Security Printing Research Articles

Adjustable emission and energy transfer in perovskite structure La2MgSnO6: Eu3+, Bi3+ phosphors for multifunctional applications

A series of Eu3+/Bi3+ single and co-doped La2MgSnO6 phosphors are synthesized by the solid-state method. The crystal structure, optical properties, energy transfer processes, and thermal stability of phosphors are investigated systematically. Under 331 nm excitation, both the orange-red emission of Eu3+ ions ranging from 500 to 750 nm and the blue emission band centered at 403 nm are observed in the La2MgSnO6:Eu3+, Bi3+ samples. With the doping concentration of Eu3+ changing, the emission of La2MgSnO6:Eu3+, Bi3+ phosphors can be adjusted from blue (0.219, 0.350) to orange-red light (0.644, 0.341) in chromaticity coordinate. Furthermore, the security ink prepared by phosphors can be effectively used for encryption writing and anti-counterfeit marking. Additionally, the latent fingerprint developed using La2MgSnO6: Eu3+, Bi3+ phosphor demonstrates excellent contrast and sensitivity.

Recent advances in photoresponsive printing inks for security encoding applications

AbstractCounterfeiting of banknotes, important documents, and branded goods continues to be a major worldwide problem for governments, businesses, and consumers. This problem has serious financial, security, and health implications. Due to their stability for printing on various substrates, the photochromic anticounterfeiting inks have received important interest. There have been various photochromic agents, such as polymer nanoparticles, quantum and carbon dots, and organic and inorganic fluorophores and luminophores, which have been broadly used for antiforging applications. In comparison to organic agents, inorganic photochromic materials have better stability under reversible/long‐term light illumination. Recently, the remarkable optical characteristics and chemical stability of photoluminescent and photochromic agents have led to their extensive usage anticounterfeiting products. There have been also several strategies to tackle the rising problem of counterfeiting. Both of solvent‐based and water‐based inks have been developed for security encoding purposes. Additionally, the printing methods, including screen printing, labeling, stamping, inkjet printing, and handwriting, that have been used to apply anticounterfeiting inks onto various surfaces are discussed. The limitations of photoluminescent and photochromic agents and the potential for their future preparation to combat counterfeiting were discussed. This review would benefit academic researchers and industrial developers who are interested in the area of security printing.

Programmable multimode optical encryption of advanced printable security inks by integrating structural color with Down/Up- conversion photoluminescence

Optical information encryption with high encoding capacities can significantly boost the security level of anti-counterfeiting in the scenario of guaranteeing the authenticity of a wide scope of common and luxury goods. In this work, a novel counterfeiting material with high-degree complexity is fabricated by microencapsulating cholesteric liquid crystals and triplet–triplet annihilation upconversion fluorophores to integrate structural coloration with fluorescence and upconversion photoluminescence. Moreover, the multimode security ink presents tailorable optical behaviors and programmable abilities on flexible substrates by various printing techniques, which offers distinct information encryption under different optical modes. The advanced strategy provides a practical versatile platform for high-secure-level multimode optical inks with largely enhanced encoding capacities, programmability, printability, and cost-effectiveness, which manifests enormous potentials for information encryption and anti-counterfeiting technology.

Investigating the influence of carbon dots on β-Ca2SiO4:Ce3+ phosphors derived from agro-waste for diverse applications

A series of blue-emitting composite based on 3 wt% carbon dots in β-Ca2SiO4:Ce3+ (3 wt% CDs@β-CSO:Ce3+) was synthesized through a hydrothermal method, aiming to enhance applications in latent fingerprint (LFP) detection, anti-counterfeiting (AC) measures, and optical thermometry. The X-ray diffraction (XRD) analysis confirmed that these phosphors possess a monoclinic crystal structure. Under 356 nm excitation, the Ce3+ doped β-Ca2SiO4 phosphors (β-CSO:Ce3+) display a broad blue emission peak at 431 nm, attributed to the 5d → 4f electric dipole transition of Ce3+, while the inclusion of Carbon dots (CDs) shifts this emission to 442 nm. This shift and the improved photoluminescence (PL) intensity are thought to result from the Fӧrster Resonance Energy Transfer (FRET) mechanism. The optimal concentration of Ce3+ ions was determined to be 5 mol%, as higher concentrations led to a decrease in emission intensity due to concentration quenching (CQ). Additionally, a fabricated white light diode using these phosphors achieved chromaticity coordinates of (0.344, 0.330) according to the Commission International de L'Eclairage (CIE), with the CIE, correlated colour temperature (CCT), and colour purity (CP) metrics indicating a bright green output with values of (0.1486, 0.0433), 1759 K, and 96.4%, respectively. The optimized 3 wt% CDs@β-CSO:5Ce3+ composite demonstrated a remarkable CP of 99.9%. Notably, the phosphors maintained 85.77% of their emission intensity at 423 K, showcasing exceptional thermal stability. A novel approach utilizing sketch pen and brush mode was developed to apply the optimized AC security ink, allowing for the creation of various intricate patterns. The resulting AC tags featured high resolution and durability. These findings underscore the 3wt%CDs@β-CSO:5Ce3+ composite as superior luminescent materials for use in fields requiring LFP, AC strategies, and optical thermometry.

Correlating semiconductor nanoparticle architecture and applicability for the controlled encoding of luminescent polymer microparticles

Luminophore stained micro- and nanobeads made from organic polymers like polystyrene (PS) are broadly used in the life and material sciences as luminescent reporters, for bead-based assays, sensor arrays, printable barcodes, security inks, and the calibration of fluorescence microscopes and flow cytometers. Initially mostly prepared with organic dyes, meanwhile luminescent core/shell nanoparticles (NPs) like spherical semiconductor quantum dots (QDs) are increasingly employed for bead encoding. This is related to their narrower emission spectra, tuneability of emission color, broad wavelength excitability, and better photostability. However, correlations between particle architecture, morphology, and photoluminescence (PL) of the luminescent nanocrystals used for encoding and the optical properties of the NP-stained beads have been rarely explored. This encouraged us to perform a screening study on the incorporation of different types of luminescent core/shell semiconductor nanocrystals into polymer microparticles (PMPs) by a radical-induced polymerization reaction. Nanocrystals explored include CdSe/CdS QDs of varying CdS shell thickness, a CdSe/ZnS core/shell QD, CdSe/CdS quantum rods (QRs), and CdSe/CdS nanoplatelets (NPLs). Thereby, we focused on the applicability of these NPs for the polymerization synthesis approach used and quantified the preservation of the initial NP luminescence. The spectroscopic characterization of the resulting PMPs revealed the successful staining of the PMPs with luminescent CdSe/CdS QDs and CdSe/CdS NPLs. In contrast, usage of CdSe/CdS QRs and CdSe QDs with a ZnS shell did not yield luminescent PMPs. The results of this study provide new insights into structure–property relationships between NP stained PMPs and the initial luminescent NPs applied for staining and underline the importance of such studies for the performance optimization of NP-stained beads.

Multimodal responsive Dy3+, Li+ activated Gd2MgTiO6 phosphors for ideal wLED, potent anti-counterfeiting, fingerprint visualization, and encryption coding

The Gd2MgTiO6 is an infant luminescence host that portrays eclectic applications in displays, security devices, and forensic studies. The perovskites are synthesized by facile combustion method, decreasing the synthesis conditions from 1573 K, 5 h to 1173 K, 4 h, from conventional routes. The phosphors are then activated with Dy3+ ions, giving photoluminescence emission in the blue, yellow, and red regions of the visible spectrum owing to (4F9/2 → 6H15/2), (4F9/2 → 6H13/2), and (4F9/2 → 6H11/2) transitions respectively. Further, monovalent Li+, divalent Sr2+, or trivalent Sm3+ ions are co-doped in the crystal matrix, which chiefly enhances the optical and crystalline properties for Li+ sensitization. Under 351 nm excitation, these samples show CIE coordinates (0.3290, 0.3313), color temperature 5759 K, color rendering index 86, and color purity of 2.5 %; signifying ideal white light emission for wLED with quantum efficiency 43 %. Under 980 nm excitation, these phosphors gave noble red emission, which can be effectually applied as a level 3 latent fingerprint visualization tool in criminology. The white and red emissions on UV and NIR excitation respectively are combined for potent anti-counterfeiting security ink and encryption coding; which marked a new methodology for the multifunctional application of a single phosphor matrix.

The one-pot synthesis of photoluminescent polycarbonate based on the pyrolysis of citrate

Photoluminescent composites that are air-stable and water-resistant are important for outdoor applications such as road marking paints, light-converting membranes, fluorescent paints, and security inks. Photoluminescent thermoplastics fulfill all conditions but their preparation methods which are vastly based on mixing pre-synthesized fluorescent dyes and plastic could lead to emission quenching due to dye aggregation or thermal degradation. Herein, we demonstrated a simple method to prepare photoluminescent polycarbonate by thermal extrusion polycarbonate with citric acid and urea. UV-vis absorption and photoluminescent studies indicate that fluorescent carbon materials were formed via pyrolysis of the citrate. The composites exhibit light blue emission and a broad excitation band. The results demonstrated herein offer a cost-effective method to prepare diverse photoluminescent composites for outdoor applications.

Photoluminescence investigation of novel red emitting NaLa(1-x)MgTeO6: XSm3+ phosphor with high color purity for n-UV based warm WLEDS and anti-counterfeiting applications

Recently, red phosphors are extensively developed to find applications in phosphor converted white LEDs (pc-WLEDs) and anti-counterfeiting. In this work, samarium doped sodium lanthanum magnesium tellurate (NaLaMgTeO6:Sm3+) red emitting phosphors have been synthesized for the first time via solid state reaction method. Rietveld refinement of XRD pattern reveals monoclinic crystal structure of NaLaMgTeO6. Under 404 nm (6H5/2 → 4F7/2) n-UV excitation, NLMT:Sm3+ phosphor shows red emission at 643 nm (45/2 → 69/2) with color purity 100 % and the obtained CCT value corresponds to warm light source. Temperature-dependent PL analysis of NLMT:Sm3+ exhibits good thermal stability. The anti-counterfeiting security ink was developed using optimized phosphor and the information was encrypted on different surfaces using the prepared security ink. The encrypted data was decoded only by n-UV light. The aforementioned results revealed that NLMT:Sm3+ is a highly effective phosphor as a red component for pc-WLEDs and luminescent dye for anti-counterfeiting applications.

Optimizing extreme manufacturing framework: a secure and efficient 3D printing integration framework

This study presents a comprehensive framework for extended manufacturing with integrated 3D printing technologies, exemplifying a paradigm shift in the manufacturing landscape. The Digital Thread Integration establishes a dynamic foundation, enabling real-time collaboration and data flow throughout the product lifecycle. Leveraging advanced AI-driven optimization, Digital Design Platforms streamline designs, processing 1,000 iterations per hour, and recommending materials based on component requirements. On-Demand Manufacturing Hubs strategically placed globally achieve substantial reductions in lead times (48 h) and material waste (15%). The Cybersecurity Infrastructure ensures the sanctity of the digital environment, employing secure communication protocols and an Intrusion Detection System (IDS) responding to threats in milliseconds. The Data Analytics Hub contributes to continual improvement by analysing 100 GB of 3D printing data daily, generating 50 actionable insights weekly. User Interface and Accessibility initiatives empower the workforce through intuitive training modules and responsive help desks. In conclusion, this framework exemplifies secure, efficient, and data-driven extended manufacturing, positioning the industry at the forefront of technological advancement.

Facile Synthesis of Carbonized Polymer Dots and their Applications in Security Inks, Sensing, Light Emitting Diodes, and UV Shielding Films

AbstractCarbonized polymer dots (CPDs) have received much attention in recent years owing to their cost‐effective synthesis, high resistance to photobleaching, environmental friendliness, and excellent biocompatibility. However, the aggregation‐induced fluorescence quenching is a great obstacle to its applications. In this work, the highly fluorescent CPDs are prepared by a facile hydrothermal method assisted by polyethylene glycol (PEG) as the surface passivation agent, where phthalic acid and ethylenediamine are used as carbon and nitrogen source, respectively. Meanwhile, five types of PEG species are applied to prepare five CPDs to investigate PEG on optical properties of the resultant CPDs, among which the best quantum yield reaches 57.0 %. The promising applications of CPDs as fluorescent inks, sensors, light emitting diodes, and UV shielding films have been demonstrated. Overall, our contribution here develops a facile and accessible route for the synthesis of CPDs and further demonstrates its versatile applications.

Comprehensive investigation of ternary dysprosium complexes for white light emission: Synthesis, spectroscopic and colorimetric analyses

Dysprosium (Dy3+) containing four single-molecule complexes with 1,3-diketone ligand, TFPB (4,4,4-trifluoro-1-phenyl-1,3-butadionate) along with neutral co-ligands of varying denticity were synthesized and two of them were explored as potential sources of near-white light emission. The choice of ligand as well as the coordination surroundings of Dy(III) ion significantly influence the blue (B: 4F9/2 → 6H15/2) and yellow (Y: 4F9/2 → 6H13/2) emissions. The inclusion of the auxiliary ligand such as topo in D1 leads to reduction in emission intensity compared to D2-D4 due to less effective sensitization. At room temperature, the CIE color coordinates for complexes D1 and D4 approach the coordinates of perfectly balanced and idealized white light (0.333, 0.333). Furthermore, Correlated Color Temperature (CCT) values for D1 and D4 characterize them as cold-white-light emitters, while the complexes D2 and D3 are categorized as a neutral-light emitter. In addition to their visible emissions, the semi-conducting properties and suitable deactivation lifetime corresponding to these synthesized complexes (D1-D4) have also been extensively studied and found potential applications in basic research, security printing, sensors, detectors and OLEDs.

Development of reddish orange-emitting Y2Sn2O7:Eu3+phosphors for latent fingerprint detection and anti-counterfeit security ink

In forensic science, fingerprint detection and anti-counterfeiting technologies are crucial. Inorganic phosphors are potentially suitable materials for high-quality visualization and security. We synthesized novel Y2Sn2O7:Eu3+ (YSO:Eu3+) phosphors by a sol–gel method. They have a cubic structure and emit reddish orange emission from the Eu3+ ions electronic transition of 5D0→7F1. The optimal doping concentration of Eu3+ is 7 mol% and dipole-dipole interaction causes the quenching mechanism. The chromaticity coordinates of YSO:7Eu3+ phosphor are (0.6086, 0.3906). We used the optimized YSO:7Eu3+ phosphors for forensic applications, such as latent fingerprints and security ink. The latent fingerprints stained with YSO:7Eu3+ phosphors showed clear images and reliable level 1–3 characteristics. The security ink was visible on different surfaces. Our results indicate that the YSO:7Eu3+ phosphor can be used for visualizing latent fingerprints and anti-counterfeiting applications.

Analysis of Physical Tourism Tickets: Can Security Printing be Used?

Selling physical tickets at tourist destinations is often a problem in the world of tourism. The number of brokers and fake tickets is always the main problem. Physical tickets are very easy to counterfeit and very easy to distribute to irresponsible brokers. As a result, many tourists are deceived and often have to pay twice or even more just because they bought fake tickets. This research analyzes the problems caused by physical tickets and analyzes alternative security printing solutions that can be applied to ticketing systems using descriptive qualitative research methods. The results of this research are that ticketing using security printing will require greater costs and still pose a risk of ticket counterfeiting. Security printing might have benefits if it were given more value, such as embossing for braille letters aimed at blind tourists. However, for greater benefits, digital ticketing will have a smaller risk of counterfeiting and have greater profits.

Novel Eu3+ doped mixed alkaline-earth zinc silico-aluminate glass for white-light-emitting diode, fingerprint, and security ink application

In this work, novel calcium strontium magnesium zinc silico-aluminate (CSrMZSAEux) glasses doped with varied concentrations of Eu2O3 (0.5, 1.0, 1.5, 2, 3, 4 and 5 mol%) were synthesized by an open-air melt quenching technique. The Raman and FTIR studies revealed that Eu3+ ions connected to both AlO4 and SiO4 units through non-bridging oxygen. The decrease in thermal stability from 158 to 141 °C with the gradual inclusion of Eu2O3 ions is showing modifier role of Eu3+ ions. The intense emission spectra (5D0→7Fi = 0-4 transitions) measured under 395 nm excitation wavelength, showed no concentration quenching within the studied dopant ions concentration. The high Judd-Ofelt parameter (Ω2 = 5.06 to 6.31 × 10−20 cm2) and red-to-orange emission intensity ratio (R = 3.627–4.102) have revealed the covalent nature of Eu-ligand bond and high color richness, respectively. Among all prepared glasses, the CSrMZSAEu5.0 glass showed high color purity (98.9%), correlated color temperature (<1000K), highest emission intensity and reasonable lifetime value (1387±16 μs). Further, the temperature-dependent photoluminescence demonstrated that the CSrMZSAEu5.0 glass has good emission thermal stability (⁓ 66% at 150 °C) with a high activation energy of 0.258 eV. Hence, the CSrMZSAEu5.0 glass can be used as red component for white-light-emitting diode, and red-light applications. Furthermore, the CSrMZSAEu5.0 glass composition is observed to be suitable for latent fingerprint and security ink applications.

Lanthanide-Polyoxometalate-Based Film with Reversible Photochromism and Luminescent Switching Properties for Erasable Inkless Security Printing.

Security printing is of the utmost importance in the information era. However, the excessive use of inks and paper still faces many economic and environmental issues. Thus, developing erasable inkless security printing materials is a remarkable strategy to save resources, protect the environment, and improve information security. To this endeavor, a photoresponsive lanthanide-polyoxometalate-doped gelatin film with high transparency was developed through the solution casting method. Attenuated total reflection Fourier-transform infrared spectroscopy confirmed the electrostatic and hydrogen bond interactions between gelatin and lanthanide-polyoxometalate. Absorption spectra, luminescent spectra, and digital images indicated that the film displayed reversible photochromism behavior and was accompanied by luminescent switching property upon exposure to UV irradiation and oxygen (in the dark) alternately, which allowed its potential application as a reprintable medium for inkless security printing. The printed information can be erased upon exposure to oxygen in the dark, and the film can be reused for printing again. The film exhibited excellent erasability, reprintability, renewability, and low toxicity. In addition, multiple encryption strategies were designed to improve information security. This work offers an attractive alternative strategy for constructing a reprintable film for inkless security printing in terms of simplifying the preparation process, saving resources, and protecting the environment.

Hidden imaging in thin polymer films with embedded fluorescent peptide nanodots.

Fluorescent (FL) encrypting nanostructures, such as quantum dots, carbon dots, organic dyes, lanthanide nanocrystals, DNA, and more, are effective tools for advanced applications in high-resolution hidden imaging. These applications include tracking, labeling, security printing, and anti-counterfeiting drug technology. In this work, what we believe to be a new FL encoding nanostructures has been proposed, which consists of recently discovered nanometer-scale peptide dots. When refolded into a beta-sheet peptide secondary structure, these biocompatible nanoparticles exhibit a strong and tunable FL effect. The biophotonic FL covers the entire visible spectrum, making the peptide dots next-generation nanoscale light sources with a quantum yield of 30%. Our studies demonstrate that these FL bio-nanodots also exhibit a significant irreversible photo-bleaching effect associated with the light-induced destruction of noncovalent intermolecular hydrogen bonds of the peptide dots' highly stable beta-sheet secondary structure. We present what we believe is a new approach for achieving high-resolution long-term optical memory by tailoring various hidden images in the developed thin polyvinyl alcohol (PVA) polymer films with an embedded dense array of FL peptide nanodots. The technology enables recording photo-bleached patterns, barcodes, and high-resolution images.

Tetraphenylethylene fused pyrrolo[3,2-b]pyrrole derivatives with reversible mechanofluorochromic and aggregation-induced emission enhancement characteristics

Modification on typical of molecular unit with aggregation-induced emission (AIE)/aggregation-induced emission enhancement (AIEE) can play a important role in obtaining solid-state fluorescence materials and mechanofluorochromic (MFC) materials. We utilize the multicomponent reaction of TPE-containing aldehyde, arylamine and butane-2,3-dione in the presence of iron(III) perchlorate to design and synthesize two novel MFC materials by combination of the tetraphenylethylene (TPE) and pyrrolo [3,2-b]pyrrole core units. Investigation of CHW-1 and CHW-2 aggregation-induced emission behaviors indicated that these materials all exhibited AIEE properties. Subsequent mechanochromic luminescence tests exhibited reversible mechanochromism natures that involve fluorescent color change from green to yellow (Grinding-induced spectral shift (△λ): 35 nm and 38 nm, respectively). Then the datas (including SEM, PXRD and DSC) revealed that this mechanofluorochromism was ascribed to the transformation of crystal state to the amorphous form. Moreover, CHW-1 and CHW-2 could be applied for optical recording devices and security printing.

Multi-responsive smart fluorophores from pyrazole-functionalized tetraphenylethene AIEgens in response to Hg(II) ion, temperature, and mechanical force

Five tetraphenylethene (TPE) derivatives 1a, 1b, 2, 3, and 4 with adjustable stimuli-responsive characteristics were designed and synthesized in this study. Using single-crystal X-ray diffraction, the effects of substitution positions and pyrazolyl numbers on molecular packing were examined in the solid state. The findings indicate that as the pyrazolyl numbers increased, the molecular packing of the compound progressively changed from the C−H···π stacked compact mode in 1 − 3 to the X-crossing stacked loose mode in 4, which results in the origin of various stimuli-responsive phenomena in compound 4. This approach facilitates the preparation of multi-stimuli-responsive (thermochromism, mechanochromism, and metal ion fluorescence switch) smart fluorophores with tunable emission color. Moreover, compound 4, with an excellent fluorescence performance, exhibited three different colors when reversible mechanochromism was selected as the candidate for an optical recording material and security ink. This study proposes an effective method to guide the design of stimuli-responsive materials, which, in turn, would facilitate the development of high-contrast MC molecules, and the optical information anticounterfeiting based on grinding was proven by utilizing the grind-responsive luminescence capabilities.

Precise molecular design for a twisted pyrene-thiophene based mechanofluorochromic probe with large Stokes shift and feasibility study towards security ink and re-writable papers

Pyrene-thiophene based AIEE active probe molecules with excellent solvatochromism (Δλ, ∼145 nm) along with a multicolor reversible MFC properties for security ink and re-writable papers

Recent progress in ion-regulated organic room-temperature phosphorescence.

Organic room-temperature phosphorescence (RTP) materials have attracted considerable attention for their extended afterglow at ambient conditions, eco-friendliness, and wide-ranging applications in bio-imaging, data storage, security inks, and emergency illumination. Significant advancements have been achieved in recent years in developing highly efficient RTP materials by manipulating the intermolecular interactions. In this perspective, we have summarized recent advances in ion-regulated organic RTP materials based on the roles and interactions of ions, including the ion-π interactions, electrostatic interactions, and coordinate interactions. Subsequently, the current challenges and prospects of utilizing ionic interactions for inducing and modulating the phosphorescent properties are presented. It is anticipated that this perspective will provide basic guidelines for fabricating novel ionic RTP materials and further extend their application potential.