Luminescence Spectra of Europium Chalcogenides: EuO, EuS, and EuSe

Electron-beam-excited luminescence spectra for EuO, EuS, and EuSe show a series of broad and sharp peaks in the energy range from 1 to 4 eV at temperatures between 12 and 300^∘{}K. The low-energy broad peaks, corresponding to 4f⁷-4f⁶5d transition, exhibit a redshift, having energies lower than the optical absorption peaks due to a Franck-Condon-like effect. At higher energies, we have observed a series of sharp peaks arising from intra-atomic transitions within the $4f$ configuration in the Eu ions.