Measurement and simulation of the energy levels of R=Pr3+ and Nd3+ in GaRGe2O7

The optical absorption spectra of GaRGe2O7, R=Pr, Nd, have been measured, o n polycrystalline powders, at 9 K. These compounds are monoclinic, space gr oup P2(1)/c, and in them R3+ occupies a Single crystallographic position wi th C-1 point symmetry. From the crystal field analysis of the spectra, ener gy 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-held paramete rs from the crystal structure. The fitting of experimental Stark level ener gies and the phenomenological calculation of crystal-field parameters were performed for the approximate C-s(C-2) symmetry. Very satisfactory correlat ions were obtained between calculated and experimental levels, with root me an square deviations sigma=14.1 and 15.7, respectively, and despite the ver y low symmetry of R3+ in the matrix, the similarity of both sets of crystal -field parameters indicates the consistence of these calculations. (C) 2000 Elsevier Science S.A. All rights reserved.