Analysis of the electron excitation spectra in heavy rare earth metals, hydrides and oxides

The energy loss spectra of 75keV electrons transmitted through thin evaporated foils of heavy rare earths (Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in three different chemical states (metal, hydride and oxide) exhibit two main peaks due to collective ''plasmon'' excitations in the 10-17eV energy range and to inner 5p excitations between 30 and 40eV. A quantitative analysis of the intensity spectral distribution allows one to calculate the energy loss function and, through a Kramers-Kroenig inversion, the dielectric constant and the dipole oscillator strength. Various results are then explained in terms of band structure, so that we are lead to propose a simple model for the interband transitions occuring in oxides