Effect of Infrared Irradiation on ZnS: Cu Phosphors

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Abstract
Infrared stimulation and quenching of ZnS: Cu phosphors are studied as a function of trap population. It is found that stimulation at low temperature increases linearly with the concentration of ionized activators and disappears when the shallowest traps are emptied. Quenching increases as the product of the concentrations of ionized activators and trapped electrons. From these results it is concluded that the main action of infrared on these phosphors is a shifting of holes to levels of higher recombination rate. This model accounts quantitatively for the dependence of stimulation and quenching on the state of excitation. It is strongly supported by infrared effects on the glow and photoconductivity and the similarity of the wave-length dependence of stimulation and quenching. Thus the light stimulation observed under infrared irradiation is not due to the usual assumption of a direct release of trapped electrons by infrared, but rather to a shifting of holes to levels of higher recombination rate.