Low temperature effect on the electron beam induced degradation of ZnS:Cu,Al,Au phosphor powders

Abstract

ZnS:Cu,Al,Au phosphor powders were bombarded by an electron beam of 2 keV with the current density of 8.7 mA/cm 2 at an oxygen pressure of 2×10 −6 Torr. The studies were carried out at temperatures between −125 and 25 °C. Auger electron spectroscopy (AES) and cathodoluminescence (CL) were used to monitor the changes in the surface chemistry of the phosphor and luminous efficiency during electron bombardment, respectively. Thermoluminescence (TL) glow curves produced by the phosphor warming up from −125 °C were also detected. Degradation was manifested by the non-luminescent ZnO layer that formed on the surface of the phosphor according to the electron stimulated surface chemical reaction (ESSCR) mechanism. A decrease in temperature lead to an increase in the surface stay time of the oxygen molecules on the surface with the increase in the ESSCR probability. The effect of thermal quenching of the initial CL was reduced at lower temperatures. The residual water vapour in the vacuum, however, had a significant effect on the rate of degradation because it was frozen at lower temperatures. The formation of O defects during electron bombardment, which act as electron traps, were confirmed through TL glow curves.