RESUMEN
The thermoluminescence (TL) of calcium silicate phosphor (CSO) prepared by the sol-gel method and sintered at 1200 °C were investigated. From Tm-Tstop curve, TL emission spectrum and computer deconvolution using electron traps with discrete and continuous distributions, the glow curves were found to be composed of four TL peaks (117, 190, 250 and 275 °C) with a single emission band centered at 370 nm. Electron paramagnetic resonance (EPR) investigation has been carried out to identify the defect centers formed in the CSO phosphor by γ-irradiation and find the centers related to the TL process in the phosphor. At room temperature, three defect centers were observed. The first center, characterized by the principal g-values of 2.014, 2.011, and 2.0080 was assigned to an O- ion. The second center with g-values 2.015, 2.013, and 2.010 is also attributed to an O- ion and is associated with the TL peak at 280 °C. The third center, with an isotropic g-value of 2.0011 was identified as the F+ center (singly ionized oxygen vacancy) and relates to the TL peak at 280 °C.
RESUMEN
The present paper reports the thermoluminescence (TL), dosimetric characteristics and electron spin resonance (ESR) of LiF: Mg, Cu,B (MCB) phosphor synthesized by a solid state method. Its glow curve structure is similar to that of LiF: Mg, Cu,P (MCP) phosphor with the main dosimetric peak at 218°C. MCB is 12 times more sensitive than LiF: Mg, Ti and about 1.9 times less sensitive than MCP phosphor. A noteworthy feature is that the phosphor exhibits a linear dose response up to 100Gy with a minimum detectable dose of 17µGy. The TL emission spectrum was recorded and the post irradiation fading in MCB at ambient temperatures and humidity was negligible for a period of one month. Room temperature ESR spectrum of irradiated phosphor consists of at least two distinct centers. Center I with an isotropic g factor 2.0061 is attributable to an F-center and is the likely recombination center for the main TL peak at 220°C. Center II characterized by a g-factor 2.0090 and an unusual broad line (linewidth ~ 415G) is also identified as an F-center. A third defect center, observable during thermal annealing at high temperature, is assigned to another F-center.
RESUMEN
Mg2SiO4:Tb phosphor exhibits four thermoluminescence (TL) peaks at 124, 244, 300 and 370°C for a heating rate of 2°C/s, 244°C peak being the main dosimetry peak. The irradiated phosphor exhibits CW-OSL response on stimulation with blue (470nm) light. Thermal decay of OSL shows that all the TL traps contribute to CW-OSL signal. Its TL and OSL sensitivities are 0.21 and 0.038, respectively, than that of Al2O3:C (Landauer Inc.). Its CW-OSL response increases linearly up to 30Gy, thereafter increase was supralinear up to the studied dose of 1000Gy. Electron Spin Resonance (ESR) studies were carried out to study the defect centers induced in the phosphor by gamma irradiation and also to identify the centers responsible for the TL process. Room temperature ESR spectrum of irradiated phosphor appears to be a superposition of at least three distinct centers. One of the centers (center I) with an isotropic g-factor 2.0122 is attributable to an intrinsic O(-) radical and this correlates with the main TL peak at 244°C. Center II with an isotropic g-factor 2.0012 is assigned to an F(+)-center (singly ionized oxygen vacancy) and is the likely recombination center for all the TL peaks. Both the centers grow with radiation dose at least up to 1 kGy. Center III with an axial symmetric g-tensor with principal g-values g||=2.0049 and gâ¥=2.0029 is identified as an F(+)-center and is not related to the observed TL peaks in the phosphor.