J. A. Caird, A. J. Ramponi, and P. R. Staver, "Quantum efficiency and excited-state relaxation dynamics in neodymium-doped phosphate laser glasses," J. Opt. Soc. Am. B 8, 1391-1403 (1991)
Radiometrically calibrated spectroscopic techniques employing an integrating-sphere detection system have been used to determine the fluorescence quantum efficiencies for two commercially available Nd3+-doped phosphate laser glasses, LG-750 and LG-760. Quantum efficiencies and fluorescence lifetimes were measured for samples with various neodymium concentrations. It is shown that the effects of concentration quenching are accurately described when both resonant nonradiative excitation hopping (the Burshtein model) and annihilation by cross relaxation are accounted for by Förster–Dexter dipole–dipole energy-transfer theory. The Förster–Dexter critical range for nonradiative excitation hopping was found to be RDD = 11 Å, while the critical range for cross relaxation was close to RDA = 4 Å in these glasses. The quantum efficiency at low Nd3+ concentrations was (92 ± 5)%, implying a nonradiative relaxation rate of 210 ± 150 s−1 for isolated ions. Improved values for the radiative lifetimes and the stimulated emission cross sections for these glasses were also deduced from the measurements.
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Fraction of fluorescence photons reabsorbed in the sample (see Appendix A).
The 0.04-wt. % sample of LG-760 had a significantly higher level of water contamination evidenced by a 9-cm−1 absorption coefficient at 3.5 μm. This apparently caused the lower-than-expected quantum efficiency and fluorescence lifetime for this sample. The data for this sample have therefore been omitted from Fig. 6 and from further analysis of nonradiative decay rates.
Table 3
Radiative and Nonradiative Relaxation Rates for the R Level of Nd3+ in Samples of Neodymium-Doped LG-750 and LG-760 Phosphate Laser Glasses
The product of the measured fluorescence decay rate and the quantum efficiency does not seem to give accurate values for the radiative decay rate in the concentrated samples.
Strong water quenching suspected.
Table 4
Nonradiative Spectroscopic Parameters for Neodymium-Doped LG-750 and LG-760 Phosphate Laser Glasses
Parameter
Symbol
Units
LG-750
LG-760
Donor–donor critical transfer range
RDD
Å
11.14
11.37
Cross-relaxation critical range (donor–acceptor)
RDA
Å
4.07
3.52 (fit)
Zero-concentration nonradiative rate
W0
s−1
216 ± 150 (fit)
209 ± 150 (fit)
Donor–donor microparameter
CDD
10−39 cm6 s−1
4.62
5.55
Donor–acceptor microparameter
CDA
10−41 cm6 s−1
1.10
0.49
Tables (4)
Table 1
Radiative Spectroscopic Properties of Neodymium-Doped LG-750 and LG-760 Phosphate Laser Glasses
Fraction of fluorescence photons reabsorbed in the sample (see Appendix A).
The 0.04-wt. % sample of LG-760 had a significantly higher level of water contamination evidenced by a 9-cm−1 absorption coefficient at 3.5 μm. This apparently caused the lower-than-expected quantum efficiency and fluorescence lifetime for this sample. The data for this sample have therefore been omitted from Fig. 6 and from further analysis of nonradiative decay rates.
Table 3
Radiative and Nonradiative Relaxation Rates for the R Level of Nd3+ in Samples of Neodymium-Doped LG-750 and LG-760 Phosphate Laser Glasses
The product of the measured fluorescence decay rate and the quantum efficiency does not seem to give accurate values for the radiative decay rate in the concentrated samples.
Strong water quenching suspected.
Table 4
Nonradiative Spectroscopic Parameters for Neodymium-Doped LG-750 and LG-760 Phosphate Laser Glasses
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