Dielectric relaxation and EPR studies of Gd3+-FI-dipoles in strontium and barium fluoride

Abstract

Dielectric relaxation measurements on SrF₂:Gd³⁺ show four absorption peaks. By correlation with EPR line broadening a relaxation (R_I) with activation energy 0.454 eV is associated with a tetragonal Gd³⁺ site, and a second (R_IV) with activation energy 0.64 eV is associated with a trigonal Gd³⁺ site. A two-shell model of ionic relaxation processes links R_I and R_IV but does not adequately account for the observed concentration dependence of the ratio of peak intensities and of the width of the R_IV peak, nor for small shifts between the relaxation frequency of the R_IV peak and the trigonal site. Two relaxations (R_II and R_III) with activation energies 0.38 eV and 0.14 eV are assigned to aggregates on the basis of their concentration dependence. In BaF₂:Gd³⁺ only two dielectric absorptions are found. One, with an activation energy 0.61 eV, is assigned to a trigonal Gd³⁺ site and the second, with activation energy 0.36 eV, is assigned to aggregates.