Near-infrared Light Absorption Research Articles

A Janus Au-Polymersome Heterostructure with Near-Field Enhancement Effect for Implant-Associated Infection Phototherapy.

Polymer-inorganic hybrid Janus nanoparticles (PI-JNPs) have attracted extensive attention due to their special structures and functions. However, achieving the synergistic enhancement of photochemical activity between polymer and inorganic moieties in PI-JNPs remains challenging. Herein, the construction of a novel Janus Au-porphyrin polymersome (J-AuPPS) heterostructure by a facile one-step photocatalytic synthesis is reported. The near-field enhancement (NFE) effect between porphyrin polymersome (PPS) and Au nanoparticles in J-AuPPS is achieved to enhance its near-infrared (NIR) light absorption and electric/thermal field intensity at their interface, which improves the energy transfer and energetic charge-carrier generation. Therefore, J-AuPPS shows a higher NIR-activated photothermal conversion efficiency (48.4%) and generates more singlet oxygen compared with non-Janus core-particle Au-PPS nanostructure (28.4%). As a result, J-AuPPS exhibits excellent dual-mode (photothermal/photodynamic) antibacterial and anti-biofilm performance, thereby significantly enhancingthe in vivo therapeutic effect in an implant-associated-infection rat model. This work is believed to motivate the rational design of advanced hybrid JNPs with desirable NFE effect and further extend their biological applications.

Controlled Release of DNA Binding Anticancer Drugs from Gold Nanoparticles with Near-Infrared Radiation

Traditional chemotherapies target rapidly developing cells in the human body resulting in harsh side effects including fatigue, immune system suppression, and nausea, among others. Delivery systems to focus the active pharmaceutical ingredients (APIs) to the diseased tissue can diminish the negative side effects while improving treatment outcomes. Gold nanoparticles (AuNP) offer many unique advantages as drug delivery vehicles, including being biologically inert, easily adaptable to various shapes and sizes, able to create a strong Au-thiol bond, and able to generate heat upon the absorption of near-infrared light. To this end, a AuNP delivery vehicle was engineered to load and release two DNA binding anti-cancer drugs, mithramycin and doxorubicin, in a controlled fashion. The drugs were loaded onto the surface of the AuNP with temperature sensitive linkages. The amount of heat generated, and subsequent release of the drugs was controlled by the irradiation time with a near-infrared laser. By modulating the linkage used to load the drugs three different release profiles were able to be achieved, indicating the feasibility of such a system for combinational therapy requiring sequential release of APIs.

In situ facile one-step solvothermal synthesizing hexagonal ammonium tungsten bronze (NH4)0.33WO3 to tap NIR light absorption ability by controlling crystallinity

Tungsten bronze (TB) has potentially high visible light transparency and excellent near-infrared (NIR) shielding ability. To fully dig out the concealed optical properties of TB with specific chemical components, in this work, hexagonal ammonium tungsten bronze (h-ATB) (NH4)0.33WO3 was fabricated by a one-step solvothermal reaction. Through X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet–visible–near infrared (UV–vis–NIR) spectroscopy to characterize h-ATB, which unraveled that controlling crystallinity could adjust the optical property of h-ATB. In particular, when the crystallinity of the h-ATB is over 95%, it exhibits the attractive NIR light shielding capability, which is in line with the predicted optical property via the first principle calculation based on density functional theory (DFT). Given the result, this work can provide a feasible research idea to explore the hidden optical properties of TB.

In-situ growth of amorphous MnO2 on C-decorated Fe-based geopolymer sphere with rich structure defects for efficient solar light-induced photo-thermal-Fenton reaction

• A-MnO 2 /C-FeGS with rich structure defects was constructed as a photo-Fenton catalyst. • Highly stable and reactive A-MnO 2 was fabricated via ion exchange anchoring strategy. • Manganese residue was used as the source of Fe and Si for environmental remediation. • A-MnO 2 and C triggered photo-thermal conversion and lattice oxygen activation. • Photo-thermal synergy promoted photo-Fenton activity for tetracycline degradation. Crystalline MnO 2 exhibits excellent photo-thermal conversion and adjustability of valence states properties, but the weak near-infrared light absorption, poor charge transportation and utilization limit its environmental applications. Herein, a novel Na-doped amorphous MnO 2 /C-decorated Fe-based geopolymer sphere (A-MnO 2 /C-FeGS) with rich structure vacancies was constructed by ion exchange anchoring strategy and used to degrade tetracycline hydrochloride (TC) in solar light-induced photo-thermal-Fenton process. Manganese residue (MR), an industrial solid waste, was used as the source of Fe and Si. A-MnO 2 /C-FeGS exhibited excellent catalytic performance with TC removal of 98.2% within 30 min, being about 4.5 and 3.3 times faster than crystalline MnO 2 and C-FeGS, respectively. The improved photocatalytic activity was attributed to that rich oxygen vacancies could provide more catalytic active sites and accelerate Fe 3+ /Fe 2+ and Mn 4+ /(Mn 2+ +Mn 3+ ) conversion for more ·OH generation. Moreover, Na-doped amorphous MnO 2 and C decoration synergistically contributed to high photo-thermal conversion rate, which could in-situ heat the catalyst and induce the activation of H 2 O 2 . This promoted the activation of the surface lattice oxygen and accelerated the secondary transition and utilization of the thermal electrons captured by the defect sites. This work provides a novel strategy for the development of highly reactive catalysts and valorization of MR in the field of environmental remediation.

Surface Normals and Shape From Water.

In this paper, we introduce a novel method for reconstructing surface normals and depth of dynamic objects in water. Past shape recovery methods have leveraged various visual cues for estimating shape (e.g., depth) or surface normals. Methods that estimate both compute one from the other. We show that these two geometric surface properties can be simultaneously recovered for each pixel when the object is observed underwater. Our key idea is to leverage multi-wavelength near-infrared light absorption along different underwater light paths in conjunction with surface shading. Our method can handle both Lambertian and non-Lambertian surfaces. We derive a principled theory for this surface normals and shape from water method and a practical calibration method for determining its imaging parameters values. By construction, the method can be implemented as a one-shot imaging system. We prototype both an off-line and a video-rate imaging system and demonstrate the effectiveness of the method on a number of real-world static and dynamic objects. The results show that the method can recover intricate surface features that are otherwise inaccessible.

Upconversion rare Earths nanomaterials applied to photodynamic therapy and bioimaging.

Light-based therapies and diagnoses including photodynamic therapy (PDT) have been used in many fields of medicine, including the treatment of non-oncological diseases and many types of cancer. PDT require a light source and a light-sensitive compound, called photosensitizer (PS), to detect and destroy cancer cells. After absorption of the photon, PS molecule gets excited from its singlet ground state to a higher electronically excited state which, among several photophysical processes, can emit light (fluorescence) and/or generate reactive oxygen species (ROS). Moreover, the biological responses are activated only in specific areas of the tissue that have been submitted to exposure to light. The success of the PDT depends on many parameters, such as deep light penetration on tissue, higher PS uptake by undesired cells as well as its photophysical and photochemical characteristics. One of the challenges of PDT is the depth of penetration of light into biological tissues. Because photon absorption and scattering occur simultaneously, these processes depend directly on the light wavelength. Using PS that absorbs photons on "optical transparency windows" of biological tissues promises deeper penetration and less attenuation during the irradiation process. The traditional PS normally is excited by a higher energy photon (UV-Vis light) which has become the Achilles' heel in photodiagnosis and phototreatment of deep-seated tumors below the skin. Thus, the need to have an effective upconverter sensitizer agent is the property in which it absorbs light in the near-infrared (NIR) region and emits in the visible and NIR spectral regions. The red emission can contribute to the therapy and the green and NIR emission to obtain the image, for example. The absorption of NIR light by the material is very interesting because it allows greater penetration depth for in vivo bioimaging and can efficiently suppress autofluorescence and light scattering. Consequently, the penetration of NIR radiation is greater, activating the biophotoluminescent material within the cell. Thus, materials containing Rare Earth (RE) elements have a great advantage for these applications due to their attractive optical and physicochemical properties, such as several possibilities of excitation wavelengths - from UV to NIR, strong photoluminescence emissions, relatively long luminescence decay lifetimes (µs to ms), and high sensitivity and easy preparation. In resume, the relentless search for new systems continues. The contribution and understanding of the mechanisms of the various physicochemical properties presented by this system is critical to finding a suitable system for cancer treatment via PDT.

Near-infrared photoactive Ag-Zn-Ga-S-Se quantum dots for high-performance quantum dot-sensitized solar cells.

The high light-harvesting ability of quantum dots (QDs) plays an eminent role in the performance of solar cells. In this study, we synthesized Ag-Zn-Ga-S-Se-based alloyed QDs by colloidal hot injection and characterized them. The X-ray photoelectron spectrum analysis confirms the +1, +2, +3, -2, and -2 oxidation states of, respectively, Ag, Zn, Ga, S, and Se in the QDs, and the energy-dispersive X-ray spectrum analysis confirms the 1:1:1:1.5:1.5 stoichiometric ratio of, respectively, Ag, Zn, Ga, S, and Se. These two results indicate the formation of I-II-III-VI3-type alloyed crystals (AgZnGaS1.5Se1.5 nanocrystals). TEM image analysis reveals the QD nature of the synthesized Ag-Zn-Ga-S-Se nanocrystals. The X-ray diffraction pattern confirms the hexagonal structure. Due to the near-infrared light absorption capability, the synthesized QDs were used as the sensitizer to fabricate QDSCs. The fabricated QDSCs were characterized by using electrochemical impedance spectroscopy and photovoltaic performance studies. The fabricated QDSC have superior electrochemical activity with a photoconversion efficiency of 4.91%.

Preparation of UV-Curable Nano-WO3Coating and Its Infrared Shielding Properties.

Nano-WO3 particles are expected to find use in new shielding materials because of their significant absorption of near-infrared light in the 1400-1600 nm and 1900-2200 nm bands and high transmittance of visible light. In this study, WO3 was ground and dispersed using high-energy ball-milling to prepare a nano-WO3 dispersion using BYK331 as the dispersant and ethanol as the solvent. The prepared nano-WO3 dispersion was added to a photo-curing system and cured using UV irradiation to form films. The cured films were characterized using FT-IR, SEM, XRD, and TGA. The results showed that the nano-WO3 powder was evenly dispersed in the coating. The infrared blocking rate of the film continuously improved and the visible light transmission rate continuously decreased with increasing amounts of nano-WO3.For the film containing 6 wt%nano-WO3, the infrared blocking rate of the coating is 90%, the visible light transmittance is 70%, the hardness of the coating is 3B, and the adhesion is 3H. The thermal stability of the coating is also improved.

Near Infrared Illumination Optimization for Vein Detection: Hardware and Software Approaches

Venepuncture is one of the most crucial processes in many medical procedures. However, finding a real-time and vibrant visualization of the vein structures faces many difficulties. Several devices were introduced to solve this problem, yet, these devices shared common drawbacks, primarily when visualizing deep veins or veins in a thicker tissue of the human body. This study proposes a novel method for visualizing vein structures using a near-infrared (NIR) imaging technique enhanced with Hessian ridge detection. Several factors, including the wavelength of NIR light, square LED and ring LED arrangement and the effect of the diffuser and number of LEDs, were evaluated in the study. This study improves the overall quality of the acquired vein images and highlights the vein-morphological structure through image processing techniques. The study’s main aim is to achieve the highest number of visible veins. Based on the optical window, the maximum absorption range in the NIR spectrum was found from 700 to 950 nm. The NIR light absorption of human deoxygenated blood in the vein was highest at 850 nm peak of wavelength. The image processing further enhances the vein image by highlighting the extracted vein. The study also suggests that the square LED arrangements of NIR illumination are much more robust than the ring LED arrangement in ensuring excellent light penetration. The light diffuser further adds promising effects to the NIR illumination process. In terms of the square LED arrangement, increasing the square LED for enlarging the illumination area did not show any degradation effects in the visualization process. Overall, this paper presents an integrated hardware and software solution for the NIR image acquisition of a vein visualization system to cope with the image visualization of the vein for a thicker part of the human tissue, particularly on the arm and palm area.

Broadband and large-depth terahertz modulation by self-assembly monolayer silver nanoparticle arrays

Broadband and large-depth THz modulation are crucially important for building next-generation THz devices in THz communication systems. Here, we present a broadband and large-depth THz modulator based on silicon/self-assembled silver nanoparticle (SAM AgNP) arrays, which exhibits a broadband modulation within the frequency range of 0.2–2.0 THz and a large modulation depth of ∼91.2% under a moderate near-infrared (NIR) light intensity of 1.77 W cm−2. For a modulation mechanism, the plasmon-enhanced NIR light absorption of SAM AgNP arrays shows a key role in increasing the photoconductivity of the device under NIR light irradiation. The experimental results are verified well by the numerical simulation. The proposed device can significantly improve the overall performance of THz systems, and opens the opportunity for designing novel nanoparticle-based THz devices.

A novel strategy to extend near-infrared light harvest of graphene for solar vapor generation and high-efficiency oil-water separation

Due to the feature of zero bandgap, graphene has presented a rapid and broadband photothermal responsibility. However, the near-infrared light absorption of graphene is relatively low, which is unfavourable for the full utilization of solar energy. Therefore, in our work, flower-like MoS2 nanostructure was used to promote the optical absorption of graphene. Further, combining with the porous skeleton of sugarcane residues and the simplified hydrophobic treatment method, a novel water treatment material (GNS@MoS2-SR) is successfully prepared. Recently, solar-assisted oily water treatment and solar steam generation were widely proposed to relieve the shortage of clean water. In the absorption test, it is confirmed that GNS@MoS2-SR can absorb 8.02–16.8 g/g oils from oil-water mixture and presents high stability during recycle. Moreover, the great hydrophobicity and photothermal conversion effect helps GNS@MoS2-SR to evaporate ∼1.778 kg/m2 water in 1 h, under one solar illumination (1 kW/m2). Besides, the optimized hydrophobicity of GNS@MoS2-SR effectively suppressed the salt precipitation and prevented the decline of spectrum absorption. The multifunctional water treatment material we designed integrates the respective advantages of graphene and MoS2, presents a significant potential in relieving water stress.

Upconverting nanoparticle-containing erythrocyte-sized hemoglobin microgels that generate heat, oxygen and reactive oxygen species for suppressing hypoxic tumors.

Inspired by erythrocytes that contain oxygen-carrying hemoglobin (Hb) and that exhibit photo-driven activity, we introduce homogenous-sized erythrocyte-like Hb microgel (μGel) systems (5–6 μm) that can (i) emit heat, (ii) supply oxygen, and (iii) generate reactive oxygen species (ROS; 1O2) in response to near-infrared (NIR) laser irradiation. Hb μGels consist of Hb, bovine serum albumin (BSA), chlorin e6 (Ce6) and erbium@lutetium upconverting nanoparticles (UCNPs; ∼35 nm) that effectively convert 808 nm NIR light to 660 nm visible light. These Hb μGels are capable of releasing oxygen to help generate sufficient reactive oxygen species (1O2) from UCNPs/Ce6 under severely hypoxic condition upon NIR stimulation for efficient photodynamic activity. Moreover, the Hb μGels emit heat and increase surface temperature due to NIR light absorption by heme (iron protoporphyrin IX) and display photothermal activity. By changing the Hb/UCNP/Ce6 ratio and controlling the amount of NIR laser irradiation, it is possible to formulate bespoke Hb μGels with either photothermal or photodynamic activity or both in the context of combined therapeutic effect. These Hb μGels effectively suppress highly hypoxic 4T1 cell spheroid growth and xenograft mice tumors in vivo.

Photovoltaic properties and enhancement in near-infrared light absorption capabilities of acceptor materials for organic solar cell applications: A quantum chemical perspective via DFT

More than 22% power conversion efficiency (PCE) of organic solar cells (OSCs) has been reported with efficient narrow bandgap acceptor materials as the active layers. And end-capped modifications of such acceptor materials are an efficient approach for designing highly stable and efficient materials for organic solar cell applications. In this study, four new molecules (TOS1 to TOS4) are designed for the active layer of organic solar cells. Density functional theory and time-dependent functional theory have been employed for the computation of various geometric, photovoltaic, optoelectronic properties of newly designed molecules. Different analyses like frontier molecular orbitals, transition density matrix, open-circuit voltage, absorption maxima, excitation and binding energies have been performed and examined with great care. Further, reorganization energy of hole and electron of novel designed molecules has been calculated and results suggested that designed systems are effective contributors for future development of organic solar cells. Overall, the outcomes of this study urge the experimentalists for the future development of highly stable and near-infrared absorbing organic solar cells.

Ultra-broadband and completely modulated absorption enhancement of monolayer graphene in a near-infrared region.

Achieving ultra-broadband and completely modulated absorption enhancement of monolayer graphene in near-infrared region is practically important to design graphene-based optoelectronic devices, however, which remains a challenge. In this work, by spectrally designing multiple magnetic plasmon resonance modes in metamaterials to be adjacent to each other, near-infrared light absorption in monolayer graphene is greatly improved to have an averaged absorption efficiency exceeding 50% in a very broad absorption bandwidth of about 800 nm. Moreover, by exerting an external bias voltage on graphene to change Fermi energy of graphene, the ultra-broadband absorption enhancement of monolayer graphene exhibits an excellent tunability, which has a nearly 100% modulation depth and an electrical switching property. This work is promising for applications in near-infrared photodetectors, amplitude modulators of electromagnetic waves, etc.

Enhancing Triplet-Triplet Annihilation Upconversion: From Molecular Design to Present Applications.

Photon upconversion, the process of converting low-energy photons into high-energy ones, has been widely applied for solar energy conversion, photoredox catalysis, and various biological applications such as background-free bioimaging, cancer therapy, and optogenetics. Upconversion materials that are based on triplet-triplet annihilation (TTA) are of particular interest due to their low excitation power requirements (e.g., ambient sunlight) and easily tunable excitation and emission wavelengths. Despite advances that have been made with respect to TTA upconversion (TTA-UC) in the past decade, several challenges remain for near-infrared light-activatable triplet-triplet annihilation upconversion (NIR TTA-UC). These challenges include low upconversion quantum yield, small anti-Stokes shift, and incompatibility with oxygen, the latter of which seriously limits the practical applications of NIR TTA-UC.This Account will summarize the recent research endeavors to address the above-mentioned challenges and the recent new applications. The first part of this Account highlights recent strategies of molecular design to modulate the excited states of photosensitizers and annihilators, two key factors to determine TTA-UC performance. Novel molecular engineering strategies such as the resonance energy transfer method, dimerization of dye units, and the helix twist molecular structure have been proposed to tune the excited states of photosensitizers. The obtained photosensitizers exhibited enhanced absorption of deep tissue penetrable near-infrared (NIR) light, produced a triplet excited state with elevated energy level and prolonged lifetime, and promoted intersystem crossing, leading to an upgraded TTA-UC system with significantly expanded anti-Stokes shift. With respect to the annihilator, the perylene derivatives were systematically explored, and their attached aromatic groups were found to be the key to adjusting the energy levels of both the triplet and singlet excited states. The resultant optimal TTA-UC system exhibits the highest recorded efficiency among NIR TTA-UC systems.Moreover, to resolve the oxygen-induced TTA-UC quenching, enzymatic reactions were recently introduced. More specifically, the glucose oxidase-catalyzed glucose oxidation reaction showed the ability to rapidly consume oxygen to turn on the TTA-UC luminescence in an aqueous solution. The resultant TTA-UC nanoparticle was able to detect glucose and an enzyme related to glucose metabolism in a highly specific, sensitive, and background-free manner. Further, the upconverted singlet excited state of the annihilator was directly utilized as the catalyst or the excited substrate. For example, the modification of annihilators and drug molecules with photolabile linkages can realize the long wavelength light-induced photolysis. Compared to direct short-wavelength-driven photolysis, this sensitized TTA photolysis (TTAP) exhibits superior reaction yield and lower photodamage, which are important in the release of drugs for tumor treatment in vivo. Moreover, the improved upconversion efficiency can enable the successful coupling of NIR TTA-UC with a visible light absorbing photocatalyst for NIR-driven photoredox catalysis. Compared to direct visible-light photocatalysis, TTA-UC mediated NIR photoredox catalysis showed superior product yield especially in large scale reaction systems owing to the deep penetration power of NIR light. More interestingly, among a few promising technology applications, three-dimensional (3D) printing based on photopolymerization can operate with faster speed and energy-input several orders of magnitude lower when the two-photon polymerization is replaced with TTA-UC mediated polymerization. We believe this Account will spur interest in the further development and application of TTA-UC in the areas of energy, chemistry, material science, and biology.

Low-voltage-modulated perovskite/organic dual-band photodetectors for visible and near-infrared imaging

Visible and near-infrared (NIR) light dual-band photodetectors (PDs) have potential applications in signal detection, bioimaging, optical communications and safety monitoring. Herein, we report an ultrafast perovskite/organic heterojunction dual-mode PD with a voltage-modulated photoresponse range in visible and NIR spectra. The PD, comprising a perovskite layer to absorb visible light (500–810 nm) and an organic bulk heterojunction layer for NIR light absorption (810–950 nm), exhibited a switchable spectral response in the visible or NIR bands. The voltage-modulated visible and NIR photoresponses of the PD were attributable to controlled charge photogeneration in perovskite and organic blend thin films under different bias polarities. The device exhibited peak responsivities of 93.5 and 102.2 mA/W in the visible and NIR bands, respectively; a high detectivity of 4.3 × 109 Jones (at forward bias of 0.7 V and incident 625 nm light) and 1.6 × 1012 Jones (at reverse bias of –1.5 V and incident 900 nm light); a fast microsecond response time; and a wide dynamic range (>120 dB) both in the visible mode and NIR mode. Also, this voltage-modulated dual-band PD shows promising applications in visible light and NIR imaging, which is proven by demonstrating a PD array with 25 pixels (5 × 5).

NIR‐triggered Tandem Photothermal and Photochemical Cancer Therapy Based on Nanoscale MOFs under Hypoxic Conditions

AbstractDue to the limited penetration depth of visible light and insufficient oxygen supply in hypoxic tumor tissues, the development of near‐infrared (NIR) triggered and oxygen‐independent photodynamic therapy (PDT) to generate active radicals is necessary for cancer treatment. Herein, we developed a NIR‐triggered photothermal therapy (PTT) and oxygen‐independent PDT system based on metal‐organic frameworks (MOFs), which integrated indocyanine green (ICG) and 2,2’‐azobis[2‐(2‐imidazolin‐2‐yl)propane] dihydrochloride (AIPH) as NIR‐triggered photothermal units and temperature‐sensitive free radical initiator into ZIF‐8, respectively. AIPH was introduced into ZIF‐8 via a one‐pot strategy with high loading capacity (125 mg g−1). Through the irradiation of 808 nm laser, the ICG units could efficiently absorb NIR light to rapidly raise the local temperature to 44 °C within 3 minutes. Meanwhile, the local high temperature further induced the AIPH to continuously generate toxic alkyl radicals (R−C⋅). The combination of PTT and free radical therapy is significantly better than the single treatment mode. More importantly, the NIR‐triggered synergistic therapy could induce extensive apoptosis of cancer cells in hypoxic conditions, which sheds new light on the development of MOFs‐based photochemical therapy platform in the actual tumor microenvironment.

The principles, design and applications of fused-ring electron acceptors.

Fused-ring electron acceptors (FREAs) have a donor-acceptor-donor structure comprising an electron-donating fused-ring core, electron-accepting end groups, π-bridges and side chains. FREAs possess beneficial features, such as feasibility to tailor their structures, high property tunability, strong visible and near-infrared light absorption and excellent n-type semiconducting characteristics. FREAs have initiated a revolution to the field of organic solar cells in recent years. FREA-based organic solar cells have achieved unprecedented efficiencies, over 20%, which breaks the theoretical efficiency limit of traditional fullerene acceptors (~13%), and boast potential operational lifetimes approaching 10 years. Based on the original studies of FREAs, a variety of new structures, mechanisms and applications have flourished. In this Review, we introduce the fundamental principles of FREAs, including their structures and inherent electronic and physical properties. Next, we discuss the way in which the properties of FREAs can be modulated through variations to the electronic structure or molecular packing. We then present the current applications and consider the future areas that may benefit from developments in FREAs. Finally, we conclude with the position of FREA chemistry, reflecting on the challenges and opportunities that may arise in the future of this burgeoning field.

Fabrication and optical performance research of VO2/SiO2/VO2 composite spherical structure films

Vanadium dioxide ( V O 2 ) is an ideal thermochromic smart window material for its infrared optical properties accompanied by reversible semiconductor-to-metal phase transition. However, it is still faced with insufficient solar energy modulation efficiency and low luminous transmittance. In order to further improve the thermochromic performance of V O 2 thin film, we proposed a V O 2 / S i O 2 / V O 2 composite spherical structure film composed of a V O 2 / S i O 2 microsphere antireflection structure and V O 2 single-layer film structure. This composite spherical structure film can form a Fabry–Perot cavity-like structure when V O 2 changes to a metal state at high temperature, which can enhance the absorption of near-infrared light. The solar energy modulation efficiency and visible light transmittance were improved simultaneously compared to a single-layer film microsphere structure with the same V O 2 thickness. The solar energy modulation efficiency was improved from 3.11% to 7.65% by increasing the difference in transmittance between the semiconductor phase and the metal phase, and the luminous transmittance was enhanced from 51.53% to 57.23% at the optimized top thickness of 25 nm and bottom thickness of 54 nm. This optical study of composite structure film will lay a foundation for the application of V O 2 film in thermochromic smart windows.

Broadband, wide-incident-angle, and polarization-insensitive high-efficiency absorption of monolayer graphene with nearly 100% modulation depth at communication wavelength

We theoretically study how to greatly improve the near-infrared light absorption of monolayer graphene through the excitation of magnetic resonance in metamaterials. The absorption maximum of monolayer graphene is able to reach up to about 77% at the communication wavelength of 1550 nm. The conventionally defined absorption bandwidth, i.e., the full width at half maximum (FWHM), is nearly 160 nm. Thanks to the localization nature of magnetic resonance, the broadband high-efficiency absorption of monolayer graphene is insensitive to the incident angle and the light polarization. The absorption maximum, the absorption bandwidth, and the resonance position all have almost no change, when the incident angle is increased to even 60 degrees for both p and s polarizations. By applying an external bias voltage to change Fermi energy, the absorption in graphene can be completely modulated, with a nearly 100% modulation depth. Furthermore, the graphene absorption has an abrupt and large change around the interband transition, which exhibits an electrical switching property. Our work may find potential applications in graphene-based optoelectronic devices such as photodetector and modulator.