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 occur for both the ZnS:Cu,Al,Au and ZnS:Ag,Cl phosphor powders during prolonged 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 aged 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 surface reactions and to an increase in the CL degradation rate due to band-bending. A much slower degradation in CL intensity was measured for ZnS:Cu,Al,Au, where no charging occurred. (C) 1999 Elsevier Science B.V. All rights reserved.