A novel self-activated ultraviolet persistent luminescence material and its anti-counterfeiting application based on intensity and time resolution from persistent luminescence

Nonstoichiometry-Induced Self-Activated Phosphors for Dynamic Anti-counterfeiting Applications

Optical signals with distinctive properties, such as contactless, fast response, and high identification, are harnessed to realize advanced anti-counterfeiting. However, the simultaneous attainment of multi-color, -temporal, and -modal luminescence performance remains a compelling and imperative pursuit. In our work, a temperature/photon-responded dynamic self-activated luminescence originating from nonstoichiometric Zn2GeO4 is developed with the modulation of intrinsic defects. The increased concentration of oxygen vacancies (VO••) contributes to an enhanced recombination of ZnGe″-VO••, ultimately improving the self-activated luminescence performance. Additionally, the photoluminescence (PL) color of the representative Zn2.2GeO4 sample changes from green to blue-white with the increased ultraviolet (UV) irradiation time. Concurrently, the emission color undergoes a variation from blue to green as the ambient temperature raises from 280 to 420 K. Remarkably, green long persistent luminescence (LPL) and photostimulated luminescence (PSL) behaviors are observed. Herein, this study elucidates a sophisticated anti-counterfeiting approach grounded in the dynamic luminescent attributes of nonstoichiometric Zn2GeO4, presenting a promising frontier for the evolution of anti-counterfeiting technologies.

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.

Viscoelasticity‐Controlled Relaxation in Wrinkling Surface for Multistage Time‐Resolved Optical Information Encryption

As counterfeit techniques continue to evolve, ensuring the security of conventional "static" encryption methods becomes increasingly challenging. Here, the viscoelasticity-controlled relaxation is introduced for the first time in a bilayer wrinkling system by regulating the density of hydrogen bond networks in polymer to construct a "dynamic" encryption material. The wrinkling surface can manipulate light during the dynamic relaxation process, exhibiting three stages with frosted glass, structural color, and mirror reflection. By regulating the viscoelasticity of skin layer through UV irradiation, the wavelength and the relaxation rate of the wrinkles can be controlled. As a result, dynamic wrinkling anti-counterfeiting patterns and time-resolved multistage information encryption are achieved. Crucially, the encryption material is developed as an anti-counterfeiting label for packing boxes in daily applications, allowing the encrypted information to be activated manually and identified by naked eyes, surpassing the existing time-resolved encryption materials in utilization potential. Besides, the dynamic hydrogen bond networks are extended to various dynamic interaction networks, demonstrating the versatility of the dynamic encryption strategy. This work not only provides an additional dimension for dynamic information encryption in daily practical use, but also offers theoretical guidance for the development of advanced optical anti-counterfeiting and smart display materials in the future.

Dynamic anti-counterfeiting and information encryption of Sr3Y2Ge3O12: Tb3+, Er3+ phosphor via carriers filling and release processes

Complex and high-security-level anti-counterfeiting strategies with multiple luminescent modes are extremely critical for meeting the requirement of constantly developing information storage and information security. In this work, Tb³⁺ ions doped Sr₃Y₂Ge₃O₁₂ (SYGO) and Tb³⁺/Er³⁺ co-doped SYGO phosphors are successfully fabricated and are unitized for anti-counterfeiting and information encoding under distinct stimuli sources. The green photoluminescence (PL), long persistent luminescence (LPL), mechano-luminescence (ML), and photo-stimulated luminescence (PSL) behaviors are respectively observed under the stimuli of ultraviolet (UV), thermal disturbance, stress, and 980 nm diode laser. Based on the time-dependence of the filling and releasing rate of the carriers from the shallow traps, the dynamic information encryption strategy is proposed by simply changing the UV pre-irradiation time or shut-off time. Moreover, a tunable color from green to red is realized by prolonging the 980 nm laser irradiation time, which is attributed to the elaborate cooperation of the PSL and upconversion (UC) behaviors. The anti-counterfeiting method based on SYGO: Tb³⁺ and SYGO: Tb³⁺, Er³⁺ phosphors herein possess an extremely high-security level with attractive performance for designing advanced anti-counterfeiting technology.

Shortwave Ultraviolet Persistent Luminescence of Sr2MgSi2O7: Pr3

Currently, extensive research activities are devoted to developing persistent phosphors which extend beyond the visible range. In some emerging applications, long-lasting emission of high-energy photons is required; however, suitable materials for the shortwave ultraviolet (UV-C) band are extremely limited. This study reports a novel Sr₂MgSi₂O₇ phosphor doped with Pr³⁺ ions, which exhibits UV-C persistent luminescence with maximum intensity at 243 nm. The solubility of Pr³⁺ in the matrix is analysed by X-ray diffraction (XRD) and optimal activator concentration is determined. Optical and structural properties are characterised by photoluminescence (PL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) spectroscopy techniques. The obtained results expand the class of UV-C persistent phosphors and provide novel insights into the mechanisms of persistent luminescence.

Can Potted Plants Catch Mosquitoes? Applying Rare-Earth Luminescent Materials and Plant Energy to the Development of Innovative Mosquito-Trapping Potted Plants

Due to the global warming crisis, the spread of various infectious diseases is worsening, with mosquito-borne contagious diseases posing a significant threat. While many residential and public spaces contain plants, often for greening the environment and improving mental and physical well-being, the carbon dioxide released by these plants produces ideal habitats for mosquitoes. Considering the quality of life of urban residents and the development of health-related products simultaneously is an important topic. This study used diverse complementary techniques, such as energy-storing rare-earth luminescent materials, sustainable power generation using plant energy, blue light-emitting diodes, and environmentally friendly fermentation formula, to develop planting products with potential mosquito control functionality. The prototype design for this mosquito-trapping potted plant has been patented. The aim of this paper is to discuss the design principles adopted to improve the defects of existing mosquito-trapping designs, the green energy materials and techniques employed, the architecture configuration of the product prototype, and the test results. By integrating green materials and technology, the prototype can be self-powered without being plugged in to yield conspicuous energy savings. The results showed that the developed multi-function products, combined with the concept of energy sustainability, can improve global public health as well as individuals' physical and mental health.

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

Persistent luminescent materials (PLMs) are promising candidates for the anti-counterfeiting and information encryption field. However, ultraviolet (UV) excitation and visible emission are partially responsible for enabling information that has been encrypted to combat counterfeiting to be accessed by trial and error, resulting in imitation and information leakage. Here, we propose the possibility of controlling the persistent luminescent (PersL) emission spectra and its excitation light source with the use of band gap engineering, while obtaining X-ray exciting, not UV exciting UV PLM for advanced anti-counterfeiting and encryption application. Cationic substitution was used to adjust the width of the band gap of Lu(X)O₄ (X = V, Nb, Ta, and P) from ∼4 to 9 eV. In addition, Bi³⁺ was introduced into the host as an emitter, which enabled the PersL emission spectra to be modulated from ∼550 to 230 nm. Among these PLMs, LuPO₄:Bi³⁺ has unique optical properties. Under UV excitation, LuPO₄:Bi³⁺ exhibits weak, inconspicuous visible down-conversion luminescence (DCL), without PersL ceasing once excitation is discontinued. Interestingly, LuPO₄:Bi³⁺ displays UV PersL after X-ray excitation, and human eyes are insensitive to UV PersL, which requires specialized optical equipment to detect. A proof-of-concept assessment of LuPO₄:Bi³⁺ for anti-counterfeiting and information encryption applications demonstrated its suitability in this regard.

High-level information encryption based on optical nanomaterials with multi-mode luminescence and dual-mode reading

High-level information encryption based on a visible up-conversion and invisible persistent luminescence material.