Soft Nanopatterning on Light‐Emitting Inorganic–Organic Composites

In this work we demonstrate the nanopatterning of nanocomposites made by luminescent zinc oxide nanoparticles and light‐emitting conjugated polymers by means of soft molding lithography. Vertical nanofluidics is exploited to overcome the polymer transport difficulties intrinsic in materials incorporating nanocrystals, and the rheology, fluorescence, absolute quantum yield, and emission directionality of the nanostructured composites are investigated. We study the effect of patterned gratings on the directionality of light emitted from the nanocomposites, finding evidence of the enhancement of forward emitted light, due to the printed wavelength‐scale periodicity. These results open new possibilities for the realization of nanopatterned devices based on hybrid organic‐inorganic systems.     

Two‐Component Molecular Materials of 2,5‐Diphenyloxazole Exhibiting Tunable Ultraviolet/Blue Polarized Emission,Pump‐enhanced Luminescence,and Mechanochromic Response

The development of π‐conjugated molecular systems with high‐efficiency generation of UV and blue light plays an important role in the fields of light‐emitting diodes, fluorescent imaging, and information storage. Herein, supramolecular construction of solid‐state UV/blue luminescent materials are assembled using 2,5‐diphenyloxazole (DPO) with four typical co‐assembled building blocks (1,4‐diiodotetrafluorobenzene, 4‐bromotetrafluorobenzene carboxylic acid, pentafluorophenol, and octafluoronaphthalene). Compared with the pristine DPO sample, the as‐prepared two‐component molecular materials feature ease of crystallization, high crystallinity, enhanced thermal stability and tunable luminescence properties (such as emissive wavelength, color, fluorescence lifetime, and photoluminescence quantum yield) as well as multicolor polarized emission in the UV/blue region. Moreover, pump‐enhanced luminescence and reversible mechanochromic fluorescence (MCF) properties can also be obtained for these molecular solids, which are absent for the pristine DPO sample. Therefore, this work provides a procedure for the facile self‐assembly of ordered two‐component molecular materials with tunable UV/blue luminescence properties, which have potential application in the areas of light‐emitting displays, polarized emission, frequency doubling, and luminescent sensors.     

Multifunctional AIEgens: Ready Synthesis,Tunable Emission,Mechanochromism, Mitochondrial,and Bacterial Imaging

Luminogens with aggregation‐induced emission characteristics (AIEgens) are intriguing due to its rapid expansion in various high‐tech applications. However, there is still in high demand on the development of novel AIEgens with easy preparation and functionalization, stable structures, tunable emissions, and high quantum efficiency. In this contribution, three AIEgens based on diphenyl isoquinolinium (IQ) derivatives are reported. They can be facilely synthesized and possess high structural stability, favorable visible light excitation, large Stokes shifts, high quantum yields, tunable colors, and sufficient two‐photon absorption of near‐infrared light. Importantly, they exhibit multifunctionalities. They exhibit mechanochromic property, making them capable to be applied for rewritable papers. They can also be applied in mitochondrial imaging with high specificity, cell permeability, brightness, biocompatibility, and photostability. They are promising for the applications in evaluation of mitochondrial membrane potential and image‐guided cancer cell ablation. Last, they are able to stain bacteria in a wash‐free manner. All these intriguing results suggest such readily accessible and multifunctional diphenyl IQ‐based AIEgens provide a new platform for construction of advanced materials for practical applications.     

Multifunctional Bismuth‐Doped Nanoporous Silica Glass: From Blue‐Green,Orange, Red,and White Light Sources to Ultra‐Broadband Infrared Amplifiers

Ultra‐broadband luminescent sources that emit light over an extremely wide wavelength range are of great interest in the fields of photonics, medical treatment, and precision measurement. Extensive research has been conducted on materials doped with rare‐earth and transition‐metal ions, but the goal of fabricating an ultra‐broadband emitter has not been attained. We present a facile method to realize this kind of novel light source by stabilizing “active” centers (bismuth) in a “tolerant” host (nanoporous silica glass). The obtained highly transparent materials, in which, unusually, multiple bismuth centers (Bi⁺, Bi²⁺, and Bi³⁺) can be stabilized, emit in an ultra‐broadband wavelength range from blue‐green, orange, red, and white to the near‐infrared region. This tunable luminescence covers the spectral range of the traditional three primary colors (RGB) and also the telecommunications windows.     

Wavelength‐Dependent Stiffening of Hydrogel Matrices via Redshifted [2+2] Photocycloadditions

Hydrogels with on‐demand tunable mechanical properties within sensitive biological environments are of critical importance for examining cellular responses to cell culture platforms. Herein, the first bio‐orthogonal hydrogel that can be formed and subsequently tuned in its mechanical properties by simply switching different wavelengths of visible light (i.e., 455 and 420 nm) is reported. Specifically, both the initial hydrogelation and the tuning of the mechanical properties can be fully decoupled and selectively initiated by different colors of light. Sparing the need for any catalysts, the development of such a dual wavelength selective hydrogel for biological applications spans four levels: First, the development of the until today most redshifted photocycloaddition to allow for the selective initiation of only one photoreaction; second, the investigation of its wavelength‐dependent ligation efficiency; third, translation of the ligation chemistry into a hydrogelator, and fourth, establishing a biocompatible hydrogel platform for applications in biomaterials engineering including detachment of fibroblasts from 2D culture areas or primary 3D culture of human mesenchymal stem cells. The introduced platform technology enables the fabrication of a hydrogel of predefined mechanical properties exclusively with visible light.     

Full‐Color Phosphors from Amine‐Functionalized Crosslinked Hybrids Lacking Metal Activator Ions

Sol–gel derived hybrids that contain OCH₂CH₂ (polyethylene glycol, PEG) repeat units grafted onto a siliceous backbone by urea, –NHC(=O)NH–, or urethane, –NHC(=O)O–, bridges have been prepared. It is demonstrated that the white light PL of these materials results from an unusual convolution of a longer lived emission that originates in the NH groups of the urea/urethane bridges with shorter lived electron–hole recombinations occurring in the nanometer‐sized siliceous domains. The PL efficiencies reported here (maximum quantum yields at room temperature of ≈ 0.20 ± 0.02 at a 400 nm excitation wavelength) are in the same range as those for tetramethoxysilane–formic acid, and APTES–acetic acid, sol–gel derived phosphors. The high quantum yields combined with the possibility of tuning the emission to colors across the chromaticity diagram present a wide range of potential applications for these hybrid materials.     

Nanoparticle Stacks with Graded Refractive Indices Enhance the Omnidirectional Light Harvesting of Solar Cells and the Light Extraction of Light‐Emitting Diodes

In this study, nanoparticles (NPs) of various types and sizes are arranged to enhance both the omnidirectional light harvesting of solar cells and the light extraction of light emitting diodes (LEDs). A graded‐refractive‐index NP stack can minimize reflectance, not only over a broad range of wavelengths but also at different incident angles; the photocurrent of silicon‐based solar cells an also be significantly improved omnidirectionally. In addition, the optical gradient of an NP stack can also enhance the light‐extraction efficiency of LEDs, due to both the graded refractive index and the moderate surface roughness. Large particles having sizes on the same order of the wavelength of the incident light roughen the LED surfaces further and extract light from beyond the critical angle, as supported by three‐dimensional finite‐difference time‐domain simulations. Using this approach, the photoluminescence intensity can be increased by up to sevenfold. The developed technique: arranging sequences of different NPs in graded‐refractive‐index stacks, and considering their ability to scatter light due to their sizes and optical constants, may also significantly improve the performance of various optoelectronic devices.     

Beyond Seashells: Bioinspired 2D Photonic and Photoelectronic Devices

The discovery of novel materials that possess extraordinary optical properties are of special interest, as they inspire systems for next‐generation solar energy harvesting and conversion devices. Learning from nature has inspired the development of many photonic nanomaterials with fascinating structural colors. 2D photonic nanostructures, inspired by the attractive optical properties found on the inner surfaces of seashells, are fabricated in a facile and scalable way. The shells generate shining clusters for preying on phototactic creatures through interaction with incident solar light in water. By alternately depositing graphene and 2D ultrathin TiO₂ nanosheets to form 2D–2D heterostructures and homostructures, seashell‐inspired nanomaterials with well‐controlled parameters are successfully achieved. They exhibit exceptional interlayer charge transfer properties and ultrafast in‐plane electron mobility and present fascinating nacre‐mimicking optical properties and significantly enhanced light‐response behavior when acting as photoelectrodes. A window into the fabrication of novel 2D photonic structures and devices is opened, paving the way for the design of high‐performance solar‐energy harvesting and conversion devices.     

Characterization of radiant emitters used in food processing.

Radiant emissions from short, medium, and long wavelength thermal radiant emitter systems typically used for food processing applications were quantified. Measurements included heat flux intensity, emitter surface temperature, and spectral wavelength distribution. Heat flux measurements were found highly dependent on the incident angle and the distance from the emitter facing. The maximum flux measured was 5.4 W/cm2. Emitter surface temperature measurements showed that short wavelength radiant systems had the highest surface temperature and greatest thermal efficiency. The emitter spectral distributions showed that radiant emitter systems had large amounts of far infrared energy emission greater than 3 microm when compared to theoretical blackbody curves. The longer wavelength energy would likely cause increased surface heating for most high moisture content food materials.     

2D Layered Material‐Based van der Waals Heterostructures for Optoelectronics

Van der Waals heterostructures (vdWHs) based on 2D layered materials with selectable materials properties pave the way to integration at the atomic scale, which may give rise to fresh heterostructures exhibiting absolutely novel physics and versatility. This feature article reviews the state‐of‐the‐art research activities that focus on the 2D vdWHs and their optoelectronic applications. First, the preparation methods such as mechanical transfer and chemical vapor deposition growth are comprehensively outlined. Then, unique energy band alignments generated in 2D vdWHs are introduced. Furthermore, this feature article focuses on the applications in light‐emitting diodes, photodetectors, and optical modulators based on 2D vdWHs with novel constructions and mechanisms. The recently reported novel constructions of the devices are introduced in three primary aspects: light‐emitting diodes (such as single defect light‐emitting diodes, circularly polarized light emission arising from valley polarization), photodetectors (such as photo‐thermionic, tunneling, electrolyte‐gated, and broadband photodetectors), and optical modulators (such as graphene integrated with silicon technology and graphene/hexagonal boron nitride (hBN) heterostructure), which show promising applications in the next‐generation optoelectronics. Finally, the article provides some conclusions and an outlook on the future development in the field.     

Simultaneously Excited Downshifting/Upconversion Luminescence from Lanthanide‐Doped Core/Shell Fluoride Nanoparticles for Multimode Anticounterfeiting

This work presents a novel anticounterfeiting strategy based on a material changing its emission color in response to a change in the excitation sources—where a single ultraviolet (UV) or near‐infrared (NIR) light source are employed or simultaneously using two excitation sources (xenon lamp and NIR laser). Following this approach, various combinations of lanthanide (Ln³⁺)‐doped LiLuF₄/LiYF₄ core/shell nanoparticles are prepared, providing a promising route to design flexible nanomaterials, as well as already a small library of luminescent materials, which change color when varying the excitation source (UV, NIR or both UV and NIR). Aside from excitation source‐dependent color change, these materials additionally show excitation‐source power‐dependent color change. This work exploits the possibility of developing a new class of multimode anticounterfeit nanomaterials, with excellent performance, which would be almost impossible to mimic or replicate, providing a very high level of security.     

Titania‐Based Spherical Mie Resonators Elaborated by High‐Throughput Aerosol Spray: Single Object Investigation

In the framework of photonics with all‐dielectric nanoantennas, sub‐micrometric spheres can be exploited for a plethora of applications including vanishing back‐scattering, enhanced directivity of a light emitter, beam steering, and large Purcell factors. Here, the potential of a high‐throughput fabrication method based on aerosol‐spray is shown to form quasi‐perfect sub‐micrometric spheres of polycrystalline TiO₂. Spectroscopic investigation of light scattering from individual particles reveals sharp resonances in agreement with Mie theory, neat structural colors, and a high directivity. Owing to the high permittivity and lossless material in use, this method opens the way toward the implementation of isotropic meta‐materials and forward‐directional sources with magnetic responses at visible and near‐UV frequencies, not accessible with conventional Si‐ and Ge‐based Mie resonators.     

利用偏振成像在复杂现场快速识别金属碎屑（特约）

爆炸犯罪杀伤群众,破坏公私财产,对公共安全造成危害。为快速侦破爆破案件,需要在爆炸现场众多残留物中识别金属,找出爆炸装置碎屑。针对在复杂背景中快速识别金属碎屑的需求,提出了一种基于线偏振成像增强金属对比的方法。基于偏振光成像的原理,搭建了两种多波长偏振图像采集装置。针对多种非金属和金属材料进行实验,发现调整入射光的线偏振角度和入射角,多波长偏振成像方法在复杂现场中可以对金属与非金属快速识别和分类。通过模拟研究了多波长下金属表面反射光的线偏振度和偏振角随入射角度变化的情况,给出识别不同金属的最佳角度和照明偏振光。进一步实验结果显示:多波长线偏振成像方法有区分不同种类金属的潜力。     

Fabrication of highly transparent self‐cleaning protection films for photovoltaic systems

A moth‐eye anti‐reflective structure was fabricated by hot‐embossing and UV nanoimprint lithography on a solar cell protective film to suppress the reflection of incident light. Moreover, a superhydrophobic surface was developed by reducing the surface energy by forming a hydrophobic self‐assembled monolayer coating on an anti‐reflective structured resin surface. Therefore, the transmittance of incident light was increased by the anti‐reflective structure. As a result, the solar cell efficiency was enhanced and the total accumulated electrical energy generated by a solar cell with a nano‐patterned polymeric film was increased. The efficiency of each solar cell was evaluated by an analysis of its I‐V characteristics using a solar simulator, and the external quantum efficiency according to the wavelength of incident light was analyzed by using an incident photon‐to‐current conversion efficiency system. Finally, the enhancement of the generated power was confirmed by a field test and a power charging experiment. Copyright © 2012 John Wiley & Sons, Ltd.     

A Non‐rare‐Earth Ions Self‐Activated White Emitting Phosphor under Single Excitation

White light phosphors have many potential applications such as solid‐state lighting, full color displays, light source for plant growth, and crop improvement. However, most of these phosphors are rare‐earth‐based materials which are costly and would be facing the challenge of resource issue due to the extremely low abundance of these elements on earth. A new white color composite consisted of a graphitic‐phase nitrogen carbon (g‐C₃N₄) treated with nitric acid and copper‐cysteamine Cu₃Cl(SR)₂ is reported herein. Under a single wavelength excitation at 365 nm, these two materials show a strong blue and red luminescence, respectively. It is interesting to find that the white light emission with a quantum yield of 20% can be obtained by mixing these two self‐activated luminescent materials at the weight ratio of 1:1.67. Using a 365 nm near‐ultraviolet chip for excitation, the composite produces a white light‐emitting diode that exhibits an excellent color rendering index of 94.3. These white‐emitting materials are environment friendly, easy to synthesize, and cost‐effective. More importantly, this will potentially eliminate the challenge of rare earth resources. Furthermore, a single chip is used for excitation instead of a multichip, which can greatly reduce the cost of the devices.     

Luminescent Colloidal Dispersion of Silicon Quantum Dots from Microwave Plasma Synthesis: Exploring the Photoluminescence Behavior Across the Visible Spectrum

Aiming for a more practical route to highly stable visible photoluminescence (PL) from silicon, a novel approach to produce luminescent silicon nanoparticles (Si‐NPs) is developed. Single crystalline Si‐NPs are synthesized by pyrolysis of silane (SiH₄) in a microwave plasma reactor at very high production rates (0.1–10 g h^?1). The emission wavelength of the Si‐NPs is controlled by etching them in a mixture of hydrofluoric acid and nitric acid. Emission across the entire visible spectrum is obtained by varying the etching time. It is observed that the air oxidation of the etched Si‐NPs profoundly affects their optical properties, and causes their emission to blue‐shift and diminish in intensity with time. Modification of the silicon surface by UV‐induced hydrosilylation also causes a shift in the spectrum. The nature of the shift (red/blue) is dependent on the emission wavelength of the etched Si‐NPs. In addition, the amount of shift depends on the type of organic ligand on the silicon surface and the UV exposure time. The surface modification of Si‐NPs with different alkenes results in highly stable PL and allows their dispersion in a variety of organic solvents. This method of producing macroscopic quantities of Si‐NPs with very high PL stability opens new avenues to applications of silicon quantum dots in optoelectronic and biological fields, and paves the way towards their commercialization.     

Photo-Responsive Azobenzene-Containing Inverse Opal Films for Information Security

Stimuli-responsive photonic crystals (PCs) have attracted increasing attentions owing to the unique optical feature in regulating the propagation of light and tunable structural colors in response to external stimuli, emerging application potential on diverse fields. However, the development of stimuli-responsive PCs with wide visible light range, broad shift of bandgaps, and adjustable responsive rates for counterfeiting remains challenging. Herein, a simple strategy for the preparation of photo-responsive azobenzene-containing inverse opal (AzoIO) films is reported. First, azobenzene-containing composites are generated by filling functional monomers into voids of silica colloids crystals. Followed by the thermal polymerization and subsequent etching, a series of AzoIO films are successfully fabricated with adjustable structural colors in wide visible wavelength. Upon irradiation with linearly polarized visible light (LPVL), a slowly broad blueshift of bandgaps (≈138 nm, 3200 s) is observed due to the anisotropic shrinkage of the periodic PC structures. However, UV light irradiation contributed to a fast broad blueshift of bandgaps (≈131 nm, 10 s), owing to the photoisomerization merit of azobenzene moiety. The proof-of-concept study on the applications in light-modulated multicolored writable paper, encryption films, and fast writing/erasing demonstrated the potential for information security. This work paves an avenue for developing promising optical anti-counterfeiting materials.     

Light‐Emitting Electrochemical Cells Based on Color‐Tunable Inorganic Colloidal Quantum Dots

Large‐area, ultrathin light‐emitting devices currently inspire architects and interior and automotive designers all over the world. Light‐emitting electrochemical cells (LECs) and quantum dot light‐emitting diodes (QD‐LEDs) belong to the most promising next‐generation device concepts for future flexible and large‐area lighting technologies. Both concepts incorporate solution‐based fabrication techniques, which makes them attractive for low cost applications based on, for example, roll‐to‐roll fabrication or inkjet printing. However, both concepts have unique benefits that justify their appeal. LECs comprise ionic species in the active layer, which leads to the omission of additional organic charge injection and transport layers and reactive cathode materials, thus LECs impress with their simple device architecture. QD‐LEDs impress with purity and opulence of available colors: colloidal quantum dots (QDs) are semiconducting nanocrystals that show high yield light emission, which can be easily tuned over the whole visible spectrum by material composition and size. Emerging technologies that unite the potential of both concepts (LEC and QD‐LED) are covered, either by extending a typical LEC architecture with additional QDs, or by replacing the entire organic LEC emitter with QDs or perovskite nanocrystals, still keeping the easy LEC setup featured by the incorporation of mobile ions.     

Photochemically Controlled Photonic Crystals

We have developed photochemically controlled photonic crystals that may be useful in novel recordable and erasable memories and/or display devices. These materials can operate in the UV, visible, or near‐IR spectral regions. Information is recorded and erased by exciting the photonic crystal with ～ 360 nm UV light or ～ 480 nm visible light. The information recorded is read out by measuring the photonic crystal diffraction wavelength. The active element of the device is an azobenzene‐functionalized hydrogel, which contains an embedded crystalline colloidal array. UV excitation forms cis‐azobenzene while visible excitation forms trans‐azobenzene. The more favorable free energy of mixing of cis‐azobenzene causes the hydrogel to swell and to red‐shift the photonic crystal diffraction. We also observe fast nanosecond, microsecond, and millisecond transient dynamics associated with fast heating lattice constant changes, refractive index changes, and thermal relaxations.     

Wavelength‐Dependent Photosensitivity in a Germanium‐Doped Sol–Gel Hybrid Material for Direct Photopatterning

Photosensitivity, as evident in permanent changes in refractive index and volume upon light exposure, is observed in a germanium‐doped methacrylate hybrid material (hybrimer) and found to depend on the wavelength of the UV light. Exposure to short‐wavelength UV illumination (220–260 nm) results in very high photosensitivity with changes in refractive index (Δn ≈ 0.0164) and film thickness (Δt ≈ –40 %) that are mainly a result of photopolymerization and Ge‐related densification. In contrast, the hybrimer is hardly photosensitive to light in the long UV‐wavelength range (350–390 nm). Direct photopatterning of a single circle on the hybrimer film creates a concave lens‐like topography upon illumination with UV light of short wavelength and a convex lens‐like one upon illumination with UV light of long wavelength.