ABSTRACT
This study aims to investigate the comparison of the thermoluminescence (TL) emission of Li+ and Tm3+ co-doped and un-doped zinc borate (ZnB2O4) phosphors prepared by wet chemical synthesis method. The crystal structure of the samples has been determined by means of X-ray powder diffraction and matched with the standard pattern of ZnB2O4 (PDF Card No. 039-1126). TL glow curves of 5 Gy beta irradiated Li+ (at different concentrations of 0.2, 0.5, 0.8 and 1.0%) and Tm3+ (1.0%) co-doped ZnB2O4 have been recorded using various band pass filters to determine both the optimum concentration and the suitable filter. The TL green emission (565 nm) of Li+ (1.0%), Tm3+ (1.0%) co-doped ZnB2O4 phosphor displays a complex structure where one can distinguish, at least, three groups of components peaked at 69, 166 and 291 °C where the more suitable dosimetric maxima appears at higher temperature. It could be observed how the 166 and 291 °C TL glow maxima of this material exhibits (i) good linearity in the range of 0.11-15 Gy, (ii) a minimum detectable dose value of 1.11 mGy, (iii) does not modify significantly the TL emission in shape and intensity after reusability (10 cycles) and (iv) a negligible fading effect for 5 Gy irradiated aliquots stored in darkness and room temperature up to 169 h. Additionally, it could be found that (v) kinetic parameters estimated by using variable heating rate method of Hoogenstraaten and initial rise method give similar results.
ABSTRACT
The effect of heating rate (HR) on thermoluminescence (TL) glow curves of 1%, 4%, and 10% Ce3 + doped ZnB2O4 phosphors was investigated in detail. The glow peaks are examined and, activation energy (E) and frequency factor (s) are determined by using various heating rate (VHR) method. In the obtained glow curves with nine different HRs between 2 and 10°C/s, it was observed that the TL intensities of the first peaks of all three samples and the second peak of 10% Ce3 + doped sample decrease with increasing HR. The decrease in TL intensity was investigated whether it may be due to the presence of thermal quenching or not. On the other hand, the second glow peaks of 1, 4% Ce3 + doped ZnB2O4 phosphors show an anomalous TL behavior, which the probability of the radiative processes increases due to recombination of free electrons, so the TL intensity increases with the HR. The graphs of full width at the half maximum (FWHM) versus HR were also plotted to evaluate the influence of HR on TL intensity. In this paper, we suggest that the non-localized Schön - Klasens model may give an explanation for the second peaks of 1, 4% Ce3 + doped ZnB2O4 phosphors showing an unexpected increase with the increasing HR. In addition, the calculated E values of all doped phosphors were found similar in the range of 0.47-0.53eV for peak 1 and 0.61-0.66eV for peak 2. However, s values of Ce3 + doped ZnB2O4 phosphors were found slightly different according to the dopant amount and the equation used. Furthermore, different amount of Ce3 + doped samples indicate the similar properties for the repeated cycles of 5Gy in the same irradiation conditions.
ABSTRACT
Here we investigated the effects of annealing, heating rate and fading (after annealing at 800 °C) on the thermoluminescence (TL) glow curves of natural quartz (NQ). All of the samples were annealed at different temperatures between 100 °C and 800 °C and then irradiated with a beta dose of about 34 Gray (Gy), in order to determine the effects of annealing treatments on TL peaks of natural quartz. TL glow curves of the samples were recorded. It was observed that the intensities of TL peaks were strongly sensitive to annealing temperatures at 800 °C. The heating rate and fading effect of TL peaks of natural quartz were examined for the annealed samples at 800 °C for 30 min. It was observed that the intensities of the TL peaks were differently affected from heating rate and fading. Additionally, TL kinetic parameters (activation energy, frequency factor and order of kinetics) of all peaks were determined for annealed samples using a computerized glow curve deconvolution (CGCD) method and Mathematica software. Copyright © 2016 John Wiley & Sons, Ltd.
