R. K. Kher

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.

A comparative study of the models dealing with localized and semi-localized transitions in thermally stimulated luminescence

Different models dealing with localized and semi-localized transitions, namely Chen–Halperin, Mandowski and the model based on the Braunlich–Scharmann (BS) approach are compared. It has been found that for recombination dominant situations (r < 1 where r is the retrapping parameter for localized transitions), the TSL glow curves arising from localized recombination coincide with all three models whereas for r 1, the three models differ. This implies that for localized transitions under recombination dominant situations, the Chen–Halperin model is the best representative of the thermally stimulated luminescence (TSL) process.It has also been found that for the TSL glow curves arising from delocalized recombination in Mandowskis semi-localized transitions model, the double peak structure of the TSL glow curve is a function of the radiation dose as well as of the heating rate. Further, the double peak structure of the TSL glow curves arising from delocalized recombination disappears at low doses as well as at higher heating rates. It has also been found that the TSL glow curves arising from delocalized recombination in the semi-localized transitions model based on the BS approach do not exhibit double peak structure as observed in the Mandowski semi-localized transitions model.

Thermoluminescence, ESR and x-ray diffraction studies of CaSO4 : Dy phosphor subjected to post preparation high temperature thermal treatment

Thermoluminescence (TL), electron spin resonance (ESR) and x ray diffraction studies of CaSO4 : Dy phosphor subjected to post preparation high temperature treatment were carried out. Analysis of the TL glow curve indicated that the dosimetric glow peak at 240 °C reduces, whereas the low temperature satellite peak increases with the increase in the annealing temperature in the range 650–1000 °C. The influence of the annealing atmosphere on the TL glow curve structure was also observed. Reduction of the photoluminescence intensity of the annealed phosphor indicated that the environment of Dy3+ ions might have undergone some change due to high temperature treatment. Reduction in the ESR signal intensity corresponding to and radicals was observed initially with the increase in the annealing temperaure; subsequently their intensity increased with temperature. Signals due to the radical vanished, when the phosphor was annealed beyond 800 °C. A signal corresponding to SH2− radicals was also observed in the ESR spectra for samples subjected to annealing in the temperature regime 800–1000 °C. XRD of the in situ annealed phosphor showed a change in the unit cell parameters. An endothermic peak at 860 °C in the DTA spectrum was observed.

Reply to comments on—The effect of the heating rate on the characteristics of some experimental thermoluminescence glow curves by Rasheedy et al

In the paper by Kumar et al, some criticism is advanced to the analysis of the glow curves measured under different heating rates in the laboratory, which appeared in our recent paper [M.S. Rasheedy and E.M. Zahran, 2006 Phys. Scr., 73 98–102]. According to this analysis the area under the glow curve is conserved in both TL–time plots and TL–temperature plots. On the contrary, Kumar et al supposed increase of the area under the glow curve with increasing the heating rate in the case of TL–temperature plots. Since this criticism discredits a physical reason for conservation of the area under the glow curves due to conservation of the imparted dose at different heating rates, a reply appears to be timely.

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.

Study on the response of indigenously developed CaSO4:Dy phosphor-based neutron dosemeter.

In the present paper, we report the indigenous development of a neutron-sensitive thermoluminescent dosemeter (TLD) based on CaSO4:Dy Teflon TL disc. The study includes indigenous development of a neutron dosemeter and its response in terms of operational quantity to different energies of neutrons under various irradiation conditions. It was found that the thermal neutron sensitivity of the CaSO4:Dy Teflon neutron disc is about one-third of TLD-600. However, the thermal neutron sensitivity with respect to CaSO4:Dy Teflon gamma disc is about 42 times for in-air irradiation and about 84 times for on-phantom irradiation condition. This newly developed neutron dosemeter can be used as a routine TLD with a slight change in the design of the TLD badge system in the mixed fields of gamma and neutrons of energy up to 500 keV for radiation workers engaged in nuclear fuel cycle operation and other applications.