Influence of sintering temperature on structural and optical properties of pure and Cl-doped ZnO nanoparticles

In this study, we conducted a detailed analysis of the sintering process of both pristine and 25 mg/g Cl-doped ZnO nanoparticles at varying temperatures to determine the optimum sintering temperature. Our findings revealed an optimal sintering temperature of 600 °C, resulting in higher phase purity (only hexagonal ZnO phase), smaller particle sizes of about 88–92 nm, and higher emission intensity for both pristine and Cl-doped ZnO nanoparticles. The band gap reduces from 3.63 eV to 3.20 for pristine and 3.63 eV to 3.10 for Cl-doped ZnO nanoparticles by increasing the sintering temperature from 200 °C to 1000 °C. The introduction of Cl in the ZnO lattice introduced a new defect level, having a broadband excitation band peaking at 374 nm. The luminescence of ZnO peaked at approximately 503 nm, which can be attributed to the transition from oxygen vacancies in the ZnO lattice. Notably, the emission intensity of the Cl-doped samples sintered at 600 °C was found to be 6.5 times higher than that of the pristine ones. Moreover, we found that the luminosity of ZnO:Cl nanoparticles was around 68% that of ZnS:Ag nanoparticles, which are typically used for radon detection and have similar efficiency to standard Lucas cells. Our preliminary findings suggest that Cl-doped ZnO nanoparticles sintered at 600 °C for 5 h could effectively develop radiation detectors, particularly for radon monitoring and related applications.