ZNS-CU,AL,AU PHOSPHOR DEGRADATION UNDER ELECTRON-EXCITATION

ZnS:Cu,Al,Au phosphor powder has been subjected to 2 keV electron bomb ardment at an oxygen pressure of 1 X 10(-6) Torr. Auger electron spect roscopy (AES) and cathodoluminescence (CL), both excited by the same e lectron beam were used to monitor changes in the surface composition a nd luminous efficiency during electron bombardment. It was found that the phosphor surface degrades during prolonged electron bombardment. T he chemical state of the surface before and after degradation was dete rmined by X-ray photoelectron spectroscopy (XPS). A residual gas analy ser was used to detect the volatile compounds coming from the surface during electron bombardment. It is shown that the electron beam stimul ates the molecular oxygen into atomic species, which react with the Zn S to form ZnO and volatile SO2 with the consequent loss of CL intensit y. The growth of a non-luminescent ZnO surface layer is one reason lea ding to the degradation in CL intensity. (C) 1997 Elsevier Science B.V .