ZnBr2-Assisted Br-Rich Regulation of Blue-Emitting CsPbBr3 Nanoplatelets Synthesized at Low Temperature

All-inorganic CsPbBr3 nanoplatelets (NPLs) have attracted considerable interest for light-emitting, wavelength-conversion, and flexible photonic applications owing to their high color purity, tunable bandgap, and excellent luminescence performance. However, their large specific surface area makes them highly susceptible to surface halide vacancies, which introduce abundant nonradiative recombination centers and thereby compromise both emission efficiency and thermal stability. Herein, CsPbBr3 NPLs with varying Br/Pb ratios were synthesized through a low-temperature hot-injection route, with ZnBr2 introduced as an additional Br source to elucidate the effects of Br-rich regulation on the microstructure, surface chemistry, and optical properties of the NPLs. The results show that ZnBr2 effectively passivates bromine-vacancy defects and optimizes the Pb-Br coordination environment while preserving the original crystal framework and ligand environment, thereby promoting radiative recombination. Under optimized conditions, the photoluminescence quantum yield increased from 26.7% at Br/Pb = 2 to 87.5% at Br/Pb = 6, while the average lifetime reached 11.78 ns. Temperature-dependent PL spectra further reveal that Br-rich regulation suppresses deep-trap-assisted nonradiative recombination and mitigates thermally activated energy dissipation. The resulting composite film not only exhibits efficient wavelength conversion but also enables direct visualization of ultraviolet optical paths on complex optomechanical components through robust interfacial adhesion. This work provides mechanistic insights into defect engineering and thermal stability enhancement in CsPbBr3 NPLs, while broadening their potential for flexible photonic integration.