A comparative study between the simulated and measured cathodoluminescence generated in ZnS:Cu, Al, Au phosphor powder

ZnS:Cu, Al, Au (P22G) phosphor powder has been subjected to 2 keV electron bombardment at an oxygen pressure of 1×10−6 Torr. Auger electron spectroscopy (AES) and cathodoluminescence (CL), both excited by the same electron beam were used to monitor changes in the surface composition and luminescent properties of the P22G phosphor during electron bombardment. It was found that the CL intensity of the P22G phosphor was degraded to 63% of the original intensity due to a 2.8 nm thick non-luminescent ZnO layer that formed on the surface during prolonged electron bombardment. Monte Carlo calculations were used to simulate the effect of the ZnO layer on the CL intensity. By comparing the experimental and simulation results, it is predicted that a diffusion interface forms between the ZnO layer and the ZnS bulk that broadens during the degradation process. Due to the formation of defects and the dissociation of the ZnS at the diffusion interface the region is non-luminescent. The simulations also pointed out that the use of a high efficient ZnS thin film is more preferable to the use of phosphor powders, because all the electrons bombard the surface at normal incidence minimising the effect of the ZnO layer. The light outcoupling is, however, worse in thin films, in which the effects of light trapping are still important and non-negligible.