The cathodoluminescence degradation and surface characterization of β-Ca3(PO4)2:Tb phosphor

Abstract

The cathodoluminescence (CL) degradation mechanism of β-Ca3(PO4)2:Tb phosphors induced under low voltage electron beam bombardment in a vacuum chamber maintained at an O2 pressure of 1×10−6Torr and a background pressure of 1×10−8Torr was investigated. The surface chemical composition of the degraded powders analyzed by X-ray photoelectron spectroscopy, suggested that a new compound of oxide based calcium layer (i.e. CaxOy; x<1, y>1) was formed on the surface. The initial removal of C from the surface and the formation of a CaxOy over layer on the phosphor surface during electron irradiation caused a noticeably change in the CL intensity. Especially, based on the Auger electron spectroscopy combined with CL spectroscopy data, it is observed that there was an obvious correlation between the metal oxide layer build-up and the small decrease in CL brightness of the phosphors. The CaxOy, however, stabilized the phosphor preventing further degradation in the CL intensity. The CL properties and possible mechanism by which the new metal oxides were formed on the surface due to a prolonged electron beam irradiation are discussed.