Resonant processes causing photon multiplication in CaSO4:Tb3+

The emission spectra of single and polyterbium centers have been measured at the excitation of CaSO4:Tb3+ phosphors with different charge compensators (Na+, calcium vacancies, etc.) by 3.8–35 eV photons or 5 and 300 keV electrons at 6–300 K. The possible mechanisms providing quantum yield above unity for green (5D4 → 7FJ) and blue emission (5D3 → 7FJ) of Tb3+ at the direct intracenter excitation, excitation of oxyanions or creation of hot (nonrelaxed) electrons and holes have been discussed. On the basis of thermally stimulated luminescence at 6–600 K, the peculiarities of the hopping diffusion of relaxed electrons and holes and their tentative low-temperature self-trapping have been considered. -- Highlights: ► One-, two- and three-terbium luminescence centers in CaSO4 are studied at 6–300 K. ► Resonant cooperative transitions in two-three Tb3+ centers are revealed. ► Manifestations of a hopping diffusion of relaxed electrons and holes are considered. ► The possibility of low-temperature self-trapping of carriers in CaSO4 is discussed