Developments in Ceramic Materials Research

82
Photon counts
300
250
200
150
100
50
T. T. Basiev, V. A. Demidenko, K. V. Dykel’skii et al.
2 Gd2O2S:Nd3+ 1 La 2O2S:Nd
(0.5 w%)
3+ (1%) 4G7/2 --> 4I13/2 T=300 K
0
640 650 660 670 680 690 700
λ, nm
Figure 28. Time-resolved fluorescence spectra of the 4 G 7/2→ 4 I 13/2 transition of Nd 3+ of La 2O 2S:Nd 3+
(1 wt%) with 79 ns time gate tgate and 59 ns gate delay t d — 1; and Gd 2O 2S:Nd 3+ (0.5 wt%) — t gate = 40
ns, td = 39 ns — 2 under 511 nm laser excitation at room temperature.
ENERGY TRANSFER IN OXYSULFIDE OPTICAL
CERAMICS [49]
The nonradiative energy transfer of electronic excitation energy in solid state laser
materials is one of the fundamental problems of solid state physics and quantum electronics,
and is of considerable applied interest. For example, the concentration quenching of
fluorescence emitted in transitions from the upper working laser level produces a reduction in
the quantum yield, a lifting of the laser threshold and an increase of dissipation heat.
In continual approximation and when W(Rmin) t 1 (W(Rmin) is the energy transfer rate
for the minimal distance between donor and acceptor) the nonexponential decay of donor
states is well described by the following expression [53] and [54]:
where 1/τ is the probability of intracenter decay, which is the sum of radiative decay (1/τR)
and multiphonon relaxation (1/τMR), γt 3/s describes the Forster kinetics of nonradiative energy
transfer from donor to the acceptor (quencher) in the absence of energy migration over the
donors, and is the nonradiative decay constant due to the migration of energy over the
donors to the acceptors.
For crystalline lattice even in the diluted case we have some order in the donor and
acceptor positions and a minimal distance between donor and acceptor RDA=Rmin is nonzero.
(1)