Extreme Stimulus Enhanced Luminescence in Rare Earth Metal Halides for Optically Unclonable Authentication

Metal halides feature stimulus responsiveness and reversible color switching, showing great potential for dynamic information anti‐counterfeiting and encryption. Traditional metal halides primarily tune luminescence via crystal phase transition, yet suffer severe luminescence quenching under harsh environments, hindering stable encrypted information recognition. Herein, we report a new photophysical regulation strategy based on suppressing surface vibrational quenching through external field stimulation. A rational design and synthesis of Sb 3+ ‐doped Cs 3 HoCl 6 rare‐earth metal halide microcrystals was achieved, enabling reversible switching of luminescent color from green to bright red under various extreme conditions—including vacuum, high temperature, and prolonged solvent exposure, while simultaneously achieving a significant enhancement in the characteristic emission intensity of Ho 3+ . Integrated first‐principles calculations and spectroscopic analyses confirm that external stimuli can effectively reduce the influence of surface non‐radiative recombination centers in the system via the suppression of resonance energy transfer between Ho 3+ ions and hydroxyl groups, ultimately enabling high‐tolerance modulation of optical properties in Cs 3 HoCl 6 : Sb 3+ microcrystals. Leveraging this dynamic stimulus‐responsive behavior, we demonstrate a secure optical physically unclonable function authentication system capable of reliable operation in extreme environments, showing great potential for advanced information anti‐counterfeiting and encryption applications.