Nanoemulsion fluorescent inks for anti-counterfeiting encryption with dual-mode, full-color, and long-term stability

Water-Soluble Quantum Dots for Inkjet Printing Color Conversion Films with Simultaneous High Efficiency and Stability

Water-soluble quantum dots (QDs) are necessary to prepare patterned pixels or films for high-resolution displays with less environmental burden but are very limited by the trade-off between photoluminescence and stability of QDs. In this work, we proposed synthesizing water-soluble QDs with simultaneous excellent luminescence properties and high stability by coating the amphiphilic poly(maleic anhydride-alt-1-octadecene)-ethanol amine (PMAO-EA) polymer on the surface of silane-treated QDs. These coated QDs show a photoluminescence quantum yield (PLQY) as high as 94%, and they have good photoluminescence stability against light irradiation and thermal attacks, owing to the suppression of the nonradiative recombination by the polymer layer and the isolation of oxygen and water by the silica layer. The water-soluble QDs, mixed with ethylene glycol, enable inkjet printing of QD color conversion films (QD-CCFs) with an average diameter of 68 μm for each pixel and a high PLQY of 91%. The QD-CCFs are demonstrated to fabricate red-emitting mini-LEDs by combining with blue mini-LED chips, which have an external quantum efficiency as high as 25.86% and a luminance of 2.44 × 107 cd/m2. We believe that the proposed strategy is applicable to other water-soluble QDs and paves an avenue for inkjet printing environmentally friendly QD-CCFs for mini/micro-LED displays.

One-step hydrothermal method synthesized pH-dependent carbon dots for multistage anti-counterfeiting

Work to combat counterfeiting has always been crucial to defending the interests of the public. The usual anti-counterfeiting marks are now fundamental and easy to imitate. Therefore, it is more beneficial to anti-counterfeiting work to develop an anti-counterfeiting mark with more variations to make forgery more difficult. Due to its exceptional stability and fluorescence variability, carbon dots (CDs), a newly developed fluorescent material, offer a wide range of potential applications in anti-counterfeiting. However, there currently needs to be more CD applications in multi-level anti-counterfeiting, and additional issues include high cost and environmental contamination. Therefore, considering the problems of green environmental protection and cost, CDs with excellent green (530 nm) and blue (475 nm, 486 nm) luminescence properties were prepared by a one-step reaction of m-phenylenediamine and glucose. The average fluorescence lifespan is longer than 5 ns, and the optimal quantum yield can reach 37%. Due to the large number of protonated amino groups and surface carboxyl functional groups, the prepared carbon dots exhibit green and blue fluorescence emission modes under acidic and alkaline conditions, respectively. Based on this situation, we produced CD ink and successfully used it for multi-level anti-counterfeiting.

Exploring Optically Stable Reddish-Orange Fluorescent Magnetic Pigment (0.90)Y2O3:(0.10-x)Eu3+:(x)Bi3+ for Anti-counterfeiting Applications

The (0.90)Y2O3:(0.10-x)Eu3+:(x)Bi3+ nanophosphors (0.00 ≤ x ≤ 0.06) are synthesised using chemical combustion citrate route and characterized via X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, UV- visible and photoluminescence spectroscopy. The scanning electron micrographs indicate that the grain size of the phosphors ranges between 40 to 50 nm. The photoluminescence (PL) spectra, acquired under the excitation wavelength of 365 nm of ultraviolet light, show emission peaks at wavelengths 580 nm, 586-598 nm, 610 nm, 629-661 nm and 686-695 nm corresponding to the 5D0 → 7FJ electronic transitions of the Eu3+ ion with J = 0, 1, 2, 3 and 4, respectively. The most intense PL spectra at 611 nm (5D0 → 7F2), showcasing reddish-orange emission, indicate a higher concentration of Eu3+ ions in asymmetric sites within the Y2O3 host matrix. The presence of the distinct electronic transitions of Eu3+ in PL spectra acclaims that Bi3+ ions transfer their energy efficiently to Eu3+ ions in the matrix. Physical and chemical tests are being conducted on nanophosphors with Bi3+ substitutional doping of x = 0.02 and x = 0.04, both demonstrating intense PL emission. Magnetisation measurements suggest the soft magnetic nature of the nanophosphors, attributing it to the presence of Eu3+ ions in the 7F2 state. The highest PL intensity is seen in the nanophosphor (x = 0.04) with substitutional doping of 6% of Eu3+ and 4% of Bi3+ in Y2O3. This nanophosphor also demonstrates excellent optical stability in the investigated conditions and exhibits soft magnetic behaviour, positioning it as a promising material for incorporation as a fluorescent magnetic pigment in security ink applications. These features serve to prevent counterfeiting of secured documents both optically and magnetically.

Dual-Color Photoluminescent Functionalized Nanoparticles for Static-Dynamic Anticounterfeiting and Encryption: First Collaboration of Spiropyran and Coumarin

Increasing the security of anticounterfeiting materials has been the most important challenge in recent years, and the development of dual-color photoluminescent inks with multi-level security, static/dynamic emission, and dynamic color change is an important solution to overcome this problem. In this study, the multi-functionalized copolymer nanoparticles containing different functional groups (with a concentration of 20 wt %), including ester, carboxylic acid, hydroxyl, epoxide, amide, and amine groups were synthesized successfully by the emulsion polymerization method. The results showed that the particle size and morphology of nanoparticles are affected by the polarity of functional groups. The prepared multi-functionalized copolymer nanoparticles were modified physically with spiropyran (photochromic and red fluorescence emission) and coumarin (cyan emission) derivatives to develop dual-color photoluminescent polymer nanoparticles with application in static-dynamic photoluminescent anticounterfeiting inks, which have multi-level security. The investigation of optical properties indicates that the kinetics of photochromism and photoluminescence properties of samples containing spiropyran is dependent on the local polarity on the surface of polymer nanoparticles. Hence, an increase in the polarity (functionalization with amide, carboxylic acid, and hydroxyl groups) has resulted in fast photochromism, high-intensity photoluminescence emission and increased the efficiency of the photoswitchable color change of emission from cyan to pink. Dual-color photoluminescent anticounterfeiting inks were prepared by mixing polymer nanoparticles containing spiropyran with polymer nanoparticles containing coumarin, in different ratios (1:1, 1:3, 1:5, 1:8, and 1:10). Obtained results showed that prepared samples have cyan emission under UV light of 254 nm (static mode), and a dynamic photoswitching of fluorescence emission from cyan to pink (as a function of irradiation time) was also observed under UV-light irradiation of 365 nm, which is well known as a dynamic mode of emission. The responsivity and intensity of dynamic photoluminescence emission are dependent on the local polarity of the surface functional groups, in which the samples based on amide functionalized copolymer nanoparticles displayed high-intensity emission in the static mode and high-intensity photoswitchable dual-color emission in the dynamic mode, in the case of all ratios of colloid solution mixtures. Printing security tags on cellulose paper by dual-color photoluminescent inks indicates advantages such as maximum printability, resolution, brightness, and static-dynamic photoluminescence emission with high intensity for inks based on amide functionalized nanoparticles. The static-dynamic dual-color photoluminescent anticounterfeiting ink with unique properties and multi-level security was reported for the first time by the collaboration of spiropyran and coumarin. This study can open a new approach and window to the future of advanced and high-security anticounterfeiting technologies.

Water-borne, durable and multicolor silicon nanoparticles/sodium alginate inks for anticounterfeiting applications

Recently, water-borne fluorescent inks have attracted extensive attention in anti-counterfeiting applications due to their convenient implementation and eco-friendliness. However, due to poor service durability, the latent authorization information from the inks is easily damaged, and even disappears when encountering water. Moreover, most of the existing fluorescent inks are monochromic, toxic, and allergic to skin, thus are unsuitable for their sustainability during real-life applications. Herein, this work presents environment-friendly, durable, and multicolor fluorescent anti-counterfeiting silicon nanoparticles (SiNPs)/sodium alginate (SA) inks. The multicolor SiNPs are synthesized by a one-pot method with defined morphologies and optical properties. Subsequently, SA is employed as the binder to prepare the fluorescent inks with optimized rheological properties. Practicability results show that the SiNPs/SA inks not only exhibit excellent printability, but also impart authentic information with superior covert performance. More notably, spraying solution of calcium dichloride can further improve fluorescent fastnesses of the SiNPs/SA inks by ionic crosslinking.

Photoluminescent Polymer Nanoparticles Based on Oxazolidine Derivatives for Authentication and Security Marking of Confidential Notes

Colloidal materials have widely been used to develop innovative anticounterfeiting nanoinks for information encryption. Latex nanoparticles based on methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) bearing hydroxyl functional groups were synthesized via semicontinuous miniemulsion polymerization. The size determination of the nanoparticles and microscopic results showed mostly spherical nanoparticles with a narrow size distribution and a mean size of about 80 nm. Two oxazolidine derivatives were physically doped at the surface of the nanoparticles to prepare photoluminescent polymer nanoparticles. Hydroxyl functional groups at the surface of the nanoparticles led to their hydrogen bonding interactions with the doped luminescent compounds. Optical analysis of the photoluminescent nanoparticles displayed different fluorescence emission and UV-vis absorbance intensities based on the amount of polar groups located at the surface of colloidal nanoparticles. Reducing the particle size to below 100 nm along with increasing the surface area can assist the decrease of the light reflectance and improvement of the latex nanoparticles' efficiency in the anticounterfeiting industry. This preparation methodology can efficiently provide remarkable photoreversible anticounterfeiting nanoinks used in different applications, such as print marking, security encoded tags, labeling, probing, and handwriting.

Highly Plasticized Lanthanide Luminescence for Information Storage and Encryption Applications

The development of new storage media to meet the demands for diverse information storage scenarios is a great challenge. Here, a series of lanthanide-based luminescent organogels with ultrastrong mechanical performance and outstanding plasticity are developed for patterned information storage and encryption applications. The organogels possessing outstanding mechanical properties and tunable luminescent colors are prepared by electrostatic and coordinative interactions between natural DNA, synthetic ligands, and rare earth (RE) ions. The organogel-REs can be stretched by 180 times and show an ultrastrong breaking strength of 80 MPa. A series of applications with both information storage and encryption, such as self-information pattern, quick response (QR) code, and barcode, are successfully demonstrated by the organogel-REs. The developed information storage systems have various advantages of good processability, high stretchability, excellent stability, and versatile design of information patterns. Therefore, the organogel-RE-based information storage systems are suitable for applications under different scenarios, such as flexible devices under repeating rude operations. The advancements will enable the design and development of luminescent organogel-REs as information storage and encryption media for various scenarios.

Photovoltaic Energy Conversion and Storage of Micro-Supercapacitors Based on Emulsion Self-Assembly of Upconverting Nanoparticles

With the rapid need for new kinds of portable and wearable electronics, we must look to develop flexible, small-volume, and high-performance supercapacitors that can be easily produced and stored in a sustainable way. An integrated system simultaneously converting recyclable energy to electricity and storing energy is sought after. Here we report photovoltaic energy conversion and storage integrated micro-supercapacitors (MSCs) with asymmetric, flexible, and all-solid-state performances constructed from thousands of close-packed upconverting nanoparticles (UCNPs) via an emulsion-based self-assembly process using oleic acid (OA)-capped upconverting nanoparticles. The carbonated-UCNPs supraparticles (CSPs) are further coated with polypyrrole (PPy) to improve their electrochemical performance. Such a design can develop CSPs@PPy as electrode materials with high gravimetric capacitance, 308.6 F g^-1 at 0.6 A g^-1. The fabricated MSCs exhibit excellent areal capacitance, C _s = 21.8 mF cm^-2 at 0.36 A cm^-2 and E = 0.00684 mWh cm^-2, and have superior flexibility and cycling ability. The MSC devices have a sensitive near-infrared ray (NIR) photoelectrical response capability, which can capture the NIR of sunlight to convert it into electrical energy and store the electric energy due to an excellent capacitive performance. We propose a method for multifunctional integration of energy conversion and storage, and provide future research directions and potential applications of self-powered flexible wearable photonic electronics.

Photoluminescent Nanoinks with Multilevel Security for Quick Authentication of Encoded Optical Tags by Sunlight: Effective Physicochemical Parameters on Responsivity, Printability, and Brightness

Investigation of developed photoactive security inks and anticounterfeiting technologies in recent years indicates significant challenges for future of this research area, such as increase of security, fast responsivity, and facile authentication. Here, amine-functionalized latex nanoparticles were synthesized by emulsion copolymerization of methyl methacrylate (MMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). Size of the latex nanoparticles was increased as a function of poly(dimethylaminoethyl acrylate) (PDMAEMA) contents, and also a decrease of particle size was obtained in response to an increase of temperature from 25 to 70 °C, above the lower critical solution temperature (LCST) of PDMAEMA. Surface physical modification of the functional latex nanoparticle with spiropyran photoswitches led to the development of anticounterfeiting nanoinks that have multilevel security and photochromic/fluorescence properties with a higher intensity and also brightness. The photoluminescent nanoinks were made of spiropyran latex nanoparticles and used for printing of the encoded optical security tags on cellulosic papers and banknotes. The results displayed that an increase of the particle size above 100 nm and an increase of the PDMAEMA contents led to a remarkable decrease of printability, fluorescent emission, brightness, intensity of photochromism, and also resolution of the printed security tags. As a significant advantage of the developed security inks, the printed security tags could be authenticated easily and fast upon sunlight irradiation by means of photochromism. The responsivity of encoded tags from the invisible to visible state is immediate upon sunlight irradiation for some seconds, whose intensity of coloration is appropriate and detectable clearly by naked eyes. The security anticounterfeiting inks based on spiropyran with multilevel security have been reported for the first time for applying in printing of encoded security tags on cellulosic papers, banknotes, and other documents, where the printed marks are detectable on sunlight exposure.