Halide‐Composition Tunable CsPbX ₃ @Porous Silica Phosphors With Tunable Emission Wavelength and High Water Stability

A green, one‐pot aqueous synthesis of halide‐mixed CsPbCl x Br 3− x nanocrystals confined within a porous silica matrix (p‐SiO 2 ) and further sealed by a dense silica‐gel (SG) overlayer has been demonstrated. By systematically tuning the pore size of the p‐SiO 2 (2.1–5.4 nm) and the Cl/Br molar ratios (Cl:Br = 2:1, 1:1, 1:2, and 0:3), continuous emission tuning from blue (460 nm) to green (520 nm) with narrow bandwidth (FWHM < 27 nm) was achieved. The nanoconfinement provided by p‐SiO 2 effectively restricted perovskite crystal growth and reduced nonradiative recombination, while the cross‐linked silica‐gel coating served as an external barrier against moisture ingress. Among the investigated conditions, the p‐SiO 2 synthesized at pH 2 exhibited a narrow pore size distribution (~2.1 nm), providing effective confinement for perovskite crystallization. As a result, the CsPbX 3 @p‐SiO 2 /SG phosphors retained approximately 90% of their initial photoluminescence intensity without detectable spectral shifts after 200 days of water immersion. This dual‐protection strategy offers an aqueous, ligand‐free approach for preparing color‐tunable, water‐stable perovskite phosphors.