Review on electron stimulated surface chemical reaction mechanism for phosphor degradation

Standard cathodoluminescent phosphors normally lose brightness upon bombardment with electron beams. A combination of techniques such as x-ray photoelectron spectroscopy, Auger electron spectroscopy, and cathodoluminescence (CL) spectroscopy was used to show that the main reason for the degradation in CL intensity is the formation of a nonluminescent "dead layer" on the surface due to an electron stimulated surface chemical reaction. The decrease in luminance was found to be a result of the growth of the dead layer. Different phosphors which include sulfide-based as well as oxide-based phosphors reacted similarly under electron bombardment. When ZnS phosphor powder was exposed to the electron beam in a water-rich O2 ambient, a chemically limited ZnO layer was formed on the surface. A layer of ZnS O4 was formed on the surface during the electron beam degradation of the ZnS phosphor powder in a dry O2 ambient. The electron stimulated reaction led to the formation of a luminescent Si O2 layer on the surface of the Y2 Si O5: Ce phosphor powder. An increase in the CL intensity at a wavelength of 650 nm was measured during the formation of a luminescent Si O2 layer.