A Dual-Mode Photoconductive Colorimetric Wearable UV-Dosimeter: Strategies for Tunable UV-Band Sensitivity

Excessive exposure to ultraviolet radiation poses serious risks to human health, necessitating the development of reliable personal UV monitoring devices. For practical use, such devices must be versatile, UV selective, and capable of providing detailed feedback on cumulative dosage. In this work, thermally evaporated CuBr thin films are employed as UV dosimeters. Owing to charge trapping at CuBr grain boundaries and surface oxide formation, the devices exhibit sustained current increase under prolonged UV exposure. The device response is markedly stronger under UV-A illumination compared to UV-B or UV-C exposure. Wearable UV dosimeters are then constructed by integrating the CuBr films with a custom-designed battery-powered circuit, enabling real-time quantification of ambient solar dosage. Additionally, with increasing solar dose, CuBr films deposited on white ceramic substrates exhibit a distinct color transition from soft amber to dark brown, facilitating dual-mode UV dosimetry. Wavelength-tunable responses are also achieved: first, by incorporating a top TiO₂ layer on CuBr, which filters UV-B radiation and further enhances the UV-A selectivity; and second, by introducing mixed compositions of SnBr₂-CuBr, which significantly improve UV-B sensitivity with increasing SnBr₂ content. This strategy paves the way toward scalable, low-cost, and wavelength-selective smart UV dosimeters for applications in personalized and environmental monitoring.