Ammonia-sensitive halide CsCu₂I₃ film for gas sensor and stimuli-responsive anti-counterfeiting

Eco-friendly lead-free halide perovskites have emerged as promising materials for multiple applications due to their unique optoelectronic properties. In this work, we investigate the ammonia (NH₃)-sensitive CsCu₂I₃ film for its potential in NH₃ sensor and stimuli-responsive fluorescence anti-counterfeiting. CsCu₂I₃-based NH₃ sensor demonstrates a high response to NH₃ (△R/R₀ = 1.07, at 100 ppm NH₃) with rapid response/recovery time (21/19 s), as well as favorable gas selectivity. We proposed a potential NH₃ sensing mechanism with the help of a series of semi-quantitative characterizations and excitation-dependent emission experiments. The electron-donating NH₃ molecules can efficiently donate electrons to the p-type CsCu₂I₃ film, bringing about a decrease in film conductivity. Additionally, the adsorption of NH₃ can also disorder the CsCu₂I₃ crystals with a high density of trap states, facilitating an energy transfer from self-trapped excitons (STEs) emission to defect-related emission, along with bright orange luminescence. Inspired by this phenomenon, we proposed a novel application of NH₃-induced stimuli-responsive fluorescence for anti-counterfeiting. The results highlight the potential of CsCu₂I₃ for effective dual-function applications in gas sensors and gas-triggered anti-counterfeiting.