Síntese e caracterização estrutural, morfológica, elementar e dosimétrica de CaSO4:Tm,Li preparado por evaporação lenta, coprecipitação e difusão em estado sólido

Abstract

Calcium sulfate (CaSO₄) based thermoluminescent dosimeters are widely used in ionizing radiation dosimetry, with CaSO₄:Dy being particularly noteworthy. In this study, the structural, thermal, morphological, elemental, and dosimetric properties of CaSO₄ phosphors doped with thulium (in metallic and oxide forms) and co-doped with lithium, produced by slow evaporation synthesis (SEL), solid-state diffusion (SES), and coprecipitation (PRE) syntheses, were investigated. The work involved the preparation and characterization of the phosphor. For structural characterization, X-ray diffractometry (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used. For dosimetric characterizations, thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques were used. The samples in the form of pellets were irradiated with a ⁹⁰Sr+⁹⁰Y source in the dose range of 0.142 Gy to 500 Gy. XRD analyses confirmed the formation of the CaSO₄ crystalline phase for all production routes, SEM analyses revealed significant morphological differences between the materials obtained by the different routes, and EDS analyses confirmed the incorporation of thulium into the compounds. The CaSO₄ samples produced by SEL showed significantly higher TL and OSL intensities than those obtained by SES and PRE. The TL emission curves exhibited multiple peaks, with predominant emissions in the blue region (455 nm), characteristic of Tm³⁺. Co-doping with lithium contributed to intensifying the luminescent signal of the samples. The OSL curves exhibited typical exponential decay for all samples, with the samples obtained via SEL exhibiting slow decay emission, indicating low photoionization cross section and charge transfer in the blue LED stimulation process. All CaSO₄:Tm,Li phosphors exhibited homogeneous TL and OSL responses to the dose (with a coefficient of variation less than 10%), adequate response linearity for the dose range studied, and TL signal stability for traps associated with peaks above 200 °C (fading). The results indicate that the CaSO₄:Tm,Li compound, especially when synthesized by slow evaporation, has high potential for applications in ionizing radiation dosimetry. Complementary studies, such as assessments of energy dependence, lower dose detection limit, and longer fading periods, will contribute to a comprehensive evaluation of its dosimetric performance, will contribute to a comprehensive evaluation of its dosimetric performance.