DEGRADATION OF ZINC-SULFIDE PHOSPHORS UNDER ELECTRON-BOMBARDMENT

ZnS phosphor powders have been subjected to electron bombardment (2 ke V, 2 mA/cm(2)) at a residual gas pressure of 1.2x10(-8) Torr and oxyge n pressures of 10(-6) Torr. Auger electron spectroscopy and cathodolum inescence (CL), both excited by the same electron beam were used to mo nitor changes in surface state and luminous efficiency during electron bombardment. A direct correlation between the surface reactions and t he degradation of CL brightness was observed. Both C and S were deplet ed from the surface during electron bombardment. The postulated mechan ism for the electron stimulated reactions on the phosphor surface is e lectron beam dissociation of molecular species to atomic species which subsequently react with C to form volatile compounds (COx, CH4, etc.) and with ZnS to form a nonluminescence layer of either ZnO or ZnSO4. The growth in thickness of the nonluminescence surface layer is direct ly responsible for the degradation in CL brightness. (C) 1996 American Vacuum Society.