Study on the Thermoluminescence Peak Temperature Shift Characteristics of NaCl, NaCl:Al, and NaCl:Ca

Abstract

To gain a deeper understanding of the thermoluminescence peak temperature shift characteristics inherent to pure NaCl and its variants doped with Al and Ca, this study integrates first-principles calculations with thermoluminescence experimental techniques. This approach examines how doping affects the electronic structure of the crystal and delves into the mechanisms behind the shift in thermoluminescence peak temperatures. The calculations indicate that doping NaCl with Al slightly increases its band gap to 5.20 eV, whereas doping with Ca decreases it dramatically to 0 eV. These alterations not only modify the band gap width but also introduce distinct defect formation energies. Such changes are likely to result in thermoluminescence peak temperatures occurring at lower temperatures, with potential shifts depending on the experimental conditions. The theoretical predictions were validated through thermoluminescence experiments, which showed that the peak temperatures of all samples increased with a higher heating rate. Notably, the change was most significant for NaCl:Al, where the peak temperature rose from 276 K to 340 K. Meanwhile, as the irradiation dose increased within the range of 1-25mGy, the growth of the thermoluminescence peak temperature was relatively minor, especially for NaCl:Ca, which only increased from 195 K to 202 K. This comprehensive analysis of the electronic structures and defect formation energies provides insight into the thermoluminescence behavior of NaCl crystals. Doping with Al and Ca introduces mid-gap states that act as traps for charge carriers. These traps play a crucial role in the thermoluminescence process, capturing electrons during irradiation and releasing them upon heating, which leads to the observed luminescence. The presence of these traps and their specific energy levels relative to the conduction and valence bands directly influences the temperature at which the peak luminescence occurs. Furthermore, the study explores how the altered electronic structure due to doping affects the recombination processes of charge carriers, which are essential for the thermoluminescence phenomenon. It also investigates the impact of external factors, such as the rate of heating and the dose of irradiation, on the stability and shift of thermoluminescence peak temperatures. These findings underscore the complex interplay between material composition, structural defects, and experimental conditions in determining the thermoluminescence characteristics of doped NaCl crystals. The results of this research have significant implications for the application of doped materials in various fields, including radiation dosimetry and solid-state lighting. The ability to manipulate the thermoluminescence peak temperatures through doping opens up new avenues for designing materials with tailored luminescence properties for specific applications. This study not only advances our understanding of the fundamental mechanisms behind thermoluminescence but also highlights the potential of first-principles calculations combined with experimental analysis in the development of new materials with desired optical and electronic characteristics.