Radiative energy transfer enabling upconverted circularly polarized persistent luminescence for multilevel information encryption

Optically active persistent luminescent materials are highly promising for anticounterfeiting applications due to their distinct luminescent features and the ability to display unique optical polarization properties. Despite significant progress in the development of circularly polarized persistent luminescence (CPPL) materials, the fabrication of upconverted circularly polarized persistent luminescence (UC-CPPL) materials remains a considerable challenge. In this study, we present an efficient strategy to construct UC-CPPL materials by embedding upconversion nanoparticles (UCNPs) and phosphors into chiral nematic liquid crystals (N*LC). The system operates through a radiative energy transfer mechanism between the UCNPs and phosphors. Upon excitation by low-energy near-infrared light (980 nm), the UCNPs emit high-energy ultraviolet light, which is effectively transferred to the phosphors, resulting in the emission of circularly polarized persistent visible light. By precisely tuning the photonic bandgap of the chiral N*LC, the UC-CPPL luminescence dissymmetry factor (<i>g</i>_UC-CPPL) can be amplified to approximately 0.6. The concept of UC-CPPL was realized through the integration of three advanced optical properties: circularly polarized luminescence, long persistent luminescence, and upconversion luminescence. This integration enables more sophisticated and secure information encryption. The incorporation of upconversion materials facilitates the controlled concealment and selective release of encrypted information, while the multileveled encoding scheme further enhances the complexity and security of the encryption process, achieving true information hiding and encryption.