Crystal fields and local lattice distortions in some tetragonal symmetry centers in fluorite crystals doped with trivalent rare-earth ions

Abstract

A semiempirical procedure was developed, within the framework of a modified electrostatic effective charge model, that links crystal field parameters with microscopic local structures of tetragonal symmetry centers in fluorite crystals doped with trivalent rare-earth ions. The procedure was used to study tetragonal centers in Er3+:CaF2, Dy3+:CaF2, and Eu3+:SrF2 systems. It is shown that satisfactory a priori predictions of experimentally observed energy level schemes of the spectra of interest, as well as reconstructions of local microscopic structures of the emitting centers in accord with other relevant information collected up to date, are thus obtained. An examination is also made of a spectrum that in the past was linked to a tetragonal center in the Eu3+:CdF2 system, and the results obtained indicate that it appears to be associated with a center (or centers) that is structurally different from the tetragonal centers present in the other rare-earth: fluorite systems.