Effect of a CdO coating on the degradation of a ZnS thin film phosphor material

A ZnS:Cu,Au,Al phosphor film coated with CdO was subjected to an electron beam with a beam energy and a current density of 2 keV and 16.1 mA/cm2, respectively, in an O2 ambient of 5×10−7 Torr. Auger electron spectroscopy (AES) and cathodoluminescence (CL), both excited by the same electron beam were used to monitor changes in surface composition and luminous intensity during electron bombardment. Both Cd and S were depleted from the surface after adventitious C was removed from the surface. The surface reactions were electron beam-stimulated. CdO was reduced by an electron beam-assisted mechanism in the presence of non-reducible ZnO, as Zn from the underlying ZnS layer emerged to the surface, in the CdO–ZnO system. The CL intensity degradation of the coated film showed a dependence on the surface composition. The intensity remained constant until Cd was reduced on the surface before a slight decrease was observed. The effect of the CdO capping layer on the intensity of the phosphor was evident until CdO eventually disintegrated.