Anti-counterfeiting Materials Research Articles

Reversible Temperature Sensing using Blue-Winged Grasshopper Coloracris azureus Wings.

Thermochromic materials have been widely investigated due to their relevance in technological applications, including anti-counterfeiting materials, fashion accessories, displays, and temperature sensors. While many organisms exhibit color changes, few studies have explored the potential of the responsive natural materials for temperature sensing, especially given the often limited and irreversible nature of these changes in live specimens. Here, it is shown that the hindwings of the blue-winged grasshopper Coloracris azureus can act as a reversible, power-free bio-thermometer, transitioning from blue to purple/red in a 30-100°C temperature range. Using microspectrophotometry, light microscopy and Raman microscopy, it is found that the blue color of the wings originates from pigmentary coloration, based on a complex of astaxanthin and proteins. The thermochromic shift from blue to red, induced by a temperature increase, is attributed to a denaturation of this carotenoprotein complex, upon which astaxanthin is released. This process is reversible upon a subsequent temperature decrease. The color changes are both swift and consistent upon temperature change, making the grasshopper's wings suitable as direct visual sensors on thermally dynamic, curved surfaces. The potential possibilities of sustainable, power-free temperature sensors or microthermometers based on biomaterials are demonstrated.

Stabilization of Ti3+ in CaTiO3 by doping Y3+ to generate visible light-activated near-infrared persistent luminescence

Near-infrared (NIR) persistent luminescence (PersL) materials have interesting invisible self-luminescent properties, but most of them can only be effectively activated by UV light. In the present study, Ca0.97TiO3:Y0.02 (CaTiO3:Y) is found with visible-light-excited PersL at ∼770 nm lasting at least for 5 h. The PersL is derived from the broad absorption of Ti3+, which is stabilized by Y3+-doping via a charge compensation strategy. The PersL excitation spectrum has a peak at ∼ 400 nm, extending to 720 nm. Y3+-doping at Ca2+ site stimulates the generation of more oxygen vacancies and the stabilization of luminescent Ti3+. The Cr-free property makes CaTiO3:Y an environmentally friendly anti-counterfeiting luminescent material. The interaction between narrow band gap CaTiO3 and proper energy levels of Ti3+ is of vital importance in the successful development of visible-light-excited PersL materials. This study provides a new member of Cr-free NIR PersL material with intense visible-light-excited luminescent property and has certain guidance on developing other visible-light-excited PersL materials.

Preparation of photoresponsive lanthanide aluminate-immobilized nanofibers from recycled bioplastic via solution blowing spinning for optical authentication labeling

Photochromism is an intriguing technology to enhance the authentication of various commercial materials. In order to produce a transparent authentication film, it is also significant to improve the engineering process of anti-counterfeiting materials. In contrast to electrospinning, the solution blowing spinning (SBS) technique has been recently developed to produce nanofibers at low-cost and high yield with no need to apply high voltage. It has been essential to reduce the toxic pollution caused by plastic waste. Herein, we develop a photoluminescent nanofibrous membrane from recycled polylactic acid (PLA) waste and nanoparticles of strontium aluminate (NSA) by using the simple SBS technique. We investigated the potential use of the NSA@PLA composite nanofibers for photochromic anti-counterfeiting driven by ultraviolet light. Encapsulating the nanoparticle form of the strontium aluminate phosphor into polylactic acid nanofibers is necessary to ensure the transparent characteristic of the nanofibrous film. The film transparency can be further improved by the efficient dispersion of NSA without aggregation in the polylactic acid solution. Nanofibrous membranes with varying emission characteristics were produced by varying the NSA ratio. Both of X-ray diffraction (XRD) and Transmission electron microscopy (TEM) demonstrated the morphology of NSA to show diameters of 5–12 nm. The morphologies of the nanofibrous membranes were examined using various analytical methods, including energy-dispersive X-ray spectroscopy (EDX), X-ray fluorescence spectroscopy (XRF) and scanning electron microscopy (SEM). The mechanical characteristics and optical luminescence were also examined. SEM analysis of the NSA@PLA nanofibers showed diameters of 100–220 nm. The NSA@PLA nanofibrous membranes exhibited an emission peak at 518 nm upon excitation at 365 nm. The contact angles of the NSA@PLA nanofibrous membranes increased from 138.2° to 144.5° as the NSA concentration was increased, indicating an improved superhydrophobicity. Exposure to ultraviolet light caused the transparent nanofibers to undergo a rapid and strongly reversible photochromism to greenish emission. The present study can be reported as an easy and efficient approach to create anti-counterfeiting materials that offer a perfect market with social and financial profits.

B ← N coordination bond reinforced dynamic fluorescence of pH-responsive amphiphile alginate aggregates for anti-counterfeiting

High quantum yield polysaccharide-based materials are significative for the dynamic anti-counterfeiting, while that are limited by weak fluorescence. However, natural polysaccharides with weak fluorescence are not suitable for anti-counterfeiting. Herein, alginate derivatives (SA-PBA) exhibiting aggregation-induced emission with high-quantum yields were synthesized by grafting phenylboronic acid (PBA) onto a sodium alginate (SA) chain. As the concentration increases, polymer assembly can be induced to form more compact soft colloidal aggregates, which enhances the fluorescence properties of alginate derivatives by introducing B ← N coordination bonds in the hydrophobic microregions. Interestingly, the clustered aggregates of SA-PBA can be dynamically controlled by pH, realizing the reversible adjustment of fluorescence. The corresponding mechanism is revealed by the combination of coarse-grained simulations and experiments. It is found that SA-PBA uses a hydrophobic driving force and hydrogen bond interaction to self-assemble in an aqueous solution and promote fluorescence emission. Moreover, the fluorescence quantum yield of SA-PBA can reach 14.4 % and can be reversibly altered by tuning soft colloidal microstructures. Therefore, a reversible information encryption system of SA-PBA is developed for anti-counterfeiting. This work shed some light on how to design novel anti-counterfeit materials based on natural polysaccharides and optimize the dynamic fluorescence conditions.

Dual-mode optical thermometry and multilevel anti-counterfeiting based on Er3+/Eu3+ doped Ba5Gd8Zn4O21 phosphors

Designing and manufacturing novel anti-counterfeiting materials with multilevel, strong readability and inexpensive is a crucial challenge. Herein, a batch of Ba5Gd8(1-x-y)Zn4O21:xEu3+/yEr3+ phosphors with long persistent and multicolor luminescence were synthesized. Their structure and luminescence properties were studied through X-ray diffraction, scanning electron microscope, lifetime decay curves, emission, excitation, thermoluminescence and diffuse reflection spectra. Under different wavelengths irradiation, Ba5Gd8Zn4O21:Eu3+, Ba5Gd8Zn4O21:Er3+ and Ba5Gd8Zn4O21:Eu3+, Er3+ emit strong red, green and multicolor (green, yellow, red) luminescence, respectively. Importantly, Ba5Gd8Zn4O21:Eu3+ and Ba5Gd8Zn4O21:Eu3+, Er3+ phosphors exhibit long-lasting luminescence after 254 nm and X-ray radiation. Combine long afterglow and multicolor emissions under X-ray, UV and 980 nm laser excitation, these materials successfully achieve multilevel anti-counterfeiting. In terms of optical temperature measurement, the maximum relative sensitivity of Ba5Gd7.44Zn4O21:0.07Er3+ based on thermal coupling levels (2H11/2/4S3/2) and non-thermal coupling levels (4F9/2/2H11/2) of Er3+ are 1.29 % K−1 and 0.34 % K−1, respectively. Both two modes exhibit superior repeatability (98 %) in 333–573 K temperature range which can realize self-calibration temperature sensing. All findings reveal great potential of these phosphors for multilevel anti-counterfeiting and efficient optical temperature sensing.

Immobilization of lanthanide-doped strontium aluminate into electrospun nanofibrous film of poly(vinyl chloride) and cellulose acetate hybrid towards smart authentication

Photochromic inks have proven an appealing authentication approach to boost the anti-counterfeiting efficiency of commercial products. However, photochromic inks have considerable drawbacks such as poor durability and high cost. Herein, we develop a cutting-edge anti-counterfeiting material using new photochromic nanofibers. Electrospun poly(vinyl chloride)/cellulose acetate (PVCA) hybrid nanofibrous (80–320 nm) films were used to encapsulate nanoparticles of lanthanide-doped strontium aluminate (NLSA; 4-14 nm). Durability and photostability were guaranteed by the current authentication nanofibrous films encapsulated with an inorganic photochromic agent. NLSA-encapsulated PVCA nanofibers (NLSA@PVCA) showed excellent reversibility and photostability. When varying the concentrations of NLSA, a wide variety of photochromic and afterglow PVCA nanofibers were created with distinct emission properties. Under normal lighting conditions, NLSA@PVCA was invisible, but under ultraviolet (UV) illumination, a green emission was detected. The photochromic fibrous films were analyzed in a number of analytical techniques to determine their structure and chemical composition. Paper coated with NLSA@PVCA was studied to learn more about its mechanical properties. The excitation wavelength was reported to be 365 nm, indicating transparency, while the emission wavelength was reported to be 520 nm, designating a green color. Anti-counterfeiting of commercialized goods can be accomplished with the help of the current PVCA nanofibrous film.

Stimulus-responsive polymer materials toward multi-mode and multi-level information anti-counterfeiting: recent advances and future challenges.

Information storage and security is one of the perennial hot issues in society, while the further advancements of related chemical anti-counterfeiting systems remain a formidable challenge. As emerging anti-counterfeiting materials, stimulus-responsive polymers (SRPs) have attracted extensive attention due to their unique stimulus-responsiveness and charming discoloration performance. At the same time, single-channel decryption technology with low-security levels has been unable to effectively prevent information from being stolen or mimicked. As a result, it would be of great significance to develop SRPs with multi-mode and multi-level anti-counterfeiting characteristics. This study summarizes the latest achievements in advance anti-counterfeiting strategies based on SRPs, including multi-mode anti-counterfeiting (static information) and multi-level anti-counterfeiting (dynamic information). In addition, the promising applications of such materials in anti-counterfeiting labels, identification platforms, intelligent displays, and others are briefly reviewed. Finally, the challenges and opportunities in this emerging field are discussed. This review serves as a useful resource for manipulating SRP-based anti-counterfeiting materials and creating cutting-edge information security and encryption systems.

Correction: Construction of energy transfer channels from [SbCl6]3− to Ln3+ (Ln3+ = Ho3+, Er3+) in Cs2NaGdCl6 for advanced anti-counterfeiting materials

Correction for ‘Construction of energy transfer channels from [SbCl6]3− to Ln3+ (Ln3+ = Ho3+, Er3+) in Cs2NaGdCl6 for advanced anti-counterfeiting materials’ by Yanyang Li et al., J. Mater. Chem. C, 2024, 12, 12589–12597, https://doi.org/10.1039/D4TC02186J.

Enhancement of the dynamic luminescence and self-recovery performance in Zn2+ co-doped Sr3Ga4O9: Sm3+

Dynamic luminescence materials overcome the disadvantage of traditional static anti-counterfeiting materials that are easy to imitate, but the repeated display of dynamic luminescence is still a challenge. In this work,...

New anti-counterfeiting materials based on hemicyanine dyes: HSO3−/SO32− encryption and UV light decryption

UV excitation, the adduction reaction products of hemi-cysteine dyes with HSO3−/SO32− generate reactive oxygen species, triggering structural restoration and color transition, which are then applied in anti-counterfeiting color-changing technology.

Stimulated-source-independent persistent luminescence phosphor Sr2Ta2O7:Tb3+, Tm3+ for multi-mode anti-counterfeiting applications

The multi-mode luminescent anti-counterfeiting materials Sr2Ta2O7:Tb3+, Tm3+ were prepared, which possessed DC, UC, PSL, and PersL modes.

A visible-light regulated luminescent switch based on a spiropyran-derived Pt(II) complex for advanced anti-counterfeiting materials.

A dual optical switch regulated by visible light has been developed through an integrated strategy, including luminescent Pt(II) and photochromic spiropyran (SP) as a triplet-sensitizer and photo-regulator building block, respectively. An efficient Förster resonance energy transfer (FRET) process is achieved, along with apparent and emissive color changes under visible light irradiation and temperature stimuli, which was utilized to develop advanced anti-counterfeiting materials.

Dynamically photo-tunable multicolor luminescence of supramolecular gel based on fluorescent gelator and used for information encryption

The ingenious collaboration of photo-isomerized molecules and luminescent gelator can create self-supporting materials used for multi-level and multi-dimensional information encryption. Herein, a supramolecular gel (SDTD) was prepared by using photoluminescent gelator 1,3:2,4-di(benzylidene)-D-sorbitol (DBS), lanthanide ions (Tb3+), as well as reversible photo-isomerized diarylethylene (DTE), and spiropyran (SP) derivative. Rheological studies showed that the prepared SDTD gel possessed good self-supporting ability owing to the 3D network structure formed by DBS aggregates. Additionally, SDTD gel displayed dynamic multicolor luminescence due to the presence of three luminescent centers including DBS, Tb3+, and MC-o (the photoisomer of SP). The luminescent color of SDTD gel can be easily tuned by irradiation wavelengths and time. It was found that a photo-tunable fluorescence resonance energy transfer (FRET) occurred between Tb3+ and MC-o, Tb3+ and DTE-c (the photoisomer of DTE), the corresponding FRET efficiency was 47 % and 52 %, respectively. The results also indicated that the photo-tunable inner filter effect (IFE) occurred between DBS and DTE-c, DBS and MC-o, respectively, which endowed SDTD gel with dynamically photo-tunable multicolor luminescence capability. SDTD gel has the advantages of simple preparation, low cost, and flexible luminescence regulation. In addition, based on the multicolor luminescence of SDTD gel, a new method of multi-dimensional information encryption was proposed, which shows a potential application in the field of anti-counterfeiting materials.

Rare earth-based halide double perovskite phosphor Cs2NaScCl6: Yb3+, Er3+ for multi-mode anti-counterfeiting application

At present, most fluorescent anti-counterfeiting technologies on the market are based on single-mode luminescence, which generally have poor anti-counterfeiting capabilities. Thus, developing multi-mode luminescent anti-counterfeiting materials that combine dynamic and static luminescence is a particularly urgent task. In this study, Cs2NaScCl6: Yb3+, Er3+phosphors were successfully prepared using the solvothermal method. These materials can emit bright green light under 980- or 1550-nm infrared laser irradiation and red light under 365-nm ultraviolet lamp illumination. In addition, by increasing the 980-nm laser power density from 20 to 309 mW/cm2, the luminescence colour can be adjusted from green to yellow, which equips this sample with an outstanding potential for dynamic anti-counterfeiting. Finally, screen printing technology was used to assess the sample's anti-counterfeiting capacity, and the sample was found to be an excellent anti-counterfeiting luminescent material.

Multiple Energy Transfer Channels in Rare Earth Doped Multi-Exciton Emissive Perovskites.

Revealing the energy transfer (ET) process from excitons to rare earth ions in halide perovskites has great guiding value for designing optoelectronic materials. Here, the multiple ET channels in multi-exciton emissive Sb3+ /Nd3+ co-doped Cs2 ZrCl6 are explored to comprehend the ET processes. Förster-Dexter ET theory reveals that the sensitizer concentration rather than the overlap integral of the spectra plays the leading function in the comparison of the ET efficiency among multiple ET channels from the host self-trapped excitons (STEs) and dopant triplet STEs to Nd3+ ions. Besides, Sb3+ /Nd3+ co-doped Cs2 ZrCl6 enables varied color delivery and has great potential as anti-counterfeiting material. Under X-ray irradiation, Sb3+ /Nd3+ co-doped Cs2 ZrCl6 presents a high light yield of ≈13300 photons MeV-1 and promising X-ray imaging ability. This work provides new insight for investigating the ET efficiency among multiple ET processes and presents great potentiality of multi-exciton emissive perovskites in the fields of anti-counterfeiting and X-ray imaging.

Overcoming thermal instability of polymeric Core-Shell-Particles: Advanced processing options for the preparation of Stimuli-Responsive structural color materials

Core-shell particles (CSP) represent one of the most promising building blocks for the artificial production of stimuli-responsive materials with iridescent structural colors. Despite tremendous efforts in the past two decades, scalable processing options for CSP are overall rare and mostly limited to 2D structures in the form of films and foils. This work investigates why common large-scale polymer-processing techniques, such as injection molding or fused filament fabrication, are hardly applicable to state-of-the-art CSP: While rheological prerequisites are fulfilled, thermal stability is proven to be surprisingly poor. Temperature instability during processing is caused by a thermally induced cross-linking reaction of residual reactive moieties. This undesired cross-linking reaction can be efficiently suppressed via optimizations of the particle architecture, in terms of adjusting the core-to-shell ratio and number of grafting anchors. Thermal stability can be further increased upon incorporation of primary antioxidants. The theoretical framework and the feasibility of the developed solution strategies are verified by a variety of thermoanalytical methods, including differential scanning calorimetry, thermogravimetric analysis, as well as rheological and mechanical measurements. Finally, advanced CSP are developed and demonstrated to be conveniently processable at elevated temperatures of up to 250 °C. These next-generation CSP formulations are advantageous for established processing techniques and may further pave the way for the design of new large-scale methods suitable for industrial use. Potential applications are smart sensors, advanced display technologies, or anti-counterfeiting materials.

A novel guanidine-containing polyoxotantalate with reversible thermochromism property

A novel guanidine-containing polyoxotantalate (POTa), H12[CN3H6]12Na2(H2O)6[Cu(en)2(H2O)]3[Ta6O19]4·32H2O (1) has been synthesized by adding the CH6N3+ as counter cations. The [Ta6O19]8− clusters in compound 1 are connected by sodium ions to form a 2-D layered structure, which is further connected through [Cu(en)2(H2O)]2+ to form a 3-D supramolecular framework structure. Moreover, it is demonstrated that compound 1 exhibits reversible thermochromism behavior, changing from purple to dark blue upon heating and dehydration, which endows it with potential application in the field of anti-counterfeiting functional materials.

Complex-Shape Solid-State Photonic Droplets Prepared via Phase Separation and Microfluidics.

Complex-shape solid-state cholesteric liquid crystal (CLCsolid) droplets were prepared via solvent removal, phase separation, and photopolymerization of uniformly sized reactive CLC (rCLC)/fluorocarbon oil (FCO)/dichloromethane (solvent) droplets produced via a microfluidic method. The interfacial energies between rCLC and FCO, rCLC and water, and FCO and water of a rCLC/FCO droplet in an aqueous solution were precisely controlled through the specified surfactants. The shape of the rCLC/FCO droplet was strongly dependent on the balances among these interfacial energies, enabling the preparation of complex-shape droplets through the controlled concentration of the used surfactants. The complex-shape rCLC/FCO droplets showed photonic patterns consisting of a central reflection from a convex surface, cross-communication from a convex surface between adjacent particles, a photonic reflection band from the outer upward-facing concave surface, and total internal reflection from the inner upward-facing surface. Complex-shape CLCsolid particles obtained after photopolymerization and extraction of a nonreactive chiral dopant and FCO showed photonic patterns similar to those before photopolymerization without much deterioration of the photonic structure. These complex patterns make CLCsolid and rCLC/FCO droplets promising anticounterfeiting materials.

The Combination of Upconversion Nanoparticles and Perovskite Quantum Dots with Temperature-Dependent Emission Colors for Dual-Mode Anti-Counterfeiting Applications.

Novel and high-security anti-counterfeiting technology has always been the focus of attention and research. This work proposes a nanocomposite combination of upconversion nanoparticles (UCNPs) and perovskite quantum dots (PeQDs) to achieve color-adjustable dual-mode luminescence anti-counterfeiting. Firstly, a series of NaGdF4: Yb/Tm UCNPs with different sizes were synthesized, and their thermal-enhanced upconversion luminescence performances were investigated. The upconversion luminescence (UCL) intensity of the samples increases with rising temperature, and the UCL thermal enhancement factor rises as the particle size decreases. This intriguing thermal enhancement phenomenon can be attributed to the mitigation of surface luminescence quenching. Furthermore, CsPbBr3 PeQDs were well adhered to the surfaces and surroundings of the UCNPs. Leveraging energy transfer and the contrasting temperature responses of UCNPs and PeQDs, this nanocomposite was utilized as a dual-mode thermochromic anti-counterfeiting system. As the temperature increases, the color of the composite changes from green to pink under 980 nm excitation, while it displays green to non-luminescence under 365 nm excitation. This new anti-counterfeiting material, with its high security and convenience, has great potential in anti-counterfeiting applications.

A temperature and pressure dual-responsive, stretchable, healable, adhesive, and biocompatible carboxymethyl cellulose-based conductive hydrogels for flexible wearable strain sensor

The study aimed to develop a novel temperature and pressure dual-responsive conductive hydrogel with self-healing, self-adhesive, biocompatible, and stretchable properties, for the development of multifunctional anti-counterfeiting and wearable flexible electronic materials. A conductive hydrogel based on carboxymethyl cellulose (CMC) was synthesized by simple “one pot” free radical polymerization of CMC, acrylamide (AAm) and acrylic acid (AAc). The hydrogel displayed temperature responsiveness and possessed an upper critical solution temperature (UCST) value. In addition, hydrogels also had surprising pressure responsiveness. The synthesized hydrogels were characterized by FTIR, TGA, DSC, and XRD analysis. Importantly, the obtained hydrogels exhibited exceptional mechanical properties (stress: 730 kPa, strain: 880%), fatigue resistance, stretchability, self-healing capability, self-adhesive properties, and conductivity. In addition, valuable insights were obtained into the synthesis and application of flexible anti-counterfeiting and camouflage materials by the temperature and pressure dual-responsive hydrogels. Moreover, the prepared hydrogel, with an electrically sensitive perception of external strain (GF = 2.61, response time: 80 ms), can be utilized for monitoring human movement, emotional changes, physiological signals, language, and more, rendering it suitable for novel flexible anti-counterfeiting materials and versatile wearable iontronics. Overall, this study provided novel insights into the simple and efficient synthesis and sustainable manufacturing of environmentally friendly multifunctional anti-counterfeiting materials and flexible electronic skin sensors.