Highly Sensitive Mechanoresponsive Smart Windows Driven by Shear Strain

Advanced optical materials with rational designs and tunable light transmission have been drawing increasing interest due to their great potential in energy-efficient buildings and on-demand optical devices. Mechanoresponsive smart windows (SWs) can modulate light transmittance by mechanical actuation, showing high energy efficiency, low cost, and chemical stability. However, current research mainly focuses on tensile strain-responsive SWs that typically require a large strain to achieve optical transparency switching-which causes great inconvenience to practical application and fatigue damage to matrix materials. Herein, a novel shear-responsive SW with high strain sensitivity is fabricated by vertically fixing a Fe₃O₄@SiO₂ nanochains (NCs) array in an elastic polyacrylamide matrix. The flexible SW exhibits optically transparent with all NCs standing vertically to the SW surface at initial relaxation state, which enables a good shielding effect, with NCs tilting along the shearing direction as the strain applied. Critically, a rather small shear displacement (1.5 mm) applied on the surface of SW gives rise to tunable optical states varying from the transparency state of 65% transmittance to the opaque state of 10%. The as-prepared SW with novel tuning modulation, high shear strain sensitivity, and optical angle-dependence holds promising potential in smart windows, optical switches, anti-voyeurism, and etc.     

Size‐Controlled Synthesis of Cu2‐xE (E = S,Se) Nanocrystals with Strong Tunable Near‐Infrared Localized Surface Plasmon Resonance and High Conductivity in Thin Films

A facile method for preparing highly self‐doped Cu_2‐xE (E = S, Se) nanocrystals (NCs) with controlled size in the range of 2.8–13.5 nm and 7.2–16.5 nm, for Cu_2‐xS and Cu_2‐xSe, respectively, is demonstrated. Strong near‐infrared localized surface plasmon resonance absorption is observed in the NCs, indicating that the as‐prepared particles are heavily p‐doped. The NIR plasmonic absorption is tuned by varying the amount of oleic acid used in synthesis. This effect is attributed to a reduction in the number of free carriers through surface interaction of the deprotonated carboxyl functional group of oleic acid with the NCs. This approach provides a new pathway to control both the size and the cationic deficiency of Cu_2‐xSe and Cu_2‐xS NCs. The high electrical conductivity exhibited by these NPs in metal‐semiconductor‐metal thin film devices shows promise for applications in printable field‐effect transistors and microelectronic devices.     

Laser Interference Lithography for the Nanofabrication of Stimuli‐Responsive Bragg Stacks

Dynamic structural coloration in Tmesisternus isabellae beetle elytra is a unique example of Bragg stack‐based wavelength tuning in response to external stimuli. The underlying principles could guide the design of quantitative optical stimuli‐responsive polymers. Existing nanofabrication techniques to create such materials are costly, time‐consuming, and require high expertise. This study reports a nanofabrication method to produce slanted Bragg stack structures in poly(acrylamide‐co‐poly(ethylene glycol) diacrylate) hydrogel films by combining laser interference lithography and silver halide chemistry in a cost‐effective and rapid process (≈10 min). The Bragg stacks consist of silver bromide nanocrystal multilayers having a lattice spacing of ≈200 nm. Upon broadband light illumination, the Bragg stacks diffract a narrow‐band peak at 520 nm at ≈10° with respect to the normal incidence. The lattice spacing of the hydrogel films can be modulated by external stimuli to shift the Bragg peak for dynamic quantitative measurements. To demonstrate the utility of this method, the Bragg stacks are functionalized with phenylboronic acid molecules. Bragg peak shift analysis allows reversible glucose sensing within a physiological dynamic range (0.0–20.0 mmol L^?1) having a sensitivity of 0.2 mmol L^?1. The developed Bragg stacks may have application in portable, wearable, and implantable real‐time medical diagnostics at point‐of‐care settings.     

Few Layered N,P Dual‐Doped Carbon‐Encapsulated Ultrafine MoP Nanocrystal/MoP Cluster Hybrids on Carbon Cloth: An Ultrahigh Active and Durable 3D Self‐Supported Integrated Electrode for Hydrogen Evolution Reaction in a Wide pH Range

Development of highly active and stable electrocatalysts is a key to realize efficient hydrogen evolution through water electrolysis. Here, the development of a 3D self‐supported integrated electrode constituting few layered N, P dual‐doped carbon‐encapsulated ultrafine MoP nanocrystal/MoP cluster hybrids on carbon cloth (FLNPC@MoP‐NC/MoP‐C/CC) is demonstrated. Benefiting from novel structural features including fully open and accessible nanoporosity, ultrasmall size of MoP‐NCs on MoP‐Cs as well as strong synergistic effects of N, P dual‐doped carbon layers with MoP‐NCs, the FLNPC@MoP‐NC/MoP‐C/CC as a 3D self‐supported binder‐free integrated electrode exhibits extraordinary catalytic activity for the hydrogen evolution reaction (HER) with extremely low overpotentials at all pH values ( j = 10 mA cm^?2 at η = 74, 106, and 69 mV in 0.5 m H₂SO₄, 1.0 m PBS, and 1.0 m KOH electrolytes, respectively). To the best of our knowledge, the ultrahigh electrocatalytic performance represents one of the best MoP‐based HER electrocatalysts reported so far. Additionally, few layered N, P dual‐doped carbon can effectively prevent MoP‐NC/MoP‐C from corrosion, making the FLNPC@MoP‐NC/MoP‐C/CC exhibit nearly unfading stability after 50 h testing in acidic, neutral, and alkaline media, which shows great promise for electrocatalytic water splitting application.     

High Hole Mobility in Long‐Range Ordered 2D Lead Sulfide Nanocrystal Monolayer Films

Coupling between colloidal semiconductor nanocrystals (NCs) with long‐range order is critical for designing advanced nanostructures with controlled energy flow and charge carrier transport. Herein, under the premise of keeping long‐range order in 2D NC monolayer, its native organic ligands are exchanged with halogen ions in situ at the liquid–air interface to enhance the coupling between NCs. Further treatments on the films with dimethyl sulfoxide, methanol, or their mixture effectively improve carrier mobility of the devices. The devices show repeatable enhanced p‐type transport behavior with hole mobility of up to 0.224 ± 0.069 cm² V^?1 s^?1, the highest value reported for lead sulfide NC solids without annealing treatment. Thanks to accurate control over the surface of NCs as well as the structure of NC film, the ordered NC monolayer film of high hole mobility suggests great potentials for making reliable high performance devices.     

Fabrication of Butt‐Coupled SGDBR Laser Integrated with Semiconductor Optical Amplifier Having a Lateral Tapered Waveguide

We have demonstrated a high‐power widely tunable sampled grating distributed Bragg reflector (SGDBR) laser integrated monolithically with a semiconductor optical amplifier (SOA) having a lateral tapered waveguide, which is the first to emit a fiber‐coupled output power of more than 10 dBm using a planar buried heterostructure (PBH). The output facet reflectivity of the integrated SOA using a lateral tapered waveguide and two‐layer AR coating of TiO₂ and SiO₂ was lower than 3 × 10^?4 over a wide bandwidth of 85 nm. The spectra of 40 channels spaced by 50 GHz within the tuning range of 33 nm were obtained by a precise control of SG and phase control currents. A side‐mode suppression ratio of more than 35 dB was obtained in the whole tuning range. Fiber‐coupled output power of more than 11 dBm and an output power variation of less than 1 dB were obtained for the whole tuning range.     

Evidence for the Band‐Edge Exciton of CuInS2 Nanocrystals Enables Record Efficient Large‐Area Luminescent Solar Concentrators

Ternary I‐III‐VI₂ nanocrystals (NCs), such as CuInS₂, are receiving attention as heavy‐metals‐free materials for solar cells, luminescent solar concentrators (LSCs), LEDs, and bio‐imaging. The origin of the optical properties of CuInS₂ NCs are however not fully understood. A recent theoretical model suggests that their characteristic Stokes‐shifted and long‐lived luminescence arises from the structure of the valence band (VB) and predicts distinctive optical behaviours in defect‐free NCs: the quadratic dependence of the radiative decay rate and the Stokes shift on the NC radius. If confirmed, this would have crucial implications for LSCs as the solar spectral coverage ensured by low‐bandgap NCs would be accompanied by increased re‐absorption losses. Here, by studying stoichiometric CuInS₂ NCs, it is revealed for the first time the spectroscopic signatures predicted for the free band‐edge exciton, thus supporting the VB‐structure model. At very low temperatures, the NCs also show dark‐state emission likely originating from enhanced electron‐hole spin interaction. The impact of the observed optical behaviours on LSCs is evaluated by Monte Carlo ray‐tracing simulations. Based on the emerging device design guidelines, optical‐grade large‐area (30×30 cm²) LSCs with optical power efficiency (OPE) as high as 6.8% are fabricated, corresponding to the highest value reported to date for large‐area devices.     

Characteristics of tunable micro-cavity based on one-dimensional photonic crystal doping KTP as defect layer

The tunable micro-cavity based on one-dimensional(1D) photonic crystal doped by KTP is designed.The optical transmission properties in the doped one-dimensional defect photonic crystals are analyzed using transfer matrix method(TMM).According to the electro-optic effect,the refractive index ellipsoid equation is established with the applied alternating current at both coordinate axes,and the characteristics of temperature-optics and modulation are studied.Numerical calculations and experimental results show that the tuning range is ～40 nm.     

Zero‐Dimensional Perovskite Nanocrystals for Efficient Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) are able to efficiently harvest solar energy through large‐area photovoltaic windows, where fluorophores are delicately embedded. Among various types of fluorophores, all‐inorganic perovskite nanocrystals (NCs) are emerging candidates as absorbers/emitters in LSCs due to their size/composition/dimensionality tunable optical properties and high photoluminescence quantum yield (PL QY). However, due to the large overlap between absorption and emission spectra, it is still challenging to fabricate high‐efficiency LSCs. Intriguingly, zero‐dimensional (0D) perovskites provide a number of features that meet the requirements for a potential LSC absorber, including i) small absorption/emission spectral overlap (Stokes shift up to 1.5 eV); ii) high PL QY (>95% for bulk crystal); iii) robust stability as a result of its large exciton binding energy; and iv) ease of synthesis. In this work, as a proof‐of‐concept experiment, Cs₄PbBr₆ perovskite NCs are used to fabricate semi‐transparent large‐area LSCs. Cs₄PbBr₆ perovskite film exhibits green emission with a high PL QY of ≈58% and a small absorption/emission spectral overlap. The optimized LSCs exhibit an external optical efficiency of as high as 2.4% and a power conversion efficiency of 1.8% (100 cm²). These results indicate that 0D perovskite NCs are excellent candidates for high‐efficiency LSCs compared to 3D perovskite NCs.     

Promoting Active Sites in Core–Shell Nanowire Array as Mott–Schottky Electrocatalysts for Efficient and Stable Overall Water Splitting

Developing earth‐abundant, active, and robust electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) remains a vital challenge for efficient conversion of sustainable energy sources. Herein, metal–semiconductor hybrids are reported with metallic nanoalloys on various defective oxide nanowire arrays (Cu/CuO_x, Co/CoO_x, and CuCo/CuCoO_x) as typical Mott–Schottky electrocatalysts. To build the highway of continuous electron transport between metals and semiconductors, nitrogen‐doped carbon (NC) has been implanted on metal–semiconductor nanowire array as core–shell conductive architecture. As expected, NC/CuCo/CuCoO_x nanowires arrays, as integrated Mott–Schottky electrocatalysts, present an overpotential of 112 mV at 10 mA cm^?2 and a low Tafel slope of 55 mV dec^?1 for HER, simultaneously delivering an overpotential of 190 mV at 10 mA cm^?2 for OER. Most importantly, NC/CuCo/CuCoO_x architectures, as both the anode and the cathode for overall water splitting, exhibit a current density of 10 mA cm^?2 at a cell voltage of 1.53 V with excellent stability due to high conductivity, large active surface area, abundant active sites, and the continuous electron transport from prominent synergetic effect among metal, semiconductor, and nitrogen‐doped carbon. This work represents an avenue to design and develop efficient and stable Mott–Schottky bifunctional electrocatalysts for promising energy conversion.     

Sampled-grating DBR laser-based analog optical transmitters

Sampled-grating distributed Bragg grating (SGDBR) laser-based widely tunable optical transmitters are investigated for application in high-performance analog links. More than 45 nm tuning range, 40 dB sidemode suppression ratio, and peak relative intensity noise below -153 dB/Hz is measured. SGDBR lasers integrated with semiconductor optical amplifiers and electroabsorption modulators (EAMs) are characterized with spurious free dynamic range of 125-127 dB/spl middot/Hz/sup 4/5/ over the wavelength tuning range. It is also shown how the modulation response of the EAM is affected by the optical power to limit the performance of the analog transmitter.     

Highly Emissive and Color‐Tunable CuInS2‐Based Colloidal Semiconductor Nanocrystals: Off‐Stoichiometry Effects and Improved Electroluminescence Performance

The off‐stoichiometry effects and gram‐scale production of luminescent CuInS₂‐based semiconductor nanocrystals, as well as their application in electroluminescence devices are reported. The crystal structures and optical properties of CuInS₂ nanocrystals can be significantly influenced by controlling their [Cu]/[In] molar ratio. A simple model adapted from the bulk materials is proposed to explain their off‐stoichiometry effects. Highly emissive and color‐tunable CuInS₂‐based NCs are prepared by a combination of [Cu]/[In] molar ratio optimization, ZnS shell coating, and CuInS₂–ZnS alloying. The method is simple, hassle‐free, and easily scalable to fabricate tens of grams of nanocrystal powders with photoluminescence quantum yields up to around 65%. Furthermore, the performance of high‐quality CuInS₂‐based NCs in electroluminescence devices is examined. These devices have lower turn‐on voltages of around 5 V, brighter luminance up to approximately 2100 cd m^?2 and improved injection efficiency of around 0.3 lm W^?1 (at 100 cd m^?2) in comparison to recent reports.     

Photon‐Memristive System for Logic Calculation and Nonvolatile Photonic Storage

Memristor‐based architectures have shown great potential for developing future computing systems beyond the era of von Neumann and Moore's law. However, the monotonous electrical input for dynamic resistance regulation limits the developments of memristors. Here, a concept of a photon‐memristive system, which realizes memristance depending on number of photons (optical inputs), is proposed. A detailed theoretical derivation is performed and the memristive characteristics, as stimulated by the optical inputs based on a hybrid system, consisting of a low‐dimension photoelectric semiconductor and a ferroelectric substrate are determined. The photon‐memristive system is also suitable for nonvolatile photonic memory since it possesses three or more‐bit data storage, desirable resistance‐change space, and an ON/OFF ratio of nearly 10⁷. The integrated circuit based on several photon‐memristive systems also realizes available photon‐triggered in‐memory computing. The photon‐memristive system expands the definition of memristors and emerges as a new data storage cell for future photonic neuromorphic computational architectures.     

Triplet Energy Transfer from PbS(Se) Nanocrystals to Rubrene: the Relationship between the Upconversion Quantum Yield and Size

Photon upconversion has attracted enormous attention due to its wide range of applications in biological imaging, photocatalysis, and especially photovoltaics. Here, the effect of quantum confinement on the efficiency of Dexter energy transfer from PbS and PbSe nanocrystals (NCs) to a rubrene acceptor is studied. A series of experiments exploring the relationship between NC size and the upconversion quantum yield (QY) in this hybrid platform show that energy transfer occurs in the Marcus normal regime. By decreasing the NC diameter from 3.5 to 2.9 nm for PbS and from 3.2 to 2.5 nm for PbSe, the relative upconversion QY is enhanced about 700 and 250‐fold respectively. In addition, the dynamic Stern–Volmer constant (K_SV) for the quenching of PbSe NCs by rubrene increases approximately fivefold with a decrease in NC diameter from 3.2 to 2.5 nm to a value of 200 m ^?1. This work shows that high quality, well‐passivated, small NCs are critical for efficient triplet energy transfer to molecular acceptors.     

Continuously tunable photonic microwave true-time delay based on tunable chirped fibre Bragg grating

A simple scheme for the photonic microwave true-time delay with high tunability based on a tunable chirped fibre Bragg grating without centre wavelength shift is experimentally demonstrated. A large dynamic range of true-time delay from 20 to 200 ps was achieved for a microwave signal carried over an optical signal.     

Electrically Sensitive Plasmonic Photonic Crystals for Dynamic Upconversion Manipulation

Local optical field modulation using plasmonic materials or photonic crystals provides a powerful strategy for enhancing upconversion emission of lanthanide-doped upconversion nanocrystals (UCNPs). However, it is restricted to static UC enhancement and the corresponding dynamic modulation of UC is yet to be reported, limiting its practical applications in information devices. Here, a dynamic UC modulation system is reported through electric stimulation by integrating UCNPs with electrically sensitive WO_3−x plasmonic photonic crystals (PPCs). The tunable emission enhancement of UCNPs varying from five to 26 folds is achieved in WO_3−x PPCs/UCNPs hybrids through external electric stimulation within +1.6 and −1.6 V. It stems from the reversible control of the photonic bandgaps and localized surface plasmon resonance of WO_3−x PPCs, ascribed to the variation of refractive index and oxygen vacancy of WO_3−x, induced by the reversible change of atomic ratio of W⁵⁺ to W⁶⁺ under different applied voltages. Moreover, the electrically triggered information encryption devices are developed, employing a programmable logic gate array based on WO_3−x PPCs/UCNPs with the ability to convert information-encrypted electrical signals into visible patterns. These observations offer a new attempt to manipulate the UC and will simulate the new applications in the display and optical storage devices.     

Semiconductor‐Based Photoelectrochemical Water Splitting at the Limit of Very Wide Depletion Region

In semiconductor‐based photoelectrochemical (PEC) water splitting, carrier separation and delivery largely relies on the depletion region formed at the semiconductor/water interface. As a Schottky junction device, the trade‐off between photon collection and minority carrier delivery remains a persistent obstacle for maximizing the performance of a water splitting photoelectrode. Here, it is demonstrated that the PEC water splitting efficiency for an n‐SrTiO₃ (n‐STO) photoanode is improved very significantly despite its weak indirect band gap optical absorption (α < 10⁴ cm^?1), by widening the depletion region through engineering its doping density and profile. Graded doped n‐SrTiO₃ photoanodes are fabricated with their bulk heavily doped with oxygen vacancies but their surface lightly doped over a tunable depth of a few hundred nanometers, through a simple low temperature reoxidation technique. The graded doping profile widens the depletion region to over 500 nm, thus leading to very efficient charge carrier separation and high quantum efficiency (>70%) for the weak indirect transition. This simultaneous optimization of the light absorption, minority carrier (hole) delivery, and majority carrier (electron) transport by means of a graded doping architecture may be useful for other indirect band gap photocatalysts that suffer from a similar problem of weak optical absorption.     

Embedding Perovskite Nanocrystals into a Polymer Matrix for Tunable Luminescence Probes in Cell Imaging

Lead halide perovskite nanocrystals (NCs) with bright luminescence and broad spectral tunability are good candidates as smart probes for bioimaging, but suffer from hydrolysis even when exposed to atmosphere moisture. In this paper, a strategy is demonstrated by embedding CsPbX₃ (X = Cl, Br, I) NCs into microhemispheres (MHSs) of polystyrene matrix to prepare “water‐resistant” NCs@MHSs hybrids as multicolor multiplexed optical coding agents. First, a facile room‐temperature solution self‐assembly approach to highly luminescent colloidal CsPbX₃ NCs is developed by injecting a stock solution of CsX?PbX₂ in N ,N ‐dimethylformamide into dichloromethane. Polyvinyl pyrrolidone (PVP) is chosen as the capping ligand, which is physically adsorbed and wrapped on the surface of perovskite NCs to form a protective layer. The PVP protective layer not only leads to composition‐tunable CsPbX₃ NCs with high quantum yields and narrow emission linewidths of 12–34 nm but also acts as an interfacial layer, making perovskite NCs compatible with polystyrene polymers and facilitating the next step to embed CsPbX₃ NCs into polymer MHSs. CsPbX₃ NCs@MHSs are demonstrated as multicolor luminescence probes in live cells with high stability and nontoxicity. Using ten intensity levels and seven‐color NCs@MHSs that show non‐overlapping spectra, it will be possible to individually tag about ten million cells.     

All‐Dielectric Programmable Huygens' Metasurfaces

Low‐loss nanostructured dielectric metasurfaces have emerged as a breakthrough platform for ultrathin optics and cutting‐edge photonic applications, including beam shaping, focusing, and holography. However, the static nature of their constituent materials has traditionally limited them to fixed functionalities. Tunable all‐dielectric infrared Huygens' metasurfaces consisting of multi‐layer Ge disk meta‐units with strategically incorporated non‐volatile phase change material Ge₃Sb₂Te₆ are introduced. Switching the phase‐change material between its amorphous and crystalline structural state enables nearly full dynamic light phase control with high transmittance in the mid‐IR spectrum. The metasurface is realized experimentally, showing post‐fabrication tuning of the light phase within a range of 81% of the full 2π phase shift. Additionally, the versatility of the tunable Huygen's metasurfaces is demonstrated by optically programming the spatial light phase distribution of the metasurface with single meta‐unit precision and retrieving high‐resolution phase‐encoded images using hyperspectral measurements. The programmable metasurface concept overcomes the static limitations of previous dielectric metasurfaces, paving the way for “universal” metasurfaces and highly efficient, ultracompact active optical elements like tunable lenses, dynamic holograms, and spatial light modulators.     

Core/Shell Perovskite Nanocrystals: Synthesis of Highly Efficient and Environmentally Stable FAPbBr3/CsPbBr3 for LED Applications

Lead halide perovskite nanocrystals (PeNCs) are promising materials for applications in optoelectronics. However, their environmental instability remains to be addressed to enable their advancement into industry. Here the development of a novel synthesis method is reported for monodispersed PeNCs coated with all inorganic shell of cesium lead bromide (CsPbBr₃) grown epitaxially on the surface of formamidinium lead bromide (FAPbBr₃) NCs. The formed FAPbBr₃/CsPbBr₃ NCs have photoluminescence in the visible range 460–560 nm with narrow emission linewidth (20 nm) and high optical quantum yield, photoluminescence quantum yield (PLQY) up to 93%. The core/shell perovskites have enhanced optical stability under ambient conditions (70 d) and under ultraviolet radiation (50 h). The enhanced properties are attributed to overgrowth of FAPbBr₃ with all‐inorganic CsPbBr₃ shell, which acts as a protective layer and enables effective passivation of the surface defects. The use of these green‐emitting core/shell FAPbBr₃/CsPbBr₃ NCs is demonstrated in light‐emitting diodes (LEDs) and significant enhancement of their performance is achieved compared to core only FAPbBr₃‐LEDs. The maximum current efficiency observed in core/shell NC LED is 19.75 cd A^‐1 and the external quantum efficiency of 8.1%, which are approximately four times and approximately eight times higher, respectively, compared to core‐only devices.