Insight into the Water-Triggered Conversion of Cs₄PbBr₆/Mesoporous Silica-Based Nanocomposites: In Situ Formation, Water Responsiveness, and Multistage Anticounterfeiting

Cs₄PbX₆ (X = Cl, Br, and I)-type all-inorganic lead halide perovskite nanocrystals (PNCs) have unique optoelectronic properties. However, their luminescence behavior demands a more in-depth study. Herein, we demonstrated a nanoconfinement strategy to fabricate a mesoporous silica nanoparticles and Cs₄PbBr₆ (MSNs@Cs₄PbBr₆) nanocomposite. Hexagonal Cs₄PbBr₆ nanocrystals (NCs) with an average particle size of 20 nm were formed in situ in the mesopores of MSNs. Benefited by crystal-phase conversion induced by water, MSNs@Cs₄PbBr₆ showed water-luminescence responsiveness, implying its feasibility for fabricating a highly stable and highly sensitive water sensor. The water test paper fabricated by dispersing MSNs@Cs₄PbBr₆ powder displayed a clear discrimination at the treated boundary line under UV light, indicating excellent sensitivity of the coated test paper in water detection. Furthermore, MSNs@Cs₄PbBr₆ was examined as an optical anticounterfeiting material for building a multilevel anticounterfeiting system. This work provides a new insight for fabricating multilevel anticounterfeiting systems based on perovskite-based materials.