On the nature of the modification of luminescence spectra of alkaline-earth sulphides doped with cerium in the case of X-ray excitation

The luminescence spectra of CaS and SrS (as well as their solid solutions Ca 1-x Sr x S) doped with cerium have been measured under excitation by X-ray tube and X-ray synchrotron radiation. The comparison of these spectra with those of photoluminescence has revealed two types of radiation-induced Ce 3+ emission centre. We suppose that the first type is an activator ion displaced from the regular site as a result of the Coulomb interaction with charged defects (trapped electrons and holes) created in its neighbourhood by the excitation in the fundamental absorption range, whereas the second type is probably due to the creation, by X-ray exciting radiation, of sulphur vacancies in the first coordination shell of Ce 3+ .