Selective excitation of activator centers in condensed media with inhomogeneous spectral line broadening

Neodymium (Nd³⁺) ions in mixed yttrofluorite crystals were excited by Y₃Al₅O₁₂:Nd³⁺ laser radiation. Luminescence spectra of these ions were recorded in 5x10^–6 sec after a delay time (relative to a short excitation pulse), which was varied within the range from 3×10^–5 to 2×10^–3sec. The spectra recorded during the initial stages of the decay of the ⁴F_3/2 metastable state were quite different from the spectra recorded under nonselective excitation conditions. The selectively excited spectra varied with time because of the migration of energy between metastable states but this migration was completed in a time of the order of 10^–3 sec at T = 300°K when the concentration of NdF₃ was 1 wt.%. The results indicated a correlation between the spectra of the energy levels of Nd³⁺ in yttrofluorite crystals and structural disorder.