Upconversion/Downshifting Circularly Polarized Luminescence over 1200 nm in a Single Nanoparticle for Optical Anticounterfeiting and Information Encryption

Abstract Multimodal upconversion and downshifting circularly polarized luminescent materials hold significant potential for optical anticounterfeiting applications due to their exceptional chiroptical properties. However, constructing these materials within a single emitter remains challenging. In this study, a conceptual model of multimodal upconversion/downshifting circularly polarized luminescence (CPL) is realized within a single nanoparticle. A new type of nanoparticles with multilayer core–shell architecture is fabricated, capable of delivering upconversion/downshifting luminescence, when excited by a 980 nm laser. Utilizing a co‐assembly strategy, multimodal upconversion/downshifting CPL emission, covering a broad emission range from ultraviolet (UV) to the second near‐infrared (NIR‐II) region, can be realized at the supramolecular level. These chiroptical properties closely follow the chirality of host matrix and are strongly dependent on the distribution mode of nanoparticles within the matrix films. The multimodal upconversion/downshifting CPL behavior enabled cutting‐edge encryption applications including optical anticounterfeiting and information encryption. This work introduces a novel approach to designing multimodal upconversion/downshifting CPL materials and opens new avenues for the development of chiroptical functional materials.