Improved electrical ideality and photoresponse in near-infrared phototransistors realized by bulk heterojunction channels

The factors that affect the electrical ideality and photoresponse in near-infrared (NIR) organic phototransistors (OPTs) are still nebulous. Here, simultaneous increase in electrical ideality and NIR response in the OPTs is realized by applying a bulk heterojunction (BHJ) channel. The acceptor in the channel helps to trap the undesirable injected electrons, avoiding the accumulation of the electrons at the active channel/dielectric interface, and thereby improving the hole transporting. Use of a BHJ channel also helps reducing the contact resistance in the OPTs. The electrical stability is then improved with mitigated dependence of charge mobility on gate voltage in the saturation region. The BHJ channel also offers an improved photoresponse through enhanced exciton dissociation, leading to more than one order of magnitude increase in responsivity than that in a control OPT. The results are encouraging, which pave the way for the development of high-performing NIR OPTs.

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The use of BHJ channel in NIR OPTs improves the electrical ideality and photoresponse

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The acceptor traps injected electrons to maintain the efficient hole transport

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The contact resistance in OPTs with BHJ channel is reduced

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The better exciton dissociation in BHJ channel offers improved photoresponse

High-entropy R2O3-Y2O3-TiO2-ZrO2-Al2O3 glasses with ultrahigh hardness, Young's modulus, and indentation fracture toughness

Glasses with high hardness, high Young's modulus, and high fracture toughness become crucial materials which are urgently needed in the protective covers for various electronic displays. Here, a paradigm is presented that the conceptual design of high-entropy materials is adaptable to high performance oxide glasses. We designed the multi-component glass compositions of 18.77R₂O₃-4.83Y₂O₃-28.22TiO₂-8.75ZrO₂-39.43Al₂O₃ (R = La, Sm, Gd) and elaborated successfully the glassy samples through a containerless solidification process. The as-prepared samples demonstrated the outstanding mechanical and optical properties. The measured hardness, Young's modulus, and indentation fracture toughness of the high-entropy (R = Gd) glass are 12.58 GPa, 177.9 GPa, and 1.52 MPa·m^0.5, respectively, in which the hardness and Young's modulus exhibit the highest value among the reported oxide glasses. Structural analysis revealed that the excellent mechanical properties are attributed to the large dissociation energies and the high field strength of Al₂O₃, TiO₂, and ZrO₂ and the complex interaction between atoms caused by high entropy.

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The conceptual design of high-entropy materials is firstly extended to oxide glass

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The as-prepared oxide glass possesses the record hardness and Young's modulus

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The as-prepared oxide glass exhibits excellent indentation fracture toughness

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The distinct mechanical properties relate to componential multiplicity of the glass

Li/Na substitution and Yb3+ co-doping enabling tunable near-infrared emission in LiIn2SbO6:Cr3+ phosphors for light-emitting diodes

Near-infrared (NIR) phosphor-converted light-emitting diode (pc-LED) has great potential in non-invasive detection, while the discovery of tunable broadband NIR phosphor still remains a challenge. Here, we report that Cr³⁺-activated LiIn₂SbO₆ exhibits a broad emission band ranging from 780 to 1400 nm with a full width at half maximum (FWHM) of 225 nm upon 492 nm excitation. The emission peaks are tuned from 970 to 1020 nm together with considerable broadening of FWHM (∼285 nm) via Li/Na substitution. Depending on Yb³⁺ co-doping, a stronger NIR fluorescence peak of Yb³⁺ appears with improved thermal resistance, which is ascribed to efficient energy transfer from Cr³⁺ to Yb³⁺. An NIR pc-LED package has been finally designed and demonstrated a remarkable ability to penetrate pork tissues (∼2 cm) so that the insertion depth of a needle can be observed, indicating that the phosphor can be applied in non-destructive monitoring.

Advances in engineering near-infrared luminescent materials

Near-infrared (NIR) luminescent materials have emerged as a growing field of interest, particularly for imaging and optics applications in biology, chemistry, and physics. However, the development of materials for this and other use cases has been hindered by a range of issues that prevents their widespread use beyond benchtop research. This review explores emerging trends in some of the most promising NIR materials and their applications. In particular, we focus on how a more comprehensive understanding of intrinsic NIR material properties might allow researchers to better leverage these traits for innovative and robust applications in biological and physical sciences.

Hypoxia-activated probe for NIR fluorescence and photoacoustic dual-mode tumor imaging

Construction of tumor microenvironment responsive probe with more than one imaging modality, in particular toward hypoxia of solid tumors, is an appealing yet significantly challenging task. In this work, we designed a hypoxia-activated probe TBTO (Triphenylamine-Benzothiadiazole-Triphenylamine derivative featuring four diethylamino N-Oxide groups) for in vivo imaging. TBTO could undergo bioreduction in a hypoxic microenvironment to yield compound TBT sharing both near-infrared (NIR) aggregation-induced emission and strong twisted intramolecular charge transfer features, which endows the probe with excellent performance in NIR fluorescence and photoacoustic dual-mode tumor imaging. This study offers useful insights into designing a new generation agent for clinical cancer diagnosis.

NIR-quantum dots in biomedical imaging and their future

Fluorescence imaging has gathered interest over the recent years for its real-time response and high sensitivity. Developing probes for this modality has proven to be a challenge. Quantum dots (QDs) are colloidal nanoparticles that possess unique optical and electronic properties due to quantum confinement effects, whose excellent optical properties make them ideal for fluorescence imaging of biological systems. By selectively controlling the synthetic methodologies it is possible to obtain QDs that emit in the first (650-950 nm) and second (1000-1400 nm) near infra-red (NIR) windows, allowing for superior imaging properties. Despite the excellent optical properties and biocompatibility shown by some NIR QDs, there are still some challenges to overcome to enable there use in clinical applications. In this review, we discuss the latest advances in the application of NIR QDs in preclinical settings, together with the synthetic approaches and material developments that make NIR QDs promising for future biomedical applications.

Rare-earth coordination polymers with multimodal luminescence on the nano-, micro-, and milli-second time scales

We present a coordination polymer based on rare-earth metal centers and carboxylated 4,4′-diphenyl-2,2′-bipyridine ligands. We investigate Y³⁺, Lu³⁺, Eu³⁺, and a statistical mixture of Y³⁺ with Eu³⁺ as metal centers. When Y³⁺ or Lu³⁺ is exclusively present in the coordination polymer, biluminescence from the ligand is observed: violet emission from the singlet state (417 nm, 0.9 ns lifetime) and orange emission from the triplet state (585 nm, 76 ms (Y³⁺) and 31 ms (Lu³⁺)). When Eu³⁺ is present in a statistical mixture with Y³⁺, red emission from the Eu³⁺ (611 nm, ∼500μs) is observed in addition to the ligand emissions. We demonstrate that this multi-mode emission is enabled by the immobility of singlet and triplet states on the ligand. Eu³⁺ only receives energy from adjacent ligands. Meanwhile, in the broad inhomogeneous distribution of ligand energies, higher energy states favor singlet emission, whereas faster intersystem crossing in the more stabilized ligands enhances their contribution to triplet emission.

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Coordination polymer exhibts nano-, micro-, and milli-second emission bands.

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Luminescence observed from ligand singlet and triplet states and lanthanide centers.

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Triluminescence is enabled by exciton immobility.

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Intersystem crossing is mediated by ligand environment.

Harvesting triplet excitons for near-infrared electroluminescence via thermally activated delayed fluorescence channel

Near-infrared (NIR) emission is useful for numerous practical applications, such as communication, biomedical sensors, night vision, etc., which encourages researchers to develop materials and devices for the realization of efficient NIR organic light-emitting devices. Recently, the emerging organic thermally activated delayed fluorescence (TADF) emitters have attracted wide attention because of the full utilization of electron-generated excitons, which is crucial for achieving high device efficiency. Up to now, the TADF emitters have shown their potential in the deep red/NIR region. Considering the color purity and efficiency, however, the development of NIR TADF emitters still lags behind RGB TADF emitters, indicating that there is still much room to improve their performance. In this regard, this perspective mainly summarizes the past progress of molecular design on constructing TADF NIR emitters. We hope this perspective could provide a new vista in developing NIR materials and enlighten breakthroughs in both fundamental research and applications.

Designable structural coloration by colloidal particle assembly: from nature to artificial manufacturing

Structural color attracts considerable scientific interests and industrial explorations in various fields for the eco-friendly, fade-resistant, and dynamic advantages. After the long-period evolution, nature has achieved the optimized color structures at various length scales, which has inspired people to learn and replicate them to improve the artificial structure color. In this review, we focus on the design of artificial structural colors based on colloidal particle assembly and summarize the functional bioinspired structure colors. We demonstrate the design principles of biomimetic structural colors via the precise structure engineering and typical bottom-up methods. Some main applications are outlined in the following chapter. Finally, we propose the existing challenges and promising prospects. This review is expected to introduce the recent design strategies about the artificial structure colors and provide the insights for its future development.

Angular-multiplexed multichannel optical vortex arrays generators based on geometric metasurface

Recently, metasurface-based multichannel optical vortex arrays have attracted considerable interests due to its promising applications in high-dimensional information storage and high-secure information encryption. In addition to the well-known wavelength and polarization multiplexing technologies, the diffraction angle of light is an alternative typical physical dimension for multichannel optical vortex arrays. In this paper, based on angular multiplexing, we propose and demonstrate multichannel optical vortex arrays by using ultrathin geometric metasurface. For a circularly polarized incident light, the desired optical vortex arrays are successfully constructed in different diffraction regions. Moreover, the diffraction angle of the optical vortex array can be regulated by changing the illumination angle of incident light. Capitalizing on this advantage, the angular-multiplexed recombination of optical vortex array is further investigated. The combination of the diffraction angle of light and optical vortex array may have significant potential in applications of optical display, free-space optical communication, and optical manipulation.

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Ultra-thin angular-multiplexed multichannel vortex array generators are demonstrated

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Geometric phase is employed to realize the desired phase profiles

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Generation of various multichannel vortex arrays and recombination of vortex array

Near-infrared mechanoluminescence crystals: a review

Due to the in situ, real-time, and non-destructive properties, mechanoluminescence (ML) crystals have been considered as intelligent stress sensors, which demonstrate potential applications such as in inner crack visualization, light source, and ultrasonic powder recording. Thereinto, it is highly expected that near-infrared (NIR) MLs can realize the visualization of inner biological stress because mechanically induced signals from them can penetrate biological tissues. However, such an energy conversion technique fails to work in biomechanical monitoring due to the limited advances of NIR ML materials. Based on those, some research groups have begun to focus on this field and initially realized this idea in vitro while related advances are still at the early stage. To advance this field, it is highly desirable to review recent advances in NIR ML crystals. In this review, to our knowledge, all the NIR ML crystals have been included in two main groups: oxysulfides and oxides. Besides, the present and emerging trends in investigation of such crystals were discussed. In all, the aim is to advance NIR ML crystals to more practical applications, especially for that of biomechanical visualization in vivo.

In situ and tunable structuring of semiconductor-in-glass transparent composite

Semiconductor-in-glass composites are an exciting class of photonic materials for various fundamental applications. The significant challenge is the scalable elaboration of composite with the desirable combination of tunable structure, high semiconductor loading ratio, and excellent transparency. Here we report that the topological engineering strategy via hybridization of the glass network former enables to surmount the aforementioned challenge. It not only facilitates the in situ precipitation of (Ga_2-xAl_x)O₃ domains with continuously tunable composition but also allows to simultaneously refine the grain size and enhance the crystallinity. In addition, the composites exhibit excellent transparency and can host various active dopants. We demonstrate the attractive broadband optical response of the composite and achieve the pulse laser operation in mid-infrared waveband. The findings are expected to provide a fundamental principle of in situ modification in hybrid system for generation of high-performance semiconductor-in-glass composites.

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In situ and tunable structuring of semiconductor-in-glass composites are presented

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The composites can host various active dopants and show broadband optical response

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A pulse laser at 2 μm based on Fe-doped composite is achieved for the first time

Recent Progress on Ultrathin Metalenses for Flat Optics

As technology advances, electrical devices such as smartphones have become more and more compact, leading to a demand for the continuous miniaturization of optical components. Metalenses, ultrathin flat optical elements composed of metasurfaces consisting of arrays of subwavelength optical antennas, provide a method of meeting those requirements. Moreover, metalenses have many other distinctive advantages including aberration correction, active tunability, and semi-transparency, compared to their conventional refractive and diffractive counterparts. Therefore, over the last decade, great effort has been focused on developing metalenses to investigate and broaden the capabilities of metalenses for integration into future applications. Here, we discuss recent progress on metalenses including their basic design principles and notable characteristics such as aberration correction, tunability, and multifunctionality.

Perovskite/CIGS Spectral Splitting Double Junction Solar Cell with 28% Power Conversion Efficiency

The highest theoretical efficiency of double junction solar cells is predicted for architectures with the bottom cell bandgap (E _g ) of approximately 0.9-1.0 eV, which is lower than that of a typical Si cell (1.1 eV). Cu(In,Ga)(Se,S)₂ (CIGS) solar cells exhibit a tunable E _g depending on their elemental composition and depth profile. In this study, various CIGS solar cells with E _g ranging from 1.02 to 1.14 eV are prepared and a spectrum splitting system is used to experimentally demonstrate the effect of using lower-E _g cells as the bottom cell of two-junction solar cells. The four-terminal tandem cell configuration fabricated using a mixed-halide perovskite top cell (E _g  = 1.59 eV; stand-alone efficiency = 21.0%) and CIGS bottom cell (E _g  = 1.02 eV; stand-alone efficiency = 21.5%) with a 775-nm spectral splitting mirror exhibits an efficiency of 28.0% at the aperture area of 1 cm².

PbS Colloidal Quantum Dot Inks for Infrared Solar Cells

Infrared PbS colloidal quantum dot (CQD)-based materials receive significant attention because of its unique properties. The PbS CQD ink that originates from ligand exchange of CQDs is highly potential for efficient and stable infrared CQD solar cells (CQDSCs) using low-temperature solution-phase processing. In this review, we present a comprehensive overview of CQD inks for the development of efficient infrared solar cells, which can effectively harvest the photons from the infrared wavelength region of the solar spectrum, including the importance of infrared absorbers for solar cells, the unique properties of CQDs, ligand-exchange determined CQD inks, and related photovoltaic performance of CQDSCs. Finally, we present a brief conclusion, and the possible challenges and opportunities of the CQD inks are discussed in-depth to further develop highly efficient and stable infrared solar cells.

Indole Carbonized Polymer Dots Boost Full-Color Emission by Regulating Surface State

Carbonized polymer dots (CPDs) are impressive imaging probes with great potential for enriching the library of metal-free fluorescent materials, yet current strategies have struggled to achieve products that emit full-color light in a single reaction system. Establishing an efficient and robust synthesis approach that unlocks the color barrier to the luminescence centers of specific CPDs remains a challenge. Herein, the surface-state engineering of pyridine and amide in the indole system to create a palette of resolvable full-color light-emissive CPDs is reported. Detailed structural analysis revealed that cationic polymerization and oxidation reactions potentially contribute to the formation of the main frameworks and emission centers of the final CPDs, with emissive oxygen- and nitrogen-based centers fixed by cross-linked polymer structures. This study provides valuable insight into the energy absorbance and photoluminescence mechanism of CPDs and introduces additional reactants (benzo heterocycle) into CPD research.

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Achieving a palette of full-color light-emissive CPDs in a single reaction system

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Providing the surface-state engineering rules for CPDs' emission centers

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Enriching the guidance library for studying the fluorescence mechanism of CPDs

Recent Advances in Super Broad Infrared Luminescence Bismuth-Doped Crystals

Bismuth (Bi)-doped materials are capable of exhibiting broadband near-infrared (NIR) luminescence in 1,000-1,700 nm; driven by the potential use in lasers and broadband optical amplifiers for modern fiber communication systems, Bi-activated NIR luminescencent glasses and related devices have attracted much attention. Compared with glass systems, Bi-doped crystals as gain media usually have more regular crystal structures to produce stronger NIR signals, and developing such materials is highly desirable. Regarding the recent advances in Bi-doped NIR crystals, here, for the first time, we summarized such crystals listed as two main categories of halogen and oxide compounds. Then, by comparing the substitution site, coordination environment, emission and excitation luminescence peaks, emitting center species, and decay times of these known Bibased NIR crystals, discussion on how to design Bi-doped NIR crystals is included. Finally, the key challenges and perspectives of Bi-doped NIR crystals are also presented. It is hoped that this review could offer inspiration for the further development of Bi-doped NIR luminescent crystals and exploit its potential applications.

Structural Diversity with Varying Disorder Enables the Multicolored Display in the Longhorn Beetle Sulawesiella rafaelae

Light control through layered photonic nanostructures enables the strikingly colored displays of many beetles, birds, and butterflies. To achieve different reflected colors, natural organisms mainly rely on refractive index variations or scaling of a fixed structure design, as opposed to varying the type of structure. Here, we describe the presence of distinct coloration mechanisms in the longhorn beetle Sulawesiella rafaelae, which exhibits turquoise, yellow-green, and orange colors, each with a variable iridescence. By optical and electron microscopy, we show that the colors originate from multilayered architectures in hair-like scales with varying amounts of structural disorder. Structural characterizations and optical modeling show that the disorder strongly influences the optical properties of the scales, allowing an independent adjustment of the optical response. Our results shed light on the interplay of disorder in multilayered photonic structures and their biological significance, and could potentially inspire new ecological research and the development of novel optical components.

Augmented Reality and Virtual Reality Displays: Perspectives and Challenges

As one of the most promising candidates for next-generation mobile platform, augmented reality (AR) and virtual reality (VR) have potential to revolutionize the ways we perceive and interact with various digital information. In the meantime, recent advances in display and optical technologies, together with the rapidly developing digital processers, offer new development directions to advancing the near-eye display systems further. In this perspective paper, we start by analyzing the optical requirements in near-eye displays poised by the human visual system and then compare it against the specifications of state-of-the-art devices, which reasonably shows the main challenges in near-eye displays at the present stage. Afterward, potential solutions to address these challenges in both AR and VR displays are presented case by case, including the most recent optical research and development, which are already or have the potential to be industrialized for extended reality displays.

Current-Induced Thermal Tunneling Electroluminescence in a Single Highly Compensated Semiconductor Microrod

Here we demonstrate a novel and robust mechanism, termed as “current-induced Joule heating activated thermal tunneling excitation,” to achieve electroluminescence (EL) by the hot electron-hole-pair recombination in a single highly compensated semiconductor microrod. The radiative luminescence is electrically excited under ambient conditions. The current-induced Joule heating reduces the thermal tunneling excitation threshold of voltage down to 8 V and increases the EL efficiency ~4.4-fold at 723 K. We interpret this novel phenomenon by a thermal tunneling excitation model corrected by electric-induced Joule heating effect. The mechanism is confirmed via theoretical calculation and experimental demonstration, for the first time. The color-tunable EL emission is also achieved by regulation of donor concentration. This work opens up new opportunities for design of novel multi-color light-emitting devices by homogeneous defect-engineered semiconductors in future.

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Current-induced thermal tunneling EL is found in a homogeneous HC-ZnO microrod

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The high temperature is beneficial to the current-induced thermal tunneling EL

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The tunneling mechanism of Joule-heating-facilitated excitation is revealed

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The color-tunable EL emission is demonstrated by regulation of donor concentration

Self-Enhanced Carbonized Polymer Dots for Selective Visualization of Lysosomes and Real-Time Apoptosis Monitoring

Protons are highly related to cell viability during physiological and pathological processes. Developing new probes to monitor the pH variation could be extremely helpful to understand the viability of cells and the cell death study. Carbonized polymer dots (CPDs) are superior biocompatible and have been widely applied in bioimaging field. Herein, a new type of extreme-pH suitable CPDs was prepared from citric acid and o-phenylenediamine (CA/oPD-CPDs). Due to the co-existence of hydrophilic and hydrophobic groups, CA/oPD-CPDs tend to aggregate in neutral condition with a dramatic decrease of fluorescence, but disperse well in both acidic and alkaline conditions with brighter emission. This specialty enables them to selectively illuminate lysosomes in cells. Moreover, CA/oPD-CPDs in the cytoplasm could serve as a sustained probe to record intracellular pH variation during apoptosis. Furthermore, CA/oPD-CPDs present a continuous fluorescence increase upon 2-h laser irradiation in living cells, underscoring this imaging system for long-term biological recording.

Interplay between Light and Functionalized Silk Fibroin and Applications

Silkworm silk has been considered to be a luxurious textile for more than five thousand years. Native silk fibroin (SF) films have excellent (ca. 90%) optical transparency and exhibit fluorescence under UV light. The silk dyeing process is very important and difficult, and methods such as pigmentary coloration and structural coloration have been tested for coloring silk fabrics. To functionalize silk that exhibits fluorescence, the in vivo and in vitro assembly of functional compounds with SF and the resulting amplification of fluorescence emission are examined. Finally, we discuss the applications of SF materials in basic optical elements, light energy conversion devices, photochemical reactions, sensing, and imaging. This review is expected to provide insight into the interaction between light and silk and to inspire researchers to develop silk materials with a consideration of history, material properties, and future prospects.

Pyrophosphate Phosphor Solid Solution with High Quantum Efficiency and Thermal Stability for Efficient LED Lighting

Phosphors with high quantum efficiency and thermal stability are greatly desired for lighting industries. Based on the design strategy of solid solution, a series of deep-blue-emitting phosphors (Sr0.99-xBax)2P2O7:0.02Eu2+ (SBxPE x = 0-0.5) are developed. Upon excitation at 350 nm, the optimized SB0.3PE phosphor shows a relatively narrow full width at half maximum (FWHM = 32.7 nm) peaking at 420 nm, which matches well with the plant absorption in blue region. Moreover, this phosphor exhibits obvious enhancement of internal quantum efficiency (IQE) (from 74% to 100%) and thermal stability (from 88% to 108% of peak intensity and from 99% to 124% of integrated area intensity at 150°C) compared with the pristine one. The white LED devices using SB0.3PE as deep-blue-emitting component show good electronic properties, indicating that SB0.3PE is promising to be used in plant growth lighting, white LEDs, and other photoelectric applications.

Two-Stage Ultraviolet Degradation of Perovskite Solar Cells Induced by the Oxygen Vacancy-Ti4+ States

The failure of perovskite solar cells (PSCs) under ultraviolet (UV) irradiation is a serious barrier of commercial utilization. Here, a two-stage degradation process of TiO₂-based PSCs is discovered under continuous UV irradiation in an inert atmosphere. In the first decay stage, oxygen vacancy-Ti³⁺ (Ti³⁺-V_O) transform into active Ti⁴⁺-V_O trap states under UV excitation and cause photocarrier loss. Furthermore, Ti⁴⁺-V_O states can convert back into Ti³⁺-V_O states through oxidizing I⁻, which result in the accumulation of I₃⁻. Sequentially, the rapid decomposition of perovskite accelerated by increasing I₃⁻ replaces the photocarrier loss as the dominant mechanism leading to the second decay stage. Then, a universal method is proposed to improve the UV stability by blocking the transformation of Ti³⁺-V_O states, which can be realized by polyethyleneimine ethoxylated (PEIE) modified layer. The optimized devices remain ∼75% of its initial efficiency (20.51%) under UV irradiation at 72 days, whereas the normal devices fail completely.

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A two-stage degradation process of TiO₂-based PSCs under continuous UV irradiation

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The transformation of Ti³⁺-V_O to Ti⁴⁺-V_O states is responsible for the UV degradation

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A universal method to enhance the UV stability of PSCs was proposed

Near-Infrared-Detached Adhesion Enabled by Upconverting Nanoparticles

Achieving efficient and biocompatible detachment between adhered wet materials (i.e., tissues and hydrogels) is a major challenge. Recently, photodetachable topological adhesion has shown great promise as a strategy for conquering this hurdle. However, this photodetachment was triggered by UV light with poor biocompatibility and penetration capacity. This study describes near-infrared (NIR) light-detached topological adhesion based on polyacrylic acid coated upconverting nanoparticles (UCNP@PAA) and a photodetachable adhesive (termed Cell-Fe). Cell-Fe is a coordinated topological adhesive consisting of carboxymethylcellulose and Fe3+ that can be photodecomposed by UV light. To prepare a substrate for NIR-detached topological adhesion, UCNP@PAA and Cell-Fe were mixed and brushed on the surface of the model adherent. The UCNP@PAA can harvest NIR light and convert it into UV light, triggering the decomposition of the Cell-Fe and inducing the detachment. This NIR-detached topological adhesion is also feasible in deep tissue because of the ability of NIR light to penetrate tissue.

Chalcogenide Taper and Its Nonlinear Effects and Sensing Applications

The nonlinear coefficient of chalcogenide glass is 200-1000 times larger than that of silica glass, and it is transparent in the 1-15 μm wavelength windows, which makes the nonlinear effects happen at much low power with a short length in near- and mid-infrared wavelength window. With tapered chalcogenide fibers, the power density in the core and the waveguide nonlinearity can be enhanced to make nonlinear signal processing unit at a compact size. The threshold of Raman scattering and supercontinuum generation is reduced due to the enhanced Kerr effect and enhanced optical power intensity. Phase-matching condition required in four-wave mixing (FWM) can be realized by tailoring fiber structures to engineer the chromatic dispersion, which enables new wavelengths creation over a large range at mW power and sub-meter length. The guided acoustic waves and longitudinal acoustic waves can be generated and detected in mW power with chalcogenide tapers. The high power density in the microwires and the high photosensitivity of chalcogenide glass in the 1550 nm band enable the inscription of FBGs in the fiber directly. The chalcogenide microwires are fragile and the core diameter cannot be tapered down to sub-microns, which can be mitigated by polymer coating that can provide mechanical strength. Polymers not only provide high mechanical strength as the coating and cladding materials but also bring over 10 times larger thermal expansion than chalcogenide cores, which enhances the sensor prospect of the chalcogenide fibers for temperature, strain, and acoustic sensing. This work reviews the present and emerging trends in investigation of chalcogenide tapers, mainly focusing on the fabrication procedure of chalcogenide microwires, the nonlinear effects, and sensing applications.

Rare Earth Doped Optical Fibers with Multi-section Core

The gain bandwidth of a single-mode fiber is limited by the atomic transitions of one rare earth gain element. Here we overcome this long-standing challenge by designing a new single-mode fiber with multi-section core, where each section is doped with different gain element. We theoretically propose and experimentally demonstrate that this configuration provides a gain bandwidth well beyond the capability of conventional design, whereas the inclusion of multiple sections does not compromise single-mode operation or the quality of the transverse modal profile. This new fiber will be beneficial in realizing all fiber laser systems with few-cycle pulse duration or octave tunability.

Long-lived Photon Upconversion Phosphorescence in RbCaF3:Mn2+,Yb3+ and the Dynamic Color Separation Effect

The development of luminescence materials with long-lived upconversion (UC) phosphorescence and long luminescence rise edge (LRE) is a great challenge to advance the technology of photonics and materials sciences. The lanthanide ions-doped UC materials normally possess limited UC lifetime and short LRE, restricting direct afterglow viewing in visual images by the naked eye. Here, we show that the RbCaF₃:Mn²⁺,Yb³⁺ UC luminescence material generates a long UC lifetime of ∼62 ms peaking at 565 nm and an ultralong LRE of ∼5.2 ms. Density functional theory calculations provide a theoretical understanding of the Mn²⁺-Yb³⁺ aggregation in the high-symmetry RbCaF₃ host lattice that enables the formation of the long-lived UC emission center, superexchange coupled Yb³⁺-Mn²⁺ pair. Through screen printing ink containing RbCaF₃:Mn²⁺,Yb³⁺, the visualized multiple anti-counterfeiting application and information encryption prototype with high-throughput rate of authentication and decryption are demonstrated by the dynamic color separation effect.

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Photon upconversion phosphorescence material RbCaF₃:Mn²⁺,Yb³⁺ is developed

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The UC emission center in RbCaF₃:Mn²⁺,Yb³⁺ is ascribed to the Yb³⁺-Mn²⁺ pair

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A multiple anti-counterfeiting prototype based on the RbCaF₃:Mn²⁺,Yb³⁺ is demonstrated

Enabling Self-passivation by Attaching Small Grains on Surfaces of Large Grains toward High-Performance Perovskite LEDs

This paper reports a new method to generate stable and high-brightness electroluminescence (EL) by subsequently growing large/small grains at micro/nano scales with the configuration of attaching small grains on the surfaces of large grains in perovskite (MAPbBr₃) films by mixing two precursor solutions (PbBr₂ + MABr and Pb(Ac)₂·3H₂O + MABr). Consequently, the small and large grains serve, respectively, as passivation agents and light-emitting centers, enabling self-passivation on the defects located on the surfaces of light-emitting large grains. Furthermore, the light-emitting states become linearly polarized with maximal polarization of 30.8%, demonstrating a very stable light emission (49,119 cd/m² with EQE = 11.31%) and a lower turn-on bias (1.9 V) than the bandgap (2.25V) in the perovskite LEDs (ITO/PEDOT:PSS/MAPbBr₃/TPBi[50 nm]/LiF[0.7 nm]/Ag). Therefore, mixing large/small grains with the configuration of attaching small grains on the surfaces of large grains by mixing two precursor solutions presents a new strategy to develop high-performance perovskite LEDs.

Hierarchical Uniform Supramolecular Conjugated Spherulites with Suppression of Defect Emission

Easily processed, well-defined, and hierarchical uniform artificial architectures with intrinsic strong crystalline emission properties are necessary for a range of light-emitting optoelectronic devices. Herein, we designed and prepared ordered supramolecular spherulites, comprising planar conformational molecules as primary structures and multiple hydrogen bonds as physical cross-links. Compared with serious aggregation-induced fluorescence quenching (up to 70%), these highly ordered architectures exhibited unique and robust crystalline emission with a high PLQY of 55%, which was much higher than those of other terfluorenes. The primary reasons for the high PLQY are the uniform exciton energetic landscape created in the planar conformation and the highly ordered molecular packing in spherulite. Meanwhile, minimal residual defect (green-band) emissions are effectively suppressed in our oriented crystalline framework, whereas the strong and stable blue light radiations are promoted. These findings may confirm that supramolecular ordered artificial architectures may offer higher control and tunability for optoelectronic applications.

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Coplanar molecular conformation is stabilized in supramolecular crystalline frameworks

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Spiro-terfluorene can self-assemble into hierarchical well-defined spherulites

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Ordered and uniform condensed structures suppress defect emission

Neuronal Receptors Display Cytoskeleton-Independent Directed Motion on the Plasma Membrane

Directed transport of transmembrane proteins is generally believed to occur via intracellular transport vesicles. However, using single-particle tracking in rat hippocampal neurons with a pH-sensitive quantum dot probe that specifically reports surface movement of receptors, we have identified a subpopulation of neuronal EphB2 receptors that exhibit directed motion between synapses within the plasma membrane itself. This receptor movement occurs independently of the cytoskeleton but is dependent on cholesterol and is regulated by neuronal activity.

Stable Sn/Pb-Based Perovskite Solar Cells with a Coherent 2D/3D Interface

Low-band-gap metal halide perovskite semiconductor based on mixed Sn/Pb is a key component to realize high-efficiency tandem perovskite solar cells. However, the mixed perovskites are unstable in air due to the oxidation of Sn²⁺. To overcome the stability problem, we introduced N-(3-aminopropyl)-2-pyrrolidinone into the CH₃NH₃Sn_0.5Pb_0.5I_xCl_3-x thin film. The carbonyl group on the molecule interacts with Sn²⁺/Pb²⁺ by Lewis acid coordination, forming vertically oriented 2D layered perovskite. The 2D phase is seamlessly connected to the bulk perovskite crystal, with a lattice coherently extending across the two phases. Based on this 2D/3D hybrid structure, we assembled low-band-gap Sn-based perovskite solar cells with power conversion efficiency greater than 12%. The best device was among the most stable Sn-based organic-inorganic hybrid perovskite solar cells to date, keeping 90% of its initial performance at ambient condition without encapsulation, and more than 70% under continuous illumination in an N₂-filled glovebox for over 1 month.

Efficient Deep-Blue Electrofluorescence with an External Quantum Efficiency Beyond 10

The design of blue fluorescent materials combining both deep-blue emission (CIE_y<0.06) and high-efficiency climbing over the typically limited exciton production efficiency of 25% is a challenge for organic light-emitting diodes (OLEDs). In this work, we have synthesized two blue luminogens, trans-9,10-bis(2-butoxyphenyl)anthracene (BBPA) and trans-9,10-bis (2,4-dimethoxyphenyl)anthracene with high photoluminescence quantum yields (PLQYs) of 89.5% and 87.0%, respectively. Intriguingly, we have proposed a strategy to avoid aggregation-caused quenching, which can effectively reduce the undesirable excimeric emission by introducing two host matrices with twisted molecular structure, 9,10-di(naphth-2-yl) anthracene and 10,10′-bis-(4-fluorophenyl)-3,3′-dimethyl-9,9′-bianthracene (MBAn-(4)-F), in the BBPA emission layer. The device containing the EML of BBPA-doped MBAn-(4)-F exhibited a high external quantum efficiency of 10.27% for deep-blue emission with the Commission International de L'Eclairage CIE coordinates of (0.15, 0.05) via the steric effect. Importantly, this represents an advance in deep-blue-emitting fluorescent OLED architectures and materials that meet the requirements of high-definition display.

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Highly efficient deep-blue luminogens BBPA and DMPA are synthesized

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Low-efficiency roll-off deep-blue OLEDs with CIE coordinate Y < 0.06

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Record-high external quantum efficiency of 10.27% for deep-blue fluorescent OLEDs

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Host matrix of twisted structure showing steric effect reduces intermolecular aggregation

Millimeter-Scale Nonlocal Photo-Sensing Based on Single-Crystal Perovskite Photodetector

Organometal trihalide perovskites (OTPs) are promising optoelectronic materials for high-performance photodetectors. However, up to now, traditional polycrystal OTP-based photodetectors have demonstrated limited effective photo-sensing range. Recently, bulk perovskite single crystals have been seen to have the potential for position-sensitive photodetection. Herein, for the first time, we demonstrate a position-dependent photodetector based on perovskite single crystals by scanning a focused laser beam over the device perpendicular to the channel. The photodetector shows the best-ever effective photo-sensing distance up to the millimeter range. The photoresponsivity and photocurrent decrease by nearly an order of magnitude when the beam position varies from 0 to 950 μm and the tunability of carrier diffusion length in CH₃NH₂PbBr₃ with the variation of the exciting laser intensity is demonstrated. Furthermore, a numerical model based on transport of photoexcited carriers is proposed to explain the position dependence. This photodetector shows excellent potential for application in future nanoelectronics and optoelectronics systems.

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Position-dependent photodetector based on perovskite single crystals is fabricated

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The photodetector demonstrates photo-sensing distance up to millimeter range

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The attenuation of carrier diffusion length in CH₃NH₂PbBr₃ is revealed

Optimal-Enhanced Solar Cell Ultra-thinning with Broadband Nanophotonic Light Capture

Recent trends in photovoltaics demand ever-thin solar cells to allow deployment in consumer-oriented products requiring low-cost and mechanically flexible devices. For this, nanophotonic elements in the wave-optics regime are highly promising, as they capture and trap light in the cells' absorber, enabling its thickness reduction while improving its efficiency. Here, novel wavelength-sized photonic structures were computationally optimized toward maximum broadband light absorption. Thin-film silicon cells were the test bed to determine the best performing parameters and study their optical effects. Pronounced photocurrent enhancements, up to 37%, 27%, and 48%, respectively, in ultra-thin (100- and 300-nm-thick) amorphous, and thin (1.5-μm) crystalline silicon cells are demonstrated with honeycomb arrays of semi-spheroidal dome or void-like elements patterned on the cells' front. Also importantly, key advantages in the electrical performance are anticipated, since the photonic nano/micro-nanostructures do not increase the cell roughness, therefore not contributing to recombination, which is a crucial drawback in state-of-the-art light-trapping approaches.

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Wave-optics allows broadband light trapping while minimizing solar cell thickness

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Photonic transparent electrodes can boost both optical and electrical performance

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Up to 48% efficiency enhancement is determined relative to conventional approaches

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Performance enhancement is demonstrated for a wide incidence angular range (0°–70°)