Dosimetric and optical properties of CaSO4:Tm and CaSO4:Tm,Ag crystals produced by a slow evaporation route

The motivation of this work was to produce TL dosimeters based on crystals of CaSO₄ doped with thulium and silver, by means of a suitable new route. The crystals were produced by an adaptation of the slow evaporation route using calcium carbonate (CaCO₃) as precursor, and incorporating the dopants (Tm₂O₃ and silver nanoparticles) in a solution of sulfuric acid, which is evaporated resulting in CaSO₄:Tm or CaSO₄:Tm,Ag crystal powders. X-ray diffraction analyses showed that the produced samples exhibit only a single phase corresponding to the crystal structure of anhydrite. Optical characterization was performed to determine the band gap of the materials. Samples did not show a reasonable OSL signal after stimulation with blue LEDs. TL characteristics such as glow curves, linearity and reproducibility of response, minimum detectable dose and fading were evaluated. The CaSO₄:Tm samples showed TL emission glow curves with peaks in temperatures proper for dosimetry. The CaSO₄:Tm,Ag samples presented a very intense peak displaced to high temperatures that could only be observed by applying heating rates below 4 °C/s. Samples doped with thulium oxide and silver nanoparticles showed the highest TL intensity and lowest fading.