The Effect of Pressure on the Luminescence of ZnS and ZnxCd1-xS Doped with Cu+, Cl-, and Al3

Photoluminescence measurements as a function of pressure were made on ZnS and ZnxCd1-xS (x = 0.937) samples doped with Cu+, Cl-, and Al3+. A limited amount of thermoluminescence and optical absorption data aided in the interpretation. In contrast to the ZnS:Cu:Cl studied earlier, these materials were light yellow in color and could be excited by the 442-nm as well as the 325-nm line of a He-Cd laser. When excited by the 325-nm line into the conduction band the emission peaks shifted to higher energy at a rate which could be related to the increase of the energy gap with pressure? Optical absorption data combined with the excitation spectra of Hoshina and Kawai demonstrated that for the ZnxCd1-xS phosphor 442-nm excitation was via an exciton band apparently pinned to the conduction band. For ZnS the 442-nm excitation was from a complex acceptor band to the conduction band. The peak shift with pressure indicated that the upper states of this band were no longer pinned to the valence band.