Multimodal Luminescence of Zero‐Dimensional Lead‐Free Metal Halide Nanocrystals Without Foreign‐Ion Doping for High‐Security Encryption

ABSTRACT Multimodal luminescent materials are pivotal for advanced anti‐counterfeiting and information encryption, but achieving multimodal luminescence in a single system remains challenging. Herein, all‐inorganic 0D lead‐free metal halide Cs 3 EuCl 6 nanocrystals (NCs) have been successfully synthesized, enabling the integration of four luminescent modes within one material. Under UV excitation, the NCs exhibit static photoluminescence (PL), while they show dynamic persistent luminescence (PersL) after the cessation of X‐ray irradiation. Moreover, the luminescent color depends on excitation wavelength and temperature. Remarkably, the NCs demonstrate reversible fluorescence responsiveness to water stimuli. The integration of four luminescent modes into a single, undoped material has not been reported so far, which benefits from the ladder‐like 4f energy levels of Eu 3+ ions and the highly confined 0D crystal structure of the NCs. Coupled with their excellent optical and thermal stability as well as water resistance, these properties enable the successful construction of sophisticated anti‐counterfeiting and dynamic information encryption systems. Furthermore, the temperature‐dependent luminescence showcases its great potential as an optical thermometer in the low temperature range (100–280 K). This work provides a novel paradigm for designing multimodal luminescent materials and opens promising avenues for complex information security applications.