Anti-counterfeiting Applications Research Articles

Near-Infrared Persistent Luminescence of CaTiO3:Cr,Y for Imaging of Bone Implants Using Red-Light Illumination Instead of X-ray.

Near-infrared (NIR) persistent luminescence (PersL) materials have unique optical properties with promising applications in bioimaging and anticounterfeiting. However, their development is currently hindered by poor red-light-exciting ability. In this study, CaTiO3:Cr0.001,Y0.02 (CTCY) was synthesized with 650 nm-excited 772 nm NIR PersL. The Y3+ doping in the Ca2+ lattice plays a key role in the PersL property. A charge compensation mechanism was proposed, in which Cr3+ in the Ti4+ lattice was stabilized by Y3+-doping while oxygen vacancies were generated to store the excitation energy at the same time. A thermal ionization mechanism might elucidate the red-light-excited NIR PersL of CTCY, which benefits from the perovskite structure of CaTiO3. CTCY has 120 times more intense red-light-excited PersL than Zn3Ga2Ge2O10:Cr. Its potential applications in luminescence anticounterfeiting and bioimaging were demonstrated using a visible/NIR dual-channel PersL flower painting and a CTCY-labeled bone screw for in situ reactivable PersL imaging using red light illumination instead of X-ray, respectively. This study not only provides a new NIR PersL material but also will add to our understanding in developing other potential red-light- or even NIR-activable PersL materials with perovskite-like structures.

Harnessing hetero-atom doped CQDs from Pyrostegia venusta for latent fingerprint and anti-counterfeit applications

The development of innovative techniques for latent fingerprint (LFP) analysis and anti-counterfeiting applications is crucial for addressing various societal challenges. Quantum dot (QD)-based fluorescent staining offers a promising approach due to its high sensitivity. However, the toxicity of traditional heavy metal-containing QDs necessitates the exploration of eco-friendly alternatives. This study presents a facile and environmentally sustainable method for synthesizing heteroatom (nitrogen, phosphorus, and potassium)-doped carbon quantum dots (N-P-K@CQDs) derived from the flower extract of Pyrostegia venusta. Characterization revealed spherical CQDs with an average size of approximately 4.7 nm, a quantum yield of 25 %, and excellent water solubility, photostability, and greenish-fluorescent properties. N-P-K@CQDs were incorporated into a cornstarch nanocomposite phosphor, which exhibited greenish fluorescence under UV excitation. The nanocomposite was utilized as a fluorescent marker for LFP analysis using a customized smartphone-based dactyloscope. Python-based image processing algorithms were employed to enhance and analyze the fluorescence images of the developed LFPs. Additionally; a proof-of-concept anti-counterfeiting tag was demonstrated using CQDs-based ink, enabling the detection of concealed security marks. The findings highlight the potential of eco-friendly N-P-K@CQDs as a versatile platform for both LFP analysis and anti-counterfeiting applications.

Controllable multicolored optical glass-ceramics based on nanostructure strategies and dopants

Novel functional materials that integrate multiple tunable luminescence modes hold significant scientific and application potential. In this study, nanostructure strategies were employed to fabricate a series of microcrystalline glasses doped with rare-earth and transition-metal ions. The crystallization behavior of the nanocrystals (NCs) was revealed through high-resolution transmission electron microscopy (HRTEM), and the photoluminescence spectra of the samples were systematically investigated, demonstrating the achievement of independent and efficient visible light emission. With the further addition of the dopant Mn2+, it can occupy different sites to generate efficient energy transfer for ions, effectively improve the luminous efficiency, and changing the Mn2+ concentration can achieve a wide tunable color gamut. In addition, by exciting the glass samples with different excitation light sources, tunable emission of both red and blue was achieved. The results demonstrated the significant potential of the experimental samples as new multifunctional materials for optical dynamic anti-counterfeiting applications.

Bio-inspired colloidal photonic crystal pattern with multiple optical variable images

Colloidal photonic crystals (CPCs) are highly significant for display and anti-counterfeiting applications due to their vibrant structural colors and light-manipulating properties. Efficient and extensive CPC patterns is required for practical applications. Additionally, it is essential to incorporate complex optical elements or responsive qualities to the CPC patterns in order to enhance their performances for security applications. Herein, we proposed CPC patterns with alterable images revealed by changes in viewing angle or exposure to certain vapors. The CPC patterns were prepared by inkjet printing method. Through substrate modification to achieve varying wettability, angle-dependent optical adaptable images could potentially be shown by the patterns. The mesoporous silica nanoparticles (MSNs) were employed as building blocks to impart vapor-chromic characteristics to the CPC patterns. The CPC complex patterns responsive optical characteristics rendered them suitable for use in public authentication and anti-counterfeiting applications.

Unclonable Encryption-Verification Strategy Based on Bilayer Shape Memory Photonic Crystals.

The ability to reversibly exhibit structural color patterns has positioned photonic crystals (PCs) at the forefront of anti-counterfeiting. However, the security offered by the mere reversible display is susceptible to illicit alteration and disclosure. Herein, inspired by the electronic message captcha, bilayer photonic crystal (BPC) systems with integrated decryption and verification modules, are realized by combining inverse opal (IO) and double inverse opal (DIO) with polyacrylate polymers. When the informationized BPC is immersed in ethanol or water, the DIO layer displayed encrypted information due to the solvent-induced ordered rearrangement of polystyrene (PS) microspheres. The verification step is established based on the different structural colors of the IO layer pattern, which result from the deformation or recovery of the macroporous skeleton induced by solvent evaporation. Moreover, through the evaporation-induced random self-assembly of PS@SiO2 and SiO2 microspheres, unclonable structurally colored identifying codes are created in the IO layer, ensuring the uniqueness upon the verification. The decrypted code in the DIO layer is valid only when the IO layer displays the pattern with the predetermined structural color; otherwise, it is a pseudo-code. This structural color-based "decryption-verification" approach offers innovative anti-counterfeiting applications in nanophotonics.

Sign Inversion of Circularly Polarized Luminescence in Cholesteric Liquid Crystals Induced by Mercury Ions through Binaphthyl Dopants' Conjugation Control

Stimuli‐responsive circularly polarized luminescence (CPL) materials based on cholesteric liquid crystal (CLC) platforms show great promise for applications in information encryption and anticounterfeiting. In this study, we constructed a mercury ion‐responsive CPL system in CLCs by controlling the conjugation degree of axially chiral binaphthyl derivatives. Two chiral binaphthyl derivatives (R/S‐1 and R/S‐2) were initially used as chiral dopants to demonstrate that CPL inversion (glum values from 0.5/‐0.44 to ‐0.53/0.48) in CLCs could be achieved by modulating the conjugation degree of the chiral binaphthyls. Based on this concept, the thioacetal binaphthyl R‐2S was developed and used as a mercury‐responsive chiral dopant in CLCs. Under Hg ion treatment, the CPL sign inverted (glum value changed from 0.22 to ‐0.29) due to the transformation of the thioacetal into an aldehyde group. Additionally, the mercury ion‐responsive CPL material was applied in information encryption.

Sign Inversion of Circularly Polarized Luminescence in Cholesteric Liquid Crystals Induced by Mercury Ions through Binaphthyl Dopants' Conjugation Control.

Stimuli-responsive circularly polarized luminescence (CPL) materials based on cholesteric liquid crystal (CLC) platforms show great promise for applications in information encryption and anticounterfeiting. In this study, we constructed a mercury ion-responsive CPL system in CLCs by controlling the conjugation degree of axially chiral binaphthyl derivatives. Two chiral binaphthyl derivatives (R/S-1 and R/S-2) were initially used as chiral dopants to demonstrate that CPL inversion (glum values from 0.5/-0.44 to -0.53/0.48) in CLCs could be achieved by modulating the conjugation degree of the chiral binaphthyls. Based on this concept, the thioacetal binaphthyl R-2S was developed and used as a mercury-responsive chiral dopant in CLCs. Under Hg ion treatment, the CPL sign inverted (glum value changed from 0.22 to -0.29) due to the transformation of the thioacetal into an aldehyde group. Additionally, the mercury ion-responsive CPL material was applied in information encryption.

Dynamic, multi-color, multi-level stimulus-responsive luminescence in a co-crystallized coordination polymer: Modulation of energy transfer by acid-induced ligand protonation and photo-induced radical generation

Stimulus-responsive luminescent materials (SLMs), which can respond to external stimuli by switching their luminescence properties, hold great promise for a variety of applications. Particularly, multi-level SLMs with a logical stimulus sequence and a dynamic, multi-color transition are highly desirable for anti-counterfeiting and information encryption, but an effective design strategy is lacking. Herein, a co-crystallized coordination polymer multi-level SLM [Cd(9-AC)4]·(HAD)2·(9-HAC)2 (9-HAC for anthracene-9-carboxylic acid and AD for acridine) with dual emission centers of coordination unit ([Cd(9-AC)4]2-) and exciplex ([9-HAC/HAD]+) has been successfully constructed by a stepwise solvent process. This SLM possesses a variety of stimulus-responsive properties, including mechanochromic (MC), mechanochromic luminescence (MCL), reversible acidochromic luminescence (ACL), and reversible photochromic luminescence (PCL). Notably, both ACL and PCL properties are achieved by modulating the energy transfer process between the coordination unit and the exciplex, while there is a logical sequence between these two stimulus actions. The acid-induced activation and radical-regulated PCL performance has been exploited in the development of anti-counterfeiting and information encryption applications. This work provides an effective strategy to realize dynamic, multi-color, multi-level stimuli-responsive luminescence by modulating the energy transfer through acid-induced ligand protonation and photo-induced radical generation.

Anti-counterfeiting labels with controllable and anti-interference coding information based on core–shell Ag@SiO2 nanomaterials for ink printing

The core–shell structured Ag@SiO2 nanomaterial integrated with surface-enhanced Raman scattering (SERS) spectroscopy promises a critical application in anti-counterfeiting. Security labels have been fabricated based on Ag@SiO2 embedded with Raman reporters. The Ag@SiO2 nanomaterial shows good stability and excellent anti-interference property for anti-counterfeiting. Multiple kinds of Raman probe molecules have been anchored in the Ag@SiO2 labels to provide specific and abundant encoding information. The flexible encoding security information could be controlled conveniently by adjusting probe molecules, which not only enrich the SERS information but also improve the level of anti-counterfeiting. Furthermore, the Ag@SiO2 shown excellent stability in organic solvent, and successfully used in ink for the anti-counterfeiting application.

Ratiometric Light Conversion of Transition Metal Doped Zinc Gallate Phosphors for Dynamic Anti-counterfeiting Application

Ratiometric Light Conversion of Transition Metal Doped Zinc Gallate Phosphors for Dynamic Anti-counterfeiting Application

Strategic engineering of cationic systems for spatial & temporal anti-counterfeiting applications in zero-dimensional Mn(II) halides

While spatial and time-resolved anti-counterfeiting technologies have gained increasing attention owing to their excellent tunable photoluminescence, achieving high-security-level anti-counterfeiting remains a challenge. Herein, we developed a spatial-time-dual-resolved anti-counterfeiting system using zero-dimensional (0D) organic–inorganic Mn(II) metal halides: (EMMZ)2MnBr4 (named M−1, EMMZ=1-Ethyl-3-Methylimidazolium Bromide) and (EDMMZ)2MnBr4 (named M−2, EDMMZ=1-Ethyl-2,3-Dimethylimidazolium Bromide). M−1 shows a bright green emission with a quantum yield of 78 %. It undergoes a phase transformation from the crystalline to molten state with phosphorescence quenching at 350 K. Reversible phase and luminescent conversion was observed after cooling down for 15 s. Notably, M−2 exhibits green light emission similar to M−1 but undergoes phase conversion and phosphorescence quenching at 390 K, with reversible conversion observed after cooling down for 5 s. The photoluminescence switching mode of on(green)-off–on(green) can be achieved by temperature control, demonstrating excellent performance with short response times and ultra-high cyclic reversibility. By leveraging the different quenching temperatures and reversible PL conversion times of M−1 and M−2, we propose a spatial-time-dual-resolved photoluminescence (PL) switching system that combines M−1 and M−2. This system enables multi-fold tuning of the PL switch for encryption and decryption through cationic engineering strategies by modulating temperature and cooling time. This work presents a novel and feasible design strategy for advanced-level anti-counterfeiting technology based on a spatial-time-dual-resolved system.

Coordination-driven in-situ controlled synthesis of cellulose-based fluorescent composite with tunable color for decoration, anti-counterfeiting, and accurate color recognition

Fluorescent composites have widespread applications in many aspects. Wood-derived cellulose is a renewable, easily processed and biodegradable, and cellulose-based fluorescent composites are highly favored for in different fields. However, the existing cellulose-based fluorescent composites still have many urgent problems to be solved, such as unstable luminescence properties and easy shedding of luminescent substances, and the development of their practical applications is still a formidable challenge. Herein, a green and mild strategy for the in-situ controllable synthesis of cellulose-based fluorescent composites membrane (CFM) was developed. Firstly, delignified wood (DW) was modified with citric acid, and then lanthanide ions were introduced on modified DW through coordinated covalent bonds. Additionally, the luminescence mechanism of CFM is proposed. CFMs show adjustable color for decorative and light conversion and can be accurately identified for data protection, which increases the high value-added of cellulose-based composites. The stable luminescent properties were maintained after sonication for 30 min or solvent immersion for three months. Therefore, this work presents a new approach for the synthesis of CFM, which provides an environment-friendly strategy for manufacturing cellulose-based fluorescent materials, which is significant for the subsequent development of environment-friendly composites for anti-counterfeiting and decorative applications.

Heavy-Atom-Free Covalent Organic Frameworks for Organic Room-Temperature Phosphorescence via Förster and Dexter Energy Transfer Mechanism.

Covalent organic frameworks (COFs), with their accessible nanoscale porosity, selectable building blocks, and precisely engineered topology, offer unique benefits in the design of room-temperature phosphorescent (RTP) materials. However, their potential has been limited by phosphorescence quenching caused by interlayer π-π stacking interactions. This paper presents a novel strategy to enhance RTP in heavy-atom-free COFs by employing a donor-acceptor (D-A) system that leverages the Förster resonance energy transfer (FRET) and Dexter energy transfer (DET) mechanisms. Among the materials investigated, the best-performing COF exhibits a phosphorescence lifetime of 4.35ms at room temperature. Spectral analysis, structural analysis, and theoretical calculations indicate the presence of intralayer FRET processes as well as interlayer DET processes within the D-A COF system. Potential anti-counterfeiting applications are explored by exploiting the unique phosphorescent properties of these materials. Additionally, the inherent permanent porosity of COFs presents new opportunities for future development and application. This strategy offers many promising prospects for advancing the RTP technology in COF materials and broadens their potential applications in various fields.

From waste to wonder: Synthesizing carbon polymer dots (CPDs) from resin

Carbon polymer dots (CPDs) are fluorescent nanomaterials with diverse applications in sensing, bioimaging, and encryption. Conventional synthesis methods use hazardous precursors, hindering sustainability. We investigate CPD synthesis from waste resins like polyester, epoxy, polyamide, and alkyd. Our eco-friendly approach employs hydrothermal crosslinking polymerization (HTCP), repurposing waste and avoiding toxic precursors. Resultant CPDs exhibit adjustable photoluminescence suitable for anti-counterfeiting. We demonstrate their efficacy in encryption and anti-counterfeiting, enhancing intellectual property protection. We study reaction parameters to optimize CPD characteristics, aiming for improved performance and quantum yield. This research establishes sustainable CPD synthesis from waste, promoting anti-counterfeiting applications and broader utilization.

NH3 gas sensing and NH3-induced anti-counterfeiting based on nontoxic ternary copper halide

Lead-free ternary copper halides are emerging environmentally friendly materials, which have recently received great attention for their favorable optoelectronic properties. However, few attention was paid to their applications in gas sensing and gas-triggered fluorescence anti-counterfeiting. In this work, we demonstrate an effective Cs3Cu2I5 halide for NH3 sensing and NH3-triggered fluorescence anti-counterfeiting applications. The Cs3Cu2I5-based electrical NH3 sensor exhibits exceptional sensing performance, in which a resistance response of 77.8 % is achieved at 50 ppm NH3 with a rapid response time (9 s). To elucidate the NH3 sensing mechanism, we investigated the NH3-induced optical and structural evolutions including absorption, photoluminescence (PL), and Raman spectra. Our findings suggest that NH3 molecules, acting as electron donors, adsorb on the Cs3Cu2I5 surface, inducing the decomposition of Cs3Cu2I5 into CsCu2I3 and CsI. During this process, the CsCu2I3·NH3 intermediate phase is generated as a shell layer onto the surface of Cs3Cu2I5 grain, leading to an increase in electrical conductivity (or decrease in resistance), and an emission of bright yellow-red fluorescence from CsCu2I3. Inspired by NH3-induced fluorescence emission, we also explored a novel gas-triggered anti-counterfeiting method using Cs3Cu2I5-paper, demonstrating favorable reversibility and convenience, compared to previously reported water-triggered anti-counterfeiting techniques. This work will promote the development of design of Cs3Cu2I5 for gas sensing and gas-triggered fluorescence anti-counterfeiting applications in the future.

Fluorescent, multifunctional anti-counterfeiting, fast response electrophoretic display based on TiO2/CsPbBr3 composite particles

Traditional optical anti-counterfeiting (AC) is achieved by static printed images, which makes them susceptible to lower levels of security and easier replication. Therefore, it is essential to develop AC device with dynamic modulation for higher security. Electrophoretic display (EPD) has the advantages of low power consumption, high ambient contrast ratio, and capability of showing dynamic images which is suitable for dynamic AC applications. Herein, we prepared a dynamical AC device based on a fluorescent EPD, and achieving the image switch between black, white, and green fluorescence states under the dual-mode driving (electronic field and UV light). We loaded perovskite quantum dots (CsPbBr3) onto the TiO2 particles and further prepared fluorescent electrophoretic particles TiO2/CsPbBr3-3-PLMA (TiO/CPB-3) by grafting and polymerizing method. In addition, we fabricated the AC devices based on the fluorescent EPD, which exhibits the multifunctional AC, where the fluorescent EPD has a fast response time of 350 ms, a high contrast ratio of 17, and bright green fluorescence. This prototype demonstrates a new way for future dynamic AC and identification.

Synchronously Improved Multiple Afterglow and Phosphorescence Efficiencies in 0D Hybrid Zinc Halides with Ultrahigh Anti-Water Stabilities.

Zero-dimensional (0D) hybrid metal halides have been emerged as room-temperature phosphorescence (RTP) materials, but synchronous optimization of multiple phosphorescence performance in one structural platform remains less resolved, and stable RTP activity in aqueous medium is also unrealized due to serious instability toward water and oxygen. Herein, we demonstrated a photophysical tuning strategy in a new 0D hybrid zinc halide family of (BTPP)2ZnX4 (BTPP = benzyltriphenylphosphonium, X = Cl and Br). Infrequently, the delicate combination of organic and inorganic species enables this family to display multiple ultralong green afterglow and efficient self-trapped exciton (STE) associated cyan phosphorescence. Compared with inert luminescence of [BTPP]+ cation, incorporation of anionic [ZnX4]2- effectively enhance the spin-orbit coupling effect, which significantly boosts the photoluminescence quantum yield (PLQY) up to 30.66% and 54.62% for afterglow and phosphorescence, respectively. Synchronously, the corresponding luminescence lifetime extend to 143.94 ms and 0.308 μs surpassing the indiscernible phosphorescence of [BTPP]X salt. More importantly, this halide family presents robust RTP emission with nearly unattenuated PLQY in water and harsh condition (acid and basic aqueous solution) over half a year. The highly efficient integrated afterglow and STE phosphorescence as well as ultrahigh aqueous state RTP realize multiple anti-counterfeiting applications in wide chemical environments.

Multimode Luminesce Tailoring PMA4Na(In,Sb)Cl8 Organic-inorganic Hybrid Metal Halidevia Rigid Benzene Ring Induced Local Lattice Distortion.

Low dimensional organic-inorganic hybrid metal halide materials have attracted extensive attention due to their superior optoelectronic properties. However, low photoluminescence quantum yields (PLQYs) caused by parity-forbidden transition hinder their further application in optoelectronic devices. Herein, a novel yellow-emitting PMA4Na(In,Sb)Cl8 (C7H10N+, PMA+) low-dimensional OIMHs single crystal with a PLQY as high as 88% was successfully designed and synthesized, originating from the fact that the doping of Sb3+ effectively relaxes the parity-forbidden transition by strong spin-orbit (SO) coupling and Jahn-Teller (JT) interaction. The as-prepared crystal shows an efficient dual emission peaking 495 and 560 nm at low temperature, which are ascribed to different levels of 3P1 → 1S0 transitions of Sb3+ in [SbCl6]3- octahedral caused by JT deformation. Moreover, wide-range luminescence tailoring from cyan to orange can be achieved through adjusting excitation energy and temperature because of flexible [SbCl6]3- octahedral in the PNIC lattice. Based on a relative stiff lattice environment, the 560 nm yellow emission under 350 nm light excitation exhibits abnormal anti-thermal quenching from 8 to 400 K owing to the suppression of non-radiative transition. The multimode luminescence regulation enriches PMA4Na(In,Sb)Cl8 great potential in the field of optoelectronics such as temperature sensing, low temperature anti-counterfeiting and WLED applications.

Multimodal anti-counterfeiting and optical storage application based on luminescence reversible modification and color change of photochromic phosphor

Reversible upconversion luminescence (RUCL) modification based on photochromism has received considerable interest due to its potential applications in optical storage and invisible optical anti-counterfeiting. Herein, white β-Ba2ScAlO5: Yb3+, Er3+ (β-BSAO-YE) phosphor was irradiated with 254 nm light, which caused the phosphor to turn blue due to the increase of oxygen vacancy. The blue β-BSAO-YE phosphor returns to its original color upon stimulation with 808 nm laser light or 125 °C, exhibiting a double photo-induced reversible photochromic change. The green and red upconversion luminescence (UCL) of the β-BSAO-YE were reversibly modified according to their photochromic properties. The UCL modification changes the luminescence color of the pattern, indicating that β-BSAO-YE phosphor is an ideal compound anti-counterfeit agent. The light information recorded on the β-BSAO-YE binary photochromic dot matrix can be read under ultraviolet (UV) and near-infrared (NIR) excitation, demonstrating the potential application of β-BSAO-YE phosphors as optical data storage media. In addition, the cyclic experiment showed good photochromic and UCL modulation repeatability. The new luminescent β-BSAO-YE not only proposes a new way to exploring upconversion red light materials, but also provides new materials for optical storage, optical information and optical anti-counterfeiting.

Vacancy Effect on the Luminescent and Water Responsive Properties of Vacancy-ordered Double Perovskite Derivatives.

Vacancy-ordered perovskites and derivatives represent an important subclass of hybrid metal halides with promise in applications including light emitting devices and photovoltaics. Understanding the vacancy-property relationship is crucial for designing related task-specific materials, yet research in this field remains sporadic. For the first time, we use the Connolly surface to quantitatively calculate the volume of vacancy (V□, □ = vacancy) in vacancy-ordered double perovskite derivatives (VDPDs). A relationship between void fraction and the structure, photoluminescent properties and humidity stability was established based on zero-dimensional (0-D) [N(alkyl)4]2Sb□Cl5□'-type VDPDs. Compared with the more commonly studied A2M(IV)X6□-type double perovskite (A = cation, M = metal ion, X = halide), [N(alkyl)4]2Sb□Cl5□' features double vacancy sites. Our results demonstrate an inverse relationship between the photoluminescent quantum yield and V□ in 0-D VDPDs. Additionally, structural transformation from A2SbCl5 to A3Sb2Cl9 was first reported, during which the novel 'gate-opening' gas adsorption phenomenon was observed in VDPDs for the first time, as evidenced by 'S'-shaped sorption isotherms for water vapor, indicating a cation-controlled water-vapor response behavior. A mixed-cation strategy was developed to modulate the humidity stability of VDPDs. Characterized by controllable water-responsive behavior and unique 'on-off-on' luminescent switching, A2M(III)□X5□'-type materials show great promise for multi-level information anti-counterfeiting applications.