Ammonia-sensitive halide CsCuI 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 (NH)-sensitive CsCuI film for its potential in NH sensor and stimuli-responsive fluorescence anti-counterfeiting. CsCuI-based NH sensor demonstrates a high response to NH (△R/R = 1.07, at 100 ppm NH) with rapid response/recovery time (21/19 s), as well as favorable gas selectivity. We proposed a potential NH sensing mechanism with the help of a series of semi-quantitative characterizations and excitation-dependent emission experiments. The electron-donating NH molecules can efficiently donate electrons to the p-type CsCuI film, bringing about a decrease in film conductivity. Additionally, the adsorption of NH can also disorder the CsCuI 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 NH-induced stimuli-responsive fluorescence for anti-counterfeiting. The results highlight the potential of CsCuI for effective dual-function applications in gas sensors and gas-triggered anti-counterfeiting.