Abstract
The detailed emission and excitation spectra and the temperature dependence of the excitation efficiency are obtained for MgS:Cu+, CaS:Cu+, SrS:Cu+ and BaS:Cu+ at various temperatures between 16 and 293 K. In the excitation spectra of all the powder phosphors, two bands assigned to the intraionic transitions in the Cu+ ion are observed. The luminescence mechanism is explained by the isolated Cu+ ion model. The temperature dependence of the excitation efficiency suggests that the Cu+ ion in CaS, SrS and BaS occupies an off-center position of the sulfur octahedron.