Fluorescence quenching of the Nd 3+ ions in different optical centers in fluorite-type crystals

Abstract

The results of measurements of fast nonradiative relaxation rates from the strongly quenched 4G 5 2 ; 2G 7 2 multiplet of the Nd 3+ ion in the LiYF 4 crystal and in the fluorite-type crystals (CaF 2 : NdF 3(0.6%), CaF 2: NdF 3(0.25%): LaF 3(0.25%) and CaF 2: NdF 3(0.25%): CeF 3(0.25%)) with different Nd 3+ optical centers by direct laser-selective-excitation and selective fluorescence kinetics decay measurements are presented. The multiphonon relaxation time of 4G 5 2 + 2G 7 2 multiplet of the Nd 3+ ion in the single-site LiYF 4 crystal ( τ = 4.5 ns); and in a multi-site CaF 2 crystal for a tetragonal symmetry the L-center ( τ L < 2.0 ns), for a rhombic symmetry pair (the M- and M′-centers) ( τ M = 5.2 ns and τ M′ = 7.1 ns, respectively), and the cross-relaxational energy transfer rate inside the Nd ∗ Nd pair in CaF 2 ( τ tr −1 = ( τ M −1 − τ M′ −1) −1 = 5.2 × 10 7 s −1) were measured. Comparison of the experimental multiphonon relaxation rates with the calculated ones by the nonlinear theory of multiphonon relaxation was done. The dependence of multiphonon relaxation rates on crystal matrix parameters is discussed. Comparison of the quenched energy transfer rate between two Nd 3+ ions at minimal distance for the 4G 5 2 ; 2G 7 2 multiplet in fluoride crystals was done. The fastest rate in CaF 2 ( W = 5.2 × 10 7 s −1) with R min = 0.386 nm and the slowest in LaF 3 ( W = 4.35 × 10 7 s −1) with R min = 0.410 nm were found. The analysis of the dominant mechanisms and possible channels of cross relaxation was made.