Edge Emission in CdS Crystals that Show Mechanically Excited Emission

Abstract

The characteristic green fluorescence of CdS single crystals that exhibit mechanically excited emission has been examined spectroscopically at 4.2° and 77°K. The fluorescence of the crystals was stimulated by either ultraviolet irradiation, or the application of an electric field. The uv-stimulated and field-induced emission spectra are compared and discussed. The low-temperature behavior of the conductivity (storage properties) in these crystals is also discussed. The uv-stimulated edge emission peaks in these crystals differ from those in normal CdS; these differences are discussed and quantitative comparisons are made. A simple trapping model is applied to the uv-stimulated emission data at 77°K. On the basis of this model, the mean number of optical phonons cooperating in the optical transitions is shown to be higher than in normal CdS. The field emission, believed to be due to carrier injection, is explained on the basis of a previously proposed energy model of Warschauer and Reynolds for mechanically excited emission.