Anti-counterfeiting Ink Research Articles

Fabrication of Cellulose Nanofiber-Reinforced Polylactic Acid Nanocomposite Containing Anthocyanidin-Based Red Cabbage Extract For Anti-counterfeiting Thermochromic Ink

Fabrication of Cellulose Nanofiber-Reinforced Polylactic Acid Nanocomposite Containing Anthocyanidin-Based Red Cabbage Extract For Anti-counterfeiting Thermochromic Ink

Photoluminescent Y2O3:Eu3+@PVA composite dispersions and films for anti-counterfeiting ink applications

The development of high-tech anti-counterfeiting inks to detect counterfeit products is a crucial task for almost every aspect of modern life around the world. Herein, we report the synthesis of photoluminescent xY2O3:Eu3+@PVA (x = 0, 1, 2.5, 5, 10, 15, and 20 wt%) composite dispersions and films and demonstrate their potential for anti-counterfeiting inks applications. Laser-synthesized m-Y2O3:Eu3+ nanoparticles (daver = 20.3 ± 6.9 nm) with strong red luminescence due to 5D0 → 7F0-4 transitions of Eu3+ were used as a pigment to create luminescent composites. Detailed photoluminescence properties of the obtained composite dispersions and films as a function of m-Y2O3:Eu3+ content were investigated in combination with SEM, EDX, UV–Vis and IR spectroscopy data. Tuning of the CIE coordinates of xY2O3:Eu3+@PVA is observed by changing the excitation wavelength. The results of SEM showed that the photoluminescent nanoparticles were uniformly distributed in the PVA film. Photoluminescent m-Y2O3:Eu3+-doped PVA composite inks can be applied via spray, brush, and screen-printing techniques to create security features on various surfaces, including glass, ceramics, paper, plastics, and currency notes. These inks remain stable for at least four months and offer a distinctive luminescent signature that is challenging to replicate, owing to the unique photoluminescence spectrum of Eu3+ in the monoclinic Y2O3 polymorph.

Double perovskite CaSrMSbO6(M = La, Gd, Y): Bi3+ phosphors for multifunctional application

Bi3+-doping luminescent materials have recently evoked considerable interest in versatile applications. In this work, we have developed a series of Bi3+-activated CaSrMSbO6(M = La, Gd, Y) phosphors with double perovskite structures, exhibiting blue emission from 350 nm to 500 nm. The emission spectral position and intensity of Bi3+ ions can be tuned by changing excitation wavelength and doping concentrations. The relationship between the local crystal field environment and the luminescence properties is comprehensively analyzed. Importantly, optical temperature properties of CaSrLaSbO6: Bi3+ were investigated and were found to reach a maximum relative sensitivity of 4.57 % K−1 at 298 K. Furthermore, the anti-counterfeiting ink was prepared using CaSrLaSbO6: Bi3+ phosphors, and it showed tunable emission under different light stimulation. These results indicate that CaSrLaSbO6: Bi3+ phosphors have application potential in optical temperature sensing and anti-counterfeiting.

A reversible photochromic covalent organic framework

Covalent organic frameworks are a type of crystalline porous materials that linked through covalent bond, and they have numerous potential applications in adsorption, separation, catalysis, and more. However, there are rarely relevant reported on photochromism. Fortunately, a hydrazone-linked DBTB-DETH-COF is rapidly generated through ultrasound method. The DBTB-DETH-COF is found to exhibit reversible photochromism (at least 50 cycles) from yellow to olive in the presence of light and air, and subsequently back to the original color upon heating. In addition, the structure of DBTB-DETH-COF remains unchanged after 15 days of light illumination. Furthermore, the reason of photochromic process is discussed by electron paramagnetic resonance, X-ray photoelectron spectroscopy, electrochemistry characterizations and transient absorption measurements. The reversible photochromic DBTB-DETH-COF can be used as anti-counterfeiting ink and optical switch in the presence of air. This work expands a stable organic photochromic material and broadens the applications of COFs.

Synthesis and luminescent properties of multi-mode core-shell-shell LaPO4:RE (RE³⁺ = Er³⁺, Eu³⁺) microspheres for anti-counterfeiting ink applications

To meet the demands for product and consumer protection, we developed biocompatible multi-mode emitting core-shell-shell rare earth phosphates for anti-counterfeiting inks. These core-shell-shell structures feature SiO2 microspheres as the core, with LaPO4 nanocrystals doped with erbium (Er) and europium (Eu) as the interlayer, and an outer SiO2 shell. The SiO2@LaPO4:Er0.1,Eux@SiO2 (x = 0.01, 0.02, 0.03, 0.04, 0.05) microspheres display dual emissions when excited by 254 nm and 365 nm UV light, offering a novel anti-counterfeiting approach. Another core-shell-shell structure was created with LaPO4:Er3+ and LaPO4:Eu3+ separately coated on SiO2 cores, mixed, and then covered with a SiO2 shell. Under 980 nm near-infrared laser excitation, these structures emit bright upconverted green light, while 254/365 nm UV light induces red/yellow down-conversion luminescence. This design minimizes up-conversion luminescence quenching of Er3+ ions from cross-relaxation with Eu3+ ions. The SiO2 core minimizes energy loss, regulates particle size, and enhances luminescence. A certain thickness of the silicon shell layer also protects against luminescence quenching. The inks exhibit high dispersibility, non-reproducibility, and excellent luminescence, making them effective for anti-counterfeiting.

Substituent effects on the mechanochromic behaviour of pyrene-based AIEgens

It is extremely significant and desirable to integrate the fascinating properties of mechanochromism and aggregation-induced emission (AIE) in one simple molecule. Herein, pyrene-based aggregation-induced emission luminogens (AIEgens) with mechanofluorochromic (MFC) properties solve the traditionally existing aggregation-caused quenching (ACQ) challenge. Three cyanoethylene-functionalized pyrene-based derivatives were designed and synthesized. All compounds exhibit remarkable aggregation-enhanced emission (AEE) activity by a 3–20 times enhancement in mixed H2O/THF solutions. More importantly, high fluorescence efficiency was recorded in the solid state, especially for the luminogen 2c, with more than 200 times observed increased efficiency from 0.3% in solution to 69.8% in the solid state. Meanwhile, excellent mechanochromism properties and reversibility against the grinding treatment was systematically investigated. The excellent fatigue resistance properties are a necessity for potential applications in the field of anti-counterfeiting fluorescent inks and for the encryption of security information.

One-step solvothermal synthesis of nitrogen-doped carbon dots with efficient red emission from conjugated perylene for multiple applications

Despite its significance for applications related to plant growth, the development of carbon dots (CDs) with bright red emissions still faces multiple obstacles. Herein, red emission hydrophobic carbon dots (RH-CDs) featuring one emission peak centered at 594 nm and a shoulder emission peak at 630 nm with a quantum yield of 34 % and a wide full width at half maximum (FWHM) of 100 nm (580 nm–680 nm) were synthesized by adopting large conjugated perylene anhydride and aromatic amine precursors under solvothermal conditions. Density functional theory calculations support the method of using larger conjugated systems and higher graphite N doping to increase red emissions from CDs. With a post-surface functionalization strategy, polyvinylpyrrolidone (PVP)-modified RH-CDs (QY = 12 %) were utilized as an anti-counterfeiting ink for information printing. Moreover, both blue-red light-emitting diodes (LEDs) and light conversion poly (methyl methacrylate) (PMMA)-CDs film were fabricated with emission spectra that are consistent with the absorption spectra of plants, suggesting that the prepared RH-CDs may have widespread application potential as a stable fluorescent material in plant growth.

A novel high-brightness and thermally-stable red phosphor Ca2GaNbO6: Eu3+ for WLEDs and anti-counterfeiting inks

A novel high-brightness and thermally-stable red phosphor Ca2GaNbO6: Eu3+ for WLEDs and anti-counterfeiting inks

Europium (III)-modified sunflower-derived carbon dots for fluorescent anti-counterfeiting inks and photocatalysis.

A highly water-soluble and fluorescent N,S-doped carbon dots/europium (N,S-CDs/Eu) was successfully synthesized via a secondary hydrothermal method. This involved surface modification of N,S-CDs derived from sunflower stem pith (SSP) with europium ions (Eu3+) doping. When excited within the range of 400-470 nm, N,S-CDs/Eu exhibited a stable and broad optimal emission wavelength ranging from 505 to 540 nm. Notably, the photoluminescence quantum yield (PLQY) of N,S-CDs/Eu is 31.4%, significantly higher than the 19.5% observed for N,S-CDs. Additionally, by dissolving N,S-CDs/Eu into polyvinyl alcohol (PVA), a uniform fluorescent anti-counterfeiting ink can be prepared. The N,S-CDs/Eu/TiO2 composite demonstrates excellent photocatalytic degradation ability towards the organic dye methylene blue (MB). N,S-CDs/Eu has potential in the field of fluorescent inks and photocatalysis due to its simple and efficient preparation and excellent properties.

An efficient red phosphor LuNb2VO9:Eu3+ with broadband excitation and abnormal thermal quenching properties for personal identification, security ink, and w-LEDs

A series of red-emitting phosphors LuNb2VO9 (LNV):xEu3+ (x = 0.5–45 mol%) were successfully obtained through the high-temperature solid-state reaction. The structure, phase purity, photoluminescence spectra, thermal stability properties, and color purity of the obtained phosphors were systematically examined. The LNV:Eu3+ phosphor exhibits broadband excitation due to the O2-→Eu3+ and O2-→V5+ charge transfer. The LNV:Eu3+ phosphor excited at 316 nm shows four emission peaks at 595, 615, 619, and 699 nm, corresponding to electron transitions from the 5D0 level to the 7F1, 7F2, 7F3 and 7F4 levels. The optimal doped concentration of LNV:xEu3+ is x = 10 mol%. The quenching mechanism is attributed to the nearest neighbor ion interaction. Furthermore, the prepared phosphor exhibits good thermal stability and remarkable activation energy Ea (0.74 eV). In addition, LNV:Eu3+@oleic acid (OA) readily exhibits the level I-III characteristics of fingerprints and the detailed characteristics of lip lines. The successful utilization of LNV:Eu3+ in anti-counterfeiting ink has yielded impressive results. The Commission International de L′ Eclairage (CIE) coordinate of the prepared white light-emitting diode (w-LED) in this study is (0.331, 0.367), accompanied by a color rendering index (Ra) of up to 95. Notably, the results of these experiments indicate that LNV:Eu3+ phosphor possesses exceptional luminescence properties and holds promising applications.

A novel thermally-stable red phosphor CaYGaO4:Eu3+ for WLEDs and anti-counterfeiting ink

In this paper, CaYGaO4:xEu3+ (CYGO:xEu3+)phosphors were synthesized for the first time using a high-temperature solid-state method. The samples were characterized by X-ray diffractometer (XRD) and scanning electron microscope (SEM). Their energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were used to further investigate the microscopic composition of the samples. The forbidden bandwidths and densities of states of CYGO and CYGO:0.25Eu3+ were calculated by first principles methods. The emission and excitation spectra of the samples were tested by fluorescence spectroscopy, which showed that the samples can be excited by both UV and blue light. When the sample heated to 473 K, the luminescence intensity under 393 and 463 nm excitation stays at 83.99 % and 85.19 % of the room temperature, respectively, which demonstrates that CYGO:0.3Eu3+ possesses excellent thermal stability. The color coordinates (CIE), correlated color temperature (CCT) and color purity (CP) of the samples were also investigated. In order to explore its application in the field of white light-emitting diodes (WLEDs), CYGO:0.3Eu3+ was mixed with commercial blue and green phosphors in a certain ratio, and the chip was made into a WLED with 395 nm excitation, and the CIE of the lamps were (0.3338, 0.3521), with a correlated CCT of 5448 K, and a color rendering index (CRI) of Ra = 86.2. The thermal imaging performance of the small lamps was also evaluated for sustained usage, revealing minimal temperature fluctuations and excellent thermal stability. Consequently, CYGO:Eu3+ exhibits promising potential for applications in the field of WLEDs. Additionally, CYGO:0.3Eu3+ was selected as a representative sample for the creation of fluorescent ink and its subsequent application on various media. The outcomes indicate that this phosphor possesses promising potential for use in the field of anti-counterfeiting ink technology.

Green synthesis of N,S dual heteroatom-doped fluorescent carbon dots (N,S-CDs) and their applications in gentamicin sensing and dual-switch anti-counterfeiting encryption

Herein, we report a facile one-step solvothermal synthesis of nitrogen and sulfur co-doped fluorescent carbon dots (N,S-CDs) using benzoic acid as the carbon source and sulfonamide as the doping agent. The synthesized N,S-CDs exhibit stable photoluminescence with an impressive fluorescence quantum yield of 16.8 %. These N,S-CDs maintain their luminescent properties under various challenging conditions, including high salt concentrations, elevated temperatures, UV radiation exposure, acidic or alkaline environments, long-term storage, and different solvents. Notably, the photoluminescence of N,S-CDs is excitation-wavelength dependent, with emission wavelengths tunable from 470 nm to 585 nm. Furthermore, the N,S-CDs display distinct fluorescent hues in aqueous and ethanolic media, presenting a novel dual-switch anti-counterfeiting ink system. Leveraging the sensitivity of N,S-CDs to gentamicin, we have developed a facile and rapid detection method for this antibiotic, which has been successfully applied to the analysis of authentic milk samples. This research contributes a novel and efficient protocol for the fabrication of high-performance carbon dots, thereby expanding their potential applications in food analysis and anti-counterfeiting technologies.

Multi-color Na3GaF6:Tm3+,Yb3+@SiO2 for dual-mode security and information encryption

The development of advanced luminescent materials is important for anti-counterfeiting applications, but still faces many challenges. In this study, Na3GaF6:Tm3+,Yb3+@SiO2 core@shell type nanocrystals with cryolite structure were synthesized for the first time by co-precipitation method. By modulating the excitation mode and Tm3+/Yb3+ doping ratio, the Na3GaF6:Tm3+,Yb3+@SiO2 nanocrystals exhibits multicolor up-conversion emission. Multicolor anti-counterfeiting ink was configured with up-conversion nanocrystals, and a variety of multi-colour anti-counterfeiting patterns were printed using screen printing technology. Additionally, multi-colour fluorescent barcodes are combined with binary coding technology to achieve encryption of anti-counterfeiting information. This work not only discovered an excellent up-conversion nanocrystals (Na3GaF6:Tm3+,Yb3+@SiO2) suitable for anti-counterfeiting applications, but also provided an effective encryption strategy for anti-counterfeiting information.

A novel fluoroapatite-type phosphor Ca2Y8(BO4)2(SiO4)4F2:Eu3+ with high quantum efficiency and good thermal stability for multimodal applications☆

A novel Eu3+ doped fluorapatite red phosphor Ca2Y8(BO4)2(SiO4)4F2:Eu3+ with pure phase was synthesized in this study. Density functional theory (DFT) calculation and diffuse reflection spectrum analysis reveal its potential as a matrix for phosphors excited by ultraviolet light. Eu3+ has a 7F0→5L6 transition at 394 nm, and the prepared phosphor exhibits a high emission intensity at 614 nm, which may be attributed to the 5D0-7F2 energy transition at the lower symmetry site of Eu3+. The optimal doping concentration of the phosphor is determined to be 11 mol%, with concentration quenching attributed to the exchange interaction mechanism. The overall color purity of the phosphor is up to 99.88%, with an internal quantum efficiency as high as 91.15%. Notably, Ca2Y8(BO4)2(SiO4)4F2:11 mol%Eu3+ (CYBSF:11 mol%Eu3+) phosphors exhibit good thermal stability, with a thermal quenching temperature (T1/2) of 552 K and the intensity of emission at 423 K still at 88.89% of that at 298 K. The activation energy of the phosphor is up to 0.30287 eV. Its comprehensive luminescence performance surpasses that of commercial red phosphor, making it suitable for near ultraviolet excited warm white light emitting diode (NUV-WLED) with a high color rendering index (Ra = 82) and a correlation color temperature (CCT) of 4339 K. Moreover, the phosphor achieves latent fingerprint visualization and anti-counterfeiting ink on different material surfaces: glass, aluminum foil, plastic and paper. Overall, the fluorapatite CYBSF:11 mol%Eu3+ phosphor holds great potential for multimodal applications due to its high quantum efficiency and good thermal stability.

Upconversion photoluminescence of the lanthanide-doped core–shell luminescent material for anti-counterfeiting recognition

Three different NaErF4:Tm@NaREF4:Er (RE = Y, Lu, Yb) core-shell luminescent material were successfully synthesized. XRD, XPS and other characterization techniques were used to analyze the composed material, morphology, and luminous characteristics of the produced microparticles. Especially, compared with the uncoated NaErF4:Tm, the luminescence intensity of the materials with active-shell structure were increased by 2.44 times, 3.46 times, and 4.01 times respectively under 980 nm laser excitation. Moreover, the generated UCMPs were reliably employed for anti-counterfeiting recognition labels when they were used as screen-printing materials for anti-counterfeiting ink.

Lanthanide conjugated colour-tunable luminescent hydrogels as direct printable inks for anticounterfeiting and forensic applications

Counterfeiting is a global concern that jeopardizes individuals, businesses, and nations, costing trillions of USD annually. To combat this, researchers are continuously developing strong security features to formulate anti-counterfeiting inks. Herein, a novel approach has been adopted to prepare advanced luminescent hydrogel with ligand H3BTC for important applications in authentication of goods and fingerprint detection. In present investigations, Tb3+ and Eu3+ ions conjugated H3BTC hydrogels have been synthesized which emits strong green (542 nm) and red (614 nm) colours under UV lamp (254 nm). Additionally, the colour tunability for intermediate colours i.e. yellow and orange have also been achieved by varying the concentrations of Eu and Tb in H3BTC hydrogel. These hydrogels can be directly printed on any substrate using conventional screen-printing techniques. Moreover, these hydrogels can directly be used for thumb impressions with green and red emissions under 254 nm UV lamp, while appearing white in normal light and making them promising for new alternative solutions to design next-generation security ink for anticounterfeiting and forensic applications.

A cucurbit[6]uril-based fluorescence supramolecular assembly for information encryption and visualization detection of nitro compounds and antibiotics

A novel CB[6]-based supramolecular assembly [K(ANS)(CB[6])2(DMF)2(H2O)0.5] (1) (CB[6] = cucurbit[6]uril, ANS- = 8-amino-1-naphthalene sulfonic acid ion) was successfully synthesized under solvothermal condition. Performance studies have shown that 1 exhibited excellent chemical stability and recycling performance. Meanwhile, 1 exhibited remarkable potential as a fluorescence sensor for the detection of 2,4,6-trinitrophenol (TNP), 4-nitrophenol (4-NP), and rifampicin (RFP) in both aqueous environments and practical samples. This sensing capability is achieved through fluorescence quenching, which offers fast response times and exceptional sensitivity, with detection limits of 0.19 μM for both TNP and 4-NP, and 0.21 μM for RFP. Even more remarkably, an anti-counterfeiting ink based on 1 and a portable test hydrogel were devised for encrypting information and visually detecting using a smartphone application. This work has the potential to expand the utilization of CB[6]-based materials in optical applications.

Study on the Luminescence Performance and Anti-Counterfeiting Application of Eu2+, Nd3+ Co-Doped SrAl2O4 Phosphor.

This manuscript describes the synthesis of green long afterglow nanophosphors SrAl2O4:Eu2+, Nd3+ using the combustion process. The study encompassed the photoluminescence behavior, elemental composition, chemical valence, morphology, and phase purity of SrAl2O4:Eu2+, Nd3+ nanoparticles. The results demonstrate that after introducing Eu2+ into the matrix lattice, it exhibits an emission band centered at 508 nm when excited by 365 nm ultraviolet light, which is induced by the 4f65d1→4f7 transition of Eu2+ ions. The optimal doping concentrations of Eu2+ and Nd3+ were determined to be 2% and 1%, respectively. Based on X-ray diffraction (XRD) analysis, we have found that the physical phase was not altered by the doping of Eu2+ and Nd3+. Then, we analyzed and compared the quantum yield, fluorescence lifetime, and afterglow decay time of the samples; the co-doped ion Nd3+ itself does not emit light, but it can serve as an electron trap center to collect a portion of the electrons produced by the excitation of Eu2+, which gradually returns to the ground state after the excitation stops, generating an afterglow luminescence of about 15 s. The quantum yields of SrAl2O4:Eu2+ and SrAl2O4:Eu2+, Nd3+ phosphors were 41.59% and 10.10% and the fluorescence lifetimes were 404 ns and 76 ns, respectively. In addition, the Eg value of 4.98 eV was determined based on the diffuse reflectance spectra of the material, which closely matches the calculated bandgap value of SrAl2O4. The material can be combined with polyacrylic acid to create optical anti-counterfeiting ink, and the butterfly and ladybug patterns were effectively printed through screen printing; this demonstrates the potential use of phosphor in the realm of anti-counterfeiting printing.

Tb3+ doped CaWO4 nanomaterials for double level multicolor mode anticounterfeiting

Numerous new demands and obstacles have been posed to contemporary luminescent materials and anti-counterfeiting systems by the ever-increasing importance of data security and identification. The legibility, repeatability, multicolorism, and stimuli-responsiveness of luminescent materials have recently garnered a lot of interest in this area. A multicolor luminescent material, CaWO4:Tb3+, was effectively synthesized using an ethylene glycol-aided solvothermal technique in our present study. Under the 254 nm UV light, the sample may change its emission color from blue to green by increasing the concentration of Tb3+ dopant from 0 to 5 at%. However, its color changes from bluish-white to greenish-white when excited at 365 nm UV light. Energy transfer from host to Tb3+ ions increases with increasing the terbium concentration with an efficiency of 62 % for 5 at% doped samples. Anti-counterfeiting ink for screen-printed alphabets is made from samples with adjustable luminescence. Luminescent security goods can benefit from the material's outstanding multicolor anti-counterfeiting qualities, as demonstrated by the results under diverse light sources.

Accessing color-tunable afterglows from single conventional chromophore-based polysaccharide films through palette strategy

Achieving multicolor afterglow modulation from single conventional chromophore-based room temperature phosphorescence (RTP) materials is attractive but challenging. Herein, a facile palette strategy based on physical doping of red afterglow-emitted chromophore (N8) into sodium alginate (SA) is proposed to achieve large range of multicolor afterglow modulation for single conventional chromophore-based RTP materials. As well as being a key luminous component in the color palette, SA with cyan afterglow (upon 254 nm UV irradiation) can also activate the red afterglow of N8 via strong hydrogen bond interactions. Through regulating the doping ratios of N8 to SA, cyan to red afterglows have been achieved in the formed amorphous N8/SA films. Significantly, the afterglow of N8/SA also exhibits excitation wavelength- and time-dependent characteristics, which further extend the range and tunability of afterglow color. Besides, the phosphorescence lifetime of N8-based SA films could be further improved by chemically grafting N8 to SA, with a lifetime of 464.9 ms. Considering the excellent multicolor afterglow tunability and hygrothermal responsiveness, these smart SA-based materials demonstrate great application prospects in information encryption, anti-counterfeit ink painting, and 3D afterglow aerogel.