Crystal-Field Splitting of Trivalent Thulium and Erbium J Levels in Yttrium Oxide

Abstract

The optical absorption and fluorescence spectra of trivalent thulium in single crystals of yttrium oxide and the absorption spectrum of pure thulium oxide, are investigated. All the 4f¹² electronic energy levels except the ¹S₀ level are identified. The three Slater F_k parameters and the spin—orbit parameter ζ, giving the best over‐all agreement between the observed spectrum and the calculated spectrum are: F₂=446.70 cm^—1, F₄=70.491 cm^—1, F₆=7.534 cm^—1, and ζ=2617 cm^—1. A detailed crystalline‐field splitting perturbation calculation is carried out for trivalent thulium and trivalent erbium ions in the C₂ sites of the Y₂O₃ lattice. The predicted crystalline‐field splitting for these ions is compared with the thulium data reported in this paper and with the erbium data reported earlier. The average deviations between the predicted and the observed splittings for 71 crystalline Stark levels in the Tm³⁺ spectrum and 65 levels in the Er³⁺ spectrum, are 13 and 11 cm^—1, respectively.