Measurement and simulation of the energy levels of R=Pr 3+ and Nd 3+ in GaRGe 2O 7

Abstract

The optical absorption spectra of GaRGe 2O 7, R=Pr, Nd, have been measured, on polycrystalline powders, at 9 K. These compounds are monoclinic, space group P2 1/c , and in them R 3+ occupies a single crystallographic position with C 1 point symmetry. From the crystal field analysis of the spectra, energy level schemes and an expression of the associated wavefunctions for the 4f 2 and 4f 3 configurations have been derived. The semi-empirical simple overlap model is used to calculate an initial set of crystal-field parameters from the crystal structure. The fitting of experimental Stark level energies and the phenomenological calculation of crystal-field parameters were performed for the approximate C s(C 2) symmetry. Very satisfactory correlations were obtained between calculated and experimental levels, with root mean square deviations σ=14.1 and 15.7, respectively, and despite the very low symmetry of R 3+ in the matrix, the similarity of both sets of crystal-field parameters indicates the consistence of these calculations.