Solid‐State Electrolyte‐Gated Graphene in Optical Modulators

The gate‐tunable wide‐band absorption of graphene makes it suitable for light modulation from terahertz to visible light. The realization of graphene‐based modulators, however, faces challenges connected with graphene's low absorption and the high electric fields necessary to change graphene's optical conductivity. Here, a solid‐state supercapacitor effect with the high‐k dielectric hafnium oxide is demonstrated that allows modulation from the near‐infrared to shorter wavelengths close to the visible spectrum with remarkably low voltages (≈3 V). The electroabsorption modulators are based on a Fabry–Perot‐resonator geometry that allows modulation depths over 30% for free‐space beams.     

Expanding the Toolbox of Upconversion Nanoparticles for In Vivo Optogenetics and Neuromodulation

Optogenetics is an optical technique that exploits visible light for selective neuromodulation with spatio‐temporal precision. Despite enormous effort, the effective stimulation of targeted neurons, which are located in deeper structures of the nervous system, by visible light, remains a technical challenge. Compared to visible light, near‐infrared illumination offers a higher depth of tissue penetration owing to a lower degree of light attenuation. Herein, an overview of advances in developing new modalities for neural circuitry modulation utilizing upconversion‐nanoparticle‐mediated optogenetics is presented. These developments have led to minimally invasive optical stimulation and inhibition of neurons with substantially improved selectivity, sensitivity, and spatial resolution. The focus is to provide a comprehensive review of the mechanistic basis for evaluating upconversion parameters, which will be useful in designing, executing, and reporting optogenetic experiments.     

Nanotransducers for Near‐Infrared Photoregulation in Biomedicine

Photoregulation, which utilizes light to remotely control biological events, provides a precise way to decipher biology and innovate in medicine; however, its potential is limited by the shallow tissue penetration and/or phototoxicity of ultraviolet (UV)/visible light that are required to match the optical responses of endogenous photosensitive substances. Thereby, biologically friendly near‐infrared (NIR) light with improved tissue penetration is desired for photoregulation. Since there are a few endogenous biomolecules absorbing or emitting light in the NIR region, the development of molecular transducers is essential to convert NIR light into the cues for regulation of biological events. In this regard, optical nanomaterials able to convert NIR light into UV/visible light, heat, or free radicals are suitable for this task. Here, the recent developments of optical nanotransducers for NIR‐light‐mediated photoregulation in medicine are summarized. The emerging applications, including photoregulation of neural activity, gene expression, and visual systems, as well as photochemical tissue bonding, are highlighted, along with the design principles of nanotransducers. Moreover, the current challenges and perspectives in this field are discussed.     

Giant and Tunable Optical Nonlinearity in Single‐Crystalline 2D Perovskites due to Excitonic and Plasma Effects

Materials with large optical nonlinearity, especially in the visible spectral region, are in great demand for applications in all‐optical information processing and quantum optics. 2D hybrid Ruddlesden?Popper‐type halide perovskites (RPPs) with tunable ultraviolet‐to‐visible direct bandgaps exhibit large nonlinear optical responses due to the strong excitonic effects present in their multiple quantum wells. Using a microscopic Z‐scan setup with femtosecond laser pulses tunable across the visible spectrum, it is demonstrated that single‐crystalline lead halide RPP nanosheets possess unprecedentedly large nonlinear refraction and absorption coefficients near excitonic resonances. A room‐temperature insulator (exciton)–metal (plasma) Mott transition is found to occur near the exciton resonance of the thinnest qunatum‐well RPPs, boosting the nonlinear response. Owing to the rapidly changing refractive index near resonance, a single RPP crystal can exhibit different nonlinear functionalities across the excitation spectrum. The results suggest that RPPs are efficient nonlinear materials in the visible waveband, indicating their potential use in integrated nonlinear photonic applications such as optical modulation and switching.     

Optical bleaching, TSL and OSL features of CVD diamond

Luminescence and optical features of chemical vapour deposition (CVD) diamond have been studied in view of the potential application of this material in ionising radiation dosimetry field. For this purpose, thermally stimulated luminescence (TSL) and optically stimulated luminescence (OSL) techniques have been used. A large amount of work has emphasised the excellent dosimetric properties of CVD diamond. Nevertheless, TSL measurements showed that after irradiation, this material is extremely sensitive to ambient light and the stored dose information is drastically affected by optical bleaching. From OSL analysis, it follows that both types of processes (TSL and OSL) were characterised by the same excitation and emission spectra and that optical bleaching originated from a broad stimulation band lying from visible to near infrared with a continuous character.     

多彩氧化钨薄膜的红外电致变色性能研究

电致变色材料能够在可见-红外宽频谱范围内对吸收率、透过率、反射率和发射率进行动态调节,是人工调制材料光谱特征的有效手段。在实际应用场合,对于色彩(可见光)与热辐射(红外线)可控调节的需求往往并存,利用单一电致变色器件实现可见、红外双波段的光学调制性能具有重要意义。现阶段对于电致变色材料的设计主要集中于可见光谱的调节能力及颜色转变,忽略了对材料红外光谱的探究。本研究选取具有法布里–铂罗(F-P)空腔结构的多彩氧化钨薄膜进行可见–红外宽频谱电致变色探究,具有F-P空腔结构的氧化钨薄膜材料在可见光区呈现多样化、明亮的颜色,再对多彩薄膜进行图案化设计,即可得到具有各种图案的多彩薄膜,并且在外加偏压的作用下可以实现多样化的颜色转变。同时,多彩氧化钨薄膜的红外反射率也可获得明显的可控调制效果,在中波段(Medium Wave, MW)3.5μm左右处不同颜色薄膜均可获得高于25.00%的红外调制率。本研究表明,多彩氧化钨薄膜可以实现可见–红外宽频谱的分立、可控调节,在智能窗、热管理、辐射制冷等应用领域有巨大潜力,可达到光、热性能协同调制的效果。     

A Silicon Nanowire as a Spectrally Tunable Light‐Driven Nanomotor

Over the last decades, scientists have endeavored to develop nanoscopic machines and envisioned that these tiny machines could be exploited in biomedical applications and novel material fabrication. Here, a visible‐/near‐infrared light‐driven nanomotor based on a single silicon nanowire is reported. The silicon nanomotor harvests energy from light and propels itself by the self‐electrophoresis mechanism. Due to the high efficiency, the silicon nanowire can be readily driven by visible and near‐infrared illumination at ultralow light intensity (≈3 mW cm^?2). The experimental study and numerical simulation also show that the detailed structure around the concentrated reaction center determines the migration behavior of the nanomotor. Importantly, due to the optical resonance inside the silicon nanowire, the spectral response of the nanowire‐based nanomotor can be readily modulated by the nanowire's diameter. Compared to other methods, light controlling potentially offers more freedom and flexibility, as light can be modulated not only with its intensity and direction, but also with the frequency and polarities. This nanowire motor demonstrates a step forward to harness the advantages of light, which opens up new opportunities for the realization of many novel functions such as multiple channels communication to nanorobots and controllable self‐assembly.     

Rolling up MoSe2 Nanomembranes as a Sensitive Tubular Photodetector

Transition metal dichalcogenides, as a kind of 2D material, are suitable for near‐infrared to visible photodetection owing to the bandgaps ranging from 1.0 to 2.0 eV. However, limited light absorption restricts photoresponsivity due to the ultrathin thickness of 2D materials. 3D tubular structures offer a solution to solve the problem because of the light trapping effect which can enhance optical absorption. In this work, thanks to mechanical flexibility of 2D materials, self‐rolled‐up technology is applied to build up a 3D tubular structure and a tubular photodetector is realized based on the rolled‐up molybdenum diselenide microtube. The tubular device is shown to present one order higher photosensitivity compared with planar counterparts. Enhanced optical absorption arising from the multiple reflections inside the tube is the main reason for the increased photocurrent. This tubular device offers a new design for increasing the efficiency of transition metal dichalcogenide–based photodetection and could hold great potential in the field of 3D optoelectronics.     

Flexible Visible‐Light Photodetectors with Broad Photoresponse Based on ZrS3 Nanobelt Films

Two new flexible visible‐light photodetectors based on ZrS₃ nanobelts films are fabricated on a polypropylene (PP) film and printing paper, respectively, by an adhesive‐tape transfer method, and their light‐induced electric properties are investigated in detail. The devices demonstrate a remarkable response to 405 to 780 nm light, a photocurrent that depends on the optical power and light wavelength, and an excellent photoswitching effect and stability. This implies that ZrS₃ nanobelts are prospective candidates for high‐performance nanoscale optoelectronic devices that may be practically applied in photodetection of visible to near infrared light. The facile fabrication method is extendable to flexible nanodevices with different nanostructures.     

Nonlinear Saturable Absorption of Liquid‐Exfoliated Molybdenum/Tungsten Ditelluride Nanosheets

Molybdenum disulfide (MoS₂) and tungsten disulfide (WS₂), two representative transition metal dichalcogenide materials, have captured tremendous interest for their unique electronic, optical, and chemical properties. Compared with MoS₂ and WS₂, molybdenum ditelluride (MoTe₂) and tungsten ditelluride (WTe₂) possess similar lattice structures while having smaller bandgaps (less than 1 eV), which is particularly interesting for applications in the near‐infrared wavelength regime. Here, few‐layer MoTe₂/WTe₂ nanosheets are fabricated by a liquid exfoliation method using sodium deoxycholate bile salt as surfactant, and the nonlinear optical properties of the nanosheets are investigated. The results demonstrate that MoTe₂/WTe₂ nanosheets exhibit nonlinear saturable absorption property at 1.55 μm. Soliton mode‐locking operations are realized separately in erbium‐doped fiber lasers utilizing two types of MoTe₂/WTe₂‐based saturable absorbers, one of which is prepared by depositing the nanosheets on side polished fibers, while the other is fabricated by mixing the nanosheets with polyvinyl alcohol and then evaporating them on substrates. Numerous applications may benefit from the nonlinear saturable absorption features of MoTe₂/WTe₂ nanosheets, such as visible/near‐infrared pulsed laser, materials processing, optical sensors, and modulators.     

Growth, processing and properties of CVD diamond for optical applications

In recent years there has been an increased need for optical materials for use in adverse chemical, thermal, abrasive, and/or radiation environments. Diamond is a natural candidate for many of these applications because of its radiation hardness, superb resistance to chemical attack and abrasive wear, high thermal conductivity, and low absorption coefficient throughout the visible and much of the infrared. The use of synthetic (high pressure-high temperature) and natural diamond in optical components has been limited by the size and shapesof available crystals, and the inability to coat optical elements. The chemical vapor deposition (CVD) of polycrystalline diamond does not suffer the same limitations, and is therefore the focus of an expanding worldwide research effort. CVD diamond is not without its own shortcomings, however, and in this paper a status report is given on the obstacles and current research related to using CVD diamond as an optical material. Natural diamond's relevant physical properties and the optical applications envisioned for CVD diamond are also discussed.     

In Situ Fabrication of Vertical Multilayered MoS2/Si Homotype Heterojunction for High‐Speed Visible–Near‐Infrared Photodetectors

c2D transition metal dichalcogenides (TMDCs)‐based heterostructures have been demonstrated to achieve superior light absorption and photovoltaic effects theoretically and experimentally, making them extremely attractive for realizing optoelectronic devices. In this work, a vertical multilayered n‐MoS₂/n‐silicon homotype heterojunction is fabricated, which takes advantage of multilayered MoS₂ grown in situ directly on plane silicon. Electrical characterization reveals that the resultant device exhibits high sensitivity to visible–near‐infrared light with responsivity up to 11.9 A W^–1. Notably, the photodetector shows high‐speed response time of ≈30.5 µs/71.6 µs and capability to work under higher pulsed light irradiation approaching 100 kHz. The high response speed could be attributed to a good quality of the multilayer MoS₂, as well as in situ device fabrication process. These findings suggest that the multilayered MoS₂/Si homotype heterojunction have great potential application in the field of visible–near‐infrared detection and might be used as elements for construction of high‐speed integrated optoelectronic sensor circuitry.     

Photocatalytic degradation of organic dyes with manganese-doped ZnO nanoparticles

Manganese-doped and undoped ZnO photocatalysts were synthesized via wet-chemical techniques. Doping of ZnO with manganese (Mn(2+)) was intended to create tail states within the band gap of ZnO. These can subsequently be used as efficient photocatalysts which can effectively degrade organic contaminants only with visible light irradiation. Photocatalysts prepared with these techniques, which were characterized with transmission electron microscopy (TEM), infrared spectroscopy (FTIR), photo-co-relation spectroscopy (PCS) and UV-vis-spectroscopy showed significant difference in the optical absorption of Mn-doped ZnO. Enhancement in optical absorption of Mn-doped ZnO indicates that it can be used as an efficient photocatalyst under visible light irradiation. The photo-reduction activities of photocatalysts were evaluated using a basic aniline dye, methylene blue (MB) as organic contaminant irradiated only with visible light from tungsten bulb. It was found that manganese-doped ZnO (ZnO:Mn(2+)) bleaches MB much faster than undoped ZnO upon its exposure to the visible light. The experiment demonstrated that the photo-degradation efficiency of ZnO:Mn(2+) was significantly higher than that of undoped ZnO and might also be better than the conventional metal oxide semiconductor such as TiO(2) using MB as a contaminant.     

Optical Response on the Colossal Magnetoresistance Effect in Manganites

The magnetorefractive effect in magnetoreflection and magnetotransmission modes in the optimally doped manganite epitaxial films possessed the colossal magnetoresistance effect was in the wide spectral region studied. The strict correlation between the magnetorefractive effect and colossal magnetoresistance in the middle infrared region for all samples was observed. It was shown that the magnetorefractive effect is an optical response to the colossal magnetoresistance in manganites. The magnetorefractive effect can reach a few tens of percents in the field of 3 kOe near the Curie point and can be explained by the change of ratio of localized and delocalized charge carriers under the magnetic field. On the contrary, in the visible range no direct correlations between magnetorefractive effect and colossal magnetoresistance were detected. The magnetorefractive effect is related with the alteration of the optical density under the magnetic field in the region of interband optical transitions. The magnitude of the effect is at least one order less in comparison with one in the infrared, but exceeds the values of traditional linear magnetooptical phenomena as the Kerr effect. Finally, huge magnetorefractive effect in manganites may be used for creation of various magnetic sensors and light modulation.     

A Retina‐Like Dual Band Organic Photosensor Array for Filter‐Free Near‐Infrared‐to‐Memory Operations

Human eyes use retina photoreceptor cells to absorb and distinguish photons from different wavelengths to construct an image. Mimicry of such a process and extension of its spectral response into the near‐infrared (NIR) is indispensable for night surveillance, retinal prosthetics, and medical imaging applications. Currently, NIR organic photosensors demand optical filters to reduce visible interference, thus making filter‐free and anti‐visible NIR imaging a challenging task. To solve this limitation, a filter‐free and conformal, retina‐inspired NIR organic photosensor is presented. Featuring an integration of photosensing and floating‐gate memory modules, the device possesses an acute color distinguishing capability. In general, the retina‐like photosensor transduces NIR (850 nm) into nonvolatile memory and acts as a dynamic photoswitch under green light (550 nm). In doing this, a filter‐free but color‐distinguishing photosensor is demonstrated that selectively converts NIR optical signals into nonvolatile memory.     

可溶性聚噻吩甲烷的制备与光学性能

利用噻吩和对二甲氨基苯甲醛在酸性条件下共聚,制备了一种具有可溶性、分子链部分共轭的聚噻吩甲烷衍生物。采用傅里叶变换红外光谱、紫外-可见吸收光谱、荧光光谱、热重分析和X射线衍射谱对聚合物的分子结构、光学性能、热稳定性能及聚集态结构进行了表征和分析。由紫外-可见吸收光谱可得,该聚合物的光学禁带宽度为1.3 eV,属于窄带隙聚合物。荧光光谱显示,该聚合物溶液在480 nm可见光的激发下,出现约600 nm的发射光,说明该聚合物为橙黄色的荧光材料。X射线衍射谱中17.3°附近存在1个较为尖锐的衍射峰,表明该聚合物聚集态结构为部分结晶态。     

Balanced Partnership between Donor and Acceptor Components in Nonfullerene Organic Solar Cells with >12% Efficiency

Relative to electron donors for bulk heterojunction organic solar cells (OSCs), electron acceptors that absorb strongly in the visible and even near‐infrared region are less well developed, which hinders the further development of OSCs. Fullerenes as traditional electron acceptors have relatively weak visible absorption and limited electronic tunability, which constrains the optical and electronic properties required of the donor. Here, high‐performance fullerene‐free OSCs based on a combination of a medium‐bandgap polymer donor (FTAZ) and a narrow‐bandgap nonfullerene acceptor (IDIC), which exhibit complementary absorption, matched energy levels, and blend with pure phases on the exciton diffusion length scale, are reported. The single‐junction OSCs based on the FTAZ:IDIC blend exhibit power conversion efficiencies up to 12.5% with a certified value of 12.14%. Transient absorption spectroscopy reveals that exciting either the donor or the acceptor component efficiently generates mobile charges, which do not suffer from recombination to triplet states. Balancing photocurrent generation between the donor and nonfullerene acceptor removes undesirable constraints on the donor imposed by fullerene derivatives, opening a new avenue toward even higher efficiency for OSCs.     

Infrared Quantum Dots

Colloidal nanocrystals are quantum‐size‐effect tunable; offer an abundance of available surface area for electronic and chemical interactions; and are processible from organic or aqueous solution onto substrates rigid or flexible, smooth or rough, flat or curved, inorganic or organic (including biological), crystalline or amorphous, conducting, semiconducting, or insulating. With the benefit of over a decade's progress in visible‐light‐emitting colloidal‐quantum‐dot synthesis, physical chemistry, and devices, significant progress has recently been made in infrared‐active colloidal quantum dots and devices. This progress report summarizes the state‐of‐the‐art in infrared colloidal quantum dots, with an emphasis on applications and devices. The applications of interest surveyed include monolithic integration of fiber‐optic and free‐space‐communications photonic components with electronic substrates such as silicon and glass; in‐vivo biological tagging in infrared spectral bands in which living tissue is optically penetrable to a depth of 5–10 cm; solar and thermal photovoltaics for energy conversion; and infrared sensing and imaging based on non‐visible, including thermal, signatures. The synthesis and properties of quantum dots are first reviewed: photoluminescence quantum efficiencies greater than 50 % are achievable in solution, and stable luminescent dots are available in organic and aqueous solvents. Electroluminescent devices based on solution processing have been reported with external quantum efficiencies approaching 1 %. Photoconductive devices have been realized with 3 % internal quantum efficiencies, and a photovoltaic effect was recently observed. Electro‐optic modulation achieved by either field‐ or charge‐induced modification of the rate of optical absorption has been demonstrated based both on interband and intersubband (intraband) transitions. Optical gain from these processible materials with a threshold of 1 mJ cm^–2 and an optical net modal gain coefficient of 260 ± 20 cm^–1 have been reported.     

Integration of Multiple Plasmonic and Co‐Catalyst Nanostructures on TiO2 Nanosheets for Visible‐Near‐Infrared Photocatalytic Hydrogen Evolution

Utilization of visible and near‐infrared light has always been the pursuit of photocatalysis research. In this article, an approach is developed to integrate dual plasmonic nanostructures with TiO₂ semiconductor nanosheets for photocatalytic hydrogen production in visible and near‐infrared spectral regions. Specifically, the Au nanocubes and nanocages used in this work can harvest visible and near‐infrared light, respectively, and generate and inject hot electrons into TiO₂. Meanwhile, Pd nanocubes that can trap the energetic electrons from TiO₂ and efficiently participate in the hydrogen evolution reaction are employed as co‐catalysts for improved catalytic activity. Enabled by this unique integration design, the hydrogen production rate achieved is dramatically higher than those of its counterpart structures. This work represents a step toward the rational design of semiconductor–metal hybrid structures for broad‐spectrum photocatalysis.     

Tunable Resonator‐Upconverted Emission (TRUE) Color Printing and Applications in Optical Security

Lanthanide‐doped nanophosphors are promising in anti‐counterfeiting and security printing applications. These nanophosphors can be incorporated as transparent inks that fluoresce by upconverting near‐infrared illumination into visible light to allow easy verification of documents. However, these inks typically exhibit a single luminescent color, low emission efficiency, and low print resolutions. Tunable resonator‐upconverted emission (TRUE) is achieved by placing upconversion nanoparticles (UCNPs) within plasmonic nanoresonators. A range of TRUE colors are obtained from a single‐UCNP species self‐assembled within size‐tuned gap‐plasmon resonances in Al nanodisk arrays. The luminescence intensities are enhanced by two orders of magnitude through emission and absorption enhancements. The enhanced emissive and plasmonic colors are simultaneously employed to generate TRUE color prints that exhibit one appearance under ambient white light, and a multicolored luminescence appearance that is revealed under near‐infrared excitation. The printed color and luminescent images are of ultrahigh resolutions (≈50 000 dpi), and enable multiple colors from a single excitation source for increased level of security.