The Temperature Dependence of the Hyperfine Coupling Constant of Eu ++ (4f 7 ) in CaF 2 and SrF 2

The electron spin resonance of Eu ++ in SrF 2 have been studied from 4°K to 800°K. The experiment showed that the hyperfine coupling constant A decreased in magnitude by approximately 3.5% over that temperature range. The calculation of the temperature dependence of A is made by using the mechanism proposed by Šimánek and Orbach with the introduction of the “modified Debye temperature.” The contribution due to acoustic phonons and optical phonons are calculated separately, the theoretical prediction agrees well with the experimental values. The zero-point contribution to the hyperfine coupling constant is -1.73×10 -5 cm -1 and the hyperfine coupling constant in the “rigid lattice” at T =0°K is -34.42×10 -4 cm -1 .