Temperature Dependence of the Crystal-Field Splittings in Gd³⁺:CaWO₄

Abstract

The spin-Hamiltonian parameters for Gd 3+ in CaWO 4 have been measured by the method of electron spin resonance at a number of temperatures between 4.2 °K and 300 °K. The results at 78 °K are in agreement with previous measurements by Hempstead and Bowers.The variations in the crystal-field parameters are interpreted in terms of a limiting low temperature value and a normalized slope at the Debye temperature for each parameter. These quantities are compared with the corresponding quantities for Eu 2+ in CaWO 4 and, in the case of the fourth-order parameters, for Eu 2+ and Gd 3+ in cubic CaF 2 , SrF 2 , and BaF 2 . We conclude that the second- and fourth-order splittings each arise from at least three competing mechanisms and that these include a dependence on the amplitude of lattice vibrations. In the case of the trivalent ion, Coulomb forces are also considered to be important.