Stimuli-Responsive Inks Based on Perovskite Quantum Dots for Advanced Full-Color Information Encryption and Decryption

Achieving Image Encryption Quantum Dot-Functionalized Encryption Camera with Designed Films

The risk of information leaks increases as images become a crucial medium for information sharing. There is a great need to further develop the versatility of image encryption technology to protect confidential and sensitive information. Herein, using high spatial redundancy (strong correlation of neighboring pixels) of the image and the in situ encryption function of a quantum dot functionalized encryption camera, in situ image encryption is achieved by designing quantum dot films (size, color, and full width at half maximum) to modify the correlation and reduce spatial redundancy of the captured image during encryption processing. The correlation coefficients of simulated encrypted image closely apporach to 0. High-quality decrypted images are achieved with a PSNR of more than 35 dB by a convolutional neural network-based algorithm that meets the resolution requirements of human visual perception. Compared with the traditional image encryption algorithms, chaotic image encryption algorithms and neural network-based encryption algorithms described previously, it provides a universal, efficient and effective in situ image encryption method.

Laser Fabrication of Multi-Dimensional Perovskite Patterns with Intelligent Anti-Counterfeiting Applications

Perovskites have gained widespread attention across various fields such as photovoltaics, displays, and imaging. Despite their promising applications, achieving precise and high-quality patterning of perovskite films remains a challenge. In this study, femtosecond laser direct writing technology is utilized to achieve rapid and highly precise micro/nanofabrication on perovskites. The study successfully fabricates multiple structured and emission-tunable perovskite patterns composed of A2(FA)n-1PbnX3n+1 (A represents a series of long-chain amine cations, and X = Cl, Br, I), encompassing 2D, quasi-2D, and 3D structures. The study delves into the intricate interplay between fabrication technology and the growth of multi-dimensional perovskites: higher repetition rates, coupled with appropriate laser power, prove more conducive to perovskite growth. By employing precise halogen element design, the simultaneous generation of two distinct color quick-response (QR) code patterns is achieved through one-step laser processing. These mirrored QR codes offer a novel approach to anti-counterfeiting. To further enhance anti-counterfeiting capabilities, artificial intelligence (AI)-based methods are introduced for recognizing patterned perovskite anti-counterfeiting labels. The combination of deep learning algorithms and a non-deterministic manufacturing process provides a convenient means of identification and creates unclonable features. This integration of materials science, laser fabrication, and AI offers innovative solutions for the future of security features.

Surficial Host-Guest Responsive CsPbBr3 Perovskite Nanocrystals for Programmable Multi-Level Information Encryption

The design of smart stimuli-responsive photoluminescent materials capable of multi-level encryption and complex information storage is highly sought after in the current information era. Here, a novel adamantyl-capped CsPbBr3 (AD-CsPbBr3) perovskite NCs, along with its supramolecular host-guest assembly partner a modified β-CD (mCD), mCD@AD-CsPbBr3, are designed and prepared. By dispersing these two materials in different solvents, namely, AD-CsPbBr3 in toluene, mCD@AD-CsPbBr3 in toluene, and mCD@AD-CsPbBr3 in methanol, the three solutions exhibit diverse photoluminescence (PL) turn-on/off or PL discoloration response upon supramolecular stimulus. Based on these responses, a proof-of-principle programmable Multi-Level Photoluminescence Encoding System (MPLES) is established. Three types of four-level and three types of three-level information encoding are achieved by the system. A layer-by-layer four-level information encryption and decryption as well as a two-level encrypted 3D code are successfully achieved.

Eu3+-Directed Supramolecular Metallogels with Reversible Quadruple-Stimuli Response Behaviors

Smart luminescent materials that have the ability to reversibly adapt to external environmental stimuli and possess a wide range of responses are continually emerging, which place higher demands on the means of regulation and response sites. Here, europium ions (Eu3+)-directed supramolecular metallogels are constructed by orthogonal self-assembly of Eu3+ based coordination interactions and hydrogen bonding. A new organic ligand (L) is synthesized, consisting of crown ethers and two flexible amide bonds-linked 1,10-phenanthroline moieties to coordinate with Eu3+. Synergistic intermolecular hydrogen bonding in L and Eu3+-L coordination bonding enable Eu3+ and L to self-assemble into shape-persistent 3D coordination metallogels in MeOH solution. The key to success is the utilization of crown ethers, playing dual roles of acting both as building blocks to build L with C2-symmetrical structure, and as the ideal monomer for increasing the energy transfer from L to Eu3+'s excited state, thus maintaining the excellent luminescence of metallogels. Interestingly, such assemblies show K+, pH, F-, and mechano-induced reversible gel-sol transitions and tunable luminescence properties. Above findings are useful in the studies of molecular switches, dynamic assemblies, and smart luminescent materials.

Multilevel Information Encryption Based on Thermochromic Perovskite Microcapsules via Orthogonal Photic and Thermal Stimuli Responses

Increasing modal variations of stimulus-responsive materials ensure the high capacity and confidentiality of information storage and encryption systems that are crucial to information security. Herein, thermochromic perovskite microcapsules (TPMs) with dual-variable and quadruple-modal reversible properties are designed and prepared on the original oil-in-fluorine (O/F) emulsion system. The TPMs respond to the orthogonal variations of external UV and thermal stimuli in four reversible switchable modes and exhibit excellent thermal, air, and water stability due to the protection of perovskites by the core-shell structure. Benefiting from the high-density information storage TPMs, multiple information encryptions and decryptions are demonstrated. Moreover, a set of devices are assembled for a multilevel information encryption system. By taking advantage of TPMs as a "private key" for decryption, the signal can be identified as the corresponding binary ASCII code and converted to the real message. The results demonstrate a breakthrough in high-density information storage materials as well as a multilevel information encryption system based on switchable quadruple-modal TPMs.

Anchoring copper nanoclusters to Al2O3 microsphere for dual-mode analysis of N-acetyl-β-D-glucosaminidase and information encryption

Herein, we attempted to confine copper nanoclusters (CuNCs) with alumina (Al2O3) as the matrix (Al2O3@CuNCs), which effectively circumvented the drawbacks of CuNCs (such as weak photoluminescence and low quantum yield). Al2O3@CuNCs demonstrated sensitive response to p-nitrophenol, the catalytic product of N-acetyl-β-D-glucosaminidase (NAG) on account of the inner filter effect and dynamic quenching effect. In light of this, a novel assay was created to identify NAG, a critical indicator of diabetic nephropathy. Additionally, a portable and instrument-free sensing platform mainly consisting of a smartphone, a cuvette, a cuvette holder, a dark box and a 365 nm UV lamp was developed for the quantitative detection of NAG. The as-prepared material was also utilized in anti-counterfeiting and information encryption based on their excellent optical properties and sensitive response to the catalyzed product of NAG. This work advanced potential applications of CuNCs composites in the areas of portable, multi-mode biosensing, anti-counterfeiting and information encryption.

Highly efficient and stable Cs3Mn0.93Zn0.07Br5@SiO2 for wide color gamut backlight displays

Mn-based perovskites have become a new candidate material for backlight display applications. However, low efficiency and poor stability are the key problems limiting the application of Mn-based perovskites. In this work, Zn-doped and SiO2-encapsulated Cs3MnBr5, denoted as Cs3Mn0.93Zn0.07Br5@SiO2 (CMZBS), was successfully synthesized to improve the photoluminescence quantum yield (PLQY) and stability. After Zn doping, the PLQY increased from 51% to 72% due to the reduction in the energy transfer between [MnBr4]2-. The PLQY can be further improved to 80% after coating SiO2. Compared with Cs3MnBr5 (CMB), CMZBS showed better stability against thermal, air, light, and polar solvents (ethanol and isopropanol). In addition, a white LED (WLED) device with a CIE of (0.323, 0.325) was fabricated by integrating CMZBS and the red phosphor K2SiF6:Mn4+ on a 465 nm blue GaN chip, which exhibited a high luminous efficiency of 92 lm W-1 and excellent stability, demonstrating its great potential application in wide color gamut displays.

Living Materials Based Dynamic Information Encryption via Light-Inducible Bacterial Biosynthesis of Quantum Dots

Microbial biosynthesis, as an alternative method for producing quantum dots (QDs), has gained attention because it can be conducted under mild and environmentally friendly conditions, distinguishing it from conventional chemical and physical synthesis approaches. However, there is currently no method to selectively control this biosynthesis process in a subset of microbes within a population using external stimuli. In this study, we have attained precise and selective control over the microbial biosynthesis of QDs through the utilization of an optogenetically engineered Escherichia coli (E. coli). The recombinant E. coli is designed to express smCSE enzyme, under the regulation of eLightOn system, which can be activated by blue light. The smCSE enzymes use L-cysteine and Cd2+ as substrates to form CdS QDs. This system enables light-inducible bacterial biosynthesis of QDs in precise patterns within a hydrogel for information encryption. As the biosynthesis progresses, the optical characteristics of the QDs change, allowing living materials containing the recombinant E. coli to display time-dependent patterns that self-destruct after reading. Compared to static encryption using fluorescent QD inks, dynamic information encryption based on living materials offers enhanced security.

Intense Hydrochromic Photon Upconversion from Lead-Free 0D Metal Halides For Water Detection and Information Encryption

Hydrochromic materials that change their luminescence color upon exposure to moisture have attracted considerable attention owing to their applications in sensing and information encryption. However, the existing materials lack high hydrochromic response and color tunability. This study reports the development of a new and bright 0D Cs3 GdCl6 metal halide as the host for hydrochromic photon upconversion in the form of polycrystals (PCs) and nanocrystals. Lanthanides co-doped cesium gadolinium chloride metal halides exhibit upconversion luminescence (UCL) in the visible-infrared region upon 980 nm laser excitation. In particular, PCs co-doped with Yb3+ and Er3+ exhibit hydrochromic UCL color change from green to red. These hydrochromic properties are quantitatively confirmed through the sensitive detection of water in tetrahydrofuran solvent via UCL color changes. This water-sensing probe exhibits excellent repeatability and is particularly suitable for real-time and long-term water monitoring. Furthermore, the hydrochromic UCL property is exploited for stimuli-responsive information encryption via cyphertexts. These findings will pave the way for the development of new hydrochromic upconverting materials for emerging applications, such as noncontact sensors, anti-counterfeiting, and information encryption.

Hydrochromic Perovskite System with Reversible Blue-Green Color for Advanced Anti-Counterfeiting

The intrinsic instability of halide perovskites toward to external stimulus, has created a competitive advantage for designing stimuli-responsive materials. However, the external environment tuning reversibly fluorescence emission of perovskite system is still limited. In this work, humidity is verified to act as a new option to modulate the emission properties of mixed-halide perovskite. The perovskite nanocrystals (PNCs) photoirradiated in dichloromethane are easily and stably redispersed in water, and emit bright fluorescence which is quite different from the original. Moreover, the perovskites confined on glass slide can reversibly switch their fluorescence between blue and green colors under moisture. It is demonstrated that the factors of different solubilities of CsCl and CsBr in water, the structural transformation of perovskites and the confine of glass matrix play key roles in the reversible transformation. Finally, the combination of hydrochromic CsPb(Brx Cly )3 and water-resistant CsPb(Brx Cly )3 -polymethyl methacrylate have been applied in advanced anti-counterfeiting, which greatly improves the information security. This work not only give an insight into the effects of humidity on fluorescence and structures of PNCs, but also offer a new class of hydrochromic PNCs materials based on reversible emission transformation for potential application in sensors, anti-counterfeiting and information encryption.

Metal-Ion-Doped Manganese Halide Hybrids with Tunable Emission for Advanced Anti-Counterfeiting

Stimuli-responsive luminescent materials have received great attention for their potential application in anti-counterfeiting and information encryption. Manganese halide hybrids have been considered an efficient stimuli-responsive luminescent material due to their low price and adjustable photoluminescence (PL). However, the photoluminescence quantum yield (PLQY) of PEA₂MnBr₄ is relatively low. Herein, Zn²⁺- and Pb²⁺-doped PEA₂MnBr₄ samples are synthesized, and show an intense green emission and orange emission, respectively. After doping with Zn²⁺, the PLQY of PEA₂MnBr₄ is elevated from 9% to 40%. We have found that green emitting Zn²⁺-doped PEA₂MnBr₄ could transform to a pink color after being exposed to air for several seconds and the reversible transformation from pink to green was achieved by using heating treatment. Benefiting from this property, an anti-counterfeiting label is fabricated, which exhibits excellent "pink-green-pink" cycle capability. Pb²⁺-doped PEA₂Mn_0.88Zn_0.12Br₄ is acquired by cation exchange reaction, which shows intense orange emission with a high QY of 85%. The PL of Pb²⁺-doped PEA₂Mn_0.88Zn_0.12Br₄ decreases with increasing temperature. Hence, the encrypted multilayer composite film is fabricated relying on the different thermal responses of Zn²⁺- and Pb²⁺-doped PEA₂MnBr₄, whereby the encrypted information can be read out by thermal treatment.

Sequential-Dependent Synthesis of Bimetallic Silver-Chromium Nanoparticles for Multichannel Sensing, Logic Computing, and 3 in 1 Information Protection

Bimetallic nanomaterials (BNMs) have been used in sensing, biomedicine, and environmental remediation, but their multipurpose and comprehensive applications in molecular logic computing and information security protection have received little attention. Herein, This synthesis method is achieved by sequentially adding reactants under ice bath conditions. Interestingly, Ag-Cr NPs can dynamically selectively sense anions and reductants in multiple channels. Especially, ClO^- can be quantitatively detected by oxidizing Ag-Cr NPs with detection limits of 98.37 nM (at 270 nm) and 31.83 nM (at 394 nm). Based on sequential-dependent synthesis process of Ag-Cr NPs, Boolean logic gates and customizable molecular keypad locks are constructed by setting the reactants as the inputs, the states of the resulting solutions as the outputs. Furthermore, dynamically selective response patterns of the Ag-Cr NPs can be converted into binary strings to exploit molecular crypto-steganography to encode, store, and hide information. By integrating the three dimensions of authorization, encryption, and steganography, 3 in 1 advanced information protection based on Ag-Cr nanosensing system can be achieved, which can enhance the anti-cracking ability of information. This research will promote the development and application of nanocomposites in the field of information security and deepen the connection between molecular sensing and the information world.

Colorimetric multi-channel sensing of metal ions and advanced molecular information protection based on fish scale-derived carbon nanoparticles

Some nanosystems based on carbon nanomaterials have been used for fluorescent chemical/biosensing, elementary information processing, and textual coding. However, little attention has been paid to utilizing biowaste-derived carbon nanomaterials for colorimetric multi-channel sensing and advanced molecular information protection (including text and pattern information). Herein, fish scale-derived carbon nanoparticles (FSCN) were prepared and used for colorimetric detection of metal ions, encoding, encrypting and hiding text- and pattern-based information. The morphology and composition of FSCN were analyzed by TEM, XRD, FTIR, and XPS, and it was found that the FSCN-based multi-channel colorimetric sensing system can detect Cr⁶⁺ (detection limit of 56.59 nM and 13.32 nM) and Fe³⁺ (detection limit of 81.55 nM) through the changes of absorption intensity at different wavelengths (272, 370, and 310 nm). Moreover, the selective responses of FSCN to 20 kinds of metal ions can be abstracted into a series of binary strings, which can encode, hide, and encrypt traditional text-based and even two-dimensional pattern-based information. The preparation of carbon nanomaterials derived from waste fish scales can stimulate other researcheres' enthusiasm for the development and utilization of wastes and promoting resource recycling. Inspired by this work, more researches will continue to explore the world of molecular information technology.

Glucose and pH responsive fluorescence detection system based on simple synthesis of silicon-coated perovskite quantum dots

Perovskite quantum dots (PQDs) are extremely unstable in ambient air due to their inherent structural instability, which limits the wide application of PQDs. In this work, silicon-coated CsPbBr₃ PQDs (CsPbBr₃@SiO₂) was synthesized via a simple method. The SiO₂ coating effectively isolated PQDs from water and oxygen in the environment, which were the main elements that destroyed the structure stability of PQDs. The synthesized CsPbBr₃@SiO₂ can be stored in water for more than 2 months and posessed wonderful dispersibility in aqueous solution. The fluorescence intensity remained unchanged within 7 days and only decreased by 11.9 % within 2 months. We found that CsPbBr₃@SiO₂ was extremely sensitive to environmental pH, and the fluorescence intensity decreased with the reduction of pH. In addition, an excellent linear relationship with pH value in the range of 1.0 ∼ 5.0 was achieved. As we all known that glucose can be catalyzed by glucose oxidase to produce gluconic acid and hydrogen peroxide, in which a good deal of protons were produced and the pH was gradually lowered. Since CsPbBr₃@SiO₂ was stable to water and oxygen, and sensitive to ambient pH, we applied CsPbBr₃@SiO₂ to the detection of glucose. CsPbBr₃@SiO₂ showed fantastic selectivity and sensitivity to glucose, and the detection limit can even reach 18.5 μM. Furthermore, CsPbBr₃@SiO₂ was successfully applied to the detection of glucose in the human serum with satisfactory performance.

Reversible Growth of Halide Perovskites via Lead Oxide Hydroxide Nitrates Anchored Zeolitic Imidazolate Frameworks for Information Encryption and Decryption

The low formation energies of metal halide perovskites endow them with potential luminescent materials for applications in information encryption and decryption. However, reversible encryption and decryption are greatly hindered by the difficulty in robustly integrating perovskite ingredients into carrier materials. Here, we report an effective strategy to realize information encryption and decryption by reversible synthesis of halide perovskites, on the lead oxide hydroxide nitrates (Pb₁₃O₈(OH)₆(NO₃)₄) anchored zeolitic imidazolate framework composites. Benefiting from the superior stability of ZIF-8 in combination with the strong bond between Pb and N evidenced by X-ray absorption spectroscopy and X-ray photoelectron spectroscopy, the as-prepared Pb₁₃O₈(OH)₆(NO₃)₄-ZIF-8 nanocomposites (Pb-ZIF-8) can withstand common polar solvent attack. Taking advantage of blade-coating and laser etching, the Pb-ZIF-8 confidential films can be readily encrypted and subsequently decrypted through reaction with halide ammonium salt. Consequently, multiple cycles of encryption and decryption are realized by quenching and recovery of the luminescent MAPbBr₃-ZIF-8 films with polar solvents vapor and MABr reaction, respectively. These results provide a viable approach to integrate the state-of-the-art materials perovskites and ZIF for applications in information encryption and decryption films with large scale (up to 6 × 6 cm²), flexibility, and high resolution (approximate 5 μm line width).

Solvent stimuli-responsive off-on fluorescence induced by synergistic effect of doping and phase transformation for Te4+ doped indium halide perovskite: Giving printable and colorless ink for information encryption and decryption

Since traditional fluorescent materials are too easily observed by the eyes just under the UV light, off-on fluorescent materials are explored as the new generation of fluorescent labels. In the "off" state, such off-on fluorescent labels cannot be observed by naked eyes under either natural light or UV light. Only after a specific decryption treatment to make the fluorescent materials turning into the "on" state, the fluorescent labels can be observed under the UV light. Up to now, it is still a challenge to prepare fluorescent inks with aforementioned ideal properties by using halide perovskite materials. Herein, we reported the first example of Te⁴⁺ doped indium halide perovskite inks with both off-on fluorescence under solvent stimuli and invisible ink color by the naked eyes. The synergistic effect of doping/undoping of Te⁴⁺ together with the reversible phase transformation between Cs₂InCl₅(H₂O) and Cs₃InCl₆ under solvent stimuli is key for the off-on fluorescence of crystals. Under acid solvent, the substitutional doping of Te⁴⁺ during the process of phase transformation from Cs₃InCl₆ to Cs₂InCl₅(H₂O):Te⁴⁺ gives rise to "turning-on" orange emission from Te-induced self-trap emission (STE). Under the stimuli of methanol, the dissolution of Te⁴⁺ from the crystals destroys the structure of Te⁴⁺ in ligand-field and results in "turning-off" Te-induced emission during the process of phase transformation from Cs₂InCl₅(H₂O):Te⁴⁺ to Cs₃InCl₆. On the basis of the Te⁴⁺ doped indium halide perovskite, printable and colorless ink can be prepared for the confidential information encryption and decryption. Since the mixture of Cs₃InCl₆ crystals and TeCl₄ have no absorption in visible light scope, the printed encrypted information by such off-state fluorescent ink is colorless and invisible by the naked eyes under either ambient light or UV light. After decryption by acid solvent stimuli, the resulted Cs₂InCl₅(H₂O):Te⁴⁺ doping crystals have a large Stokes shift with absorption below 450 nm from the excitation of Te⁴⁺ in ligand-field and emission around 570 nm from Te-induced STE. It makes the decryption information still colorless and invisible by the naked eyes under the ambient light but visible and readable under the UV light. In comparison to traditional undoped CsPbBr₃/CsPb₂Br₅ perovskites with small Stokes shift and eye-visible ink color, the current colorless Te⁴⁺doped indium halide perovskites are no doubt providing better security level for both encrypted and decrypted information.

Sophisticated yet Convenient Information Encryption/Decryption Based on Synergistically Time-/Temperature-Resolved Photonic Inks

Exploring high-safety but convenient encryption and decryption technologies to combat threats of information leakage is urgently needed but remains a great challenge. Here, a synergistically time- and temperature-resolved information coding/decoding solution based on functional photonic inks is demonstrated. Encrypted messages can be stored into multiple channels with dynamic-color patterns, and information decryption is only enabled at appointed temperature and time points. Notably, the ink can be easily processed into quick-response codes and multipixel plates. With high transparency and responsive color variations controlled by ink compositions and ambient temperatures, advanced 3D stacking multichannel coding and Morse coding techniques can be applied for multi-information storage, complex anticounterfeiting, and information interference. This study paves an avenue for the design and development of dynamic photonic inks and complex encryption technologies for high-end anticounterfeiting applications.

Ligands engineering of gold nanoclusters with enhanced photoluminescence for deceptive information encryption and glutathione detection

Gold nanoclusters (Au NCs) have appeared as an essential alternative to traditional quantum dots and fluorescent molecules for the development of intelligent stimuli-responsive photoluminescence (PL), but the low PL emission of Au NCs restricts their broad applications. Herein, we reported a simple yet effective strategy for preparing Au NCs with high PL by ligands engineering of 4-hydroxy-2-mercapto-6-methylpyrimidine (MTU) and L-Arginine (Arg). Owing to the rigidified shell and the ligand-to-metal charge transfer (LMCT) effects, it was found that the assembly of Arg ligand on MTU-protected Au NCs (Arg/MTU-Au NCs) led to a significantly enhanced PL in the alkaline solution up to 30 times. Moreover, utilizing the tunable LMCT, the Arg/MTU-Au NCs displayed rapid responses to multi-type ionic interaction in a reversible manner, such as H+/OH- and Cu2+/glutathione (GSH) pairs. Inspired by these intriguing ions-responsive LMCT and the associated switchable PL emission, the Arg/MTU-Au NCs were successfully used as excellent stimuli-responsive PL probes for intriguing deceptive information encryption and biosensing as well. This work would provide new insight into regulating the PL emission of Au NCs by ligands engineering and advance their potential applications in information encryption and bioassay.

RGB Tricolor and Multimodal Dynamic Optical Information Encryption and Decoding for Anti-Counterfeiting Applications

Conventional optical anti-counterfeiting strategies are based on the single-color emission, which are easily deciphered and thus greatly limited in the application of information security. Herein, a multimodal dynamic optical information coding with red, green, and blue (RGB) tricolors has been developed by photoluminescence (PL), persistent luminescence (PersL), thermally stimulated luminescence (TSL), and thermally stimulated persistent luminescence (TSPL). The BaSi₂O₂N₂:Eu²⁺ phosphors with a blue emission peak at 494 nm were used as the crucial blue optical information coding material and exhibited the distinctive response properties to light, heat, and force stimuli with intrinsic trap depths of 0.674 and 0.82 eV. More importantly, by combining the red Sr₂Si₅N₈:Eu²⁺,Dy³⁺ and green SrSi₂O₂N₂:Eu²⁺,Dy³⁺ nitride phosphors, a RGB tricolor and multimodal strategy has been successfully developed for anti-counterfeiting applications. The "RGB tricolor flower" with RGB emissions is given as a typical example to achieve the dynamic display of optical information encryption and decoding through the various PL, PersL, TSL, and TSPL modes. Finally, the traditional quick response (QR) code mechanism has been integrated into the design of multi-information encrypted RGB tricolor anti-counterfeiting devices with different identifiabilities of the encrypted information in natural light, PL, PersL, TSL, and TSPL modes. The laminated layers of RGB QR code patterns containing different specific information, such as "DLPU" and "116034", can be effectively recognized in the corresponding modes. The design strategy of RGB tricolor and multimodal optical information encryption and decoding devices in this work greatly improves the security level of advanced optical information technologies and extends the potential applications in dynamic anti-counterfeiting fields.

One material, many possibilities via enrichment of luminescence in La2Zr2O7:Tb3+ nanophosphors for forensic stimuli aided applications

Engineering a single material with multidirectional applications is crucial for improving productivity, low cost, flexibility, least power consumption, etc. To achieve these requirements, novel design structures and high-performance materials are in urgent need. Lanthanide-doped nanophosphors have the greatest strengths and ability in order to tune their applications in various dimensions. However, applications of nanophosphor in latent fingerprints visualization, anti-counterfeiting, and luminescent gels/films are still in their infancy. This study demonstrated a simple strategy to enhance the luminescence of Tb³⁺ (1-11 mol %) doped La₂Zr₂O₇ nanophosphors by conjugating various fluxes via a simple solution combustion route. The photoluminescence emission spectra reveal intense peaks at ~ 491, 546, 587, and 622 nm, which arises from ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) transitions of Tb³⁺ ions, respectively. The highest emission intensity was achieved in the NH₄Cl flux assisted nanophosphor as compared to NaBr and NH₄F assisted samples. The colorimetric images of fingerprints visualized using the optimized nanophosphor on forensic related surfaces exhibit level -III ridge details, including sweat pores, the width of the ridges, bifurcation angle, and the successive distance between sweat pores, etc. These results are decisive parameters that clearly support the statement "no two persons have ever been found to have the same fingerprints". The anti-counterfeiting security ink was formulated using optimized nanophosphor and various patterns were designed by simple screen printing and dip pen technologies. The encoded information was decrypted only under ultraviolet 254 nm light. All the designed patterns are exhibit not just what it looks/feel like and how better it works. As a synergetic contribution of enhanced luminescence of the prepared nanophosphor, the green-emissive films were fabricated, which display excellent flexibility, uniformity, and transparency in the normal and ultraviolet 254 nm light illumination. The aforementioned results revealed that the prepared NH₄Cl flux-assisted La₂Zr₂O₇: Tb³⁺(7 mol %) NPs are considered to be the best candidate for multi-dimensional applications.

Microwave-Assisted Synthesis of Silver Nanoparticles for Multimode Colorimetric Sensing of Multiplex Metal Ions and Molecular Informatization Applications

Plasmonic materials have been widely used in chemo/biosensing and biomedicine. However, little attention has been paid to the application of plasmonic materials in terms of the transition from molecular sensing to molecular informatization. Herein, we demonstrated that silver nanoparticles (AgNPs) prepared through facile and rapid microwave heating have multimode colorimetric sensing capabilities to different metal ions (Cr³⁺, Hg²⁺, and Ni²⁺), which can be further transformed into interesting and powerful molecular information technology (massively parallel molecular logic computing and molecular information protection). The prepared AgNPs can quantitatively and sensitively detect Cr³⁺ and Hg²⁺ in actual water samples. The AgNPs' multimode-guided multianalyte sensing processing was further investigated to construct a series of basic logic gates and advanced cascaded logic circuits by considering the analytes as the inputs and the colorimetric signals (like color, absorbance, wavelength shift) as the outputs. Moreover, the selective responses and molecular logic computing ability of AgNPs were also utilized to develop molecular cryptosteganography for encrypting and hiding some specific information, which proves that the molecular world and the information world are interconnected and use each other. This research not only opens the door for the transition from molecular sensing to molecular informatization but also provides an excellent opportunity for the construction of the "metaverse" of the molecular world.

Fabry-Perot Mode-Limited High-Purcell-Enhanced Spontaneous Emission from In Situ Laser-Induced CsPbBr3 Quantum Dots in CsPb2Br5 Microcavities

The patterned metal halide perovskites exhibit novel photophysical properties and high performance in photonic applications. Here, we show that a UV continuous wave laser can induce in situ crystallization of individual and patterned CsPbBr₃ quantum dots (QDs) inside the CsPb₂Br₅ microplatelets. The microplatelet acts as a natural Fabry-Perot cavity and causes the high-Purcell-effect-enhanced (by 287 times) cavity mode spontaneous emission of the embedded CsPbBr₃ QDs. The luminescence exhibits a superlinear emission intensity-excitation intensity relation I(p) ∝ p^2.83, and the exponent is much bigger than that of the free-space exciton spontaneous emission, suggesting arising of stimulated emission at higher photon concentrations. These laser-driven crystallized and patterned cavity mode luminescent perovskite QDs in a waterproof wider-bandgap perovskite microcavity act as an ideal platform for studying the cavity quantum electrodynamics phenomena and for applications in information storage and encryption, anticounterfeiting, and low-threshold lasers.

Structured light using carbon nanostructures driven by Kerr nonlinearities and a magnetic field

A substantial influence of a magnetic field on the third-order nonlinear optical properties exhibited by aggregated networks of aligned carbon nanotubes (CNT) is reported by systematic measurements. A two-wave mixing was employed to explore and modulate the refractive index in the nanostructures in the nanosecond and picosecond regime. The presence of a magnetic field was able to modify the optical transmittance in the sample and the potentiality to generate structured light was proposed. Numerical simulations were conducted to analyze the magnetic field phenomena and the oscillations of the electric field in the studied sample. We discussed theoretical concepts, experimental methods, and computational tools employed to evaluate the third-order nonlinear optical properties of CNT in film form. Immediate applications of the system to modulate structured light can be contemplated.

Facile synthesis of Mn2+ doped ultrathin (n=2) NPLs and their application to anti-counterfeiting

Ultrathin 2D perovskite nanoplatelets (NPLs) have many excellent optical properties including narrow absorption and emission spectra and large exciton binding energies. Doping Mn2+ into perovskite NPLs also introduces strong orange...

Selective Ligand Sensitization of Lanthanide Nanoparticles for Multilevel Information Encryption with Excellent Durability

Durable and multilevel information encryption technology has been of great importance in recent decades. Here, an inkjet printer-adaptable invisible ink was prepared with lanthanide nanoparticles, and optical decoding of information could only be achieved when specific ligand dipicolinic acid was utilized in the presence of UV illumination. In addition, the proposed protocols displayed long shelf life (>one year) and excellent durability even at harsh conditions such as in the presence of strong acids (1 M HCl) and alkalis (1 M NaOH). Meanwhile, such invisible inks could be further employed on a soft matrix via screen-printing, holding great potential for practical applications.

Magnetic perovskite nanoparticles for latent fingerprint detection

Fingerprints form when fingers touch a solid surfaceand are considered the best way for individual identification. However, the current latent fingerprint (LFP) developing methods cannot meet the demand for high sensitivity and being convenient and healthy. Herein, bifunctional Fe3O4@SiO2-CsPbBr3 powders have been designed and fabricated and exhibit good magnetic and strong fluorescent properties. The magnetism of Fe3O4 can avoid dust flying, while the fluorescence of CsPbBr3 ensures the high definition of LFPs. Clear fingerprints have been detected on various solid substrates using the Fe3O4@SiO2-CsPbBr3 powders instead of eikonogen. Detailed characterization studies suggest that the ammonium cationic groups on the surface of nanoparticles (NPs) have strong adhesive interactions with the residues of fingerprints because of the electrostatic attraction between them. Therefore, the convenient operation and excellent resolution offer great opportunity in the practical application of fingerprint detection and other areas.

Bi and Sb Codoped Cs2Ag0.1Na0.9InCl6 Double Perovskite with Excitation-Wavelength-Dependent Dual-Emission for Anti-Counterfeiting Application

The growing demands for optical anti-counterfeiting technology require the development of new environmentally friendly materials with single component, multimodal fluorescence and high stability. Herein, the Bi/Sb codoped Cs₂Ag_0.1Na_0.9InCl₆ lead-free double perovskite material is reported as an efficient multimodal luminescence material with excitation-wavelength-dependent emission. When excited by 360 nm UV light, dual-emission is observed at 455 and 560 nm, which comes from the ³P₁-¹S₀ transition of Sb³⁺ ions and self-trapped excitons (STEs), respectively. Under the 320 nm UV lamp, the microcrystals show only a blue emission centered at 455 nm. Therefore, the Bi/Sb codoped Cs₂Ag_0.1Na_0.9InCl₆ double perovskite emits blue and yellow lights under the 320 and 360 nm UV lamp, respectively. Moreover, the obtained double perovskite shows a high PLQY up to 41% and excellent stability against both air and high temperature, which make it a promising anti-counterfeiting material.

A new strategy to fabricate multifunctional luminescent MOFs, extending their application range from pH sensing to amino acid information coding

Herein, we propose a new strategy for designing new types of wide range pH-sensitive metal-organic frameworks (MOFs) with double luminescent centers on UiO-66-2OH. The UiO-66-2OH has a ligands-based emission at 530 nm. To introduce another luminescent center, PMA (1,2,4,5-benzenetetracarboxylic acid), as the functional site, is used to substitute the initial ligand, BDC-2OH (2,5-dihydroxyterephthalic acid), of UiO-66-2OH. Eu³⁺ ions, another luminescent center at 613 nm, are coordinated to the free carboxyl group on PMA. Finally, TTA (2-Thenoyltrifluoroacetone) is coordinated with Eu³⁺ ions to balance the emission at 613 nm (Eu³⁺ ions) and 530 nm (BDC-2OH). For the sake of both strong emissions, we explored the loading levels of PMA. The optimized structure is Eu(TTA)@MUM5 ("MUM" is the abbreviation of "Mixed ligand UiO-66-2OH MOFs" and "5" represents the molar percentage of PMA is 50%), which exhibits strong emission at 530 nm (alkaline solution) and 613 nm (neutral solution). Remarkably, the synthesized material has an exponential relationship (R² = 0.9973) over the pH range of 1.87 to 9.65 and a linear relationship (R² = 0.9987) when pH = 11.01-13.35. Further experiments have proved that Eu(TTA)@MUM5 could distinguish different amino acids. Based on that, we build an information transferring circle with two coding modes on Eu(TTA)@MUM5 using aseptic acid and arginine as coding factors.

In Situ Inkjet Printing Patterned Lead Halide Perovskite Quantum Dot Color Conversion Films by Using Cheap and Eco-Friendly Aqueous Inks

Inkjet-printed perovskite quantum dot (PQD) color conversion films (CCFs) have great potentials for mini/micro-LED displays because of their ultrahigh color purity, tunable emissions, high efficiency, and high-resolution. However, current PQD inks mainly use expensive, toxic, and flammable organic substances as solvents. In this work, water is proposed to be used as the solvent for inkjet printing PQD/polymer CCFs. The green-emitting patterned MAPbBr₃ /polyvinyl alcohol (PVA) films are in situ prepared by using halides and the PVA-based aqueous ink. The as-printed CCFs exhibit a high-resolution dot matrix of 90 µm with a bright green emission (λ_em  = 526 nm), a high photoluminescence quantum yield of 85%, and a narrow full width at half maximum of 22 nm. They have both air- and photo-stabilities under ambient conditions, and each pixel of CCFs is relatively uniform in morphology and fluorescence when the substrate temperature is 80 °C. The patterned blue-emitting MAPbCl_x Br_3-x /PVA and red-emitting Cs_0.3 MA_0.7 PbBr_x I_3-x /PVA can also be printed by aqueous inks. These results indicate that the designed aqueous inks are promising for in situ inkjet printing high resolution and reliability PQD CCFs for mini/micro-LED displays.

Blue luminescent N,S-doped carbon dots encapsulated in red emissive Eu-MOF to form dually emissive composite for reversible anti-counterfeit ink

Lanthanide metal-organic frameworks (Ln-MOFs) have demonstrated great potential in luminescence sensing and optical anti-counterfeiting. High-security anti-counterfeiting technology is of great importance and requires the development of universal luminescent materials with multiple modes of emission and adjustable photoluminescence. Herein, a 3D red light emission microporous europium(iii) metal-organic framework [Eu₃(OH)(1,3-db)₂(H₂O)₄]·3H₂O (1) (1,3-db = 1,3-di(3',5'-dicarboxylpheny) benzene) was constructed from a zigzag [Eu₃(COO)₈] chain and π-electron-rich terphenyl-tetracarboxylate. Notably, the quenched fluorescence of 1 under hydrogen chloride vapor could be recovered upon fuming by a vapor of Et₃N. Most strikingly, the strong blue light emission by nitrogen and sulfur co-doped carbon dots (N,S-CDs) could be encapsulated in 1 to generate a dual-emission composite, namely, N,S-CDs@Eu-MOF, which shows solvent-dependent photoluminescence: N,S-CD-related blue luminescence in water and Eu-MOF-related red emission in organic solvents. Taking advantage of the above unique reversible fluorescent behavior, Eu-MOF and N,S-CDs@Eu-MOF are prepared as fluorescent high-security inks to achieve data encryption and decryption on specific flower patterns.

Lead-free, stable orange-red-emitting hybrid copper based organic-inorganic compounds

Metal halide perovskites have been extensively studied recently by virtue of their extraordinary luminescence characteristics. However, they still suffer from severe stability issues, and contain a toxic metal lead. Here, single crystals of (PEA)₄Cu₄I₄, a lead-free orange-red-emitting organic-inorganic copper-halide compound with a photoluminescence quantum yield (PLQY) of 68%, were synthesized via a simple solvent vapor diffusion process with commercially-available phenylethylamine (PEA) as a ligand. The crystals show superior stability to perovskites with retaining 60% of their initial photoluminescence (PL) intensity after 60 days in water, which is due to the hydrophobic nature of PEA and the stable Cu-N bonds. Phase transition is found to take place upon lowering the temperature, which causes a redshift of the PL peak. The emission band is identified to be associated with triplet cluster-centered (CC) excited states because of their shortened Cu-Cu distances, excitation-independent PL and long PL lifetime. In addition, micron-sized oleic acid capped (PEA)₄Cu₄I₄ particles were developed by a hot-injection method, and they possess similar stability to that of bulk crystals. A monochrome LED was further fabricated by employing the as-prepared micron-sized particles as phosphors, demonstrating their potential for optoelectronic applications.

Dual information encryption of carbon dots endowed with recoverable functions after interception

Hiding real information in deluded information can mislead others.

Synthesis, photochemical isomerization and photophysical properties of hydrazide–hydrazone derivatives

The structure–property relationships for the hydrazide–hydrazone derivatives were investigated to provide new insights into the design of photo-responsive materials.

Chemically stable fluorescent anti-counterfeiting labels achieved by UV-induced photolysis of nanocellulose

Carbon-based fluorescent security labels are effective methods to prevent counterfeiting. However, the properties of poor optical stability, complex and energy-consuming synthesis processes and weak bonding with substrates of carbon-based fluorescent materials limit their application prospects. Here, a novel in situ fluorescent patterning strategy is developed to achieve covert, chemically stable and solvent-tolerant cellulose-based security labels by UV exposure. The unsaturated double bonds as the origin of the fluorescence were generated during the photodegradation process under UV exposure. The fluorescent emission of cellulose-based materials reveals excellent stability under acidic, alkaline, reducing, oxidizing and non-polar solvent environments. These advantages give the cellulose nanofiber based security label fantastic potential applications.

The cellulose-based fluorescent patterning strategy is developed by UV exposure to achieve covert, chemically stable and solvent tolerant security labels.

Photoluminescent and Chromic Nanomaterials for Anticounterfeiting Technologies: Recent Advances and Future Challenges

Counterfeiting and inverse engineering of security and confidential documents, such as banknotes, passports, national cards, certificates, and valuable products, has significantly been increased, which is a major challenge for governments, companies, and customers. From recent global reports published in 2017, the counterfeiting market was evaluated to be $107.26 billion in 2016 and forecasted to reach $206.57 billion by 2021 at a compound annual growth rate of 14.0%. Development of anticounterfeiting and authentication technologies with multilevel securities is a powerful solution to overcome this challenge. Stimuli-chromic (photochromic, hydrochromic, and thermochromic) and photoluminescent (fluorescent and phosphorescent) compounds are the most significant and applicable materials for development of complex anticounterfeiting inks with a high-security level and fast authentication. Highly efficient anticounterfeiting and authentication technologies have been developed to reach high security and efficiency. Applicable materials for anticounterfeiting applications are generally based on photochromic and photoluminescent compounds, for which hydrochromic and thermochromic materials have extensively been used in recent decades. A wide range of materials, such as organic and inorganic metal complexes, polymer nanoparticles, quantum dots, polymer dots, carbon dots, upconverting nanoparticles, and supramolecular structures, could display all of these phenomena depending on their physical and chemical characteristics. The polymeric anticounterfeiting inks have recently received significant attention because of their high stability for printing on confidential documents. In addition, the printing technologies including hand-writing, stamping, inkjet printing, screen printing, and anticounterfeiting labels are discussed for introduction of the most efficient methods for application of different anticounterfeiting inks. This review would help scientists to design and develop the most applicable encryption, authentication, and anticounterfeiting technologies with high security, fast detection, and potential applications in security marking and information encryption on various substrates.

Metal Halide Perovskite@Metal-Organic Framework Hybrids: Synthesis, Design, Properties, and Applications

Metal halide perovskites (MHPs) have excellent optoelectronic and photovoltaic applications because of their cost-effectiveness, tunable emission, high photoluminescence quantum yields, and excellent charge carrier properties. However, the potential applications of the entire MHP family are facing a major challenge arising from its weak resistance to moisture, polar solvents, temperature, and light exposure. A viable strategy to enhance the stability of MHPs could lie in their incorporation into a porous template. Metal-organic frameworks (MOFs) have outstanding properties, with a unique network of ordered/functional pores, which render them promising for functioning as such a template, accommodating a wide range of MHPs to the nanosized region, alongside minimizing particle aggregation and enhancing the stability of the entrapped species. This review highlights recent advances in design strategies, synthesis, characterization, and properties of various hybrids of MOFs with MHPs. Particular attention is paid to a critical review of the emergence of MHP@MOF for comprehensive studies of next-generation materials for various technological applications including sensors, photocatalysis, encryption/decryption, light-emitting diodes, and solar cells. Finally, by summarizing the state-of-the-art, some promising future applications of reported hybrids are proposed. Considering the inherent correlation and synergic functionalities of MHPs and MOFs, further advancement; new functional materials; and applications can be achieved through designing MHP@MOF hybrids.

Putting Ink into Polyion Micelles: Full-Color Anticounterfeiting with Water/Organic Solvent Dual Resistance

Anticounterfeiting paintings are usually with limited colors and easy blurring and need to be dispersed in an environmentally unfriendly organic solvent. We report a set of water-based polyion micellar inks to solve all these problems. Upon complexation of reversible coordination polymers formed with rare earth metal ions Eu³⁺ and Tb³⁺ and the aggregation-induced emission ligand tetraphenylethylene-L₂EO₄ with oppositely charged block polyelectrolyte P2MVP₂₉-b-PEO₂₀₅, we are able to generate polyion micelles displaying three elementary emission colors of red (R) (Φ_Eu³⁺ = 24%), green (G) (Φ_Tb³⁺ = 7%), and blue (B) (Φ_TPE = 9%). Full-spectrum emission and white light emission (0.34, 0.34) become possible by simply mixing the R, G, and B micelles at the desired fraction. Strikingly, the micellar inks remain stable even after soaking in water or organic solvents (ethyl acetate, ethanol, etc.) for 24 h. We envision that polyion micelles would open a new paradigm in the field of anticounterfeiting.

Plasmonic nanopapers: flexible, stable and sensitive multiplex PUF tags for unclonable anti-counterfeiting applications

Highly flexible and stable plasmonic nanopaper comprised of silver nanocubes and cellulose nanofibres was fabricated through a self-assembly-assisted vacuum filtration method. It shows significant enhancement of the fluorescence emission with an enhancement factor of 3.6 and Raman scattering with an enhancement factor of ∼104, excellent mechanical properties with tensile strength of 62.9 MPa and Young's modulus of 690.9 ± 40 MPa, and a random distribution of Raman intensity across the whole nanopaper. The plasmonic nanopapers were encoded with multiplexed optical signals including surface plasmon resonance, fluorescence and SERS for anti-counterfeiting applications, thus increasing security levels. The surface plasmon resonance and fluorescence information is used as the first layer of security and can be easily verified by the naked eye, while the unclonable SERS mapping is used as the second layer of security and can be readily authenticated by Raman spectroscopy using a computer vision technique.

Chameleon Luminophore for Erasable Encrypted and Decrypted Devices: From Dual-Channel, Programmable, Smart Sensory Lanthanide Hydrogel to Logic Devices

With the rapid development of the data security technology, increasing attention has been paid to programmable memory materials with desirable security. However, most conventional memory devices only have a single switchable color state. In this research, a kind of pH-responsive Chameleon luminescent sensor (Lap@Eu-OFX, Lap = laponite, OFX = ofloxacin) based on lanthanide doping has been fabricated, which can realize highly contrast, dynamically controlled full-color display by changing the pH value of the solution. The advanced programmable security inks, including the green and red luminescent inks, have been prepared and used to protect confidential information. More interestingly, triethylamine and hydrochloric acid are selected as encryption and decryption reagents, which can repeatedly switch the emission color of important data. Hence, the high-tech security inks show great potential in data coding, multiencryption, and decryption under UV light. Furthermore, the designed dual-channel memory device, Lap@Eu-OFX@CS (CS = Chitosan), enables reversible synchronous switching of sol-gel and emission color when converting from acid to base conditions. This can be dynamically monitored by a subsequent logic gate system and can be converted and stored into binary values. This work provides an effective approach for the design and promising application of information encryptor, smart monitor, and circuit controllers.

Invisible Inks for Secrecy and Anticounterfeiting: From Single to Double-encryption by Hydrochromic Molecules

Secret information recorded by traditional single-encrypted invisible inks is easily cracked because the inks can switch only between "NONE" and "TRUTH". Developing double-encrypted systems makes the information reversibly switchable between "FALSE" and "TRUTH", which is helpful to ensure the safety of the secret information during transport. Here, we prepared heat-developed invisible inks by hydrochromic molecules donor-acceptor Stenhouse adducts (DASAs) and oxazolidines (OXs) and promoted the invisible inks from single to double encryption. DASAs coordinate with water molecules and form stable colorless cyclic DASA·xH₂O molecules, which lose coordinated water molecules after heating and switch to colored linear DASAs. In contrast, OXs are colored with water and are colorless after heating. Single-encrypted secrecy was realized by DASA invisible inks. The information is invisible under the encrypted state and becomes bright purple after heating. Vapor treating re-encrypted the information in ∼5 min. Furthermore, the single-encryption was promoted to double-encryption by a DASA/OX invisible inks system. Heating and vapor treating switch the information between the "FALSE" and "TRUTH" reversibly. The DASA/OX invisible ink system is applied for secrecy of texts, graphic images, and quick response (QR) codes.

Highly efficient Mn-doped CsPb(Cl/Br)3 quantum dots for white light-emitting diodes

White light-emitting diodes (WLEDs) based on all-inorganic perovskite CsPbX₃ (X = Cl, Br, I) quantum dots (QDs) have attracted much attention and rely on mixing several colors of perovskites. However, this inevitably leads to a non-uniform light distribution and serious light loss. Here, a novel strategy was demonstrated to obtain white emission by combining the orange and blue emission from CsPb/Mn(Cl/Br)₃ QDs. Notably, highly efficient white emission with a photoluminescence quantum yield of 94% was achieved by an anion exchange surface engineering (AESE) strategy. After AESE treatment the surface traps can be eliminated, resulting in improved exciton and Mn²⁺ emission. A prototype WLED device was fabricated and exhibited excellent optical stability, demonstrating great potential for perovskite QDs in the field of optoelectronics.

Printable CsPbBr3 perovskite quantum dot ink for coffee ring-free fluorescent microarrays using inkjet printing

Printable perovskite quantum dot (QD) ink is very important for achieving high quality coffee ring-free fluorescent microarrays for different kinds of emerging perovskite optoelectronic applications using inkjet printing. In this work, we prepared a printable CsPbBr₃ perovskite QD ink by mixing high-boiling point dodecane with low-boiling point toluene as a solvent. The evaporation rate, viscosity and surface tension of the ink were carefully optimized by tuning the volume ratio of these two solvents for forming appropriate Marangoni flow, so as to balance the capillary flow and eliminate the coffee ring effect further. Successfully, CsPbBr₃ perovskite microarrays with uniform surface, low roughness and no coffee rings were achieved by inkjet printing the optimized perovskite QD ink on a PVK (poly-(9-vinylcarbazole)) layer. Furthermore, we patterned the CsPbBr₃ perovskite QD ink, and the printed patterns were only visible under ultraviolet (UV) light, which can be applied in invisible anti-counterfeiting labels and encryption in the future.

Inkjet-printed aligned quantum rod enhancement films for their application in liquid crystal displays

Semiconductor quantum rods (QRs) show a polarized emission, which opens up the possibility of the enhancement of both brightness and color for liquid crystal displays (LCD) in the form of quantum rod enhancement films (QREFs) for LCD backlights. However, the QR alignment over a large area, suitable for displays, is a challenge. Inkjet printing of QREFs, introduced here, allows fabrication of well-aligned, uniform QREFs on photoaligned substrates using optimized QR inks. We observed that the ink composition and printing conditions affect the QR alignment quality significantly. A relative humidity of 50% with an exposure energy of 1 J cm^-2 for the photoalignment process provided optimal conditions for QREFs. We have successfully shown a good QR alignment for 2.5-inch films and were able to align QRs in multiple layers. Thus, fabricated QREFs show a polarization ratio of 7.2 : 1 for the emitted light. These QREFs were combined with a blue LED and deployed as a backlight unit for an LCD which shows a brightness of ∼250 nits with an optical efficiency of ∼8%, reaching an NTSC of 109% in a CIE1976 color space. Thus, these printed QREFs, over a large area, provide an unprecedented increase of 77% in the optical efficiency of the LCDs and simultaneously offer better color performance.

Dynamic anti-counterfeiting security features using multicolor dianthryl sulfoxides

A new concept for difficult-to-replicate security inks for use in advanced anti-counterfeiting applications is presented. Inks fabricated from a mixture of photoactive dyes result in a unique fluorescent color upon irradiation that differs from the starting fluorescence. The dyes are substituted 9,9'-dianthryl sulfoxides that undergo photochemical extrusion of a sulfoxide moiety (SO) to produce emissive red, blue, and green emitters. The resulting emissive feature has specific Commission international de l'éclairage (CIE) coordinates that are used for authentication. Additionally, the temporal evolution of the fluorescence can be monitored, introducing a dynamic nature to these security features. The three compounds show different rates of photoconversion dependent on the irradiation wavelength, allowing selective wavelengths for activation to be used for additional security. CIE coordinates can be extracted from patches containing the three compounds using an inexpensive, commercially available smartphone application (app) and compared against a known value to confirm the validity of the method.

Orange to Red, Emission-Tunable Mn-Doped Two-Dimensional Perovskites with High Luminescence and Stability

Lead halide perovskites are emerging as promising candidates for high-efficiency light-emitting diode (LED) applications because of their tunable band gaps and high quantum yield (QY). However, it remains a challenge to obtain stable red emitting materials with high QY. Herein, we report a facile and convenient hot-injection strategy to synthesize Mn-doped two-dimensional (2D) perovskite nanosheets. The emission peak can be tuned from 597 to 658 nm by manipulating the crystal field strength. In particular, a QY as high as 97% for 2D perovskite is achieved. The as-prepared perovskite also possesses excellent stability, whose emission property can be maintained for almost one year. A monochrome LED is further fabricated by employing the as-prepared perovskite as phosphor, which also shows high long-term stability. We believe that these highly efficient and stable perovskites will open up new opportunities in LED applications.

White light-emitting diodes based on carbon dots and Mn-doped CsPbMnCl3 nanocrystals

CsPbX₃ perovskite nanocrystals (NCs) are becoming a promising material for optoelectronic devices that possess an optically tunable bandgap, and bright photoluminescence. However, the toxic Pb is not environmentally friendly and the quantum yield (QY) of blue emitting NCs is relatively low. In addition, the red emitting perovskite containing iodine is not stable under light illumination. In this paper, high QY, blue emitting, non-toxic fluorescent nanomaterial carbon dots and orange-emitting CsPb_0.81Mn_0.19Cl₃ NCs with partial Pb replacement are combined to fabricate white light-emitting diodes (WLEDs). A WLED with color coordinates of (0.337, 0.324) and a correlated color temperature of 4804 K is fabricated. Compared to red emitting perovskite containing iodine, the CsPb_0.81Mn_0.19Cl₃ NCs are stable no matter whether they are stored in the air or exposed under ultraviolet light. Therefore, the as-fabricated WLED shows good color stability against increasing currents and long-term working stability.

Integration of Environmental Friendly Perovskites for High-efficiency White Light-emitting Diodes

Perovskite quantum dots (QDs) have been widely used in white light-emitting diodes (WLEDs), due to their high quantum yield (QY), tunable bandgap, and simple preparation. However, the red-emitting perovskite QDs are usually containing iodine (I), which is not stable under continuous light irradiation. Herein, perovskite-based WLED is fabricated by lead-free bismuth (Bi)-doped inorganic perovskites Cs₂SnCl₆ and less-lead Mn-doped CsPbCl₃ QDs, which emits white light with color coordinates of (0.334, 0.297). The Bi-doped Cs₂SnCl₆ and Mn-doped CsPbCl₃ QDs both show excellent stability when kept in the ambient air. As benefits from this desired characteristic, the as-prepared WLED shows excellent stability along with operating time. These results can promote the application of inorganic perovskite QDs in the field of WLEDs.