THERMOLUMINESCENCE RESPONSE OF LITHIUM TRIBORATE PHOSPHOR ACTIVATED WITH ZINC OXIDE NANOPARTICLE FOR MEDICAL DOSIMETRY APPLICATION

Abstract

This study reports on the synthesis and characterization of two sets of micro-sized lithium triborate (LBO) with one set doped with Zinc oxide nanoparticle (ZnO NP) via solid state sintering method for possible application in radiation dosimetry and the other set left undoped. A stoichiometric amount of the mechanically processed precursors were mixed and sintered at a temperature of 800 o C for one hour. The synthesized undoped LBO and the 0.1 to 0.5% ZnO NP doped LBO (LBO:ZnO NP) were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Differential thermal analysis (DTA) and Thermoluminescent (TL) dosimeter (TLD) reader. When matched with standard crystallography open database (COD) references, the X-ray diffraction patterns of the new TL materials confirmed a lithium triborate phase structure with high crystallinity. SEM presented an interesting morphology of the new material with clear display of the distribution of the nanoparticles on all concentrations of LBO:ZnO NP. DTA data showed early endothermic peak within 100 and 200 o C which is assigned to the dehydration of the hygroscopic water in the system and the major endothermic peaks of interest existed within 813 and 836 o C, which are ascribed to the incongruent melting of lithium triborate. The new TL materials in powder form were pressed into TL discs in order to adequately analyze them for their TL properties using an indigenous novel pellet presser which can produce TL discs compatible with Thermo Scientific Harshaw 3500 TLD reader. The thermoluminescent glow curves of the TL discs exposed to a low dose of 10 mGy and high dose of 10 Gy exhibited interesting response to ionizing radiation. The activation energy (E) and frequency factor (s) were calculated for each peak shape parameter τ (low temperature half width), δ (high temperature half-width) and ω (total half width) using Chen’s peak shape (PS) method and the order of kinetics was deduced from the symmetry factor (μ g ) and Balarin parameter (γ). The activation energy and frequency factor withrespect to the peak shape parameters E τ , E δ , E ω and s τ , s δ , s ω across the dopant concentrations were in the range of 1.02 to 2.20 eV and 7.71 x 10 22 to 2.03 x 10 10 s -1 respectively. Intrinsic LBO (peak 2), LBO:ZnO NP 0.1, 0.2, 0.3 and 0.5 follow first-order kinetics while undoped LBO (peak 1) and LBO:ZnO NP 0.4% predict a second-order kinetics. The results from the simple glow curve structure which relates to stability, high-temperature peaks which correspond to deep trap states and E values which correlate to low fading tendencies positions LBO doped with ZnO NP as a good material for dosimetric application.