Developments in Ceramic Materials Research

Optical Fluoride and Oxysulfide Ceramics: Preparation and Characterization 81
27) under pulsed copper vapor laser excitation at 511 nm (tp = 10 ns; f = 10 kHz) and a timecorrelated
single-photon counting detection technique. The time- resolved fluorescence
spectrum at the 4 G7/2→ 4 I13/2 transition is measured at room temperature for the La2O2S:Nd 3+
(1 wt%) optical ceramics with gate width tgate=79 ns and gate delay td=59 ns (curve 1 at
Figure 28) and for the Gd2O2S:Nd 3+ (0.5 wt%) optical ceramics these values are set to tgate =
40 ns and td= 39 ns (curve 2 at Figure 28) using the same technique and a special program of
our own for multichannel amplitude analyzer (MCA, EGandG Ortec) operation. The gate
delays are set to minimize the influence of a small fraction of the powerful pump radiation
passing through the monochromator and KS-11 glass filter. The decay times are measured at
the long time scale of fluorescence kinetics decay. The measured decay times (Table 2) are
determined by MR of the 4 G7/2→ 4 G5/2; 2 G7/2 transition, because a contribution of radiative
decay is negligible [52]. The MR rate of the 4 I11/2→ 4 I9/2 transition is of the order of magnitude
of the measured rate of the 4 G7/2→ 4 G5/2; 2 G7/2 transition. So, the depletion of the low laser
level is not slower than several hundred nanoseconds.
Photon counts
10 1
10 0
10 -1
10 -2
10 -3
10 -4
4
G7/2 level
T=77 K
3
1 La2O2S:Nd 3+ τ=75 ns
2Gd2O2S:Nd 3+ τ=27 ns
3 set-up response function τ=12 ns
0 100 200 300 400 500 600
2
time, ns
Figure 27. Fluorescence kinetics of the 4 G 7/2 manifold in La 2O 2S:Nd 3+ (1 wt%)—1, Gd 2O 2S:Nd 3+
(0.5 wt%)−2 at 77 K under 511 nm excitation detected at the 4 G 7/2 → 4 I 13/2 transition and the set- up
response function—3.
Table 2. The measured and multiphonon relaxation decay times for the 4 G7/2 level of
Nd 3+ in optical ceramics with low-phonon spectra at 77 K and room temperature and
parameters having influence on multiphonon transition rate
Optical
samples
ΔEmin (cm −1 ) ωmax pmin τmeas = τMR at 77 K (ns)
La2O2S:Nd 3+ 1517 400 4 75 38
Gd2O2S:Nd 3+ 1500 440 4 27 19
1
τmeas = τ MR at 300 K
(ns)