Anti-counterfeiting Labels Research Articles

Dynamic coloration of polymerized cholesteric liquid crystal networks by infiltrating organic compounds

We demonstrate the dynamic coloration of polymerized cholesteric liquid crystal (PCLC) networks templated by the “wash-out/refill” method in the presence of organic compounds. The reflection colors were modulated by two key approaches, that is, the injection of mutually soluble organic fluids into a microfluidic channel and the diffusion of volatile organic compounds (VOCs). The reversible tuning of reflected colors with central wavelengths between ∼450 nm and ∼600 nm was achieved by alternative injection of nematic liquid crystal E7 (nav = 1.64) and benzyl alcohol (n = 1.54) using syringe pumps. The fascinating iridescence with reflection centers from ∼620 nm to ∼410 nm was presented from the volatilization and diffusion of alcohol as a model VOC. Additionally, the flow velocity of fluid and the diffusion time were adjusted to explore the underlying mechanism for the dynamic coloration of cholesteric networks. This work is expected to extend the study of PCLCs as a dynamically tunable optofluidic reflector, visually readable sensor, or compact anti-counterfeit label in response to organic compounds.

N-Doped Carbon Dots Embedded in Silica Nanoparticles with Multicolor Luminescence for Light-Emitting Devices

To overcome the aggregation-caused quenching of carbon dots (CDs) in the solid state, this work presented a facile approach for in situ synthesis of N-doped CDs (N-CDs) in silica particles with the assistance of a bifunctional organic base, tetramethylammonium hydroxide (TMAOH). In this approach, TMAOH first acted as a basic catalyst, which can dissociate into TMA+ and OH–, to direct the growth of TMA+-embedded SiO2 particles. The TMA+ in silica particles was then used as the precursor for in situ synthesis of N-CDs via pyrolysis, resulting in the formation of N-CD-embedded SiO2 (N-CDs/SiO2) particles. The N-CDs/SiO2 particles presented tunable emission color from blue to green and yellow, depending on the amounts of TMAOH used in the reactions. More importantly, the resulting N-CDs/SiO2 particles exhibited bright and stable emission in both solution and solid states, making them potentially useful in the fabrication of anti-counterfeiting labels and light-emitting devices.

Bioinspired Quasi-3D Multiplexed Anti-Counterfeit Imaging via Self-Assembled and Nanoimprinted Photonic Architectures.

Innovative multiplexing technologies based on nano-optics for anti-counterfeiting have been proposed as overt and covert technologies to secure products and make them difficult to counterfeit. However, most of these nano-optical anti-counterfeiting materials are metasurfaces and metamaterials with complex and expensive fabrication process, often resulting in materials that are not damage tolerant. Highly efficient anti-counterfeiting technologies with easy fabrication process are targeted for intuitive and effective authentication of banknotes, secure documents, and goods packing. Here, a simple strategy exploiting self-assembling and nanoimprinting technique to fabricate a composite lattice photonic crystal architecture featuring full spatial control of light, multiplexed full-pixel imaging, and multichannel cryptography combined with customized algorithms is reported. In particular, the real-time encryption/recognition of mobile quick response codes and anti-counterfeiting labels on a postage stamp, encoded by the proposed photonic architecture, are both demonstrated. The wave optics of scattering, diffraction, and polarization process involved are also described, validated with numerical simulations and experiments. By introducing a new degree of freedom in the 3D space, the multichannel image switching exhibits unprecedented variability of encryption, providing a promising roadmap to achieve larger information capacity, better security, and higher definition for the benefit of modern anti-counterfeiting security.

An ultrastrong, reversible thermochromic film based on TEMPO-oxidized nanofibrillated cellulose

Despite the growing interest in polydiacetylene (PCDA)-based materials in recent years due to their thermal-stimuli responsive discoloration characteristics, it is still a huge challenge to fabricate high-performance and environment-friendly thermochromic materials. In this work, we demonstrated ultrastrong thermochromic materials based on 1,6-Diaminohexane (DH) crosslinked 2,2,6,6-tetramethylpiperidine-1-oxylradi-cal (TEMPO)-oxidized nanofibrillated cellulose (TNFC) matrix and poly-PCDA chains through a vacuum-assisted filtration assembly technique. The synergistic interactions of covalent cross-linking networks efficiently prevented crack propagation under loading, endowed the resulting TNFC-polyPCDA-DH nanocomposites with super high tensile strength of 281.63 ± 5.63 MPa and Young's modulus of 13.68 ± 1.09 GPa. Moreover, the resultant nanocomposites exhibited a rapidly reversible thermal discoloration (up to 140 °C), and excellent thermal reversible cycling performance. This strategy offers a promising approach to design and prepare flexible high-performance intelligent nanocomposite, which may be widely applied in wearable sensors, displays, and anti-counterfeiting labels.

Water-based flexographic ink using chalcones exhibiting aggregation-induced enhanced emission for anti-counterfeit applications

In pursuit of fluorescent pigments, a pyrene-based chalcone 1-(4-chlorophenyl)-3-(3a1,6,8a,10a-tetrahydropyrene-1-yl)prop-2-en-1-one (CPP), which exhibited aggregation-induced enhanced emission was synthesized. Water-based eco-friendly flexographic inks were formulated using CPP (in batch ink) and Luminous yellow RG-3 (in standard ink) as pigments. The batch and standard inks were coated on security paper and printed on security and packaging papers as well as boards. The printed substrates displayed yellow fluorescence upon excitation under UV light. The gloss, light-fastness, abrasion resistance and colorimetric values of the batch ink were superior to that of standard ink. The study revealed the potential of CPP as a fluorescent pigment for security printing applications, optical-electronic devices such as transistors, anti-counterfeiting labels, etc.

Pixelated Microsized Quantum Dot Arrays Using Surface-Tension-Induced Flow.

Quantum dots (QDs) are semiconducting nanoparticles that exhibit unique fluorescent characteristics when excited by an ultraviolet light source. Owing to their highly saturated emissions, display panels using QDs as pixels have been presented. However, the complications of the nanofabrication procedure limit the industrial application of QDs. This study suggests a method to arrange high-aspect-ratio QD pixels by inducing both Laplace-pressure-driven capillary flow and thermally driven Marangoni flow. The evaporation of colloidal QDs induces a capillary flow that drives the QDs toward the inner tips of V-shaped structures. Additionally, the Marangoni flow arranges the gathered QDs at the tip; thus, they could form a high dune, overcoming the limitations of the existing capillary assembly method using evaporation. Using these phenomena, clover-shaped (assembly of V-shaped edges) templates were made to gather numerous QDs, and the clover with a 30° angle afforded the highest brightness among all the angle structures. Finally, by demonstrating a 100-cm2-sized QD microarray with high uniformity (98.6%), our method shows the feasibility of large-area fabrication, which has extensive application in manufacturing QD displays, anti-counterfeiting labels, and other QD-based optical devices.

Carbon Dots‐in‐EuAPO‐5 Zeolite: Triple‐Emission for Multilevel Luminescence Anti‐Counterfeiting

Multilevel luminescence materials have aroused wide attention for their advanced anti-counterfeiting abilities. However, various complicated stimuli factors involved in multilevel luminescence anti-counterfeiting (MlLA) limit the practical applications of such materials. Herein, carbon dots (CDs) are in situ introduced into Eu-substituted AlPO4 -5 zeolite (named CDs@EuAPO-5) via a solvent-free thermal crystallization method, which exhibits triple emissions including pink fluorescence mainly associated with Eu3+ in the zeolite framework, blue fluorescence and green room temperature phosphorescence (RTP) associated with CDs. CDs are uniformly embedded in the EuAPO-5 zeolite matrix. Such composite displays excellent photo-, thermo-, and solvent resistance, as well as long-term storage-stability. Moreover, the triple emissions of the composite only need two kinds of common excitation lights to trigger, without involving other complicated stimuli. A triple-level luminescence anti-counterfeiting (TlLA) label has been built, realizing facile, quick, and advanced luminescence anti-counterfeiting that is hard to copy.

Photo masking via breaking alkyl C Se bond of selenium-containing maleimide polymers by ultraviolet light

• Obtained polymer with alkyl C Se bond has similar transparency with polystyrene (PS), higher the refractive index than PS and comparable thermostability with PS. • The pattern is directly visual under natural light without any extra treatments and the reaction condition of photo-corsslinking does not require photoacid, photoinitiator and other agents. • The obtained pattern has excellent solution resistance, duo to its cross-linked structure. • The pattern keeps a smooth surface without deformation, which avoides its distortion. To investigate the complexity of breaking aryl C Se bond, alkyl C Se bond and alkyl C S bond by ultraviolet light, three maleimide polymers are employed as objects, including SePhP which reported in our previous work having aryl C Se bond, SePP which synthesized via radical copolymerization of N -(4-selenophenyl)-propyl maleimide and styrene having alkyl C Se bond and SPP which synthesized via radical copolymerization of N -(4-thiophenyl)-propyl maleimide and styrene having alkyl C S bond. After careful structure characteristics, SePhP, SePP and SPP are treated by ultraviolet light, as a result, only C Se bond of SePP can be broken. When SePP is irradiated by ultraviolet light in an oxygen-free condition, it can make a structure change from linear to cross-linked and refractive index decrease of polymer. Furthermore, utilizing photo-crosslinking and changing of refractive index of SePP after ultraviolet light irradiation, we realize visual photomask patterning in a simple system, which will bring great potential in display devices, anti-counterfeit labels, and etc.

Development of Eco-Efficient Smart Electronics for Anticounterfeiting and Shock Detection Based on Printable Inks

Printed electronics are expected to meet an increasing demand for improved functionality and autonomy of products in the context of Internet-of-Things. With this trend, the environmental performance of novel technologies is of growing importance. The current study presents the life cycle assessment of two novel devices: an anticounterfeit label based on the electrochromic display and a shock-detection tag based on the piezoelectric sensor, designed for the use in packaging of pharmaceuticals and luxury items to improve the safety and accountability in the supply chain. The devices are manufactured by means of energy-efficient printing techniques on a low-cost flexible and recyclable paper substrate. Comprehensive cradle-to-grave analysis contributes to industrial-scale energy and material life cycle inventories and identifies the main impact hotspots evaluated for a broad range of categories of the ReCiPe midpoint (H) impact assessment method. Results show that major impact burdens are associated with the near-field communication chip and radio-frequency identification antenna, while the impacts of solvents, process energy, electrochromic display/piezoelectric sensor, Li-ion battery, and substrate are comparatively small. In terms of their global warming potential, both the anticounterfeit label and shock-detection tag embody around 0.23 kg of CO2-equiv. Several material-use reduction and material-substitution strategies are quantified and discussed for their potential to reduce high impacts of the antenna.

Sustainable roll-to-roll manufactured multi-layer smart label

Sustainability in electronics has a growing importance due to, e.g. increasing electronic waste, and global and European sustainability goals. Printing technologies and use of paper as a substrate enable manufacturing of sustainable electronic devices for emerging applications, such as the multi-layer anti-counterfeit label presented in this paper. This device consisted of electrochromic display (ECD) element, NFC (near field communication) tag and circuitry, all fully roll-to-roll (R2R) printed and assembled on plastic-free paper substrate, thus leading to a sustainable and recyclable device. Our setup uses harvested energy from HF field of a smartphone or reader, to switch an electrochromic display after rectification to prove authenticity of a product. Our novelty is in upscaling the manufacturing process to be fully printable and R2R processable in high-throughput conditions simulating industrial environment, i.e. in pilot scale. The printing workflow consisted of 11 R2R printed layers, all done in sufficient quality and registration. The printed antennas showed sheet resistance values of 32.9±1.9 mΩ/sq. The final yield was almost 1500 fully printed devices, and in R2R assembly over 1400 labels were integrated with 96.5% yield. All the assembled tags were readable with mobile phone NFC reader. The optical contrast (ΔE*) measured for the ECDs was over 15 for all the printed displays, a progressive switching time with a colour change visible in less than 5 s. The smart tag is ITO-free, plastic-free, fully printed in R2R and has a good stability over 50 cycles and reversible colour change from light to dark blue.

Multi-functional plasmonic fabrics: A flexible SERS substrate and anti-counterfeiting security labels with tunable encoding information

Multi-functional plasmonic fabric comprised of silver nanoparticles (Ag NPs) and cotton gauze was fabricated through an in-situ growth method. Ag NPs with high density were immobilized on the surface of cotton fibers. The plasmonic cotton gauze exhibits excellent flexible features, temporal stability and SERS enhancement factors close to 105 × . The plasmonic cotton gauze was labelled with multiplexed Raman probes and used for anti-counterfeiting applications. The encoding information could be readily changed by adjusting the ratio between components in the mixture of Raman probe molecules. This novel strategy could create rich Raman information based on the combination of a few Raman probes, which significantly increases the security levels in anti-counterfeiting. The plasmonic cotton gauze was also employed as a flexible SERS substrate for sensing pesticide from irregular surfaces of orange by a simple swiping process.

Rare-Earth Doping Graphitic Carbon Nitride Endows Distinctive Multiple Emissions with Large Stokes Shifts

Rare-Earth Doping Graphitic Carbon Nitride Endows Distinctive Multiple Emissions with Large Stokes Shifts

A pH-sensitive ESIPT molecule with aggregation-induced emission and tunable solid-state fluorescence multicolor for anti-counterfeiting and food freshness detection

Achieving stimulus-responsive multicolor solid-state photoluminescence based on a single fluorescence compound has potential applications in anti-counterfeiting labels and visual detection. However, few such organic chromophores have these features and been used in this fields. In this study, multiple pH-sensitive sites were incorporated into a single molecule of succinimide substituted 2-(2′-hydroxyphenyl)Benzothiazole derivative (BTSA) that was Aggregation induced emission (AIE) and Excited state intramolecular proton transfer (ESIPT) active, exhibiting multilevel and highly secured anti-counterfeiting abilities. Under ammonia atmosphere, BTSA exhibits reversible switching between the green and blue fluorescence. By rationally manipulating two stimuli (acid and base), BTSA labels incredibly shows four different emission colors. The multicolor fluorescence changes are irreversible and evidently depend on the order of acid-base added. Together with smartphone that can quickly and accurately identify the multiple colors, BTSA affords a new covert fluorescent anti-counterfeiting technique with high security through the combination of reversible and irreversible fluorescence multicolor changes, as well as order and stimuli-dependent luminescent patterns. In addition, BTSA labels are successfully applied for real-time and visual monitoring the food freshness of pork and shrimp. The molecular design rationale presented here provide a new design strategy for the purposes of multicolor anti-counterfeiting and food freshness detection.

Unclonable Micro-Texture with Clonable Micro-Shape towards Rapid, Convenient, and Low-Cost Fluorescent Anti-Counterfeiting Labels.

An ideal anti-counterfeiting label not only needs to be unclonable and accurate but also must consider cost and efficiency. But the traditional physical unclonable function (PUF) recognition technology must match all the images in a database one by one. The matching time increases with the number of samples. Here, a new kind of PUF anti-counterfeiting label is introduced with high modifiability, low reagent cost (2.1 × 10-4 USD), simple and fast authentication (overall time 12.17 s), high encoding capacity (2.1 × 10623 ), and its identification software. All inorganic perovskite nanocrystalline films with clonable micro-profile and unclonable micro-texture are prepared by laser engraving for lyophilic patterning, liquid strip sliding for high throughput droplet generation, and evaporative self-assembling for thin film deposition. A variety of crystal film profile shapes can be used as "specificator" for imagerecognition, and the verification time of recognition technology based on this divide-and-conquer strategy can be decreased by more than 20 times.

A system for identifying an anti-counterfeiting pattern based on the statistical difference in key image regions

An important aspect of identifying whether items are likely to be forged or infringe upon a copyright is the use of an anti-counterfeiting pattern because it can help in determining and detecting forged anti-counterfeiting labels and patterns. At present, most anti-counterfeiting systems require special materials or large samples of images for training. Once they are geometrically attacked or forged by printing and scanning, they will be completely invalid. Therefore, this paper proposes an anti-counterfeiting system that uses a single corresponding feature difference sequence of the key regions for statistical analysis. The aim of our technology is to use the inks to generate random subtle texture patterns, and construct a supervised and guided segmentation algorithm and bone width transformation algorithm to locate the key regions of the sample images, which is used to identify the authenticity of the inspected product. The experiment shows that the system not only has high anti-counterfeiting performance and good robustness but also provides a convenient and practical idea for anti-counterfeiting technology.

Nonvolatile Optically Reconfigurable Radiative Metasurface with Visible Tunability for Anticounterfeiting.

Control of thermal emission underpins fundamental science, as it is related to both heat and infrared electromagnetic wave transport. However, realizing nonvolatile reconfigurable thermal emission is challenging due to the inherent complexity or limitation in conventional radiative materials or structures. Here, we experimentally demonstrate a nonvolatile optically reconfigurable mid-infrared coding radiative metasurface. By applying laser pulses, infrared emissive patterns are directly encoded into an ultrathin (∼25 nm) Ge2Sb2Te5 layer integrated into a planar optical cavity with the optically crystallized Ge2Sb2Te5 spots, and the peak spectral emissivity is repeatedly switched between low (∼0.1) and high (∼0.7) values. In addition, the visible scattering patterns are independently modulated with submicron-sized bumps generated by high-power laser pulses. An anticounterfeiting label is demonstrated with spatially different infrared emission and visible light scattering information encoded. This approach constitutes a new route toward thermal emission control and has broad applications in encryption, camouflage, and so on.

The Effect of Nitrogen Incorporation on the Optical Properties of Si-Rich a-SiCx Films Deposited by VHF PECVD.

The influence of N incorporation on the optical properties of Si-rich a-SiCx films deposited by very high-frequency plasma-enhanced chemical vapor deposition (VHF PECVD) was investigated. The increase in N content in the films was found to cause a remarkable enhancement in photoluminescence (PL). Relative to the sample without N incorporation, the sample incorporated with 33% N showed a 22-fold improvement in PL. As the N content increased, the PL band gradually blueshifted from the near-infrared to the blue region, and the optical bandgap increased from 2.3 eV to 5.0 eV. The enhancement of PL was suggested mainly from the effective passivation of N to the nonradiative recombination centers in the samples. Given the strong PL and wide bandgap of the N incorporated samples, they were used to further design an anti-counterfeiting label.

Anticounterfeiting Labels with Smartphone‐Readable Dynamic Luminescent Patterns Based on Tailored Persistent Lifetimes in Gd2O2S:Eu3+/Ti4+

AbstractDynamic luminescent labels, in which a luminescent image changes with time after ultraviolet excitation is turned off, are attractive for anticounterfeiting. A sequence of Gd2O2S:Eu3+/Ti4+ phosphors is presented in which the Ti4+ doping concentration allows the persistent emission lifetime to be varied from 1.17 ± 0.02 to 5.95 ± 0.07 s. While this persistent lifetime is tuned, the photoluminescence quantum yield remains over 46% ± 3%. A broad charge‐transfer band allows these phosphors to be excited with inexpensive and relatively safe 375 nm light‐emitting diodes. By developing patterns with phosphors that have differing persistent lifetimes, dynamic changes in the luminescent image after the excitation source is removed can be observed. For patterns made from phosphor materials that have big differences in persistent lifetimes, these dynamic changes are observable by the eye. By contrast, the dynamic changes in patterns made by phosphors with comparable persistent lifetimes (0.20 s delayed lifetime difference) are difficult to observe by the naked eye but can be easily determined by analysis of a 30‐frames‐per‐second video taken with a smartphone. Thus, these bright phosphors with tunable persistent lifetime allow both overt (observable by eye) and covert (requiring smartphone video analysis) dynamic anticounterfeiting labels to be created.

Optical Fireworks Based on Multifocal Three-Dimensional Color Prints.

Colorful three-dimensional (3D) prints are promising as practical anticounterfeiting labels with easily recognizable and striking visual effects. However, existing colorful 3D displays either require specific illumination conditions with multiple coherent lasers, hence suffer from speckles, or are unsuitable as passive labels. Here, we report a concept of a virtual 3D color object consisting of colorful focal spots in free space. The colors and corresponding "floating heights" of these spots are independently controlled via the design of 3D printed microlens profiles and heights of nanopillars that act as structural-color filters. Despite the unremarkable appearance of the printed substrate under both optical and electron microscopy, illumination with incoherent white light reveals information in the form of bright colorful spots appearing at designated heights above the plane of the substrate. The term "optical fireworks" refers to the way these spots appear and disappear under an optical microscope as one continuously shifts the focal plane. Our 3D printed optical fireworks security labels introduce applications for optical elements integrated with nanostructures in 3D colorful displays and anticounterfeiting labels.

Dual-stimuli responsive color-changing nanofibrous membranes as effective media for anti-counterfeiting and erasable writing

The development of reusable paper-like media that respond to more than one stimulus to achieve anti-counterfeiting and erasable writing remains challenging. Herein, dual-stimuli responsive color-changing nanofibrous membranes were fabricated based on solvo- and thermochromoic prussian blue analogues (PBAs) and electrospinning technology. The prepared Co-PBA and polyacrylonitrile (Co-PBA/PAN) composite nanofibrous membranes exhibited instantaneous and obvious color changes upon exposure to heat or solvents e.g. ethanol. Together with excellent flexibility, stability, reversibility and cycle performance, Co-PBA/PAN nanofibrous membranes have been successfully applied for fabricating anti-counterfeiting labels and rewritable paper with dual stimulus response capabilities. Moreover, anti-counterfeiting labels with extended complexity were also fabricated by exploiting the tunable transition temperature and loading content of Co-PBA.