Study the effect of Tm+2 co-dopant on afterglow suppression in CsI:Tl crystal by thermoluminescence models

There are many applications with the CsI:Tl crystal, including spectroscopy, dosimetry, medical imaging, etc. The characteristics of this crystal, such as its atomic number, purity, and high density, have caused more attention to it. However, despite these advantages, the presence of an afterglow phenomenon in its emission spectrum limits CsI: Tl. In order to reduce the afterglow phenomenon, various elements have been used as co-dopants. In this research, Tm2+ and Eu elements were added to the CsI:Tl crystal. The glow curve of the crystal (heating rate of 10 oC/sec) was measured after irradiating the samples for 2 hours with a 90Sr source. The combination of the glow curve with the first and second-order kinetic models showed that the CsI: Tl crystal follows first-order kinetics. The glow curve from the CsI: Tl crystal in the presence of Eu and Tm2+ follows second-order kinetics. Then, with the deconvolution method, glow curves were separated into their individual constituent peaks, and the results showed that adding the co-dopant can reduce the contribution of the Tl element in the formation of the glow curve and shift it to higher temperatures thanks to the increase in the activation energy, as well as the new peak caused by co-dopant at low temperatures. The intensities of the upcoming peaks were lower than the peak caused by thallium. This is due to the high activation energy of the levels created by Eu and Tm2+ in the crystal structure. This phenomenon is due to the fact that electrons cannot be released at low temperatures. It can be concluded from the comparison of the Eu and Tm2+ peaks that Tm2+ elements create deeper traps in the crystal structure than Eu elements. This means that the effect of the element on reducing the afterglow in CsI:Tl crystals is more significant than the effect of the Eu element.