Behavior of Excited Electrons and Holes in Zinc Sulfide Phosphors

The luminescent properties of silver and copper activated ZnS phosphors have been investigated at room and liquid air temperatures using uv, blue light, and $\beta$-ray excitation. In many cases it was found that the deficiency area was considerably smaller than the glow curve area, especially for $\beta$-ray excitation of ZnS: Cu. This is explained by the hole production causing quenching during $\beta$-ray excitation, while during the glow curve the smaller amount of holes produced causes a much smaller amount of quenching. However, even with blue light where excitation does not directly produce holes, the deficiency area is smaller than the glow curve area. The effects of infrared radiation on the fluorescence, phosphorescence, and glow curve has been investigated, and the quenching and stimulation at room and liquid air temperature reported. For ZnS: Cu the long wavelength infrared band (∼12 000 A) produces quenching at room temperature but only stimulation at low temperature. A determination of trap density from the glow curves shows ∼${10}^{17}$/${\mathrm{cm}}^3$ for ZnS: Cu and ∼${10}^{16}$/${\mathrm{cm}}^3$ for ZnS: Ag at liquid air temperatures. Finally, a theoretical discussion of the possible transition mechanisms giving rise to these effects is given.