Charge fluctuations and local-environment dependence of the energy of the 4f virtual localized level of Eu in EuxLa1-xRh2

The recoilless-absorption spectra of the 21.6-keV rays of Eu151 in EuxLa1-xRh2 are composed of a few lines which exhibit strongly temperature-dependent isomer shifts. The results are interpreted in terms of fast fluctuations of electrons between a localized 4f level and the conduction band. The energy released by removing an electron from the 4f level to the conduction band (0.01-0.1 eV) depends significantly on the number of La nearest neighbors. The levels have a width of 0.01 eV.