The influence of residual gas pressures on the degradation of ZnS powder phosphors

Abstract

Phosphor powder of ZnS:Cu,Al,Au has been subjected to electron bombardment (2 keV, 2 mA/cm2) in residual gas pressures ranging from 0.6×10−8 to 7.0×10−8 Torr. Auger electron spectroscopy and cathodoluminescence (CL), both excited by the same electron beam, were used to monitor changes in the surface chemistry and cathodoluminescent brightness versus vacuum conditions during electron bombardment. A direct correlation between the surface reactions and the degradation of CL brightness was observed. The formation of a nonluminescent ZnO layer on the surface of the phosphor was largely responsible for the degradation of the ZnS. The aging of the phosphor was not only a function of the charge per unit area (Coulomb dose) bombarding the surface, but also a function of residual gas pressure and composition. In particular, H2O had the greatest effect on the rate of degradation. The results are interpreted in terms of an electron-beam stimulated surface chemical reaction.

A review on ZnS phosphor degradation

“…Sebastian, et al [8] and Swart, et al [9,10] collected extensive data from ZnS in both the film and powder form, both doped with activators such as Ag :Cl, Cu :Au :Al, or Mn. Their data support a model called the Electron Stimulated Surface Chemical Reactions (ESSCR) [11].…”

“…The surface reactions and degraded luminescence intensity resulting from the electron bombardment were monitored using Auger electron spectroscopy (AES) and cathodoluminescence spectroscopy (CL). The experimental details are described elsewhere [8][9][10][11][12][13].…”

Ionoluminescent response of several phosphor screens to keV ions of different masses

“…However, smoother degradation effects have been reported and studied for cathodoluminescence ͑CL͒ of similar luminescence screens. 24 In the case of electron luminescence excitation, the relationship between I a , the aged intensity of the phosphor, I 0 , the initial phosphor intensity, and N, the number of electrons deposited per cm 2 , is normally given by Pfahnl´s law, 25 where I a = I 0 / ͑1+C B N͒, and C B is the burning parameter. Its reciprocal is the number of electrons needed to reduce the intensity of the luminescence to one-half of its initial value.…”

Degradation of ZnS FED phosphors

“…C cm 2 ), on the partial pressure of gas and on the primary electron beam voltage. 3,7 Although the interactive constants and CL burning parameters calculated from data collected at different current densities (45-58 mA cm 2 ) were the same within experimental error, 7 the variation in electron flux was too small for comparison. Results from different laboratories show that there is a big difference in the degradation rate of the CL of ZnS phosphors degraded at lower current densities in comparison with those degraded at higher current densities.…”

“…Sebastian et al 1 and Swart et al 2,3 collected extensive data from ZnS in both the film and powder form, both doped with activators such as Ag : Cl, Cu : Au : Al or Mn. Their data support a model called electron-stimulated surface chemical reaction (ESSCR).…”