Designing X-ray-Excited UVC Persistent Luminescent Material via Band Gap Engineering and Its Application to Anti-Counterfeiting and Information Encryption

Luminescent nanomaterials based covert tags for anti-counterfeiting applications: A review

Counterfeiting has emerged as a new global threat that challenges companies, securities, governments, and customers. Because of the banal advancements in technology, it is extremely prevalent. Ultimately have a more concerning effect than terrorism in terms of the standard of goods, organizations, banks' financial standing, people's health, the nation's financial situation, etc. Thus, it requires an urgent high-tech solution to combat counterfeiting. The present review surveys the anti-counterfeiting technologies that have been applied to combat and discourage counterfeiting. It presents the photoluminescence properties of quantum dots, metal-organic-framework, and lanthanide-doped nanomaterials and their applications in anti-counterfeiting. Recently, lanthanide-doped nanomaterials have emerged as potential candidates that provide strong security for the products due to their excellent color tunable luminescence properties under the wide range (UV to NIR) of excitation. Therefore, the present review mainly focused on the strategies of luminescence features of lanthanide-doped downconversion/downshifting and upconversion nanomaterials and their potential uses in fighting counterfeiting. Moreover, the key barriers and opportunities to combat counterfeiting advances are discussed. In addition, the crucial factors, such as the fabrication of luminescent ink, various printing techniques employed for printing different kinds of fluorescent security labels, patterns, and codes, etc., have been highlighted. This review will provide detailed information to the readers to design the security labels based on the lanthanide-doped luminescent nanomaterials for high-tech security against counterfeiting.

Current Developments in Emerging Lanthanide-Doped Persistent Luminescent Scintillators and Their Applications

Lanthanide-doped scintillators have the ability to convert the absorbed X-ray irradiation into ultraviolet (UV), visible (Vis), or near-infrared (NIR) light. Lanthanide-doped scintillators with excellent persistent luminescence (PersL) are emerging as a new class of PersL materials recently. They have attracted great attention due to their unique "self-luminescence" characteristic and potential applications. In this review, we comb through and focus on current developments of lanthanide-doped persistent luminescent scintillators (PersLSs), including their PersL mechanism, synthetic methods, tuning of PersL properties (e. g. emission wavelength, intensity, and duration time), as well as their promising applications (e. g. information storage, encryption, anti-counterfeiting, bio-imaging, and photodynamic therapy). We hope this review will provide valuable guidance for the future development of PersLSs.

Multimode Dynamic Photoluminescence of Bi3+-Activated ZnGa2O4 for Optical Information Encryption

Optical storage technology for information encryption is a popular means of safeguarding information. Herein, a Bi³⁺-activated ZnGa₂O₄ multimode dynamic photoluminescence (PL) material is developed. Upon being irradiated with an ultraviolet lamp at a fixed excitation wavelength of 254 nm, the ZnGa₂O₄: x% Bi³⁺ (x = 0.5-5.0) samples exhibit varying degrees of dynamic PL emission due to a distinct Bi³⁺ doping effect. The mechanism underlying the dynamic PL of ZnGa₂O₄: Bi³⁺ associated with Bi³⁺-activated trap concentration modulation is investigated using thermoluminescence spectra. Additionally, the ZnGa₂O₄: 5% Bi³⁺ sample shows a reversible thermally responsive dynamic PL with a color variation from blue to red upon heating from 283 to 393 K. Predesigned procedures based on single-wavelength-mediated photochromic and thermochromic dynamic PL emissions of ZnGa₂O₄: Bi³⁺ are designed for rewritable optical data storage and high-level information encryption. Also, an enhanced encryption scheme with a mask encoding technique applying a ZnGa₂O₄: Bi³⁺ hybridized polyvinylidene difluoride film is then proposed to increase the security level. Accordingly, this work provides a feasible way to rationally design dynamic PL material offering more creative designs for safeguarding information via encryption.