Fluorescence Lifetime-Tunable Water-Resistant Perovskite Quantum Dots for Multidimensional Encryption

Large Capacity of Data Storage and Information Encryption in Optical Encoder Disk by Integrating Phase Angle and Time Lock Based on Luminescence Metal Nanoclusters

The traditional "matrix" symbol patterns from the luminescence materials are mainly involved in a 2D plane, which seriously limits the information security and storage capacity. Here, a novel strategy is designed to extend two additional dimensions into a 2D plane by integrating time-gated response and phase angle changes of luminescent patterns. The strong orange fluorescence assemblies in an optical encoder disk are obtained after adding metal ions (Zn2+ or Al3+) and ammonia into copper nanoclusters (CuNCs) mainly due to aggregation-induced emission (AIE) behavior. The number of CuNCs-based aggregates is closely related to rotating angle changes. On the contrary, these aggregates can be reversibly dissembled upon exposing to adenosine triphosphate (ATP) in concomitant with their luminescence quenching. Their different quenching rates are on-demand controlled by the coordination reaction kinetics between ATP and metal ions in different pH value, which is conducive to the design of a series of time-locked information. The encoding patterns comprehensively utilize the static and dynamic characteristics of materials by rotating the phase angle at the specific time. The phase angle and time double locks is added into 2D plane to form a 4D storage models, which realizes higher-level information encryption and larger data storage capacity.

Superhydrophobic Luminescent Pixel Array Based on Perovskite Quantum Dots for Outdoor Displays

Perovskite quantum dots (PQDs) have garnered significant attention in the display industry as high-performance luminescent materials in recent years. However, in outdoor applications, it is highly challenging to maintain the luminescent performance of PQDs while simultaneously ensuring superhydrophobicity and self-cleaning functionality in rainy weather conditions. Here, we report a luminescent pixel array fabricated using superhydrophobic PQDs with a photoluminescence quantum yield (PLQY) of 32%. The surface exhibits a high static contact angle of 168° and a rolling angle of <1°, demonstrating excellent self-cleaning ability. Specifically, by loading encapsulated PQDs onto fluorinated silica particles of varying particle sizes, a multilevel micronano hierarchical raspberry-like interface is formed. Simultaneously, local evaporation quenching induced by pulsed laser irradiation is employed to create a photoluminescent array with individual pixel diameters of 300 μm and a spacing of 80 μm. This achievement fills the gap in the application of PQDs for outdoor displays.

Hydrochromic Effect of Perovskite-Polymer Composites

Hydrochromic materials undergo magical color changes when interacting with water and are receiving widespread attention for their frontier applications such as sensing and information security. The hydrochromic effect is observable in perovskite materials via the mechanism of water-induced fluorescence quenching. However, due to water isolation, achieving a hydrochromic effect in perovskite-polymer composite remains elusive, notwithstanding its importance as a potentially commercial-ready material. Here, we demonstrate a hydrochromic effect of perovskite-polymer-based porous composite via a nonsolvent-induced phase separation method, comprising of FA2PbBr4/poly(vinylidene fluoride) (FA = formamidinium). The naturally formed pores serve as microchannels, facilitating moisture diffusion. The penetrated water induces a phase transition of perovskite material from the nonfluorescent two-dimensional FA2PbBr4 to the fluorescent three-dimensional FAPbBr3. This work has developed the hydrochromic perovskite-polymer composites, enabling various commercial-ready chromatic applications as conceptually demonstrated custom-made fingerprint labels, quick response code anticounterfeiting labels, encrypted document protections, and water-ink inkjet printing.

Dynamically Tunable Circularly Polarized Selectivity in Plasmon-Enhanced Halide Perovskite Nanocrystal Glasses

Ultrafast spin manipulation for optical spin-logic applications requires material systems with strong spin-selective light-matter interactions. The optical Stark effect can realize spin-selective light-matter interactions by breaking the degeneracy of spin-selective transitions with an external electric field. Halide perovskites have large exciton binding energies, which enable a room-temperature optical Stark effect. However, halide perovskites are prone to degradation when interacting with light and polar solvents, limiting further integration with nanophotonic structures. We demonstrate a hybrid material system consisting of CsPbBr3 nanocrystal glass weakly coupled to resonant plasmonic silver nanoparticles, showing ultrafast tunable spin-based polarization selectivity at room temperature. We performed circularly polarized pump-probe characterizations to investigate the optical Stark effect in this material system, which resulted in a maximum energy shift of ∼3.67 meV (detuning energy of 0.11 eV and pump intensity of 0.62 GW/cm2). We show that halide perovskite nanocrystal glasses have excellent resistance to heat and moisture, which may be favorable for integration with nanophotonic structures for further engineering polarization states, energy tuning, and coherence time.

Biocompatible Perovskite Nanocrystals with Enhanced Stability for White Light-Emitting Diodes

Recently emerged lead halide perovskite CsPbX3 (X = Cl, Br, and I) nanocrystals (PNCs) have attracted tremendous attention due to their excellent optical properties. However, the poor water stability, unsatisfactory luminescence efficiency, disappointing lead leakage, and toxicity have restricted their practical applications in photoelectronics and biomedical fields. Herein, a controllable encapsulated strategy is investigated to realize CsPbX3 PNCs/PVP @PMMA composites with superior luminescence properties and excellent biocompatibility. Additionally, the synthesized CsPbBr3 and CsPbBr0.6I2.4 PNCs/PVP@PMMA structures exhibit green and red emissions with a maximal photoluminescence quantum yield (PLQY) of about 70.24% and 98.26%, respectively. These CsPbX3 PNCs/PVP@PMMA structures show high emission efficiency, excellent stability after water storage for 18 months, and low cytotoxicity at the PNC concentration at 500 μg mL-1. Moreover, white light-emitting diode (WLED) devices based on mixtures of CsPbBr3 and CsPbBr0.6I2.4 PNCs/PVP@PMMA perovskite structures are investigated, which exhibit excellent warm-white light emissions at room temperature. A flexible manipulation method is used to fabricate the white light emitters based on these perovskite composites, providing a fantastic platform for fabricating solid-state white light sources and full-color displays.

Finely manipulating room temperature phosphorescence by dynamic lanthanide coordination toward multi-level information security

Room temperature phosphorescence materials have garnered significant attention due to their unique optical properties and promising applications. However, it remains a great challenge to finely manipulate phosphorescent properties to achieve desirable phosphorescent performance on demand. Here, we show a feasible strategy to finely manipulate organic phosphorescent performance by introducing dynamic lanthanide coordination. The organic phosphors of terpyridine phenylboronic acids possessing excellent coordination ability are covalently embedded into a polyvinyl alcohol matrix, leading to ultralong organic room temperature phosphorescence with a lifetime of up to 0.629 s. Notably, such phosphorescent performance, including intensity and lifetime, can be well controlled by varying the lanthanide dopant. Relying on the excellent modulable performance of these lanthanide-manipulated phosphorescence films, multi-level information encryption including attacker-misleading and spatial-time-resolved applications is successfully demonstrated with greatly improved security level. This work opens an avenue for finely manipulating phosphorescent properties to meet versatile uses in optical applications.

Covalent Coupling Assisted Hydrophilic Perovskite Spheres for Ratiometric Fluorescent Visual Multichannel Immunoassay

Quantitative fluorescence immunoassay is essential for the construction of biosensing mechanisms and the quantification of trace markers. But the interference problems caused by low fluorescence efficiency and broad fluorescence spectrum of fluorescent probes have hindered the continued development of ratiometric fluorescence sensing in biosensing. Perovskite materials, with ultra-high color purity (FWHM < 30 nm) and photoluminescence quantum yield (PLQY) (close to 100%), are expected to be next-generation fluorescent probes. However, poor water stability and biocompatibility are still non-negligible in biosensor applications. In this work, hyperstatic perovskite fluorescent microspheres prepared by swelling-shrinking method can be used as ratiometric fluorescence signals and biological immunoassay platforms. Meanwhile, inspired by p-aminophenol (AP) controlled synthesis and the catalytic reaction of 4-aminophenol phosphate (APP) triggered by alkaline phosphatase (ALP), a strategy to prepare fluorescent nanoparticles as fluorescence signals for ALP detection is proposed. Most importantly, it is proposed for the first time to combine this enzymatic fluorescence with perovskite materials using covalent linkage to create a novel cascade immunoassay and use it for quantitative and visualization determination of hepatitis B surface antigen (HBsAg) for application verification. These results indicate the biosensing potential of perovskite materials and provide a pathway for high sensitivity enzyme detection and enzyme triggered immune detection.

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.

Fluorescence Lifetime Control of Nitrogen Vacancy Centers in Nanodiamonds for Long-Term Information Storage

Today's huge amount of data generation and transfer induced an urgent requirement for long-term data storage. Here, we demonstrate and discuss a concept for long-term storage using NV centers inside nanodiamonds. The approach is based upon the radiation-induced generation of additional vacancies (so-called GR1 states), which quench the initial NV centers, resulting in a reduced overall fluorescence lifetime of the NV center. Using the tailored fluorescence lifetime of the NV center to code the information, we demonstrate a "beyond binary" data storage density per bit. We also demonstrate that this process is reversible by heating the sample or the spot of information. This proof of principle shows that our technique may be a promising alternative data storage technology, especially in terms of long-term storage, due to the high stability of the involved color centers. In addition to the proof-of-principle demonstration using macroscopic samples, we suggest and discuss the usage of focused electron beams to write information in nanodiamond materials, to read it out with focused low-intensity light, and to erase it on the macro-, micro-, or nanoscale.

Tuning the Photochromism of Spiropyran in Functionalized Nanoporous Silica Nanoparticles for Dynamic Anticounterfeiting Applications

Here, we report a novel invisible ink with different decay times based on thin films with different molar ratios of spiropyran (SP)/Si, which allows the encryption of messages over time. Nanoporous silica has been found to be an excellent substrate to improve the solid photochromism of spiropyran, but the hydroxyl groups of silica have a serious effect on fade speeds. The density of silanol groups in silica has an influence on the switching behavior of spiropyran molecules, as they stabilize the amphiphilic merocyanine isomers and thus slow down the fading process from the open to the closed form. Here, we investigate the solid photochromic behavior of spiropyran by sol-gel modification of the silanol groups and explore its potential application in UV printing and dynamic anticounterfeiting. To extend its applications, spiropyran is embedded in organically modified thin films prepared by the sol-gel method. Notably, by using the different decay times of thin films with different SP/Si molar ratios, time-dependent information encryption can be realized. It provides an initial "false" code, which does not display the required information, and only after a given time will the encrypted data appear.

Intelligent Colorimetric Indicators for Quality Monitoring and Multilevel Anticounterfeiting with Kinetics-Tunable Fluorescence

The spoilage and forgery of perishable products such as food, drugs, and vaccines cause serious health hazards and economic loss every year. Developing highly efficient and convenient time-temperature indicators (TTIs) to realize quality monitoring and anticounterfeiting simultaneously is urgent but remains a challenge. To this end, a kind of colorimetric fluorescent TTI, based on CsPbBr₃@SiO₂ nanoparticles with tunable quenching kinetics, is developed. The kinetics rate of the CsPbBr₃-based TTIs is easily regulated by adjusting temperature, concentration of the nanoparticles, and addition of salts, stemming from the cation exchange effect, common-ion effect, and structural damage by water. Typically, when combined with europium complexes, the developed TTIs show an irreversible dynamic change in fluorescent colors from green to red upon increasing temperature and time. Furthermore, a locking encryption system with multiple logics is also realized by combining TTIs with different kinetics. The correct information only appears at specific ranges of time and temperature under UV light and is irreversibly self-erased afterward. The simple and low-cost composition and the ingenious design of kinetics-tunable fluorescence in this work stimulate more insights and inspiration toward intelligent TTIs, especially for high-security anticounterfeiting and quality monitoring, which is really conducive to ensuring food and medicine safety.

Water-soluble long afterglow carbon dots/silica composites for dual-channel detection of alkaline phosphatase and multi-level information anti-counterfeiting

Water-soluble carbon dots/silica (CDs/SiO₂) composites with an ultra-long lifetime of 846.9 ms and an ultra-high afterglow quantum yield of 12.1% were successfully obtained by incorporating CDs into a SiO₂ network. Within the aqueous solution, the SiO₂ layer isolates CDs from the surrounding oxygen. Meanwhile, hydrogen bonds and covalent bonds are formed between the CDs and SiO₂, and these bonds restrict the movement and vibration of the CDs. Accordingly, the non-radiative inactivation rate of the triplet excitons of the CDs is reduced, thereby enhancing the room-temperature phosphorescence of the CDs and triggering thermally activated delayed fluorescence. The multiple properties of the material effectively protect the CDs from the external environment, making CDs/SiO₂ emit a long afterglow in the solid and liquid phases. The prepared CDs/SiO₂ composites have exceptional stability against strong oxidants, acids, bases, and polar solvents. The composites were successfully used in the dual-optical mode detection of alkaline phosphatase, as an anti-counterfeiting ink, and in multi-level information anti-counterfeiting and encryption.

Recent Progress of Perovskite Nanocrystals in Chem/Bio Sensing

Perovskite nanocrystals (PNCs) are endowed with extraordinary photophysical properties such as wide absorption spectra, high quantum yield, and narrow emission bands. However, the inherent shortcomings, especially the instability in polar solvents and water incompatibility, have hindered their application as probes in chem/bio sensing. In this review, we give a fundamental understanding of the challenges when using PNCs for chem/bio sensing and summarize recent progress in this area, including the application of PNCs in various sensors and the corresponding strategies to maintain their structural integrity. Finally, we provide perspectives to promote the future development of PNCs for chem/bio sensing applications.

Dynamic Fluorescent Anti-Counterfeiting Labels Based on Conjugated Polymers Confined in Submicron Fibrous Membranes

Developing a new anti-counterfeiting strategy is of great significance to combating the global counterfeiting problem. Here we report the construction of a dynamic fluorescence response system for anti-counterfeiting by combining the photochromism induced by the ring-opening of spiropyran (SP) to merocyanine (MC) with the fluorescence resonance energy transfer (FRET) between the conjugated polymer and MC. After elucidating the design principle, a new conjugated polymer, PPETE-SP, consisting of a poly[p-(phenylene ethynylene)-alt-(thienylene-ethynylene)] (PPETE) backbone with pendant SP, was synthesized and characterized. With poly(methyl methacrylate) (PMMA) as the matrix, the PPETE-SP/PMMA fibrous membrane was prepared via electrospinning. Under the irradiation of UV light, the fluorescent color of the membrane dynamically changed from green to light green, then light pink, and finally pink, and this process was reversible under visible light. The fluorescence emission switch was examined for 10 cycles and proved to have good repeatability, indicating that the membrane can be directly used as an anti-counterfeiting label for multiple verifications. The FRET efficiency was found to be about 61% based on the FRET study with confocal laser scanning microscopy. The covalent bonding between PPETE backbone and SP, the confinement of PPETE-SP chains in the fibrous membrane, as well as employing PMMA as the matrix were demonstrated to be crucial in realizing the photochromism and the FRET. Different anti-counterfeiting modes were proposed, providing rich selections for operation of verification. Such facile-to-operate and hard-to-imitate dynamic fluorescent responsive materials are very promising for use in practical anti-counterfeiting applications.

Progress of Backlight Devices: Emergence of Halide Perovskite Quantum Dots/Nanomaterials

The technology behind the display is becoming ever more prevalent in our daily lives. It has many applications, including smartphones, tablets, desktop monitors, TVs, and augmented reality/virtual reality devices. The display technology has progressed drastically over the past decade, from the bulky cathode ray tube to the flat panel displays. In the flat panel displays, the liquid crystal display (LCD) and organic light-emitting diodes (OLEDs) are the two dominant technologies. Nevertheless, due to low stability and color tunability, OLEDs remain behind the LCDs. The LCD screen has a backlight, usually a white LED, which comprises a blue LED covered with a red and green enhanced layer (color-converting layers). Although InP/CdSe QDs attracted more attention due to their solution processability and better color gamut than the previous technologies, the complexity of their synthesis was still an obstacle to their commercialization. Later, the emergence of perovskite with highly intense and tunable PL emission, high color purity, and low-cost synthesis route attracted the attention of display researchers. Owing to the relatively higher performance of perovskite quantum dots (PQDs) than that of bulk (3D) perovskite in backlit display devices, these PQDs are being used for high color contrast and bright display devices. Furthermore, the color gamut for PQDs was observed as 140% of the NTSC standard, that is, close to that of the commercial OLED devices. In this review, we have discussed the progress of display technologies with a clear classification of the pros and cons of each technology. Also, the application of perovskite QD/nanomaterials in LCD backlit devices has been discussed, and the future direction of further improvement in their stability and performance has been listed.

Binary temporary photo-response of ZnSe:Mn/ZnS quantum dots for visible time-domain anti-counterfeiting

The development of multi-level anti-counterfeiting techniques is of great significance for economics and security issues, particularly the newly emerged temporal-domain techniques based on lifetime coding. However, the intricate reading methods required to obtain temporal-level information are inevitably cumbersome and expensive, which greatly limits the practical applications of these techniques. Herein, we report a novel, unclonable time-domain anti-counterfeiting strategy for the first time, which is achieved using photo-responsive ZnSe:Mn/ZnS quantum dots (QDs) with dynamic luminescence and can be authenticated by the naked eye. Through introducing electron traps and constructing cascade electron channels in the QDs, the binary temporary photo-response is tailored and manifested as distinctive response rates between the band-edge and Mn ⁴T₁-⁶A₁ transition emissions. Impressively, the generated photo-response is instantaneous, is capable of delayed recovery, and can be visibly detected under UV irradiation. The prospective use of colorless, nontoxic aqueous-phase ZnSe:Mn/ZnS QDs provides a new idea and important guidance for developing the next generation of multi-level anti-counterfeiting techniques without the need for complex time-gated decoding instrumentation.

Paper without a Trail: Time-Dependent Encryption using Pillar[5]arene-Based Host-Guest Invisible Ink

A stimuli-responsive invisible ink for time-dependent encryption of information is reported. Consisting of a pillar[5]arene-based supramolecular network grafted with spiropyran moieties, these materials display time-dependent photochromic behavior with tailorable fading rates. Ultraviolet (UV) light results in isomerization of the colorless spiropyran to the corresponding colored merocyanine, while visible light or heat causes the reverse isomerization with a rate that is dependent on the density of host-guest crosslinks. The kinetics of discoloration are a function of merocyanine aggregation, which becomes more pronounced as the host-guest crosslink density is increased, leading to a reduced conversion rate and slower time-dependent fading. The degree of crosslinking, and hence the fading rate, may be modulated via the addition of unbound pillar[5]arene host or nitrile guest as competitors. Time-dependent information encryption is enabled by combining selective placement of host and guest competitors and UV patterning. UV patterning provides an initially "false" image that does not reveal the desired information, and it is only after a given time that the encrypted data appears. This work provides a unique approach to enhance the security of information storage associated with offline portable data encryption.

Polyacrylamide-Based Binary Luminescent Copolymer Materials Exhibit Color-Tunable and Efficient Long-Lived Room Temperature Phosphorescence

Polymer-based pure organic room temperature phosphorescence (RTP) materials have garnered considerable interest, among which RTP systems with prolonged lifetimes and tunable emission colors are promising for applications in sensing, flexible electronics, bioassay, anti-counterfeiting, and data encryption. Herein, facile doping method is reported based on two types of copolymers with benzene/biphenyl-based light-emitting cores as their side chains, whereby the two copolymers are robustly crosslinked via noncovalent interactions including hydrogen bonding and halogen bonding that occur between the light-emitting cores and polyacrylamide backbones. Persistent RTP emission with prolonged lifetime up to 1.9 s and phosphorescence quantum yield as high as 40.1% are obtained in single copolymers, attributed to the conformation restriction of phosphorescent dyes originating from the rigid microenvironment. Furthermore, multicolor phosphorescence signals are observed in the doped binary luminescent copolymer systems that can be effectively regulated by the feed ratio of luminescent cores and irradiation wavelengths. Possible mechanisms for this efficient and long-lived color-tunable RTP system are discussed on the basis of the experimental data and theoretical calculations. In addition, it is also demonstrated that the color-tunable RTP emission of the doped copolymer systems under ambient conditions allows for further exploitation in the application of dynamic information encryption.