Comparison of 4f² energy parameters for Pr³⁺ in cubic elpasolite crystals

Abstract

Energy level data recently reported for the Cs₂NaPrCl₆, Cs₂NaYCl₆:Pr³⁺, and Cs₂NaYBr₆:Pr³⁺ systems are analysed in terms of a model hamiltonian that includes 14 ‘free-ion’ energy parameters and either two or four crystal-field energy parameters. Only one-electron crystal-field interactions are represented in the two-parameter crystal-field model, whereas the four-parameter model includes some (partial) consideration of two-electron crystal-field effects. Both crystal-field models assume octahedral (O_h ) site symmetry for the Pr³⁺ ions. The empirical energy level data for the respective systems are reasonably well fitted by calculations in which either nine or eleven of the parameters in the model hamiltonian are allowed to freely vary. Comparisons of the parameter values obtained from these data fits reveal significant differences in the crystal-field perturbations experienced by the 4f electrons of Pr³⁺ in Cs₂NaPrCl₆, Cs₂NaYCl₆:Pr³⁺, and Cs₂NaYBr₆:Pr³⁺. These perturbations are strongest in Cs₂NaYCl₆:Pr³⁺ and weakest in Cs₂NaYBr₆:Pr³⁺. ‘Intrinsic’ crystal-field parameters are derived for each system, and the values of these parameters are compared to those reported previously for LaCl₃:Pr³⁺. Spin-correlated crystal-field (SCCF) parameters are reported for the Cs₂NaPrCl₆ and Cs₂NaYCl₆:Pr³⁺ systems.