Superior Multimodal Luminescence in a Stable Single‐Host Nanomaterial with Large‐Scale Synthesis for High‐Level Anti‐Counterfeiting and Encryption

Abstract Multimode luminescent materials exhibit tunable photon emissions under different excitation or stimuli channels, endowing them high encoding capacity and confidentiality for anti‐counterfeiting and encryption. Achieving multimode luminescence into a stable single material presents a promising but remains a challenge. Here, the downshifting/upconversion emissions, color‐tuning persistent luminescence (PersL), temperature‐dependent multi‐color emissions, and hydrochromism are integrated into Er 3+ ions doped Cs 2 NaYbCl 6 nanocrystals (NCs) by leveraging shallow defect levels and directed energy migration. The resulting NCs display strong static and dynamic colorful luminescence in response to ultraviolet, 980‐nm laser, and X‐ray. Additionally, the NCs exhibit distinct luminescent colors as the temperature increases from 330 to 430 K. Surprisingly, it also demonstrates the ability of the reversible emission modal and color in response to water. Theoretical calculations and experimental characterizations reveal that self‐trapped exciton state (STEs), chlorine vacancy defects, and ladderlike 4f energy levels of Er 3+ ions contribute to multimodal luminescence. More importantly, it has extremely remarkable environmental stability, which can be stored in the air for more than 18 months, showing promising commercial prospects. This work not only gives new insights into lanthanide‐based metal halide NCs but also provides a new route for developing multimodal luminescent nanomaterials for anti‐counterfeiting and encryption.