Optically‐Controlled Quantum Size Effect in a Hybrid Nanocavity Composed of a Perovskite Nanoparticle and a Thin Gold Film

Metal halide perovskites have attracted great interest in recent years and their emission wavelength can be adjusted either by doping impurities or by exploiting quantum size effect. Here, it is reported that the realization of optically‐controlled quantum size effect in a hybrid nanocavity composed of a perovskite (CsPbBr 3 ) nanoparticle and a thin gold (Au) film. Such nanocavities are created by synthesizing polycrystalline CsPbBr 3 nanoparticles composed of quantum dots on a thin Au film via chemical vapor deposition, which emit luminescence at ≈488 nm under the excitation of femtosecond laser pulses with a low repetition rate. The phase transition from polycrystalline to monocrystalline, which quenches the quantum size effect and shifts the emission wavelength to ≈515 nm, can be introduced in CsPbBr 3 nanoparticles by simply increasing the laser power. Interestingly, such a phase transition is reversible provided that the laser power is lower than a threshold. Consequently, four optical states including dual‐wavelength emission, can be achieved by deliberately setting the laser power. The underlying physical mechanism is unveiled by the static and transient temperature distributions simulated for the hybrid nanocavity. The findings open a new avenue for designing novel photonic devices based on perovskite nanoparticles and plasmonic nanostructures.