All-inorganic halide perovskites, such as CsPbBr₃, are leading candidates for next-generation photonic and display technologies due to their high color purity and quantum efficiency [1]. However, their practical implementation is limited by poor moisture stability due to their inherently ionic nature. Embedding CsPbBr₃ within a Cs₄PbBr₆ host is a widely used strategy for improving stability due to their structural compatibility [2]. However, the resulting composites often suffer from low emission intensity as large non-emissive Cs₄PbBr₆ domains (>100 nm) dominate over the smaller luminescent CsPbBr₃ nanocrystals (<5 nm). Additionally, they exhibit poor solution dispersibility, and rapid degradation upon water exposure.

In this study, we introduce a novel Phosphate Matrix Assisted Re-Precipitation (PARP) strategy by incorporating exfoliated zirconium phosphate (Exf-ZrP) nanosheets as an inorganic matrix to guide perovskite crystallization. Utilizing a modified ligand-assisted reprecipitation method, we integrated less than 1 wt% Exf-ZrP during the nucleation of perovskite. Despite this minimal loading, this matrix-assisted route significantly enhances the perovskite dispersion and promotes defect passivation. Further, this PARP process enhances the growth of CsPbBr₃ domains (up to 45 nm) and suppresses the formation of large, non-emissive Cs₄PbBr₆ domain. As a result, the photoluminescence quantum yield (PLQY) is boosted to 75%, representing a 2.4× improvement over unassisted synthesis.

Importantly, we demonstrate for the first time that the phosphate matrix enables a solid-state, water-assisted phase transformation of Cs₄PbBr₆ into CsPbBr₃ without structural collapse. Unlike conventional liquid–liquid methods [3] that require biphasic systems (e.g., water–toluene mixtures) and large solvent volumes, our approach achieves the transformation simply by exposing the solid composite to water, eliminating the need for toxic organic solvents. This controlled, matrix-guided conversion enhances fluorescence by 1.2× and redshifts the emission to 530 nm, moving closer to the pure green required for display technologies.

Our results underscore the multifunctional role of the inorganic phosphate matrix: (i) it promotes the growth of high-quality CsPbBr₃ crystals, enhancing optical performance; (ii) it stabilizes the composite by passivating surface defects; and (iii) it mediates a controlled, water-triggered solid-state phase transformation. The proposed strategy offers a versatile framework for integrating metal phosphate matrices with halide perovskite systems, and solvent-free pathway to engineer light emitting perovskites for high-performance.