Water-Driven Self-Encapsulation of Stable Aqueous CsPbBr3@CsPb2Br5 Colloids

Abstract We report a facile and environmentally benign strategy to produce highly stable aqueous colloids of the CsPbBr3@CsPb2Br5 core−shell nanocomposites via water-driven in situ reconstruction. A combination of X-ray diffraction, energy-dispersive X-ray spectroscopy, and real-time conductometry confirms the water-induced phase transformation. This reconstruction process involves the selective leaching of Cs+ and Br− ions during brief ultrasonication in water from the multiphase CsPbBr3/Cs4PbBr6 precursor, synthesized via a facile, low-toxicity ligand-assisted reprecipitation method. Transmission electron microscopy establishes the matrix-inclusion nanocomposite geometry, confirming that monodisperse orthorhombic CsPbBr3 cores with a mean diameter of (3.58 ± 0.57) nm are embedded within the tetragonal CsPb2Br5 matrix. Time-resolved photoluminescence spectroscopy proves effective surface defect passivation, exhibiting an extension of the average carrier lifetime from 4.43 ns to 5.30 ns upon shell crystallization. Driven by this defect passivation, photoluminescence spectroscopy confirms a maximum photoluminescence quantum yield of 48.6% after 72 h of storage. Laser Doppler microelectrophoresis determines a high positive surface potential of (74.5 ± 13.7) mV ensuring long-term colloidal stability exceeding >1000 h without sedimentation. Time-dependent fluorescence spectroscopy reveals a continuous hypsochromic shift of the emission peak from 543 nm to 519 nm (at 120 h) and 491 nm (at 1152 h), governed by subtractive water-driven etching and enhanced quantum confinement. This self-encapsulation framework provides a robust solution to halide perovskite instability in polar media.