Electron–hole and excitonic processes in CaSO4 doped with Gd3+, Tb3+ and Dy3+ luminescent ions

The spectra of cathodoluminescence and phosphorescence (T=6 K) as well as recombination thermostimulated luminescence of rare-earth centres (T=8–400 K) have been measured for CaSO4:Gd3+,Na+; CaSO4:Tb3+,Na+; CaSO4:Dy3+,Na+ and CaSO4:Gd3+,Dy3+,Na+ phosphors synthesized in Tartu. The tunnel luminescence and photo-stimulated (by 2–3 eV photons) luminescence of Gd3+ centers have been revealed. A comparison of the excitation spectra for fast and recombination emissions allowed to separate the processes of photoionization (hν>9.5 eV) and photoexcitation (hν=8–9 eV) of SO42− molecular oxyanions. In CaSO4:Dy3+,Gd3+,Na+ polydoped phosphors, thermoluminescence at 6–750 K has been studied.