Designing Yolk–Shell Nanostructures for Reversible Water-Vapor-Responsive Dual-Mode Switching of Fluorescence and Structural Color

Metal halide perovskites offer ample opportunities to develop advanced optoelectronic devices. This work showcases that the integration of metal halide perovskites into metal oxide nanoshells with controllable interior cavities can enable water-vapor-responsive dual-mode switching of fluorescence and structural color. Through a ship-in-a-bottle method to introduce a controlled amount of CsPbBr₃ into MnO₂ nanoshells, we have designed CsPbBr₃@MnO₂ yolk–shell nanostructures, which can uptake a defined amount of water to exhibit rapid (less than 1 s) and reversible (≥100 cycles) responses in both fluorescence on–off and color change when exposed to dynamic water vapor. These responses originate from the water-triggered phase transformation of CsPbBr₃ to CsPb₂Br₅ and the structural color change of the MnO₂ shell. The altered electronic and bonding structure at the oxide–halide interface, rapid water accumulation in the yolk–shell cavity, and protective effect of the oxide shell facilitate the reversible transformations. The response characteristics of the yolk–shell nanostructures have been further demonstrated in fabricating patterned films capable of multiple fluorescence/structural color responses, highlighting their potential for applications in advanced anticounterfeiting and encryption.