Evaluation of thermoluminescence trapping parameters in Li2B4O7 co-doped with Ag+ and Gd3+ using various experimental techniques

Abstract

The aim of this study is to determine the thermoluminescence (TL) kinetic parameters, including the activation energy (E), frequency factor (s) and order of kinetics (b), for the traps of silver and gadolinium co-doped lithium tetraborate (Li2B4O7:Ag,Gd) phosphor. Four different experimental techniques were applied, including Fractional Glow Technique (FGT), Computerized Glow Curve Deconvolution (CGCD), as well as both Isothermal TL (ITL) and Optically Stimulated Luminescence (OSL) measurements at various stimulation temperatures. The TL glow curve of the phosphor was determined to be composed of two single peaks with delocalization temperatures around 80 °C and 360 °C with a heating rate of 2 °C/s after 10 Gy beta dose. Moreover, a composite TL signal is observed within the temperature region between 110 °C and 320 °C. Both the deconvolution analysis as well as the FGT partially indicates that this composite signal consists of two overlapping TL glow peaks along with a satellite TL peak of suppressed intensity. The reusability of the phosphor was studied up to 20 experimental cycles using beta dose values of 0.5, 5 and 10 Gy to support the FGT procedure. The plot of activation energy vs measured temperature yielded a smooth continuum, with the presence of three not so prominent plateau regions. On the contrary, the CGCD analysis indicated the presence of five TL peaks with increasing activation energy values ranging between 0.63 and 1.56 eV. The ITL results indicate that for the constituents of the composite TL signal within 110 °C and 320 °C, the activation energy is less than 0.5 eV, while the corresponding OSL results of the same signal indicate an activation energy value of 0.83 eV. Based on the results of the present study, (a) the continuum shape of the E vs Tfin plot of the FGT analysis and (b) the behavior of the normalized ITL decay curves provide adequate arguments for the existence of a tunneling recombination pathway in the phosphor. The argumentation is also supported by recent related literature.