0.0512
4 I9/2 9 700 1 030.93 0.0212 0.0108
4 I11/2 11 850 843.88 0.0188 0.0177
4 I13/2 15 450 647.25 0.2267 0.4793
4 I15/2 21 950 455.58 0.0697 0.4403
4 F3/2→ 4 F 5/2 350 28 571.43 0.0065 0.78 0.0000
4 F7/2 2 000 5 000.00 0.0067 0.0001
2 H211/2 3 150 3 174.60 0.0000 0.0000
4 S3/2 3 950 2 531.65 0.0007 0.0000
4 F9/2 7 150 1 398.60 0.0050 0.0018
4 I9/2 10 050 995.02 0.1080 0.1073
4 I11/2 12 200 819.67 0.3471 0.6219
4 I13/2 15 800 632.91 0.0017 0.0066
4 I15/2 22 300 448.43 0.0226 0.2624
2 G19/2→ 4 F 3/2 2 100 4 761.90 0.0010 0.80 0.0000
4 F5/2 2 450 4 081.63 0.0015 0.0000
4 F7/2 4 100 2 439.02 0.0174 0.0005
2 H211/2 5 250 1 904.76 0.0728 0.0042
4 S3/2 6 050 1 652.89 0.0000 0.0000
4 F9/2 9 250 1 081.08 0.0039 0.0012
4 I9/2 12 150 823.05 0.0003 0.0002
4 I11/2 14 300 699.30 0.0330 0.0395
4 I13/2 17 900 558.66 0.2090 0.4992
4 I15/2 24 400 409.84 0.0718 0.4552
4 G11/2→ 2 G1 9/2 2 000 5 000.00 0.1412 0.07 0.0000
4 F3/2 4 100 2 439.02 0.0130 0.0000
4 F5/2 4 450 2 247.19 0.0121 0.0000
4 F7/2 6 100 1 639.34 0.0410 0.0003
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023102-5 Sardar et al. J. Appl. Phys. 104, 023102 2008
10 −20 cm 2 for the 4 I 13/2→ 4 I 15/2 intermanifold transition
and 3.9310 −21 and 3.4910 −21 cm 2 for the 4 S 3/2→ 4 I 15/2
intermanifold transition, respectively.
B. Crystal-field analysis
TABLE III. Continued.
Transition State Energy cm −1
nm
One of the remarkable aspects of the room temperature
absorption spectrum is the detail that is observed in the in-
FIG. 3. Room temperature absorption spectrum of 4 I 15/2→ 4 I 13/2; the Stark
levels are identified in Table IV.
ed −20 2 Scal 10 cm rad ms J→J
2 H211/2 7 250 1 379.31 0.0499 0.0006
4 S3/2 8 050 1 242.24 0.0333 0.0005
4 F9/2 11 250 888.89 0.1949 0.0087
4 I9/2 14 150 706.71 0.0066 0.0006
4 I11/2 16 300 613.50 0.0051 0.0007
4 I13/2 19 900 502.51 0.2427 0.0627
4 I15/2 26 400 378.79 1.4570 0.9258
4 G9/2→ 4 G 11/2 950 10 526.32 0.1176 0.10 0.0000
2 G19/2 2 950 3 389.83 0.0036 0.0000
4 F3/2 5 050 1 980.20 0.0739 0.0005
4 F5/2 5 400 1 851.85 0.0415 0.0003
4 F7/2 7 050 1 418.44 0.4120 0.0075
2 H211/2 8 200 1 219.51 0.2419 0.0070
4 S3/2 9 000 1 111.11 0.0536 0.0021
4 F9/2 12 200 819.67 0.4405 0.0425
4 I9/2 15 100 662.25 0.0001 0.0000
4 I11/2 17 250 579.71 0.0543 0.0152
4 I13/2 20 850 479.62 1.5069 0.7613
4 I15/2 27 350 365.63 0.1356 0.1635
2 K15/2→ 4 G 9/2 350 28 571.43 0.0053 1.36 0.0000
2 G11/2 1 300 7 692.31 0.6453 0.0006
2 G19/2 3 300 3 030.30 0.9982 0.0151
4 F3/2 5 400 1 851.85 0.0000 0.0000
4 F5/2 5 750 1 739.13 0.0030 0.0002
4 F7/2 7 400 1 351.35 0.0000 0.0000
2 H211/2 8 550 1 169.59 1.8448 0.4902
4 S3/2 9 350 1 069.52 0.0000 0.0000
4 F9/2 12 550 796.81 0.0120 0.0102
4 I9/2 15 450 647.25 0.1108 0.1784
4 I11/2 17 600 568.18 0.0888 0.2141
4 I13/2 21 200 471.70 0.0010 0.0041
4 I15/2 27 700 361.01 0.0086 0.0870
dividual manifold spectra that show well resolved structure
attributed to the crystal-field splitting of each manifold. 21
Figure 3 shows the spectrum representing transitions between
many of the Stark levels of the ground-state manifold
4 I15/2 Z 1 through Z 8 to the first excited manifold 4 I 13/2 Y 1
through Y 7 observed between 1450 and 1625 nm. The transitions
between the Stark levels shown in Fig. 3 were analyzed
to give the splitting of the 4 I 13/2 and 4 I 15/2 manifolds
reported in Table IV. The values agree within the experimental
error to those reported by Donlan and Santiago. 34 The
calculated splitting for these manifolds is given in Table IV
column 4 and was first reported by O’Hare and Donaln. 35
The room temperature crystal-field splitting is similar to that
reported earlier at 4.2 K. 35
Of equal interest is the detailed structure observed in the
room temperature fluorescence from 4 I 13/2 to 4 I 15/2 shown in
Fig. 4. The analysis of this fluorescence is given in Table V
and confirms the crystal-field analysis of these two manifolds
shown in absorption in Fig. 3. For some time, it was hoped
that an efficient, low-threshold eye safe laser near 1.5 m
could be developed. 16,20,36,37 With the more recent investigations
on upconversion processes however, it is apparent that
IR stimulated emission can be obtained between other manifolds
as well.
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023102-6 Sardar et al. J. Appl. Phys. 104, 023102 2008
TABLE IV. Crystal-field splitting of the 4 S 3/2, 4 I 13/2, and 4 I 15/2 manifolds at
room temperature.
2S+1 LJ a
Label b
Ecm −1 obs c
Ecm −1 calc d
4 S3/2 U 2 18 484 18 480
U 1 18 405 18 408
4 I13/2 Y 7 6864 6871
Y 6 6812 6810
Y 5 6770 6767
Y 4 6712 6709
Y 3 6666 6666
Y 2 6639 6637
Y 1 6600 6594
4 I15/2 Z 8 522 519
Z 7 446 440
Z 6 386 391
Z 5 257 267
Z 4 217 214
Z 3 171 172
Z 2 51 45
Z 1 0 0
a Multiplet manifolds of Er 3+ 4f 11 .
b Stark level label.
c Energy of Stark level cm −1 at room temperature.
d Calculated manifold splitting see Ref. 34.
TABLE V. Room temperature fluorescence from 4 I 13/2 to 4 I 15/2.
Trans. a
b
nm
I c
E d cm −1 E e
cm −1
E calc f
cm −1
Y 7→Z 1 1456.45 0.16 6864 0 0
Y 7→Z 2 1467.35 0.10 6813 51 45
Y 6→Z 1 1467.55 0.20 6812 0 0
Y 5→Z 1 1476.65 0.25 6770 0 0
Y 6→Z 2 1478.60 0.21 6761 51 45
Y 5→Z 2 1488.15 0.46 6718 52 45
Y 4→Z 1 1489.40 0.22 6712 0 0
Y 7→Z 3 1493.65 0.23 6693 171 172
Y 3→Z 1 1499.70 0.44 6666 0 0
Y 6→Z 3 1505.38 0.47 6641 171 172
Y 2→Z 1 1505.80 0.40 6639 0 0
Y 3→Z 2 1511.25 0.57 6615 51 45
Y 1→Z 1 1514.70 1.42 6600 0 0
Y 5→Z 3 1514.90 1.16 6599 171 172
Y 6→Z 4 1517.20 1.10 6595 217 214
Y 2→Z 2 1517.20 1.10 6588 51 45
Y 2→Z 3 1526.25 0.53 6550 50 0
Y 3→Z 3 1539.20 0.42 6495 171 172
Y 1→Z 3 1554.70 0.25 6430 170 172
Y 1→Z 4 1566.20 0.10 6383 217 214
a
Emission from Yn see Table IV to Zn Stark levels.
b
Wavelength in nanometers.
c
Relative intensity.
d
Energy of transition in vacuum wave numbers.
e
Energy difference between emitting and terminal Stark level.
f
Calculated splitting of ground-state manifold based on the parameters given in Ref. 34.
FIG. 4. Room temperature fluorescence spectrum of the 4 I 13/2→ 4 I 15/2 transition
of Er 3+ in YAlO 3.
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023102-7 Sardar et al. J. Appl. Phys. 104, 023102 2008
FIG. 5. Room temperature fluorescence spectrum of the 4 S 3/2→ 4 I 15/2 transition
of Er 3+ in YAlO 3.
The intense green fluorescence observed between 540
and 560 nm for the 4 S 3/2→ 4 I 15/2 intermanifold transition, as
shown in Fig. 5, has been of interest for sometime that it
competes with other emissions initiated among 4 I 9/2, 4 I 11/2,
and 4 I 13/2 manifolds. However, this competition can be reduced
by pumping with arrays of IR diode lasers at wavelengths
that avoid green IR-pumped 4 S 3/2→ 4 I 15/2 stimulated
emission. In Table VI, we report the room temperature fluorescence
from 4 S 3/2 to 4 I 15/2, where stimulated emission is
observed associated with the U 1→Z 4 transition 549.66 nm,
representing the most intense fluorescence transition in the
spectrum.
IV. CONCLUSIONS
An in-depth spectroscopic analysis of Er 3+ 4f 11 in the
Er 3+ :YAlO 3 host has been performed following the JO
TABLE VI. Room temperature fluorescence from 4 S 3/2 to 4 I 15/2.
Trans. a
b
nm
I c
model. The three phenomenological intensity parameters 2,
4, and 6 are determined for Er 3+ :YAlO 3. From the values
of the JO intensity parameters, the spectroscopic quality factor
X= 4/ 6 for Er 3+ in Er 3+ :YAlO 3 host is determined to
be 1.40. The spectroscopic quality factor, first introduced by
Kaminiskii, 32 is an important predictor for stimulated emission
in a laser active medium.
The branching ratio is a critical laser parameter because
it characterizes the possibility of attaining stimulated emission
from any specific transition. The branching ratio of the
4 I13/2→ 4 I 15/2 transition is 100%, and the radiative lifetime of
this transition is calculated at 3.54 ms, which is comparable
to the value 4.40 ms reported by Weber. 38 The branching
ratio of the 4 S 3/2→ 4 I 15/2 transition is determined to be approximately
90%, thereby suggesting that this transition can
result in strong lasing action the transition that was labeled
as U 1→Z 4 corresponding to 549.66 nm in Table VI. The
room temperature fluorescence lifetime of the 4 S 13/2→ 4 I 15/2
transition is measured to be 0.43 ms. Using the measured
lifetime 0.43 ms and the predicted radiative lifetime 1.10
ms for the Er 3+ 4 S 13/2→ 4 I 15/2 transition, the quantum efficiency
is determined to be 39%. The emission cross section
for the 4 I 13/2→ 4 I 15/2 intermanifold transition and the peak
emission cross section within the manifold have been obtained
as 1.8210 −20 and 1.4410 −20 cm 2 , respectively.
Similarly, for the 4 S 3/2→ 4 I 15/2 intermanifold transition, the
value for emission cross section has been obtained as 3.93
10 −21 cm 2 and the peak emission cross section as 3.49
10 −21 cm 2 . Finally, the Stark splittings within the individual
multiplet manifolds have been identified from the detailed
structures observed in the corresponding manifold-tomanifold
transitions.
E d cm −1 E e
cm −1
E calc f
cm −1
U 2→Z 1 540.86 11.20 18 484 0 0
U 2→Z 2 542.33 13.69 18 434 50 45
U 1→Z 1 543.18 14.75 18 405 0 0
U 1→Z 2 544.75 20.15 18 352 53 45
U 2→Z 3 546.03 17.25 18 309 175 172
U 2→Z 4 547.47 26.34 18 261 223 214
U 1→Z 3 548.46 15.14 18 228 177 172
U 2→Z 5 548.82 16.20 18 216 268 267
U 1→Z 4 549.66 40.28 18 188 217 214
U 1→Z 5 551.24 27.80 18 136 269 267
U 2→Z 6 552.58 24.63 18 092 392 391
U 2→Z 7 554.39 14.89 18 033 451 440
U 1→Z 6 554.91 15.80 18 016 389 391
U 1→Z 7 556.85 17.25 17 953 452 440
U 1→Z 8 559.16 11.99 17 879 526 519
a
Emission from Un see Table IV to Zn Stark levels.
b
Wavelength in nanometers.
c
Relative intensity.
d
Energy of transition in vacuum wave numbers.
e
Energy difference between emitting and terminal Stark level.
f
Calculated splitting based on the parameters given in Ref. 34.
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023102-8 Sardar et al. J. Appl. Phys. 104, 023102 2008
ACKNOWLEDGMENTS
This research was supported in part by the National Science
Foundation Grant No. DMR-0602649 and the American
Chemical Society Grant No. PRF 43862-B6. The authors
would like to thank Robert C. Dennis UTSA, Laser
Research Laboratory for his assistance in obtaining some
visible emission spectra.
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