The difference in degradation behaviour of ZnS : Cu,Al,Au and ZnS : Ag,Cl phosphor powders

Auger electron spectroscopy (AES) and cathodoluminescence (CL) measurements showed that surface reactions with the consequent loss of CL intensity occ ur for both the ZnS:Cu,Al,Au and ZnS:Ag,Cl phosphor powders during prolonge d electron bombardment. Although ZnO layers formed on both the ZnS phosphor surfaces there is a difference between the degradation behaviour of these two phosphors. Surface charging occurs during electron bombardment of the a ged ZnS:Ag,Cl phosphor due to the formation of a non-conductive ZnO surface layer. Charging of the ZnS:Ag,Cl phosphor resulted in a delay in the surfa ce reactions and to an increase in the CL degradation rate due to band-bend ing. A much slower degradation in CL intensity was measured for ZnS:Cu,Al,A u, where no charging occurred. (C) 1999 Elsevier Science B.V. All rights re served.