Photoluminescence and ESR identification of γ-ray irradiation induced defects responsible for thermoluminescence in Tb3+ activated hibonite (CaAl12O19) powder material.

Abstract

CaAl12O19 powder activated with Tb ions has been prepared by the urea combustion route. Phase evolution of the powder is determined by X-ray diffraction techniques. Photoluminescence emission of CaAl12O19:Tb consists of a dominant peak at 544 nm when excited with UV radiations. Thermoluminescence (TL) peaks at approximately 140 °C, 245 °C and 458 °C are observed in the CaAl12O19:Tb phos phor. Investigations using the technique of electron spin reso nance (ESR) were carried out to study the defect centers in duced in the phosphor by γ-ray irradiation. ESR study reveals the presence of several distinct centers. One of the centers (center I) with an isotropic g factor 2.0110 is tentatively assigned to an intrinsic O− type center and this center relates with the TL peak at 140 °C. Center II with an axially symmet ric g-tensor with principal values g∥ = 2.0324 and g⊥ = 2.0060 is attributable to an O2 − ion and also appears to correlate with the 140 °C TL peak. Several F+ -centers have been identified and their correlation with the observed TL peaks will be discussed.