Normal and anomalous heating rate effects on thermoluminescence of Ce-doped ZnB2O4

The effect of heating rate (HR) on thermoluminescence (TL) glow curves of 1%, 4%, and 10% Ce-3 (+) 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 degrees C/s, it was observed that the TL intensities of the first peaks of all three samples and the second peak of 10% Ce-3 (+) 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% Ce-3 (+) 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 Schon - Klasens model may give an explanation for the second peaks of 1, 4% Ce-3 (+) 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 0.47-0.53 eV for peak 1 and 0.61-0.66 eV for peak 2. However, s values of Ce-3 (+) doped ZnB2O4 phosphors were found slightly different according to the dopant amount and the equation used. Furthermore, different amount of Ce-3 (+) doped samples indicate the similar properties for the repeated cycles of 5 Gy in the same irradiation conditions.