Thermoluminescence peak temperature shift characteristics of NaCl, NaCl:Al, and NaCl:Ca

Abstract

To gain a more in-depth understanding of the thermoluminescence peak temperature shift characteristics of pure NaCl itself and its Al and Ca doped variants, a combination of the first-principles calculations and thermoluminescence experiments is used to explore how doping affects the electronic structure of the crystal and further analyze the mechanism of peak temperature shift in thermoluminescence. The calculations indicate that doping NaCl with Al slightly increases its band gap to 5.20 eV, whereas doping with Ca reduces it dramatically to 0 eV. These changes can modify the band gap width but introduce distinct defect formation energy values. Such changes may cause the thermoluminescence peak temperature to occur at lower temperatures and shift with the change of experimental conditions. The theoretical predictions are validated through thermoluminescence experiments, showing that the thermoluminescence peak temperatures of all samples rise with heating rate increasing. Notably, the change is most significant for NaCl:Al, where the peak temperature rises from 276 to 340 K. Meanwhile, as the irradiation dose increases in a range of 1–25 mGy, the growth of the thermoluminescence peak temperature turns relatively small, especially for NaCl:Ca, the peak temperature rises only from 195 to 202 K. This comprehensive analysis of the electronic structures and defect formation energy provides an insight into the thermoluminescence behavior of NaCl crystal. 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. In addition, this study explores how the changes of electronic structure, caused by doping, affects the recombination process of charge carriers, which is very important for the thermoluminescence phenomenon. It also investigates the influence of external factors, such as the rate of heating and the dose of irradiation, on the stability and shift of thermoluminescence peak temperature. These findings emphasize the complex interactions between material composition, structural defects, and experimental conditions in determining the thermoluminescence characteristics of doped NaCl crystals. The results of this research are of great significance 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 ways for designing materials with tailored luminescence properties for specific applications. This study not only deepens our understanding of the fundamental mechanisms of 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.