Luminescent properties, intensity degradation and X-ray photoelectron spectroscopy analysis of CaS:Eu²⁺ powder

In the present work, we report the structure, particle morphology, surface chemical states, photoluminescent properties and cathodoluminescence intensity degradation of the CaS:Eu²⁺ powder phosphors. X-ray diffraction, X-ray photoelectron spectroscopy, and photoluminescence (PL) spectroscopy data suggest that the powder contains secondary phases that were possibly formed during the preparation or due to unintended contamination. These phases presented an opportunity to demonstrate the dependence of the emission of the Eu²⁺ ion on the host lattice. An intense red PL broad band with a maximum at 650 nm was observed when the powder was excited at 484 nm using a monochromatized xenon lamp. When the powder was excited using a 325 nm He-Cd laser an additional PL emission peak was observed at 384 nm. The origin of this emission is discussed. Auger electron spectroscopy and Cathodoluminescence (CL) spectroscopy were used to monitor the changes in the surface chemical composition and CL intensity of the CaS:Eu²⁺ phosphors when the phosphor was irradiated with a 2 keV electron beam in vacuum. The CL degradation is attributed to, among other things, the formation of a non-luminescent layer of CaSO₄, surface charging, and possibly the presence of O defects. This phosphor is evaluated for applications in low voltage field emission displays and light emitting diodes.