Resonant processes causing photon multiplication in CaSO4:Tb3+

► 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.