High-energy emission band nature in ZnS-type phosphors activated with silver and chlorine

The cathodoluminescence emission spectra of cubic blue-emitting ZnS:Ag, Cl, hexagonal green-emitting (Zn_0.675, Cd_0.325) S:Ag, Cl as well as hexagonal red-emitting (Zn_0.27, Cd_0.73) S:Ag, Cl phosphors have been measured at 293, 77 and 4.2 K. The measured spectra of the phosphors exhibited a single broad emission band at 293 K, while they had two emission bands at 77 and 4.2 K. The two emission bands shifted to a lower energy with increase of their corresponding half-widths as the temperature at which the spectra were measured was raised. The time-resolved emission spectra measured showed that the low-energy band also shifted in the lower energy direction during the decay of luminescence, confirming its donor-acceptor (DA) transition nature. The high-energy band decayed faster than the low-energy one and no energy shift occurred during its decay; it was attributed to donor-isoelectronic pair (DI) transition. The lifetimes of 0.625 and 4.2 µsec were estimated for high- and low-energy bands, respectively, in the emission spectra of ZnS:Ag, Cl at 4.2 K.