Photoluminescence properties of Cu+ centers in MgS, CaS, SrS and BrS

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.