THE INFLUENCE OF RESIDUAL-GAS PRESSURES ON THE DEGRADATION OF ZNS POWDER PHOSPHORS

Phosphor powder of ZnS:Cu,Al,Au has been subjected to electron bombard ment (2 keV, 2 mA/cm(2)) in residual gas pressures ranging from 0.6X 1 0(-8) to 7.0X 10(-8) Torr. Auger electron spectroscopy and cathodolumi nescence (CL), both excited by the same electron beam, were used to mo nitor changes in the surface chemistry and cathodoluminescent brightne ss versus vacuum conditions during electron bombardment. A direct corr elation between the surface reactions and the degradation of CL bright ness was observed. The formation of a nonluminescent ZnO layer on the surface of the phosphor was largely responsible for the degradation of the ZnS. The aging of the phosphor was not only a function of the cha rge per unit area (Coulomb dose) bombarding the surface, but also a fu nction of residual gas pressure and composition. In particular, H2O ha d the greatest effect on the rate of degradation. The results are inte rpreted in terms of an electron-beam stimulated surface chemical react ion. (C) 1998 American Institute of Physics.