Developments in Ceramic Materials Research

Optical Fluoride and Oxysulfide Ceramics: Preparation and Characterization 89
the microparameter of donor–donor interaction CDD is found to be 6.2×10 −38 cm 6 /s for
La2O2S:Nd 3+ at 300 K which is about one order of magnitude higher than that in the Nddoped
glasses. The boundary time tbound2 between the disordered Förster stage and the
migration-controlled stationary stage can be determined using the following equation:
The value of tbound2 was found to be 54.6 μs for La2O2S:Nd 3+ (1%) at T=300 K. The value
of CDD is found to be about 30 times larger than CDA which confirms a hopping model of
energy migration.
ln(I transfer (t))
0
-lg[-ln( I transfer (t) )]
2
1
0
1 2
La 2 O 2 S:Nd 3+ (1 w.%)
lg t
t 1/2 , μs 1/2
1 /2
a)
La 2 O 2 S:Nd 3+ (1 w.%)
γ=0.070 μs -1/2
CDA = 2.16*10 -39 cm 6 /s
-1
0 2 4 6 8 10
Figure 33. Nonradiative energy transfer kinetics from the 4 F 3/2 manifold of the Nd 3+ ion in the
La 2O 2S:Nd 3+ (1 wt%) ceramic samples at 300 K: −lg[−ln I(t)] as a function of lg t—a; and ln I(t) as a
function of t 1/2 —b.
b)
(9)