High-Purity Blue Emission and Anti-Counterfeiting Mechanism of Ga-Doped CsCu ₂ I ₃ -Derived Cs ₃ Cu ₂ I ₅ Composite

Owing to their environmental friendliness and excellent luminescent properties, lead-free copper-based halide perovskites have attracted significant attention for use in next-generation optoelectronic devices. In this work, Ga-doped Cs 3 Cu 2 I 5 phosphors derived from CsCu 2 I 3 were synthesized using a high-temperature solid-state method. Ga doping effectively modulated the crystal growth behavior and electronic structure, enabling high-performance emission tuning. The optimized material exhibited high-color-purity blue emission centered at ∼446 nm, with a CIE color purity as high as 97.7%. Owing to its exceptional optical properties, a blue LED device was fabricated, exhibiting stable and high-color-purity emission, thereby highlighting its practical potential for high-resolution display technologies and solid-state lighting applications. Furthermore, the material demonstrates remarkable water-induced color-switching behavior, enabling reversible color changes upon exposure to water. This characteristic renders it a promising candidate for applications in anticounterfeiting and information encryption. This study provides new insights and strategic directions for the development of copper-based perovskites aimed at achieving high-color-purity blue emission and multifunctional intelligent material applications.