In Situ Heteroepitaxial Growth of CsPbX ₃ @CsPb ₂ X ₅ Core–Shell Nanocrystals in Zeolite Framework toward Extraordinary Brightness and Stability

Abstract Highly crystalline CsPbX ₃ (X = Cl, Br, I) nanocrystals (NCs) are in situ grown in silicalite‐1 zeolite framework by a high‐temperature solid‐state reaction at 600 °C without ligand addition. Subsequently, a CsPb ₂ X ₅ shell is hetero‐epitaxial grown to form a CsPbX ₃ /CsPb ₂ X ₅ core–shell structure. The resulting nanocomposites exhibit high photoluminescence quantum yields (PLQYs) and remarkable stability in a solid powder situation. The green‐emitting (Br‐based) and red‐emitting (I‐based) composites demonstrate nearly identical high PLQYs up to 82.9 and 83.2%, respectively, due to high crystallinity and core–shell structure. By easily adjusting halide compositions, the photoluminescence peak wavelengths of the NCs can be continuously tuned in the whole visible spectrum from 413 to 697 nm. These nanocomposites exhibit remarkable resistance to both photo‐degradation under UV light irradiation and hydrolytic degradation in humid environments due to a hydrothermal treatment. The superior optoelectronic performance is ascribed to heterostructure formation and the protective confinement provided by the mesoporous silicalite‐1 framework, which effectively passivates surface defects. Finally, the NCs are successfully applied to white light‐emitting devices, achieving a chromaticity coordinate of (0.33, 0.32) and a correlated color temperature of 4793 K. This dual‐passivation strategy, combining zeolite encapsulation and surface reconstruction, renders the nanocomposites particularly suitable for implementation in next‐generation display technologies.