Optical spectra, energy levels, and crystal-field analysis of tripositive rare-earth ions in Y2O3. II. Non-Kramers ions in C2 sites

Abstract

Optical absorption and fluorescence spectra of the non‐Kramers ions Pr³⁺, Tb³⁺, and Ho³⁺ in the C₂ sites of Y₂O₃ are reported. A crystal‐field analysis of these data and previously reported data for Eu³⁺ and Tm³⁺ is performed that is based on a Hamiltonian of C₂ point‐group symmetry, including J‐mixing effects. A best‐fit analysis is performed for all five ions; resulting rms deviations between calculated and experimental levels range from 2.8 to 26.4 cm⁻¹. Results of this analysis and of our previous analysis of Kramers ions in C₂ sites are used to obtain a set of phenomenological crystal‐field components A_km for the C₂ sites. We predict the crystal‐field splittings for Pm³⁺ in Y₂O₃, and we compare our previous prediction of the splittings of Gd³⁺ in Y₂O₃ with recently reported measurements. We also describe an effective point‐charge model for the Y₂O₃ lattice in which good agreement between calculated and phenomenological A_km is obtained with q_Y1 = 2.53, q_Y2 = 1.26, and q₀ = −1.052. (The quantities q_Y1, q_Y2, and q₀, are, respectively, the charges on the C_3i yttrium site, the C₂ yttrium site, and the oxygen site, in units of e.) With this model, we calculate A_km for the C_3i sites.