Turn-on fluorescence humidity sensing based on Cs₄PbBr₆ nanocrystal array

All-inorganic cesium lead halide perovskite (CsPbX3, X = Cl, Br, and I) nanocrystals (NCs) have attracted significant attention as promising photoelectric materials in recent years. Their non-fluorescent derivative, Cs4PbX6, can be transformed into highly fluorescent CsPbX3 through a CsX extraction process under appropriate aqueous conditions. This highly responsive turn-on fluorescence holds great promise in humidity sensing applications. Here, we assembled Cs4PbBr6 NCs into a nanoarray using a nanoxerography technique and investigated their application in micro-region humidity sensing. Due to the nanoscale reaction unit of each spot, the Cs4PbBr6 nanoarray exhibited high sensitivity towards trace water molecules. The detection range of 10-86% and the limit of detection (LOD) of 9.5% were obtained. In addition, the fluorescence could rapidly respond within 1 minute upon exposure to humid gas and achieve stability in less than 6 minutes, thereby significantly improving response speed compared to previous reports. Furthermore, the array pattern ensured statistical data acquisition, enhancing detection reliability.