Photoswitchable lanthanide-doped core-multishell nanoparticles for tunable triple-mode information encryption and dynamic anti-counterfeiting patterns

Defect-assisted dynamic multicolor modulation in KLu3F10:Tb crystals for anti-counterfeiting

Excitation-dependent dynamic multicolor luminescent materials show potential for promising applications in the field of anti-counterfeiting. However, for most ultraviolet (UV)-excited lanthanide-doped materials, more than two types of activators are incorporated to realize multicolors. In this study, for the first time, KLu₃F₁₀:Tb crystals were used to realize excitation-dependent multicolor emissions. The morphology was modified by tuning the surface-coated citric acid (CA) content. During hydrothermal reactions, fluorine vacancy defects are formed on the crystal surface, and carboxyl groups (-COOH) are coated on the crystal surface to maintain the charge balance. Under 254 nm UV excitation, typical Tb³⁺ green emissions were observed, while a strong broadband emission peaking at 442 nm appeared in addition to these Tb³⁺ emissions under 365 nm excitation. The energy transfer (ET) process between the defect state and Tb³⁺ is clarified. This work may promote the development of single-type activator-doped multicolor luminescent materials for high-level anti-counterfeiting.

RGB Tricolor and Multimodal Dynamic Optical Information Encryption and Decoding for Anti-Counterfeiting Applications

Conventional optical anti-counterfeiting strategies are based on the single-color emission, which are easily deciphered and thus greatly limited in the application of information security. Herein, a multimodal dynamic optical information coding with red, green, and blue (RGB) tricolors has been developed by photoluminescence (PL), persistent luminescence (PersL), thermally stimulated luminescence (TSL), and thermally stimulated persistent luminescence (TSPL). The BaSi₂O₂N₂:Eu²⁺ phosphors with a blue emission peak at 494 nm were used as the crucial blue optical information coding material and exhibited the distinctive response properties to light, heat, and force stimuli with intrinsic trap depths of 0.674 and 0.82 eV. More importantly, by combining the red Sr₂Si₅N₈:Eu²⁺,Dy³⁺ and green SrSi₂O₂N₂:Eu²⁺,Dy³⁺ nitride phosphors, a RGB tricolor and multimodal strategy has been successfully developed for anti-counterfeiting applications. The "RGB tricolor flower" with RGB emissions is given as a typical example to achieve the dynamic display of optical information encryption and decoding through the various PL, PersL, TSL, and TSPL modes. Finally, the traditional quick response (QR) code mechanism has been integrated into the design of multi-information encrypted RGB tricolor anti-counterfeiting devices with different identifiabilities of the encrypted information in natural light, PL, PersL, TSL, and TSPL modes. The laminated layers of RGB QR code patterns containing different specific information, such as "DLPU" and "116034", can be effectively recognized in the corresponding modes. The design strategy of RGB tricolor and multimodal optical information encryption and decoding devices in this work greatly improves the security level of advanced optical information technologies and extends the potential applications in dynamic anti-counterfeiting fields.