Environmentally Friendly Synthesis of Near-Unity UV/Violet-Emitting Cerium-Based Metal Halides with Reversible Structural Switching for Smart Anticounterfeiting

Ultraviolet (UV) and violet luminescent materials with high efficiency and facile synthesis have attracted significant attention for photoelectric applications. However, conventional preparation routes are hindered by complicated processes, harsh conditions, and toxic solvents, making scalable production challenging. Herein, we report a green, low-cost, and scalable solution-phase synthesis of Cs₃CeCl₆·3H₂O and Cs₃CeCl₆, which exhibit photoluminescence quantum yields (PLQY) of 93.54% and 91.82%, respectively. Notably, Cs₃CeCl₆·3H₂O shows dual emission peaks at 334 and 356 nm, representing one of the shortest emitting metal halide perovskites reported. Moreover, reversible phase transitions between the hydrated and anhydrous phases can be triggered by thermal, solvent, and moisture stimuli. Based on this characteristic, we demonstrate a multilevel information encryption system. This work not only introduces a new family of highly efficient UV-violet phosphors but also offers novel design strategies for smart luminescent materials in information security and anticounterfeiting applications.