Cathodoluminescent properties and surface characterization of bluish-white LiAl₅O₈:Tb phosphor

Cathodoluminescence (CL) characteristics and electron-beam induced surface chemical changes in nanocrystalline Tb³⁺ doped LiAl₅O ₈ powder phosphors are presented. Bluish-white CL with a maximum at ∼543 nm was observed when the powders were irradiated with a 2 keV electron beam. The emissions in the green and the blue regions arise from the magnetic dipole ⁵D_4-⁷F_J (J =6-0) and ⁵D_3-⁷F_J transitions of the Tb ³⁺ ion. The appearance of the line emissions in the blue region are discussed in terms of Tb oxidation states and their corresponding interconversion. Auger electron spectroscopy and x-ray photoelectron spectroscopy (XPS) were used to probe the chemical changes on the surface of the LiAl₅O₈ phosphor under electron bombardment. The XPS data suggest that the Tb ions exist both in trivalent and tetravalent oxidation states which could be the reason for the observed green as well as blue CL emissions. A thermodynamically stable Al₂O₃ layer formed on the surface as a result of the electron stimulated surface chemical reactions is possibly contributing to the CL stability of the LiAl₅O ₈:Tb phosphor. The time stability of thephosphor under prolonged electron beam exposure suggests that it can be used in information displays.