A Study of the Electron Traps in Zinc Sulfide Phosphor

Abstract

The thermoluminescence characteristics of a hexagonal zinc sulfide phosphor, copper activated, were measured as a function of the wavelength of the exciting light. The glow curve had maxima at 120, 220, and 280°K. It was found that the heights of these maxima at saturation varied with the wavelength of the exciting light, reaching the greatest values at 4270A for the 120°K maximum, 4400A for the 220°K maximum, and 4500A for the 280°K maximum. When the sample was irradiated with 4400A light for a definite time interval and then irradiated with monochromatic radiation of either shorter or longer wavelength for another time interval, it was found that the subsequently measured glow curve showed a decrease in the heights of the maxima from that with 4400A light alone. Since the glow curve can be interpreted as a process of emptying electrons from traps, the above results are interpreted to mean that light which is capable of filling the traps is also capable of stimulating electrons out of the traps. There is a long wavelength limit beyond which irradiation does not affect electrons present in traps. It is 0.7 micron for the trap represented by the 280°K maximum.