Photoelectronic Processes in ZnS Single Crystals

Abstract

A simultaneous series of luminescence and photoelectronic measurements as a function of excitation energy, intensity, and temperature were made on ZnS:Cu:Cl single crystals grown by a chemical-transport method. Hall-effect measurements show that the charge carriers under steady-state excitation are electrons, and optical quenching of thermally stimulated luminescence and conductivity is found to be identical with steady-state optical quenching. Various models, such as those of Lambe and Klick, Klasens and Schön, Williams and Prener, and those involving unassociated pair transitions, are examined in view of all the evidence available, including the present measurements. It is concluded that a basic Klasens-Schön model is the most suitable. The measurements also show that the centers responsible for long photoconductivity lifetimes, i.e., the sensitizing centers, are not the same as the centers responsible for luminescence, i.e., luminescence-activator centers. Similar results are indicated in less detailed studies of ZnS:Cl and ZnS:Ag:Cl single crystals.