SITE-SELECTIVE MEASUREMENTS OF (4)G(5 2),(2)G(7/2) NONRADIATIVE RELAXATION RATE IN ND-SRF2, ND-LA-SRF2, AND ND-SR-LAF3 LASER CRYSTALS/

The results of measurements of the multiphonon relaxation rates of the (4)G(5/2); (2)G(7/2) manifold of the Nd3+ optical centers in cubic Sr F2 : Nd3+ and mixed (1 - x)SrF2 : xLaF(3) : Nd fluoride crystals by di rect laser-selective-excitation and selective fluorescence kinetics de cay registration are presented. The low-temperature (T= 77 K) multipho non relaxation rate of the tetragonal L-center (Nd-Sr(3+)-F-i) in SrF2 : NdF3 (0.75 wt%) tau(meas) = 5.2 ns) with a strong crystal field is found to be six times faster than in rhombic symmetry pair M' (Nd-Sr; La-Sr[F-i](2)) optical center in SrF2 : LaF3(1.96 wt %) : NdF3(0.62 wt %) (tau approximate to 32.0 ns) with a weak crystal field. Thus, the correlation between the values of the crystal fields parameters and th e total Stark splitting of the manifolds participating in the transiti on on the one hand and multiphonon relaxation rate on the other hand w as detected, which is in a qualitative agreement with the existing the ory of multiphonon relaxation. The nonradiative lifetime of the (4)G(5 /2); (2)G(7/2) multiplet of the pair M-center (Nd-Sr-F-i)(2) in the Sr F2 : NdF3 (0.75 wt %) crystal was found to be 13 ns, which is 2.5 time s shorter than in the M'-center. The fast nonradiative energy transfer between Nd3+ ions in the Nd --> Nd pair is most likely to be the reas on of the strong lifetime reduction.