Anti-counterfeiting Labels Research Articles

Dynamic Anti-Counterfeiting Labels with Enhanced Multi-Level Information Encryption

Information encryption is an important means to improve the security of anti-counterfeiting labels. At present, it is still challenging to realize an anti-counterfeiting label with multi-function, high security factor, low production cost, and easy detection and identification. Herein, using inkjet and screen printing technology, we construct a multi-dimensional and multi-level dynamic optical anti-counterfeiting label based on instantaneously luminescent quantum dots and long afterglow phosphor, whose color and luminous intensity varied in response to time. Self-assembled quantum dot patterns with intrinsic fingerprint information endow the label with physical unclonable functions (PUFs), and the information encryption level of the label is significantly improved in view of the information variation in the temporal dimension. Furthermore, the convolutional residual neural networks are used to decode the massive information of PUFs, enabling fast and accurate identification of the anti-counterfeit labels.

Synthesis of MAPbBr3 -Polymer Composite Films by Photolysis of DMF: Toward Transparent and Flexible Optical Physical Unclonable Functions (PUFs) with Hierarchical Multilevel Complexity.

Physical entities with inherent randomness have been investigated as anti-counterfeiting labels based on physical unclonable functions (PUFs). Herein, a transparent and flexible optical PUF label associated with multilevel complexity is demonstrated by taking advantage of the optical properties of hierarchical morphologies of the composite film composed of metal halide perovskite nanoparticles (MAPbBr3 NPs) and the intrinsic spinodal-decomposition-like phase separation of polymer blend (PMMA/PS blend). Due to the combinatorial effects of the photolysis synthesis of MAPbBr3 and the thermodynamic instability of the PMMA/PS blend, randomized patterns emerge at two-level scales. These patterns are intrinsically non-deterministic, and therefore, the PUF labels from the multilevel random patterns are challenging to replicate. This is mainly attributed to random spot patterns (higher-level patterns) confined within intricate bicontinuous patterns (lower-level patterns).

Dual Responsive Dependent Background Color Based on Thermochromic 1D Photonic Crystal Multilayer Films.

In this paper, we present dual responsive one-dimensional (1D) photonic crystal (PC) multilayer films that utilize a high-humidity environment and temperature. Dual responsive 1D PC multilayer films are fabricated on precoated thermochromic film by sequential alternate layer deposition of photo-crosslinkable poly(2-vinylnaphthalene-co-benzophenone acrylate) (P(2VN-co-BPA)) as a high refractive index polymer, and poly(4-vinylpyrollidone-co-benzophenone acrylate) P(4VP-co-BPA) as a low refractive index polymer. The thermochromic film shows a vivid color transition from black to white at 28 °C. Three different colors of thermochromic 1D PC multilayer films are prepared by thickness modulation of P(4VP-co-BPA) layers, and the films on a black background exhibit visible spectrum color only in a high-humidity environment (over 90% relative humidity (RH)). For the three films placed on a hands display, three different composite colors are synthesized by the reflection of light, including yellow, magenta, and cyan, due to the changing of backgrounds from black to white with temperature. Additionally, the films show remarkable color transitions with reliable reversibility. The films can be applied as anti-counterfeiting labels and can be used for smart decoration films. To the best of our knowledge, this is the first report of dual response colorimetric films that change color in various ways depending on temperature and humidity changes, and we believe that it can be applied to various applications.

4D Direct Laser Writing of Submerged Structural Colors at the Microscale.

Biomimetic stimuli-responsive structure colors (SCs) can improve the visualization and identification in the micro functional structure field such as information encryption/decryption and smart actuators. However, it is still challenging to develop the ability to 4D print arbitrary submerged colorful patterns with stimuli-responsive materials at the microscale. Herein, a hydrogel photoresist with feature resolution (98nm) for the fabrication of 4D microscopic SCs by the femtosecond direct laser writing method is developed. The 4D printed woodpile SCs are grouped as pixel palettes with various laser parameters and they spanned almost the entire color space. The coloring mechanism of diffraction gratings is not only investigated by optics microscopy and spectroscopy but also supported by simulation. Moreover, the 4D printed hydrogel-integrated amphichromatic fish constructions and pixelated painting can visually discolor reversibly by regulating the solution pH. This finding promises an ideal coloring method for sensors, anti-counterfeiting labels, and transformable photonic devices.

Stable Core–Shell Structure Nanocrystals of Cs4PbBr6-Zn(moi)2 Achieved by an In Situ Surface Reconstruction Strategy for Optical Anticounterfeiting

Zero-dimensional Cs4PbBr6 nanocrystals (NCs) possess attractive photoluminescence (PL) properties and feature facile chemical synthesis, making them promising for application in luminescent materials. However, Cs4PbBr6 remains sensitive to polar solvents and thermal stimuli because of soft ionic nature of Cs4PbBr6 and dynamic behavior of surface ligands. Herein, a strategy controlled by an in situ surface coordination reaction is developed to fabricate stable NCs with a Cs4PbBr6-Zn(moi)2 core-shell structure. It was found that the Cs4PbBr6 surface regulated by the use of 2-mercaptoimidazole (called moi) and the coordination between the -NH group of moi and Zn2+ is critical for the formation of Cs4PbBr6-Zn(moi)2 core-shell NCs. Meanwhile, the thickness of the Zn(moi)2 shell can be facilely controlled by the growth time because of the solubility of moi and Zn(OAc)2·2H2O in ethyl acetate. Compared to bare Cs4PbBr6, Cs4PbBr6-Zn(moi)2 NCs exhibited highly improved polar solvent resistance and thermal stability. By combining the sensitivity of Cs4PbBr6 and the stability of Cs4PbBr6-Zn(moi)2, we used two NCs as PL security inks to fabricate optical anticounterfeiting labels. Thus, the disposable or reusable optical anticounterfeiting label is achieved by changing the external dual-stimuli. This work provides a novel strategy to enhance the stability of Cs4PbBr6 and develop its potential interest for application in anticounterfeiting technologies.

Multiple stimuli-responsive properties of Coumarin-Salicylaldehyde Schiff Bases

Organic small-molecules of multiple stimuli-responses were widely paid attention, which can be applied in multiple fields simultaneously, such as thermal sensor, force response, pH probe, reagents for the detection of metal ion and so forth. In the present work, three novel coumarin derivatives (XDS-R) were synthesized from various salicylaldehydes containing different substituents (R = H, Cl, Br), following by investigations about their multiple stimuli-responsive properties concerning aggregation-induced emission (AIE), mechanochromism, thermochromism and pH response. Single crystals of XDS-R indicate that intramolecular hydrogen bonds cause the restriction of intramolecular vibration, leading to AIE character and mechanochromic property. Interestingly, two substituents (H, Cl) have little effect on fluorescence intensity and color, and whereas have distinguishable influences on functionalized fluorescence response. In the pH range of 2.00–8.00, only XDS-H exhibited regular pH-response, while XDS-Cl and XDS-Br showed excellent pH tolerance. Mechanochromic XDS-R is able to recover to original state under heating. A simple multilevel anticounterfeit label was made by the combination of XDS-Cl and previous-reported DDHAC without an automatic heat-inspired recovery. Combined multilevel stimuli-responsive material of XDS-Cl and previous DDHAC displayed potential application of anti-counterfeiting mark.

Charge transfer band excited (Sr,Ba)2YTaO6:Eu3+ reddish-orange-emitting phosphors for luminescence lifetime thermometry and flexible anti-counterfeiting labels

Strong reddish-orange-emitting (Sr,Ba)2YTaO6:Eu3+ phosphors were synthesized via a facile solid-state reaction. Due to the occupation of Y3+ ions in the high symmetry (Oh) sites as an inversion symmetry site, the 5D0 → 7F1 magnetic dipole transition peak was dominant in the (Sr,Ba)2YTaO6:Eu3+ phosphors under the charge transfer band excitation. Both Sr2YTaO6:Eu3+ (SYTO:Eu3+) and Ba2YTaO6:Eu3+ (BYTO:Eu3+) phosphors exhibited good thermal stability and quantum yield. Their luminescence sensing performances (relative sensing sensitivity) were determined to be 0.18% K−1 (BYTO:0.1Eu3+) and 0.13% K−1 (SYTO:0.1Eu3+) with the aid of the Struck and Fonger models. Furthermore, novel deep ultraviolet-excited phosphors-based polydimethylsiloxane flexible light-emitting films were fabricated for anti-counterfeiting applications. Consequently, this work reveals that the strong reddish-orange-emitting (Sr,Ba)2YTaO6:Eu3+ phosphors are suitable for dual-functional applications including luminescence lifetime thermometry and flexible anti-counterfeiting labels.

Controllable in situ generated carbon black hollow silica (C@h-SiO2) photonic crystal inks with highly saturated structural colors

The structural color of photonic crystals is usually whitish and has low saturation due to multiple incoherent scattering effects, limiting its application in practical visual observation. Herein, by controlling the calcination time of PS@SiO2 nanoparticles, we obtain hollow SiO2 with different in situ generated carbon black contents and assemble them into photonic crystal inks (PCIs). PCIs have excellent saturation and high crystallinity due to the in-situ generated carbon black capable of absorbing incoherently scattered light without affecting particle assembly. PCIs are further converted into non-close-packed photonic crystal films with highly saturated structural colors by photopolymerization of resins. This photonic crystal film can be swollen by an ethanol-water mixture, resulting in structural color changes and shifts in reflection peaks. Moreover, the photonic crystal film can dynamically change from a dry opaque state to an ethanol-wetted translucent state. Such solvent-responsive photonic crystal films with highly saturated structural colors are expected to be used in alcohol sensors and color anti-counterfeiting labels.

Three-Dimensional Printing of Dipeptides with Spatioselective Programming of Crystallinity for Multilevel Anticounterfeiting.

The functionalities of peptide microstructures and nanostructures can be enhanced by controlling their crystallinity. Gaining control over the crystallinity within the desired structure, however, remains a challenge. We have developed a three-dimensional (3D) printing method that enables spatioselective programming of the crystallinity of diphenylalanine (FF) dipeptide microarchitectures. A femtoliter ink meniscus is used to spatially control reprecipitation self-assembly, enabling the printing of a freestanding FF microstructure with programmed shape and crystallinity. The self-assembly crystallization of FF can be switched on and off at will by controlling the evaporation of the binary solvent. The evaporation-dependent crystallization was theoretically studied by the numerical simulation of supersaturation fields in the meniscus. We found that a 3D-printed FF microarchitecture with spatially programmed crystallinity can carry a 3D digital optical anisotropy pattern, applicable to generating polarization-encoded anticounterfeiting labels. This crystallinity-controlled additive manufacturing will pave the new way for facilitating the creation of peptide-based devices.

Efficient luminescence of doped bismuth oxychloride nanophosphors and its surfaces prompted applications

The materials which cater to excellent sensitivity, superior contrast, inexpensive and eco-friendly are in urgent need for law enforcement applications. To overcome these barriers, red-emitting BiOCl:Eu3+ (1–9 ​mol %) nanophosphors were prepared by the self-ignited combustion method. The powdered x-ray diffraction profiles were well indexed to a tetragonal phase of BiOCl without any traces of impurities. The 2-dimensional agglomerated irregular flake-like structures without any clear boundaries were clearly revealed. The photoluminescence emission spectra consist of distinct sharp peaks at ∼ 536, 555, 594, 621, 652 and 698 ​nm, which were owing to 5D1→7F1, 5D1→7F2, 5D0→7F1, 5D0→7F2, 5D0→7F3 and 5D0→7F4 transitions of Eu3+ ions, respectively. A noticeable increment in the photoluminescence emission intensity with an increase of activator Eu3+ concentration up to 5 ​mol % and later it diminished. The dipole-dipole interaction was mainly responsible for observed concentration quenching. The estimated commission international de l'eclairage coordinates are found in orange-red as well as a red region in the diagram, indicating that the emission color can be tuned by varying activator Eu3+ ions concentration. The fingerprints developed using optimized nanophosphor showed distinctive papillary ridge particulars and hence specifies the higher sensitivity without any background hindrance. The aged fingerprints developed on the glass surface retained their ridge characteristics up to level 2 even after being stored for 180 days. The developed anti-counterfeiting labels can only be decoded under ultra-violet 365 ​nm light with clear intense red color. The obtained results clearly demonstrated the effectiveness of the fluorescence nanophosphor for latent fingerprint visualization and data encryption applications.

A novel highly thermal-stable red-emitting CaGdSbWO8:Eu3+ phosphor with scheelite structure for high CRI w-LEDs,security ink, and latent fingerprint

Recently, rare-earth doped phosphors have been newly developed and applied in hot issues such as phosphor-converted light-emitting diodes (pc-LEDs), anti-counterfeiting, and fingerprint visualization. Herein, an Eu 3+ -activated CaGdSbWO 8 (CGSW) red phosphor was synthesized by a high-temperature solid-state reaction. The phosphors can exhibit narrow red-light emission at 614 nm due to the electric dipole transition 5 D 0 → 7 F 2 of Eu 3+ . Impressively, this phosphor has excellent thermal stability, its emission intensity of optimum sample doped with 0.30 Eu 3+ remained 90.61% at 420 K and thermal quenching temperature exceeds 480 K. The Commission International del’Eclairage (CIE) chromaticity coordinates of CGSW:0.30Eu 3+ are (0.662, 0.338) with a high color purity (98.5%). The fabricated white light diode (w-LED) has a high color rendering index (91.4) and a low correlated color temperature (4986 K) with CIE coordinates (0.343, 0.327). Further experimental results showed that the prepared security ink can be applied to anti-counterfeit labels and information encryption. The latent fingerprint developed by CGSW:0.30Eu 3+ phosphor present the excellent selectivity and contrast. The level 1–3 structural characteristics of latent fingerprints could be well identified under ultraviolet irradiation. Therefore, the Eu 3+ -activated CGSW red-emitting phosphor has broad application prospects due to its excellent luminescence properties. • Novel CaGdSbWO 8 :Eu 3+ phosphors have been synthesized via high-temperature solid-state method. • The CaGdSbWO 8 :Eu 3+ phosphors with scheelite structure have good thermal stability ( T 0.5 >480 K). • The w-LED fabricated by the phosphor exhibits a high CRI value of 91.4 and a good CCT of 4986 K. • The applications in security ink and latent fingerprint of CaGdSbWO 8 :Eu 3+ phosphors are investigated in details.

Enhanced Upconversion Photoluminescence of LiYF4: Yb3+/Ho3+ Crystals by Introducing Mg2+ Ions for Anti-Counterfeiting Recognition

By doping appropriate lanthanide ions, LiYF4 as a host luminescent material can simultaneously exhibit bright visible-light emission. A series of LiYF4:Yb3+/Ho3+ microparticles with different Mg2+ doping concentrations were synthesized and investigated. The crystal structure of the synthesized microparticles was tested by X-ray diffraction (XRD). Notably, a significant increase in the upconversion photoluminescence intensity of upconversion microparticles (UCMPs) was obtained by introducing Mg2+ ions under 980 nm laser excitation, and achieved a maximum level when the concentration of Mg2+ ions was 8 mol%. Additionally, the practicality of the resultant UCMPs used as the raw material of anti-counterfeiting ink was systematically investigated. These results prove that the Mg2+-doped LiYF4:Yb3+/Ho3+ are very promising as screen-printing materials for anti-counterfeiting recognition labels.

Surface regulation by bifunctional BODIPY to fabricate stable CsPbBr3 for multi-layered optical anti-counterfeiting

Cesium lead halide perovskite quantum dots (QDs) have attracted immense attention for luminescent materials due to their narrow emission bands and color-tunable emission. However, indispensable surface ligands originating from ligand-assisted synthesis strategies severely deteriorate the stability and luminescence properties of QDs since these ligands have a highly dynamic binding. Herein, we used a green fluorescence BODIPY molecule containing thiol (named SH-BDP) to regulate the CsPbBr3 QDs surface by ligand regulation. Density functional theory calculations proved that the SH-BDP molecule could bind to the exposed Pb of CsPbBr3 QDs stronger than traditional ligands to form stable SH-BDP-QDs. Moreover, the SH-BDP fixed on the CsPbBr3 QDs surface can improve water and light resistance. It also served as a knob to tune their luminescence properties and the reversible thermal-stimuli response. Finally, the multi-response property of SH-BDP-QDs was realized under polar solvent or heat along with UV light. In addition, we used the SH-BDP-QDs to create various anti-counterfeiting labels; several luminous modes were achieved under different external stimuli, which improved the quality of the optical anti-counterfeiting labels and ensured information security. This work indicates the immense potential of surface ligand manipulation in improving the stability and multi-stimuli-responsive optical encoding of perovskite quantum dots.

Mie-Resonant Silicon Nanoparticles for Physically Unclonable Anti-Counterfeiting Labels

Mie-Resonant Silicon Nanoparticles for Physically Unclonable Anti-Counterfeiting Labels

Environmentally friendly gelatin-based ink with durability on low surface energy substrates for anti-counterfeiting printing

Recent research is keen to introduce biomass materials into inks to develop "green” printing, but little attention has been given to whether these inks can be truly widely used in printing industry. There are few bio-based inks suitable for low surface energy plastic such as polyethylene glycol terephthalate (PET), which is one of the most common printing substrates. Herein, waterborne polyurethane with polyfluoroalkyl side chain (F-WPU) was designed and synthesized to prepare fluorocarbon quantum dots (F-CDs). F-WPU and F-CDs were mixed together with gelatin to obtain environmentally friendly inks which were utilized to print on a low surface energy substrate. F-WPU (30 wt%) and F-CDs (0.5 wt%) significantly improve the mechanical properties of composites by forming an interpenetrating network system and hydrogen bonds , respectively. Abundant carbon-fluorine bonds effectively reduce the surface energy of gelatin, resulting in excellent hydrophobicity and strong adhesion to the PET surface. The thermal stability of the composite could significantly enhance to meet the promising needs for the further engineering applications. Besides, F-CDs could emit blue-green fluorescence based on conjugated structure and π→π* transition under a wider excitation wavelength. Therefore, the complex exhibited good transparency under sunlight and performed significant cyan fluorescence under an ultraviolet irradiation, in which can be efficiently developed and used in anti-counterfeiting labels and printing. Furthermore, the friction, soaking and kneading tests have been measured to seriously take the considerations for the stable dry and wet fastness for the PET films, which could industriously expand the ink applications. • A durable and environmentally friendly gelatin-based ink was prepared. • Fluorinated waterborne polyurethane and carbon quantum dots were obtained. • F-WPU and F-CDs enhanced the mechanical strength and hydrophobicity of gelatin. • F-CDs contributes fluorescence characteristics and anti-counterfeiting value. • Composite gelatin is a potential anti-counterfeiting ink for PET surface printing.

Whispering-gallery-mode full-color laser textiles and their anticounterfeiting applications

Light-emitting fabric can facilitate the innovation of wearable display applications. Electronic and luminescent textiles capable of communicating, sensing, and supplying energy have been achieved. However, a facile strategy for fabricating large-area flexible lasing textiles has not yet been reported. In this work, we propose a gravity-assisted rotatory drawing method for fabricating flexible lasing microfibers, which can be woven into multicolor lasing textiles. By regulating the doped dyes and solution viscosity, we achieve the mass manufacturing of lasing microfibers with different emission colors and modes and further weave them into full-color textiles with a wide color gamut, approximately 79.1% larger than that of standard RGB space. For application, we print nanoparticle patterns on the lasing textile and encode it with programmable lasing signal distribution, which can supply an anticounterfeiting label for efficient authentication. This work unifies the fabrication and application of lasing textiles, and we expect that this will provide a new platform for flexible lasing devices.

Bio-derived chlorophyll dye doped cholesteric liquid crystal films and microdroplets for advanced anti-counterfeiting security labels

Herein, we have shown security codes based on an advanced anti-counterfeiting material that are difficult to duplicate and are substantially distinct from the present technology. The anti-counterfeiting material can be made by dispersing green synthesized chlorophyll from spinach leaves into cholesteric liquid crystal (Red, Green and Blue reflections). The resultant anti-counterfeiting material reflects color in daylight (Red/Green/ Blue) due to the reflection property of CLCs and magenta color in UV light due to the fluorescence property of chlorophyll. Furthermore, we have shown that anti-counterfeiting material confined to spherical microdroplets produced by glass capillary microfluidic approach exhibit dual-mode display and security ink properties under daylight and ultraviolet light, including authenticate/non-authenticate QR codes, implying their potential applications in anti-counterfeiting technologies for the protection of valuable objects. These color variations are easily detectable in real time and may be used to create anti-counterfeiting patterns with color changesin both reflection and fluorescence modes. Because of the easy technique, we believe this can give a new platform for numerous security and color-based applications that is more cost-effective and environmentally friendly than traditional approaches.

The pH sensitive fluorescence SiO2@TEuTTA/CS composite films and inks for anti-counterfeiting

Functional chitosan (CS) composite films have wide application prospects in many fields. Herein, the lanthanide inorganic-organic hybrid nanospheres with an average diameter of 252 nm (SiO2@TEuTTA) were synthesized by surface modification of silica nanospheres. And the SiO2@TEuTTA was used as luminescent materials and SiO2@TEuTTA/CS composite films were prepared by a simple solution casting method. Subsequently, the compositions and structure, fluorescence and mechanical properties of the SiO2@TEuTTA/CS composite films were characterized. The results show that the SiO2@TEuTTA/CS composite films not only have the smooth surface, high fluorescence property, good flexibility and transparency, but also can emit a bright red color under a 365 nm UV lamp. These provide an important basis for the application of the SiO2@TEuTTA/CS composite films on the anti-counterfeiting packing labels. Additionally, the SiO2@TEuTTA/CS solutions have been successfully used as anti-counterfeiting inks due to its transparency and pH sensitive properties. Compared with the traditional luminescent anti-counterfeiting inks, the pH sensitive SiO2@TEuTTA/CS inks can improve the level of information security, which indicates that the SiO2@TEuTTA/CS inks hold great promise for anti-counterfeiting fields.

Dynamic Fluorescent Anti-Counterfeiting Labels Based on Conjugated Polymers Confined in Submicron Fibrous Membranes.

Developing a new anti-counterfeiting strategy is of great significance to combating the global counterfeiting problem. Here we report the construction of a dynamic fluorescence response system for anti-counterfeiting by combining the photochromism induced by the ring-opening of spiropyran (SP) to merocyanine (MC) with the fluorescence resonance energy transfer (FRET) between the conjugated polymer and MC. After elucidating the design principle, a new conjugated polymer, PPETE-SP, consisting of a poly[p-(phenylene ethynylene)-alt-(thienylene-ethynylene)] (PPETE) backbone with pendant SP, was synthesized and characterized. With poly(methyl methacrylate) (PMMA) as the matrix, the PPETE-SP/PMMA fibrous membrane was prepared via electrospinning. Under the irradiation of UV light, the fluorescent color of the membrane dynamically changed from green to light green, then light pink, and finally pink, and this process was reversible under visible light. The fluorescence emission switch was examined for 10 cycles and proved to have good repeatability, indicating that the membrane can be directly used as an anti-counterfeiting label for multiple verifications. The FRET efficiency was found to be about 61% based on the FRET study with confocal laser scanning microscopy. The covalent bonding between PPETE backbone and SP, the confinement of PPETE-SP chains in the fibrous membrane, as well as employing PMMA as the matrix were demonstrated to be crucial in realizing the photochromism and the FRET. Different anti-counterfeiting modes were proposed, providing rich selections for operation of verification. Such facile-to-operate and hard-to-imitate dynamic fluorescent responsive materials are very promising for use in practical anti-counterfeiting applications.

Direct laser printing of high-resolution physically unclonable function anti-counterfeit labels

Security labels combining facile structural color readout and physically unclonable one-way function (PUF) approach provide promising strategy for fighting against forgery of marketable products. Here, we justify direct femtosecond-laser printing, a simple and scalable technology, for fabrication of high-resolution (12 500 dots per inch) and durable PUF labels with a substantially large encoding capacity of 10895 and a simple spectroscopy-free optical signal readout. The proposed tags are comprised of laser-printed plasmonic nanostructures exhibiting unique light scattering behavior and unclonable 3D geometry. Uncontrollable stochastic variation of the nanostructure geometry in the process of their spot-by-spot printing results in random and broadband variation of the scattering color of each laser printed “pixel,” making laser-printed patterns unique and suitable for PUF labeling.