Determination of the probability of relaxation of the population of the 4I11/2 level of neodymium ions from luminescence dumping in a small external sample

An improved method was developed for determining the probability W₂₁ of relaxation of the population of the ⁴I_11/2 level of neodymium ions. The relationship between W₂₁ degree of dumping, and parameters of the dumping pulses was obtained by solving the rate equations for the populations subject to an allowance for the Stark structure of the energy levels ⁴F_3/2 and ⁴I_11/2. At T=300°K the probability values were W₂₁=10⁸ sec^–1 for Y₃Al₅O₁₂:Nd³⁺ and W₂₁=1.5×10⁸ sec^–1 for La₂O₂S:Nd³⁺. In the case of a BaGd_2-xNd_x(MoO₄)₄ crystal at 77°K the probability was W₂₁=2.5×10⁸ sec^–1. The influence of Wn on the efficiency of utilization of the stored energy was found to depend on the energy gap between the lower Stark sublevel of the ⁴I_11/2 level and the final sublevel in the stimulated transitions.