Spectroscopy of traps by fractional glow technique

Abstract

A method is presented and applied which permits determination of trap depths with greater accuracy than is obtainable from a normal glow curve when the different groups of traps are not well separated in energy or are continuously distributed. Moreover, it gives better resolving power and does not require knowledge of the frequency factors and retrapping probabilities. The method is based on a demonstration that it is possible to determine the average depth of those traps which are preferentially emptied at any time in the course of the glow curve if a large number of small temperature oscillations is superposed on the uniform warming (‘fractional glow technique’). The method has been demonstrated by studying the trap spectra of some ZnS phosphors. ZnS:Cu,Ga and ZnS:Cu,In show a strong and narrow group of traps at 0.26 and 0.34 eV respectively (along with other weaker traps and a continuous background). ZnS:Cu,Cl phosphors show a broad trap distribution between 0.1 and 0.3 eV, with a distinct substructure not indicated in the normal glow curve. Some striking deviations from normal phosphor behavior are described and partially interpreted.