Identification of defect centres using TSL, PL, OSL and ESR studies in LiAlO(2) based phosphors
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LiAlO(2) : Mn/Ce/Tb phosphors were prepared by combustion synthesis. LiAlO(2) : Mn exhibits two thermally stimulated luminescence (TSL) peaks around 150 and 320 degrees C, while LiAlO(2) : Ce/Tb exhibits TSL peaks around 170 and 280. C. Photoluminescence emission of LiAlO(2) : Mn consists of a peak around 500 nm when excited with 450 nm, while LiAlO(2) : Ce shows a broad band around 400 nm when excited by 320 nm. The TSL emission spectra of LiAlO(2) : Mn/Tb indicate that Mn(2+)/Tb(3+) is the luminescence centre. LiAlO(2) : Ce and LiAlO(2) : Tb exhibit optically stimulated luminescence when stimulated with 470 nm light. Electron spin resonance (ESR) studies were carried out to identify defect centres responsible for TSL peaks observed in LiAlO(2) : Ce. Room temperature ESR spectra of irradiated LiAlO(2) : Ce/Tb phosphor appear to be in a superposition of at least four distinct centres. Two defect centres (centre I and centre II) are identified in irradiated LiAlO(2) : Ce/Tb phosphor and these centres are assigned to O(-) and F(+) centres, respectively. O(-) centre appears to correlate with the 170 degrees C TSL peak and F(+) centre appears to correlate with both 170 and 280 degrees C TSL peaks in LiAlO(2) : Ce.
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