多色长余辉材料的发光性质及动态防伪应用

发光防伪具有可视性强、设计简便的特点, 是众多防伪技术中常用的方法。传统防伪材料存在发光颜色单一、防伪图案和颜色静态的缺点, 易于模仿, 亟需开发可实现动态、可靠防伪性能的发光材料。本工作采用水热法制备了铬掺杂镓锗酸锌多色长余辉材料, 并对其余辉性能和动态防伪应用进行研究。实验结果表明: 通过改变镓锗比, 可以调节蓝绿光和红光区的发射强度, 实现发光颜色的可调。该系列样品在波长为254和365 nm的紫外光激发下分别呈现白色和红色, 发光颜色具有多模态发光特征。此外该系列样品具有多色的余辉发光, 不同颜色的衰减速率不同, 可以实现余辉颜色随时间发生动态变化的效果。据此设计成的防伪图案, 发光颜色在时间维度上具有动态变化特性, 可显著提高防伪安全性, 表明所制备的铬掺杂镓锗酸锌多色长余辉材料在动态防伪领域有重要的应用前景。     

A Fluorescence–Phosphorescence–Phosphorescence Triple‐Channel Emission Strategy for Full‐Color Luminescence

Organic luminogens constitute promising prototypes for various optoelectronic applications. Since gaining distinct color emissions normally requires the alternation of the conjugated backbone, big issues remain in material synthetic cost and skeleton compatibility while pursuing full‐color luminescence. Upon a facile one‐step coupling, three simple but smart perchalcogenated (O, S, and Se) arenes are synthesized. They exhibit strong luminescent tricolor primaries (i.e., blue, green, and red, respectively) in the solid state with a superior quantum yield up to >40% (5–10 times higher than that in corresponding solutions). The properties originate from a fluorescence–phosphorescence–phosphorescence triple‐channel emission effect, which is regulated by S and Se heavy atoms–dependent intersystem crossing upon molecular packing, as well as Se–Se atom interaction–caused energy splittings. Consequently, full‐color luminescence, including a typical white‐light luminescence with a Commission Internationale de I'Eclairage coordinate of (0.30, 0.35), is realized by complementarily incorporating these tricolor luminescent materials in the film. Moreover, mechanochromic luminescent color conversions are also observed to achieve the fine‐tuning of the luminescent tints. This strategy can be smart to address full‐color luminescence on the same molecular skeleton, showing better material compatibility as an alternative to the traditional multiple‐luminophore engineering.     

Photon Upconverted Circularly Polarized Luminescence via Triplet–Triplet Annihilation

Circularly polarized luminescent materials are of increasing attention due to their potential applications in advanced optical technologies, such as chiroptical devices and optical sensing. Recently, in all reported circularly polarized luminescent materials, high‐energy excitation results in low‐energy or downconverted circularly polarized luminescence (CPL) emission. Although photon upconversion—i.e., the conversion of low‐energy light into higher‐energy emission, with a wide variety of applications—has been widely reported, the integration of photon upconversion and CPL in one chiral system to achieve higher‐energy CPL emission has never been reported. Herein, a brief review is provided of recent achievements in photon‐upconverted CPL via the triplet–triplet annihilation mechanism, focusing on the amplified dissymmetry factor g_lum through energy transfer process and dual upconverted and downconverted CPL emission through chirality and energy transfer process.     

Eu掺杂KNN陶瓷的制备及可调性发光研究

稀土离子掺杂铁电陶瓷是一类新型光致变色材料, 在光开关、光信息存储等领域具有潜在应用价值。本研究采用水热法制备了(K_0.5 Na_0.5)_1-xEu_xNbO₃(KNN:xEu)前驱体粉体, 随后利用高温烧结得到对应陶瓷样品。在465 nm激发下, 观察到615 nm处有强的红色发光, 对应于Eu ³⁺的 ⁵D₀→ ⁷F₂跃迁。通过紫外光照射, KNN:Eu陶瓷从乳白色变为深灰色。随后经过200 ℃加热10 min, 着色陶瓷又变回到初始颜色, 显示出良好的光致变色行为。紫外照射和反复加热循环可以有效调控该陶瓷的发光强度。且经过多次循环之后, 发光强度没有明显衰减。在紫外光照射下, KNN:0.06Eu陶瓷发光强度的可调比(ΔR_t)高达83.9%, 说明发光具有良好的可调性。进而结合发光中心和色心之间的能量转移, 对KNN:Eu陶瓷的光致变色和发光机理进行了解释。     

长余辉蓄光玻璃的制备及其性能研究

利用传统陶瓷制备方法合成了SrAl2O4:Eu,Dy长余辉发光粉体,该磷光体主发射波长位于520nm,余辉时间长达8h以上。并以硼硅酸盐低熔点玻璃为底材,掺杂该发光粉体,在一定温度下烧成,结果制得长余辉蓄光玻璃。研究还表明,烧成温度对该玻璃的发光性能影响较大,随着温度的升高,发光强度及余辉时间明显下降。     

Highly Luminescent–Paramagnetic Nanophosphor Probes for In Vitro High‐Contrast Imaging of Human Breast Cancer Cells

Highly luminescent–paramagnetic nanophosphors have a seminal role in biotechnology and biomedical research due to their potential applications in biolabeling, bioimaging, and drug delivery. Herein, the synthesis of high‐quality, ultrafine, europium‐doped yttrium oxide nanophosphors (Y_1.9O₃:Eu_0.1³⁺) using a modified sol–gel technique is reported and in vitro fluorescence imaging studies are demonstrated in human breast cancer cells. These highly luminescent nanophosphors with an average particle size of ≈6 nm provide high‐contrast optical imaging and decreased light scattering. In vitro cellular uptake is shown by fluorescence microscopy, which visualizes the characteristic intense hypersensitive red emission of Eu³⁺ peaking at 610 nm (⁵D₀–⁷F₂) upon 246 nm UV light excitation. No apparent cytotoxicity is observed. Subsequently, time‐resolved emission spectroscopy and SQUID magnetometry measurements demonstrate a photoluminescence decay time in milliseconds and paramagnetic behavior, which assure applications of the nanophosphors in biomedical studies.     

Lanthanide‐Doped Core@Multishell Nanoarchitectures: Multimodal Excitable Upconverting/Downshifting Luminescence and High‐Level Anti‐Counterfeiting

The development of luminescent materials with concurrent multimodal emissions is a great challenge to improve security and data storage density. Lanthanide‐doped nanocrystals are particularly appropriate for such applications for their abundant intermediate energy states and distinguishable spectroscopic profiles. However, traditional lanthanide luminescent nanoparticles have a limited capacity for information storage or complexity to shield against counterfeiting. Herein, it is demonstrated that the combination of upconverting and downshifting emissions in a particulate designed lanthanide‐doped core@multishell nanoarchitecture allows the generation of multicolor dual‐modal luminescence over a wide spectral range for complex information storage. Precise control of lanthanide dopants distribution in the core and distinct shells enables simultaneous excitation of 980/808 nm focusing/defocusing laser and 254 nm light and produces complex upconverting emissions from Er, Tm, Eu, and Tb via multiphoton energy transfer processes and downshifting emissions from Eu and Tb via efficient energy transfer from Ce to Eu/Tb in Gd‐assisted lattices. It is experimentally proven that multiple visualized anti‐counterfeit and information encryption with facile decryption and authentication using screen‐printing inks containing the present core@multishell nanocrystals are practically applicable by selecting different excitation modes.     

Engineering of Lanthanide‐Doped Upconversion Nanoparticles for Optical Encoding

Lanthanide‐doped upconversion nanoparticles (UCNPs) are an emerging class of luminescent materials that emit UV or visible light under near infra‐red (NIR) excitations, thereby possessing a large anti‐Stokes shift property. Due to their sharp excitation and emission bands, excellent photo‐ and chemical stability, low autofluorescence, and high tissue penetration depth of the NIR light used for excitation, UCNPs have surpassed conventional fluorophores in many bioapplications. A better understanding of the mechanism of upconversion, as well as the development of better approaches to preparing UCNPs, have provided more opportunities to explore their use for optical encoding, which has the potential for applications in multiplex detection and imaging. With the current ability to precisely control the microstructure and properties of UCNPs to produce particles of tunable emission, excitation, luminescence lifetime, and size, various strategies for optical encoding based on UCNPs can now be developed. These optical properties of UCNPs (such as emission and excitation wavelengths, ratiometric intensity, luminescence lifetime, and multicolor patterns), and the strategies employed to engineer these properties for optical encoding of UCNPs through homogeneous ion doping, heterogeneous structure fabrication and microbead encapsulation are reviewed. The challenges and potential solutions faced by UCNP optical encoding are also discussed.     

Temporal and Remote Tuning of Piezophotonic‐Effect‐Induced Luminescence and Color Gamut via Modulating Magnetic Field

Light‐emitting materials have been extensively investigated because of their widespread applications in solid‐state lighting, displays, sensors, and bioimaging. In these applications, it is highly desirable to achieve tunable luminescence in terms of luminescent intensity and wavelength. Here, a convenient physical approach of temporal and remote tuning of light‐emitting wavelength and color is demonstrated, which is greatly different from conventional methods. It is shown that by modulating the frequency of magnetic‐field excitation at room temperature, luminescence from the flexible composites of ZnS:Al, Cu phosphors induced by the piezophotonic effect can be tuned in real time and in situ. The mechanistic investigation suggests that the observed tunable piezophotonic emission is ascribed to the tilting band structure of the ZnS phosphor induced by magnetostrictive strain under a high frequency of magnetic‐field excitation. Furthermore, some proof‐of concept devices, including red–green–blue full‐color displays and tunable white‐light sources are demonstrated simply by frequency modulation. A new understanding of the fundamentals of both luminescence and magnetic–optics coupling is thus provided, while offering opportunities in magnetic–optical sensing, piezophotonics, energy harvesting, novel light sources, and displays.     

Triple‐Mode Emissions with Invisible Near‐Infrared After‐Glow from Cr3+‐Doped Zinc Aluminum Germanium Nanoparticles for Advanced Anti‐Counterfeiting Applications

Materials exhibiting persistent luminescence (PersL) have great prospect in optoelectronic and biomedical applications such as optical information storage, bio‐imaging, and so on. Unfortunately, PersL materials with multimode emission properties have been rarely reported, although they are expected to be very desirable in multilevel anti‐counterfeiting and encryption applications. Herein, Cr³⁺‐doped zinc aluminum germanium (ZAG:Cr) nanoparticles exhibiting triple‐mode emissions are designed and demonstrated. Upon exposure to steady 254 nm UV light, the ZAG:Cr nanoparticles yield steady bluish‐white emission. After turning off the UV light, the emission disappears quickly and the mode switches to transient near‐infrared (NIR) PersL emission at predominantly 690 nm. The transient NIR PersL emission which arises from Cr³⁺ is induced by non‐equivalent substitution of Ge⁴⁺. After persisting for 50 min, it can be retriggered by 980 nm photons due to the continuous trap depth distribution of ZAG:Cr between 0.65 and 1.07 eV. Inspired by the triple‐mode emissions from ZAG:Cr, multifunctional luminescent inks composed of ZAG:Cr nanoparticles are prepared, and high‐security labeling and encoding encryption properties are demonstrated. The results indicate that ZAG:Cr nanoparticles have great potential in anti‐counterfeiting and encryption applications, and the strategy and concept described here provide insights into the design of advanced anti‐counterfeiting materials.     

Controlled synthesis of carbon-based alumina nanophosphors with tunable blue-green luminescence

Carbon-based alumina nanophosphors were prepared by a facile liquid process. The nanophosphors showed high photoluminescence properties, and tunable color emission from blue to green. The luminescent intensity and color were controlled by simply manipulating of polyethylene glycol and urea amounts, respectively. Oxygen deficiency, surface defects, and carboxylic impurities are considered to be possible emission mechanisms.     

Electrostatic Assembly Guided Synthesis of Highly Luminescent Carbon‐Nanodots@BaSO4 Hybrid Phosphors with Improved Stability

Carbon nanodots (CNDs)@BaSO₄ hybrid phosphors are fabricated in an easy and low‐cost process by sequentially assembling Ba²⁺ and SO₄^2? ions onto the surface of carbon nanodots through electrostatic attraction. CNDs act as the nucleus to attract these reactive ions and provide the luminescent centers in the hybrid phosphors. This strategy is versatile for a variety of negatively charged CNDs with different emission colors. The advantage of the resultant hybrid phosphors is that their luminescence exhibits excellent thermal and photostability, as well as remarkable resistance to strong acid/alkali and common organic solvents. These merits allow for the fabrication of CNDs‐based light‐emitting diodes using the CNDs@BaSO₄ hybrid phosphors as a color conversion layer.     

Modular Molecular Self‐Assembly for Diversified Chiroptical Systems

Bottom‐up multicomponent molecular self‐assembly is an efficient approach to fabricate and manipulate chiral nanostructures and their chiroptical activities such as the Cotton effect and circular polarized luminescence (CPL). However, the integrated coassembly suffers from spontaneous and inherent systematic pathway complexity with low yield and poor fidelity. Consequently, a rational design of chiral self‐assembled systems with more than two components remains a significant challenge. Herein, a modularized, ternary molecular self‐assembly strategy that generates chiroptically active materials at diverse hierarchical levels is reported. N‐terminated aromatic amino acids appended with binding sites for charge transfer and multiple hydrogen bonds undergo the evolution of supramolecular chirality with unique handedness and luminescent color, generating abundant CPL emission with high luminescence dissymmetry factor values in precisely controlled modalities. Ternary coassembly facilitates high‐water‐content hydrogel formation constituted by super‐helical nanostructures, demonstrating a helix to toroid topological transition. This discovery would shed light on developing complicated multicomponent systems in mimicking biological coassembly events.     

Sm3+/Ce3+/Tb3+共掺CaO-B2O3-SiO2发光玻璃的制备及发光性能研究

采用高温熔融法制备了Sm3+/Ce3+/Tb3+共掺杂的CaO-B2O3-SiO2发光玻璃材料,并用荧光分光光度计和CIE色度坐标对其发光性能进行了研究。发射光谱表明,在374nm激发下,Sm3+/Ce3+/Tb3+共掺杂CaO-B2O3-SiO2发光玻璃的发射光谱中同时观测到了红橙光、蓝光和绿光的发射带,这些发射带的混合实现了白光发射。此外,在Sm2O3和Tb4O7含量不变的情况下,随着CeO2含量的减小,Sm3+/Ce3+/Tb3+共掺杂发光玻璃的发光颜色在白光区逐渐由蓝光区附近过渡到黄光区附近。     

Luminescence Lifetime–Based In Vivo Detection with Responsive Rare Earth–Dye Nanocomposite

For years, luminescence lifetime imaging has served as a quantitative tool in indicating intracellular components and activities. However, very few studies involve the in vivo study of animals, especially in vivo stimuli‐responsive activities of animals, as both excitation and emission wavelengths should fall into the near‐infrared (NIR) optical transparent window (660–950 and 1000–1500 nm). Herein, this work reports a lifetime‐responsive nanocomposite with both excitation and emission in the NIR I window (800 nm) and lifetime in the microsecond region. The incorporation of Tm³⁺‐doped rare‐earth nanocrystals and NIR dye builds an efficient energy transfer pathway that enables a tunable luminescence lifetime range. The NaYF₄:Tm nanocrystal, which absorbs and emits photons at the same energy level, is found to be 33 times brighter than optimized core–shell upconversion nanocrystals, and proved to be an effective donor for NIR luminescence resonance energy transfer (LRET). The anti‐interference capability of luminescence lifetime signals is further confirmed by luminescence and lifetime imaging. In vivo studies also verify the lifetime response upon stimulation generated in an arthritis mouse model. This work introduces an intriguing tool for luminescence lifetime–based sensing in the microsecond region.     

Color-Tunable Polymeric Long-Persistent Luminescence Based on Polyphosphazenes

Organic long-persistent luminescence (OLPL) materials have attracted wide attention on account of their fascinating luminescence properties, presenting application prospects in the fields of bioimaging, information security, displays, anti-counterfeiting, and so on. Some effective strategies have been developed to promote the intersystem crossing (ISC) of the excited singlet state to triplet state and limit nonradiative transition, and thus OLPL materials with long lifetime (more than 1s) and high quantum yield have been explored. However, OLPL materials with dynamic and excitation-dependent characteristics are rarely reported. In this work, two novel polyphosphazene derivatives containing carbazolyl units are designed and synthesized successfully, and then they are doped into poly(vinyl alcohol) (PVA) films to achieve polymeric long-persistent luminescence (PLPL). Unexpectedly, excitation-dependent PLPL (ED-PLPL) is obtained under ambient conditions (in air at room temperature), and the persistent luminescence color can be changed from blue to green upon varying the excitation wavelength. At the same time, a dynamic cycle of ED-PLPL is realized based on the formation and destruction of hydrogen bonding interactions between the PVA chains and polyphosphazene phosphor. This work provides a new strategy for the design of color-tunable polymeric luminescent materials under ambient conditions.     

Large‐Scale Noniridescent Structural Color Printing Enabled by Infiltration‐Driven Nonequilibrium Colloidal Assembly

Structural colors originating from interaction of light with intricately arranged micro‐/nanostructures have stimulated considerable interest because of their inherent photostability and energy efficiency. In particular, noniridescent structural color with wide viewing angle has been receiving increasing attention recently. However, no method is yet available for rapid and large‐scale fabrication of full‐spectrum structural color patterns with wide viewing angles. Here, infiltration‐driven nonequilibrium assembly of colloidal particles on liquid‐permeable and particle‐excluding substrates is demonstrated to direct the particles to form amorphous colloidal arrays (ACAs) within milliseconds. The infiltration‐assisted (IFAST) colloidal assembly opens new possibilities for rapid manufacture of noniridescent structural colors of ACAs and straightforward structural color mixing. Full‐spectrum noniridescent structural colors are successfully produced by mixing primary structural colors of red, blue, and yellow using a commercial office inkjet printer. Rapid fabrication of large‐scale structural color patterns with sophisticated color combination/layout by IFAST printing is realized. The IFAST technology is versatile for developing structural color patterns with wide viewing angles, as colloidal particles, inks, and substrates are flexibly designable for diverse applications.     

Addressable and Color‐Tunable Piezophotonic Light‐Emitting Stripes

Piezophotonic light‐emitting devices have great potential for future microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) due to the added functionality provided by the electromechanical transduction coupled with the ability of light emission. Piezophotonic light‐emitting source based on Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMN–PT) bulk is severely restricted by many challenges, such as high voltage burden, low integration density, and micromanufacturing complexity. Developing chip‐integrated devices or incorporating such photonic components onto a Si platform is highly sought after in this field. In this work, the authors overcome the abovementioned problems by introducing single‐crystal PMN–PT thin films on Si as central active elements. Taking advantage of mature microfabrication techniques, arrays of PMN–PT actuators with small footprints and low operation voltages have been implemented. Each actuator can be individually addressed, generating local deformation to trigger piezophotonic luminescence from ZnS:Mn thin films. Moreover, the authors have realized continuous and reversible color manipulation of piezophotonic luminescence on a bilayer film of ZnS:Cu,Al/ZnS:Mn. The color tunability promises an extra degree of freedom and distinctly suggests its great potential in developing a more compact and colorful piezophotonic light sources and displays related applications together with the “single pixel” addressability.     

Crystallization‐Induced Emission Enhancement of a Deep‐Blue Luminescence Material with Tunable Mechano‐ and Thermochromism

Organic luminescent materials with the ability to reversibly switch the luminescence when subjected to external stimuli have attracted considerable interest in recent years. However, the examples of luminescent materials that exhibit multiresponsive properties are rarely reported. In this work, a new stimuli‐responsive dye P1 is designed and synthesized with two identical chromophores of naphthalimide, one at each side of an amidoamine‐based spacer. This amide‐rich molecule offers many possibilities for forming intra‐ and intermolecular hydrogen bond interactions. Particularly, P1 has an intrinsic property of cocrystallizing with methanol. Compared with the pristine P1 sample, the as‐prepared two‐component cocrystalline material displays an exceptive deep‐blue emission, which is extremely rare among naphthalimide‐based molecules in the solid state. Furthermore, the target material exhibits an obvious mechanochromic fluorescent behavior and a large spectral shift under force stimuli. On the other hand, the cocrystalline material shows an unusual “turn off” thermochromic luminescence accompanied by solvent evaporation. Moreover, using external stimuli to reversibly manipulate fluorescent quantum yields is rarely reported to date. The results demonstrate the feasibility of a new design strategy for solid‐state luminescence switching materials: the incorporation of solvents into organic compounds by cocrystallization to obtain a crystalline state luminescence system.     

On the relationship between the optical transmission and photoluminescence characteristics of porous silicon

The characteristics of free-standing porous silicon (por-Si) films were studied using their optical transmission, photoluminescence (PL), and photoluminescence excitation spectra. The transmission spectra exhibit no features within the emission bands or near PL excitation thresholds, which is evidence that nonluminescent por-Si fragments play a dominating role in the process of light absorption. This fact indicates that the optical transmission spectra cannot be used as a source of information on the bandgap energy of charge carriers in luminescent silicon nanocrystallites. The required energy spectrum parameters can be roughly evaluated using the PL excitation spectrum.