Eu2+/Eu3+-Based Smart Duplicate Responsive Stimuli and Time-gated Nanohybrid for Optical Recording and Encryption

Divalent ansa-Octaphenyllanthanocenes: Synthesis, Structures, and EuII Luminescence

Reductive dimerization of fulvenes using low-valent metal precursors is a straightforward one-step approach to access ethylene-bridged metallocenes. This process has so far mainly been employed with fulvenes carrying one or two substituents in the exocyclic position. In this work, a new synthesis of the unsubstituted exocyclic 1,2,3,4-tetraphenylfulvene (1), its full structural characterization by NMR spectroscopy and single-crystal X-ray diffraction, as well as some photophysical properties and its first use in reductive dimerization are described. This fulvene reacted with different lanthanoid metals in thf to provide the divalent ansa-octaphenylmetallocenes [Ln(C5Ph4CH2)2(thf)n] (Ln = Sm, n = 2 (2); Ln = Eu, n = 2 (3); and Ln = Yb, n = 1 (4)). These complexes were characterized by X-ray diffraction, laser desorption/ionization time of flight mass spectrometry, and, in the case of Sm and Yb, multinuclear NMR spectroscopy, showing the influence of the ansa-bridge on solution and solid-state structures compared to previously reported unbridged metallocenes. Furthermore, the luminescence properties of the Eu ansa complex 3 were studied in solution and the solid state, revealing significant differences with the known octa- and deca-phenyleuropocenes, [Eu(C5Ph4H)2(dme)] and [Eu(C5Ph5)2].

Ultralow pressure sensing and luminescence thermometry based on the emissions of Er3+/Yb3+ codoped Y2Mo4O15 phosphors

Pressure and temperature are fundamental physical parameters, so their monitoring is crucial for various industrial and scientific purposes. For this reason, we developed a new optical sensor material that allows monitoring of both the physical parameters. The synthesized material exhibits upconversion (UC) emission of Er3+ in the red and green spectral regions under NIR (975 nm) laser irradiation. These UC emissions are strongly temperature-dependent, allowing multimode temperature sensing, either based on the luminescence intensity ratio between thermal-coupled energy levels (TCLs) or non-thermal-coupled energy levels (NTCLs) of Er3+ ions. Meanwhile, the luminescence lifetime of the 4S3/2 state of Er3+ ions was used as the third temperature-dependent spectroscopic parameter, enabling multi-parameter thermal sensing. Moreover, the observed enhancement of laser-induced heating of the sample under vacuum conditions allows for the conversion of the luminescent thermometer into a remote vacuum sensor. The pressure variations in the system are correlated with changes in the band intensity ratio (525/550 nm) of Er3+ TCLs, which are further applied for optical, contactless vacuum sensing. This is because of the light-to-heat conversion effect, which is greatly enhanced under vacuum conditions and manifests as a change in the intensity ratio of Er3+ bands (525/550 nm). The obtained results indicate that an Y2Mo4O15:Er3+/Yb3+ (YMO) phosphor has great application potential for the development of multi-functional and non-invasive optical sensors of pressure and temperature.

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.

Design of a biomimetic cellulose nanofibre-based double information encryption sensor for fingerprint imaging

The development of double encryption system enables information to switch reversibly between "False" and "True", which helps to ensure information security in the transmission process. Herein, a biomimetic cellulose nanofibre-based double information encryption sensor (CNF-DIES) with an excellent pH response and fluorescence colour-switching performance was prepared with fluorescein isothiocyanate and protoporphyrin IX modified acetylated cellulose nanofibres (ACNF) as the pH response switch and background, respectively. Interestingly, with the addition of cellulose, CNF-DIES can be regarded as both a dye and an ink binder, which can realize direct writing function. The fluorescein grafted to ACNF guaranteed the stability of writing and avoided the "coffee ring" phenomenon. The handwriting written by CNF-DIES processes excellent light/pH double encryption performance. Besides, the film prepared by CNF-DIES can realize high resolution fingerprint imaging. This work demonstrated a strategy for pH-responsive colour-tunable materials for sensors and double information encryption.

Self-reduction-induced BaMgP2O7:Eu2+/3+: a multi-stimuli-responsive phosphor for X-ray detection, anti-counterfeiting and optical thermometry

Mixed-valence Eu^2+/3+-activated phosphors have attracted wide attention due to their excellent luminescence tunability. Steady control of the Eu²⁺/Eu³⁺ ratio is the key to achieving reproducible Eu^2+/3+ co-doped materials. In this work, BaMgP₂O₇:xEu^2+/3+ (BMPO:Eu, x = 0.001-0.20) was successfully prepared by the traditional solid-state method in air. Eu³⁺ undergoes selective self-reduction at Ba²⁺ sites surrounded by a [P₂O₇] framework, leading to quantitive Eu²⁺/Eu³⁺. The phosphors exhibit a blue-violet emission band at ∼410 nm due to 5d-4f transitions of Eu²⁺ and a group of red emission peaks from ⁵D₀-⁷F_J of Eu³⁺. Controllable multicolor emissions are realized by regulating the Eu content and excitations. A linear response of overall luminescence intensity to irradiation dose makes the phosphor appropriate for X-ray detection. The combination of UV-blue excitation-dependent color evolution and X-ray luminescence qualifies the phosphors with great potential for multi-level anti-counterfeiting. In addition, Eu³⁺ presents abnormal anti-thermal quenching, so that the fluorescence intensity ratio (FIR) of Eu²⁺/Eu³⁺ changes in the temperature range of 300-520 K, suggesting a promising application in optical thermometry. Therefore, selectively partial self-reduction in a multi-cationic host is an effective strategy to design mixed-valence co-doped materials, providing a multiplicity of applications.

Manipulating Electroluminochromism Behavior of Viologen-Substituted Iridium(III) Complexes through Ligand Engineering for Information Display and Encryption

Electrically controlling photoluminescence has attracted great research interest and offers many opportunities for technological developments. Electroluminochromic materials undergo redox reactions under low-voltage stimuli to achieve reversible luminescence switching. Till now, photoluminescence switching of a single molecule caused by electrical stimuli is restricted to intensity response because the redox-active moieties are good electron donors or acceptors and electrical stimuli can regulate the photoinduced electron-transfer and affect the luminescence intensity. In this work, the manipulation of the electroluminochromism behavior of a series of viologen-substituted iridium(III) complexes through the regulation of ligand orbital energy levels and electronic communication between the viologen pendants and the iridium(III) complex core is reported. Electrochemical redox reactions reversibly modulate either the luminescence quenching effect or the push-pull electronic effect of the viologen substituents, achieving multicolor "on-off" luminescence response toward electrical stimuli and luminescence manipulation between two emissive states with different wavelengths and lifetimes. To illustrate the promising applications of these electroluminochromic materials, recording and displaying luminescence information under electrical stimuli are demonstrated. Information encryption is realized by letting the electroluminochromism occur in the near-infrared region or in the time domain. Near-infrared camera or time-resolved luminescence analysis can be used to help read the invisible information.

Rare Self-Luminous Mixed-Valence Eu-MOF with a Self-Enhanced Characteristic as a Near-Infrared Fluorescent ECL Probe for Nondestructive Immunodetection

Steady and efficient sensitized emission of Eu²⁺ to Eu³⁺ can be achieved through a rare mixed-valence Eu-MOF (L₄Eu^III₂Eu^II). Compared with the sensitization of other substances, the similar ion radius and configuration of the extranuclear electron between Eu²⁺ and Eu³⁺ make sensitization easier and more efficient. The sensitization of Eu²⁺ to Eu³⁺ is of great assistance for the self-enhanced luminescence of L₄Eu^III₂Eu^II, the longer luminous time, and the more stable electrochemiluminescence (ECL) signal. Simultaneously, L₄Eu^III₂Eu^II possesses near-infrared (NIR) fluorescence of around 900 nm and a mighty self-luminous characteristic, which render it useful as a NIR fluorescent probe and as a luminophore to establish a NIR ECL biosensor. This NIR biosensor can greatly reduce the damage to the detected samples and even achieve a nondestructive test and improve the detection sensitivity by virtue of strong susceptibility and environmental suitability of NIR. In addition, the CeO₂@Co₃O₄ triple-shelled microspheres further enhanced the ECL intensity due to two redox pairs of Ce³⁺/Ce⁴⁺ and Co²⁺/Co³⁺. The NIR ECL biosensor based on these strategies owns an ultrasensitive detection ability of CYFRA 21-1 with a low limit of detection of 1.70 fg/mL and also provides a novel idea for the construction of a highly effective nondestructive immunodetection biosensor.

Water-stable lanthanide-organic macrocycles from a 1,2,4-triazole-based chelate for enantiomeric excess detection and pesticide sensing

Water-stable anionic Ln2L2-type (Ln = LaIII and EuIII) lanthanide-organic macrocycles have been constructed by deprotonation self-assembly of a bis-tridentate ligand consisting of two 2,6-bis-(1,2,4-triazole)-pyridine chelation arms bridged by a dibenzofuran chromophore, of which the luminescent Eu2L2 macrocycle can be used for enantiomeric excess (ee) detection toward pybox-type chiral ligands and selective colorimetric sensing of omethoate (OMA) in water.

Electrochemical Eu(iii) behaviours and Eu oxysulfate recovery over terpyridine-functionalized indium tin oxide electrodes

The Eu element was recovered as EuSO₄ over new terpyridine-functionalized ITO by an electrochemical method and luminescent Eu₂O₂SO₄ was obtained by post-thermal annealing.

An AIE-active dual fluorescent switch with negative photochromism for information display and encryption

A negative photochromic molecular switch with AIE and two-color fluorescence conversion properties was synthesized.

Recent advances in optical and optoelectronic data storage based on luminescent nanomaterials

The substantial amount of data generated every second in the big data age creates a pressing requirement for new and advanced data storage techniques. Luminescent nanomaterials (LNMs) not only possess the same optical properties as their bulk materials but also have unique electronic and mechanical characteristics due to the strong constraints of photons and electrons at the nanoscale, enabling the development of revolutionary methods for data storage with superhigh storage capacity, ultra-long working lifetime, and ultra-low power consumption. In this review, we investigate the latest achievements in LNMs for constructing next-generation data storage systems, with a focus on optical data storage and optoelectronic data storage. We summarize the LNMs used in data storage, namely upconversion nanomaterials, long persistence luminescent nanomaterials, and downconversion nanomaterials, and their applications in optical data storage and optoelectronic data storage. We conclude by discussing the superiority of the two types of data storage and survey the prospects for the field.

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

Using temporal dimension in optical multiplexing is a promising method to increase the security of data encryption. However, adjusting the fluorescence lifetime of light-emitting material often results in inevitable changes in their fluorescence spectra, which is unfavorable for confidential information protection. Here, we report the preparation of various perovskite quantum dot/polymer nanospheres (PQD/polymer) with tunable and long fluorescence lifetimes but identical fluorescence spectra, which are ideal multidimensional data encryption materials. This new data encryption strategy utilizes the water sensitivity of perovskite and achieves spatial dimension encryption of information using different water stabilities between uncoated perovskite quantum dots and PQD/polymer. The fluorescence lifetime of PQD/polymer is used as the coding element to achieve temporal dimension data encryption, and the data are decrypted by fluorescence lifetime imaging microscopy and time-gated luminescence imaging techniques. This study shows the potential of PQD/polymer as a new class of materials for advanced data encryption.

Photoluminescence and Stoichiometry Correlation in Nanocrystalline EuO x Thin Films: Tunable Color Emission

The development of broadband and ultracompact optoelectronic devices relies on the possibility of fabricating bright and tunable emitters at the nanoscale. Here, we show emission from EuO x (1 ≤ x < 1.4) thin films on silicon formed by nanocrystals with average sizes in the range of 5 nm. The photoluminescence emission of the nano-EuO x films is tunable as a function of the oxygen concentration changing from a green broadband Eu2+-related emission to a narrow red Eu3+-related emission. To reach these results has been instrumental through the use of a new methodology specially designed to achieve high-quality europium oxide films whose compositional properties are controlled by the growth base pressure and preserved thanks to a chemically stable and transparent cover layer of Al2O3. Our findings confirm the outstanding potential of nanostructured EuO x films as "one-compound" optical elements with tunable emission properties for their implementation in integrated silicon-based devices.

Multi-Responsive Lanthanide-Based Hydrogel with Encryption, Naked Eye Sensing, Shape Memory, Self-Healing, and Antibacterial Activity

In this work, we reported a multi-responsive luminescent hydrogel with properties of encryption, naked eye sensing of glucose, shape memory, self-healing, and antibacterial activity. The hydrogel (GA/CCS/DNSA/Eu³⁺) was obtained by mixing phenylboronic acid-modified gelatin (GA-DBA), catechol-modified carboxymethyl chitosan (CCS-PCA), 3,5-dinitrosalicylic acid (DNSA), and Eu³⁺ ions through a facile heating-cooling process. The resultant hydrogel exhibits reversible luminescence and color and phase changes in response to temperature, acid/base, salt, and redox stimuli. Based on the multiple responsiveness, information encryption and decryption, naked eye sensing of glucose, remarkable shape memory, and enhanced mechanical properties of the as-prepared hydrogel were realized. In addition, the self-healing capacity was also achieved due to the dynamic bonds in GA/CCS/DNSA/Eu³⁺ hydrogels. Specifically, the GA/CCS/DNSA/Eu³⁺ hydrogels possess antibacterial activity owing to the bacteriostasis of the CCS-PCA and DNSA/Eu³⁺ complex. Thus, GA/CCS/DNSA/Eu³⁺ hydrogels have potential applications in the fields of anticounterfeiting, wearable devices, biomedicine, sensing, etc.

Sequential halochromic/mechanochromic luminescence of pyridyl-substituted solid-state emissive dyes: thermally controlled stepwise recovery of the original emission color

A stepwise temperature-controlled emission-color switch has been achieved in a system that combines halochromic and mechanochromic luminescence in series.