Optical characterization of Er3+and Yb3+ co-doped barium ...

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Table 3
Fluorescence lifetime (tf), emission cross-section (se), and full width at half max (FWHM) for the emission at 1571 nm in tellurite glass with different compositions.
Sample (mol%) t f (ms) s e (10 21 cm 2 ) FWHM (nm) s e FWHM (10 28 cm 3 )
80TeO2þ 15(BaF2þBaO)þ3La2O3þ1Er2O3þ1Yb2O3 a
2.693 6.82 91 621
75TeO2þ20ZnOþ5Na2Oþ0.5Er2O3þ1Yb2O3[21] 3.15 8.8 56 493
70TeO2þ20ZnOþ5Li2Oþ5La2O3þ0.5Er2O3þ0.5Yb2O3[27] 4.02 8.5 65 553
70TeO2þ10ZnOþ5BaF2þ15PbCl2þ0.5Er2O3þ1Yb2O3[17] 4.16 8.15 52 424
70TeO2þ5BaF2þ10ZnBr2þ15PbF2þ0.5Er2O3þ1Yb2O3[17] 4.05 8.3 56 465
70TeO2þ5BaF2þ10ZnBr2þ15PbCl2þ0.5Er2O3þ1Yb2O3[17] 3.85 8.45 55 465
75TeO2þ15WO3þ10La2O3þ1Er2O3þ5Yb2O3[33] 3.0 10 77 770
65TeO2þ15B2O3þ20SiO2 þ0.5Er2O3þ2.5Yb2O3[37] 2.38 7.49 71 532
70TeO2þ20ZnOþ10PbOþ1Er2O3þ5Yb2O3[34] 2.69 8.77 72 631
a Sample under study.
Table 4
Fluorescence lifetime (t f), emission cross-section (s e), and full width at half max (FWHM) for the emission at 1571 nm in different
glasses.
Glass type t f (ms) s e (10 21 cm 2 ) FWHM (nm) s e FWHM (10 28 cm 3 ) s e t f (10 23 cm 2 s)
Tellurite [21] 3.15 8.8 56 493 2.77
Silicate [36] 3.81 5.5 40 220 2.09
Bismuth [38] 4.5 8.5 75 637 3.82
Germanate [35] 9.55 5.7 53 302 5.44
Oxyfluoride silicate [39] 9.4 7.4 60 444 6.95
((Ba,La)-tellurite) a
2.693 6.82 91 621 1.84
a Sample under study.
power. A higher excited state population with high emission cross
section enables to achieve high optical gain. Thus in the design of
high gain amplifiers the product of emission cross section and
excited state lifetime (s et) is very important and is found to be
threshold pump power [40,41], The set value obtained for the
present glass composition is listed in Table 4 along with other
glass compositions, indicating that high gain could be achieved in
the present glass.
In analyzing the amplifier performance for broadband applications
gain cross section is an important parameter. By measuring
the absorption and emission cross sections using standard procedure
[11] one can simulate the gain spectrum using the
expression
sg ¼ Nse ð1 NÞsa, ð3Þ
where sa is the absorption cross section, se is the emission cross
section and N is the fractional population inversion in the
emitting level. The calculated gain spectra for different population
inversions shown in Fig. 6 indicate that the gain increases with
the population inversion and positive gain in the system can be
achieved only for a population inversion of 20% and above. It is
interesting to notice from Fig. 6 that even for a 20% of population
a flat gain was observed in the L-band side and further increase in
the population 50–60% a better gain was observed both in the S
and L band regions. Moreover, the obtained gain spectrum spread
from 1440 nm to 1650 nm with a spectral width of over 210 nm.
3.4. Non-radiative processes and internal quantum yield
A quantitative way of measuring the internal quantum yield
for a particular emission band is done through the fluorescence
lifetime measurements. Non-radiative processes such as multiphonon
relaxation, vibrational losses by hydroxyl and other
functional groups and energy transfer interaction quench the
fluorescence intensity and the efficiency. The observed lifetime
M. Pokhrel et al. / Journal of Luminescence 132 (2012) 1910–1916
Gain corss section, σ g (10 -20 cm 2 )
0.5
0.0
-0.5
1450 1500 1550 1600 1650
Wavelength (nm)
of the emission can be written as [42]
Ν =0
Ν =10
Ν =20
Ν =30
Ν =40
Ν =50
Ν =60
Ν =70
Ν =80
Ν =90
Ν =100
Fig. 6. Gain cross section spectrum for the 4 I13/2- 4 I15/2 transition showing the
possible spectral width and peak gain cross section. The spectrum was simulated
for different population inversion P.
1
¼ AradþWmp þWOH þWET, ð4Þ
tlum where A rad, W mp, W HO, W ET are the radiative transition rate,
transition rate from multiphonon relaxation, hydroxyl groups
and energy transfer interactions, respectively. The contribution
to non-radiative decay comes from multiphonon relaxation from
the host and energy transfer interaction between nearby ions. The
transition probability by energy transfer depends on the distance
between the donor (D) and acceptor (A) ions, R DA, and hence
depends on the concentration of the ions. When the ions are
homogeneously distributed in the matrix, the energy transfer