Infrared-stimulated luminescence in ZnS grown by chemical vapor deposition

Abstract

When ZnS crystals that have been doped with nearly equal amounts of Cu activator and a coactivator are held at liquid-He temperature, they exhibit an enhancement of the normal uv-excited luminescent emission when illuminated with infrared radiation near 10 μm. A study of this effect in epitaxial films grown and doped with Cu and Cl by chemical vapor deposition (CVD) is presented. Measurements of the spectral dependence, the temperature dependence, and the time dependence of this effect are reported. The measurements indicate no fundamental difference between the effect in CVD-grown epitaxial films and bulk ZnS. At the same time, the spectral- and time-dependence measurements extend beyond previous results. The spectral-dependence measurements support the current model in terms of release of electron into the conduction band by the ir photons before the electrons decay. The time dependence results and an analysis of temperature effects deepen inconsistencies between the ir stimulation and the related ir absorption. A modification of the model in terms of two traps is proposed. With this modification, the model accounts qualitatively for all the observed effects.