Far-infrared spectra of Strontium Fluoride doped with rare earth

Far-infrared measurements (17–170 cm⁻¹) are reported for SrF₂:RE³⁺ (RE = Pr, Nd, Tb, Dy, Ho, Er, Tm).The vibrations of the F⁻_i compensation ions reveal the local symmetry (Oh, C_4v, C_3v). The concentration of ions in each local site and the frequencies of the F⁻_i vibrations in the C_4v site show a regular evolution vs RE ionic radii.The study of electronic transitions within the ground manifold of the RE ions shows a similar evolution. For Dy³⁺ we detect lines already attributed to C_3v (F⁻_i) sites. New lines observed with Er³⁺ and Dy³⁺ can be attributed to C_4v (F⁻_i) sites, and the crystal field parameters that we have calculated are close to those of the C_4v (F⁻_i) site in CaF₂.For Nd³⁺ the electronic line is close to a C_4v level observed by EPR.