ZnS:Cu,Al,Au phosphor degradation under electron excitation

ZnS:Cu,Al,Au phosphor powder has been subjected to 2 keV electron bombardment at an oxygen pressure of 1 X 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 luminous efficiency during electron bombardment. It was found that the phosphor surface degrades during prolonged electron bombardment. The chemical state of the surface before and after degradation was determined by X-ray photoelectron spectroscopy (XPS). A residual gas analyser was used to detect the volatile compounds coming from the surface during electron bombardment. It is shown that the electron beam stimulates the molecular oxygen into atomic species, which react with the ZnS to form ZnO and volatile SO2 with the consequent loss of CL intensity. The growth of a non-luminescent ZnO surface layer is one reason leading to the degradation in CL intensity. (C) 1997 Elsevier Science B.V.