Relation Between Photoconduction and Luminescence in Zinc Sulphide

Abstract

A LARGE part of the studies on the afterglow or phosphorescence of solids has been made on zinc sulphide activated by copper (ZnS–Cu). Most of the theories of phosphorescence of ZnS–Cu have been based on the assumption that, when light is absorbed by the phosphor, electrons are freed from the luminescence centres and wander about the crystal. These free electrons may then be captured by traps, where they may spend appreciable time before they are freed by thermal energy, and may, then, either be retrapped, or are recaptured directly by empty luminescence centres, thus producing luminescence. The time the electron spends in the trap corresponds to the time delay of emission in phosphorescence.