Degradation of ZnSFED phosphors

The degradation of cathodoluminescent brightness under prolonged electron b eam excitation of phosphors has been identified as one of the outstanding c ritical issues for the flat-panel field emission industries. The ZnS : Cu,A l,Au phosphor powders have been subjected to electron beam bombardment of 2 keV with different electron beam current densities (2.5-88 mA cm(-2)) at a n oxygen pressure of 1 x 10(-6) Torr, Auger electron spectroscopy (AES) and cathodoluminescence, both excited by the same electron beam, were used to monitor changes in surface composition and luminous efficiency during elect ron bombardment. Degradation was manifested by a non-luminescent ZnO layer that formed on the surface of the phosphor according to electron-stimulated surface chemical reaction (ESSCR). Lower current densities lead to a highe r surface reaction rate, due to a lower local temperature beneath the beam, which resulted in more severe cathodoluminescence degradation. A lower tem perature beneath the electron beam may lead to an increase in the surface r eaction rate due to the longer time spent by the adsorbed molecules on the surface, with a direct increase in the ESSCR probability. Copyright (C) 200 0 John Wiley & Sons, Ltd.