Photoluminescence and ESR identification of γ-ray irradiation induced defects responsible for thermoluminescence in Tb3+ activated hibonite (CaAl12O19) powder material
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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 phosphor. Investigations using the technique of electron spin resonance (ESR) were carried out to study the defect centers induced 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 symmetric 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.
KeywordsTb3+ Hibonite Defect centers Luminescence, electron spin resonance
This paper was supported by the KU Research Professor Program of Konkuk University. T. K. Gundu Rao is grateful to CAPES, Brazil for the research fellowship.
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