E. Alagu Raja

Identification of defect centres using TSL, PL, OSL and ESR studies in LiAlO2 based phosphors

LiAlO2 : Mn/Ce/Tb phosphors were prepared by combustion synthesis. LiAlO2 : Mn exhibits two thermally stimulated luminescence (TSL) peaks around 150 and 320 °C, while LiAlO2 : Ce/Tb exhibits TSL peaks around 170 and 280 °C. Photoluminescence emission of LiAlO2 : Mn consists of a peak around 500 nm when excited with 450 nm, while LiAlO2 : Ce shows a broad band around 400 nm when excited by 320 nm. The TSL emission spectra of LiAlO2 : Mn/Tb indicate that Mn2+/Tb3+ is the luminescence centre. LiAlO2 : Ce and LiAlO2 : 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 LiAlO2 : Ce. Room temperature ESR spectra of irradiated LiAlO2 : 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 LiAlO2 : Ce/Tb phosphor and these centres are assigned to O− and F+ centres, respectively. O− centre appears to correlate with the 170 °C TSL peak and F+ centre appears to correlate with both 170 and 280 °C TSL peaks in LiAlO2 : Ce.

ESR and TL mechanism in CaSO4?:?Ag co-doped phosphors

Thermoluminescence (TL) studies have been carried out on CaSO4?:?Mn, CaSO4?:?Ag,Mn, CaSO4?:?Ag,Nd, CaSO4?:?Ag,Mn,Nd, CaSO4?:?Ag,Zr and CaSO4?:?Ag,Mn,Zr phosphors. It is found that TL at 360??C in CaSO4?:?Ag,Mn,Nd is about 40 times that of CaSO4?:?Ag,Mn and about 170 times that of CaSO4?:?Ag,Nd. This shows that the presence of an efficient luminescent centre (Mn2+) as well as a trivalent impurity (such as Nd3+ or Y3+) is important for enhancement of TL at 360??C in the CaSO4?:?Ag,Mn,Nd phosphor system. Electron spin resonance (ESR) studies show that the peak at 360??C correlates with an Ag2+ centre formed due to ?-irradiation and observable only below ?170??C. The Ag2+ centre is characterized by an axial g-tensor with principal values g|| = 2.38 and g? = 2.41. ESR studies further indicate that the precursor to a centre observable at low temperature (?170??C) appears to act as the recombination centre for the TL peak at 360??C. The low temperature centre is characterized by the g-values g|| = 2.0023 and g? = 2.0038 and is assigned to the radical.