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

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 × 10−6 Torr and a background pressure of 1 × 10−8 Torr 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.

► A highly efficient and stable β-Ca3(PO4)2:Tb phosphor was synthesized.
► Very good optical properties under both photon and electron excitation.
► The β-Ca3(PO4)2:Tb phosphor withstand prolonged electron bombardment.
► CaO formed on the surface of the phosphor during prolonged electron bombardment.
► Correlation between CaO layer build-up and change in CL brightness was observed.