A review on ZnS phosphor degradation

Abstract

Standard ZnS cathodoluminescent phosphors normally lose brightness upon bombardment with electron beams. The main reason for the degradation is the formation of a non-luminescent “dead layer” on the surface due to the electron stimulated surface chemical reaction (ESSCR) mechanism. The decrease in luminance was found to be a result of the growth of the “dead layer”. Calculations showed that the thickness of the oxide layer that formed during electron bombardment, cannot completely explain the magnitude of the decline of the CL intensity. Iso-electronic point defects due to the presence of oxygen that diffuse into the ZnS matrix at the interface further contribute to the degradation. When the ZnS phosphor powder was exposed to the electron beam in a water-rich O2 ambient, a chemically-limited ZnO layer was formed on the surface. A layer of ZnSO4 was formed on the surface during the electron beam degradation of the ZnS phosphor powder in a dry O2 ambient. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)