LAUSR

Abstract The nature of intrinsic emission and the formation mechanisms of electron-hole trapping centers in a CaSO4 crystal irradiated by UV photons (4.9–11 eV) over a wide temperature range from 15 to 300 K are investigated by vacuum-ultraviolet and thermoactivated spectroscopy. It is shown that the emission of 4.3 eV, 3.64 eV and 3.8 eV are produced by recombination of electrons from the s states of the conduction band with various nonequivalently located S O 4 − - centers near top of the valence band of the CaSO4 crystal. Long-wavelength emission at 3.0–3.1 eV, 2.6–2.7 eV, 2.2–2.4 eV, and 1.7–2.0 eV is connected to electronic transitions on the trapping centers. The trapping centers are created when electrons and holes are localized on anionic complexes or during the decay of excited anionic complexes.