A comparison of the degradation mechanisms in ZnS and Y2O2S:Eu powder FED phosphors

The degradation of Y2O2S:Eu phosphor powders was studied using Auger electron spectroscopy (AES) and cathodoluminescence (CL). The phosphors were exposed to electron bombardment (2 keV, 2 mA/cm2) at residual background gas pressures from 2 × 10−8 to 10 × 10−8 Torr. The results indicate that the degradation is due to electron‐stimulated surface reactions caused by electron‐beam dissociation of molecular species at the phosphor surface. AES data show that the surface was initially contaminated by C‐containing impurities, and that both C and S were depleted during electron bombardment. Increased rates of depletion of C and S were observed for higher pressures, suggesting that the concentration of molecular species on the phosphor surface was limiting the rate of reaction and removal of C and S. Quantification of the AES results and inspection of CL spectrum suggest that the surface was converted to a non‐activated Y2O3. Comparison of the degradation of Y2O2S:Eu and ZnS:X (X = Ag, Cl or X = Al, Au, Cu) showed that ZnS phosphors were more susceptible to degradation caused by surface changes induced by electron‐beam bombardment. The degradation rate of the ZnS phosphors was approximately 3 times faster than the Y2O2S:Eu.