Catalyst-Free Growth of Atomically Thin Bi2O2Se Nanoribbons for High-Performance Electronics and Optoelectronics

1D materials have attracted significant research interest due to their unique quantum confinement effects and edge-related properties. Atomically thin 1D nanoribbons are particularly interesting because it is a valuable platform with the physical limits of both thickness and width. Here, a catalyst-free growth method is developed and the growth of Bi₂O₂Se nanostructures with tunable dimensionality is achieved. Significantly, Bi₂O₂Se nanoribbons with a thickness down to 0.65 nm, corresponding to a monolayer, are successfully grown for the first time. Electrical and optoelectronic measurements show that Bi₂O₂Se nanoribbons possess decent performance in terms of mobility, on/off ratio, and photoresponsivity, suggesting their promise for devices. This work not only reports a new method for the growth of atomically thin nanoribbons but also provides a platform to study properties and applications of such nanoribbon materials at a thickness limit.     

Unusual Formation of ZnCo2O4 3D Hierarchical Twin Microspheres as a High‐Rate and Ultralong‐Life Lithium‐Ion Battery Anode Material

A facile two‐step strategy involving a polyol method and subsequent thermal annealing treatment is successfully developed for the large‐scale preparation of ZnCo₂O₄ various hierarchical micro/nanostructures (twin mcrospheres and microcubes) without surfactant assistance. To the best of our knowledge, this is the first report on the synthesis of ZnCo₂O₄ mesoporous twin microspheres and microcubes. More significantly, based on the effect of the reaction time on the morphology evolution of the precursor, a brand‐new crystal growth mechanism, multistep splitting then in situ dissolution recrystallization accompanied by morphology and phase change, is first proposed to understand the formation of the 3D twin microshperes, providing new research opportunity for investigating the formation of novel micro/nanostructures. When evaluated as anode materials for lithium‐ion batteries (LIBs), ZnCo₂O₄ hierarchical microstructures exhibit superior capacity retention, excellent cycling stability at the 5 A g^?1 rate for 2000 cycles. Surprisingly, the ZnCo₂O₄ twin microspheres show an exceptionally high rate capability up to the 10 A g^?1 rate. It should be noted that such super‐high rate performance and cycling stability at such high charge/discharge rates are significantly higher than most work previously reported on ZnCo₂O₄ micro/nanostructures and ZnCo₂O₄‐based heterostructures. The ZnCo₂O₄ 3D hierarchical micro/nanostructures demonstrate the great potential as negative electrode materials for high‐performance LIBs.     

Antiphotobleaching: A Type of Structurally Rigid Chromophore Ready for Constructing Highly Luminescent and Highly Photostable Europium Complexes

Antiphotobleaching is a critical challenge in the field of luminescent lanthanide complexes (LLCs) as well as in many disciplines concerning organic luminescent processes. In this work, a type of structurally rigid organic ligand, 4‐hydroxy‐1,5‐naphthyridine (ND), is developed, which can not only efficiently sensitize the europium emission but also demonstrate unique photostability. A series of ND derivatives with different substituent groups are synthesized and their singlet and triplet excited state energy levels are systematically investigated. Photophysical characterizations of the corresponding europium complexes reveal that the sensitization efficiencies (η_sens) are close to 100% and the total photoluminescence quantum yields can reach up to 84%. Most importantly, these structurally rigid luminescent europium complexes exhibit outstanding photostability and thermostability. Unlike the widely used β‐diketone complexes that are easily photodegraded, ND‐based chelates show no obvious degradation during the UV aging test (10 W m^?2 340 nm Ultraviolet A irradiation) within 200 h. Such superior UV resistance is even better than that of the famous compound tris(8‐hydroxyquinolate)aluminum (Alq₃). Possible reasons are discussed and a general rule for designing photostable LLCs is proposed. Such a chromophore is very promising for introducing luminescent materials with good photostability in potential application in many disciplines.     

Luminescent Metal‐Organic Frameworks for Selectively Sensing Nitric Oxide in an Aqueous Solution and in Living Cells

Cu²⁺‐based metal‐organic framework (Cu? TCA ) (H₃ TCA = tricarboxytriphenyl amine) having triphenylamine emitters was assembled and structurally characterized. Cu? TCA features a three‐dimensional porous structure consolidated by the well‐established Cu₂(O₂CR)₄ paddlewheel units with volume of the cavities approximately 4000 nm³. Having paramagnetic Cu²⁺ ions to quench the luminescence of triphenylamine, Cu? TCA only exhibited very weak emission at 430 nm; upon the addition of NO up to 0.1 mM , the luminescence was recovered directly and provided about 700‐fold fluorescent enhancement. The luminescence detection exhibited high selectivity – other reactive species present in biological systems, including H₂O₂, NO₃^?, NO₂^?, ONOO^?, ClO^? and ¹O₂, did not interfere with the NO detection. The brightness of the emission of Cu? TCA also led to its successful application in the biological imaging of NO in living cells. As a comparison, lanthanide metal‐organic framework Eu? TCA having triphenylamine emitters and characteristic europium emitters was also assembled. Eu? TCA exhibited ratiometric fluorescent responses towards NO with the europium luminescence maintained as the internal standard and the triphenylamine emission exhibited more than 1000‐fold enhancement.     

MOF Nano‐Vesicles and Toroids: Self‐Assembled Porous Soft‐Hybrids for Light Harvesting

Metal‐organic vesicular and toroid nanostructures of Zn(OPE)·2H₂O are achieved by coordination‐directed self‐assembly of oligo‐phenyleneethynylenedicarboxylic acid (OPEA) as a linker with Zn(OAc)₂ by controlling the reaction parameters. Self‐assembled nanostructures are characterized by powder X‐ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and adsorption study. The amphiphilic nature of the coordination‐polymer with long alkyl chains renders different soft vesicular and toroidal nanostructures. The permanent porosity of the framework is established by gas adsorption study. Highly luminescent 3D porous framework is exploited for Froster's resonance energy transfer (FRET) by encapsulation of a suitable cationic dye ( DSMP ) which shows efficient funneling of excitation energy. These results demonstrate the dynamic and soft nature of the MOF, resulting in unprecedented vesicular and toroidal nanostructures with efficient light harvesting applications.     

A New Paradigm for Materials Discovery: Heuristics‐Assisted Combinatorial Chemistry Involving Parameterization of Material Novelty

The combinatorial chemistry (combi‐chem) of inorganic functional materials has not yet led to the discovery of commercially interesting materials, in contrast to the many successful discoveries of heterogeneous catalysts leading to commercialization. Novel materials for practical use are likely hidden in the multicompositional search space that contains an infinite number of possible stoichiometries, as well as a large number of well‐known materials. To discover new, inorganic luminescent materials (phosphors) from the SrO‐CaO‐BaO‐La₂O₃‐Y₂O₃‐Si₃N₄‐Eu₂O₃ search space, heuristics optimization strategies, such as the non‐dominated‐sorting genetic algorithm (NSGA) and particle swarm optimization (PSO) are coupled with high‐throughput experimentation (HTE) in such a manner that the experimental evaluation of fitness functions for the NSGA and PSO is accomplished by the HTE. The proposed strategy also involves the parameterization of the material novelty to avoid systematically a futile convergence on well‐known, already‐established materials. Although the process starts with random compositions, we finally converge on a novel, single‐phase, yellow‐green‐emitting luminescent material, La_4–xCa_xSi₁₂O_3+xN_18?x:Eu²⁺, that has strong potential for practical use in white light‐emitting diodes (WLEDs).     

Bowtie‐Shaped NiCo2O4 Catalysts for Low‐Temperature Methane Combustion

Bowtie‐shaped NiCo₂O₄ nanostructures are prepared using a hydrothermal method. Variation of the synthesis parameters, including reaction time, additives, and calcination temperature, allows an understanding of the origin of the bowtie‐shaped structure to be developed. Methane oxidation experiments performed using temperature‐programed oxidation (TPO) show that the new materials, which do not contain precious metals, have excellent activity for low‐temperature methane combustion, with 100% conversion at ≈410 °C (gas hourly space velocity (GHSV): 90 000 mL (STP) g^?1 h^?1). The structure–activity relationships of the bowtie‐shaped nanostructures are explored.     

Broadband Defects Emission and Enhanced Ligand Raman Scattering in 0D Cs3Bi2I9 Colloidal Nanocrystals

Excitonic 0D and 2D lead‐halide perovskites have been recently developed and investigated as new materials for light generation. Here broadband (>1 eV) emission from newly synthesized 0D lead‐free colloidal Cs₃Bi₂I₉ nanocrystals (NCs) is reported. The nature of their emissive states as well as the relative dynamics which are currently hotly debated are investigated. In particular, it is found that the broadband emission is made by the coexistence of emissive excitons and sub‐bandgap emissive trap‐states. Remarkably, evidence of enhanced Raman scattering from the ligands is observed when attached to the NCs surface, an effect that is preliminarily attributed to strong exciton‐ligands electronic coupling in these systems.     

Blue–Green Emission in Terbium‐Doped Alumina (Tb:Al2O3) Transparent Ceramics

Alumina (Al₂O₃) is one of the most versatile ceramics, utilized in an amazing range of structural and optical applications. In fact, chromium‐doped single crystal Al₂O₃ was the basis for the first laser. Today, most photoluminescent (PL) materials rely on rare earth (RE) rather than transition‐metal dopants because RE doping produces greater efficiencies and lower lasing thresholds. RE‐doped alumina could provide an extremely versatile PL ceramic, opening the door for a host of new applications and devices. However, producing a transparent RE:Al₂O₃ suitable for PL applications is a major challenge due to the very low equilibrium solubility of RE (～10^?3%) in Al₂O₃ in addition to alumina's optical anisotropy. A method is presented here to successfully incorporate Tb³⁺ ions up to a concentration of 0.5 at% into a dense alumina matrix, achieving a transparent light‐emitting ceramic. Sub‐micrometer alumina and nanometric RE oxide powders are simultaneously densified and reacted using current‐activated, pressure‐assisted densification (CAPAD), often called spark plasma sintering (SPS). These doped ceramics have a high transmission (～75% at 800 nm) and display PL peaks centered at 485 nm and 543 nm, characteristic of Tb³⁺ emission. Additionally, the luminescent lifetimes are long and compare favorably with lifetimes of other laser ceramics. The high transparencies and PL properties of these ceramics have exciting prospects for high energy laser technology.     

Bright Blue Photo‐ and Electroluminescence from Eu2+‐Doped GaN/SiO2 Nanocomposites

In this article we demonstrate the synthesis of Eu²⁺‐doped GaN/SiO₂ nanocomposites using a simple solid state reaction and their use in light‐emitting devices. The nanocomposite exhibits a bright blue luminescence when excited in the UV region (quantum yield = 23 %). The origin of the blue emission is attributed to the presence of europium ions in the +2 oxidation state in the GaN/SiO₂ nanocomposites. Analysis of the EPR spectrum of europium‐doped GaN/SiO₂ nanocomposites confirms the existence of Eu²⁺ in the nanocomposites. Various control experiments show that the blue emission arises from these europium ions and that the interface of GaN and silica plays a crucial role. The Eu²⁺‐doped GaN/SiO₂ nanocomposite also exhibits a bright blue electroluminescence. Furthermore, the nanocomposites can be coated with a polymer to tune their dispersibility in organic medium.     

Dual Functionalization of Liquid‐Exfoliated Semiconducting 2H‐MoS2 with Lanthanide Complexes Bearing Magnetic and Luminescence Properties

Liquid exfoliated, atomically thin semiconducting transition metal dichalcogenides (TMDs), as inorganic equivalents of graphene, have attracted great interest due to their distinctive physical, optoelectronic, and chemical properties. Functionalization of 2D TMDs brings new prospects for applications in optoelectronics, quantum technologies, catalysis, and medicine. In this report, dual functionalization of 2D semiconducting 2H‐MoS₂ nanosheets through simultaneous incorporation of magnetic and luminescent properties is demonstrated. A facile method is proposed for tuning the properties of the TDM semiconductors and accessing multimodal platforms, consisting in covalent grafting of lanthanide complexes onto the surface of 2D TMDs. Dual functionalization of liquid‐exfoliated MoS₂ nanosheets is demonstrated simultaneously with both europium (III) and gadolinium (III) complexes to form a colloidally stable luminescent (with millisecond lifetimes) and paramagnetic MoS₂‐based nanohybrid material. This work is the first example of transition metal dichalcogenide nanosheets functionalized with preformed lanthanide complexes. These findings open new prospects for covalent functionalization of TMDs with molecular species bearing specific functionalities as a means to tune the optoelectronic properties of the semiconductors, in order to create advanced materials and devices with a wide range of functionalities.     

Photoluminescence Tuning in Stretchable PDMS Film Grafted Doped Core/Multishell Quantum Dots for Anticounterfeiting

The development of new luminescent materials for anticounterfeiting is of great importance, owing to their unique physical, chemical, and optical properties. The authors report the use of color‐tunable colloidal CdS/ZnS/ZnS:Mn²⁺/ZnS core/multishell quantum dots (QDs)‐functionalized luminescent polydimethylsiloxane film (LPF) for anticounterfeiting applications. Both luminescent QDs and as‐fabricated, stretchable, and transparent LPF show blue and orange emission simultaneously, which are ascribed to CdS band‐edge emission and the ⁴T₁ → ⁶A₁ transition of Mn²⁺, respectively; their emission intensity ratios are dependent on the power‐density of a single‐wavelength excitation source. Additionally, photoluminescence tuning of CdS/ZnS/ZnS:Mn²⁺/ZnS QDs in hexane or embedded in LPF can also be realized under fixed excitation power due to a resonance energy transfer effect. Tunable photoluminescence of these flexible LPF grafted doped core/shell QDs can be finely controlled and easily realized, depending on outer excitation power and intrinsic QD concentration, which is intriguing and inspires the fabrication of many novel applications.     

Filling the Gaps between Graphene Oxide: A General Strategy toward Nanolayered Oxides

Despite extraordinary developments in the research of 2D inorganic nanomaterials, a scalable and generalized synthetic method toward 2D oxide materials that lack layered lattice structures is still challenging. Herein, an easy and versatile solution‐based route to synthesize oxides with layered nanostructures by combining sol–gel method with graphene oxide (GO) paper templates is reported. GO can stack together to form a paper‐like membrane, the gap between two GO layers provides ideal 2D space to template the growth of oxide nanolayers. By this simple strategy, the gaps are filled successfully with polycrystalline TiO₂, ZnO, Fe₂O₃, and amorphous SiO₂ nanolayers with thickness of 1–5 nm. Single or multilayers of the oxide‐based ceramic/glass nanolayers for applications in electronics, catalysts, energy storage, and gas separation can be expected; as an example, it is shown that layered Fe₂O₃ electrodes exhibit high performance for lithium‐ion battery due to enhanced electrical connections between the 2D nanolayers.     

Design and Synthesis of Multifunctional Drug Carriers Based on Luminescent Rattle‐Type Mesoporous Silica Microspheres with a Thermosensitive Hydrogel as a Controlled Switch

A novel approach for the fabrication of multifunctional microspheres integrating several advantages of mesoporous, luminescence, and temperature responses into one single entity is reported. First, the hollow mesoporous silica capsules are fabricated via a sacrificial template route. Then, Gd₂O₃:Eu³⁺ luminescent nanoparticles are incorporated into the internal cavities to form rattle‐type mesoporous silica nanocapsules by an incipient‐wetness impregnation method. Finally, the rattle‐type capsules serve as a nanoreactor for successfully filling temperature‐responsive hydrogel via photoinduced polymerization to form the multifunctional composite microspheres. The organic–inorganic hybrid microspheres show a red emission under UV irradiation due to the luminescent Gd₂O₃:Eu³⁺ core. The in vitro cytotoxicity tests show that the samples have good biocompatibility, which indicates that the nanocomposite could be a promising candidate for drug delivery. In addition, flow cytometry and confocal laser scanning microscopy (CLSM) confirm that the sample can be effectively taken up by SKOV3 cells. For in vitro magnetic resonance imaging (MRI), the sample shows the promising spin‐lattice relaxation time (T₁) weighted effect and could potentially apply as a T₁‐positive contrast agent. This composite drug delivery system (DDS) provides a positive temperature controlled “on‐off”drug release pattern and the drug, indomethacin (IMC), is released fast at 45 °C (on phase) and completely shut off at 20 °C (off phase). Meanwhile Gd₂O₃:Eu³⁺ plays an important role as the luminescent tag for tracking the drug loading and release process by the reversible luminescence quenching and recovery phenomenon. These results indicate that the obtained multifunctional composite has the potential to be used as a smart DDS for biomedical applications.     

Process Pathway Controlled Evolution of Phase and Van‐der‐Waals Epitaxy in In/In2O3 on Graphene Heterostructures

Many applications of 2D materials require deposition of non‐2D metals and metal‐oxides onto the 2D materials. Little is however known about the mechanisms of such non‐2D/2D interfacing, particularly at the atomic scale. Here, atomically resolved scanning transmission electron microscopy (STEM) is used to follow the entire physical vapor deposition (PVD) cycle of application‐relevant non‐2D In/In₂O₃ nanostructures on graphene. First, a “quasi‐in‐situ” approach with indium being in situ evaporated onto graphene in oxygen‐/water‐free ultra‐high‐vacuum (UHV) is employed, followed by STEM imaging without vacuum break and then repeated controlled ambient air exposures and reloading into STEM. This allows stepwise monitoring of the oxidation of specific In particles toward In₂O₃ on graphene. This is then compared with conventional, scalable ex situ In PVD onto graphene in high vacuum (HV) with significant residual oxygen/water traces. The data shows that the process pathway difference of oxygen/water feeding between UHV/ambient and HV fabrication drastically impacts not only non‐2D In/In₂O₃ phase evolution but also In₂O₃/graphene out‐of‐plane texture and in‐plane rotational van‐der‐Waals epitaxy. Since non‐2D/2D heterostructures' properties are intimately linked to their structure and since influences like oxygen/water traces are often hard to control in scalable fabrication, this is a key finding for non‐2D/2D integration process design.     

Highly Sensitive Detection of Polarized Light Using Anisotropic 2D ReS2

Due to the novel optical and optoelectronic properties, 2D materials have received increasing interests for optoelectronics applications. Discovering new properties and functionalities of 2D materials is challenging yet promising. Here broadband polarization sensitive photodetectors based on few layer ReS₂ are demonstrated. The transistor based on few layer ReS₂ shows an n‐type behavior with the mobility of about 40 cm² V^?1 s^?1 and on/off ratio of 10⁵. The polarization dependence of photoresponse is ascribed to the unique anisotropic in‐plane crystal structure, consistent with the optical absorption anisotropy. The linear dichroic photodetection with a high photoresponsivity reported here demonstrates a route to exploit the intrinsic anisotropy of 2D materials and the possibility to open up new ways for the applications of 2D materials for light polarization detection.     

Controlled Vapor–Solid Deposition of Millimeter‐Size Single Crystal 2D Bi2O2Se for High‐Performance Phototransistors

Atomically thin 2D materials have received intense interest both scientifically and technologically. Bismuth oxyselenide (Bi₂O₂Se) is a semiconducting 2D material with high electron mobility and good stability, making it promising for high‐performance electronics and optoelectronics. Here, an ambient‐pressure vapor–solid (VS) deposition approach for the growth of millimeter‐size 2D Bi₂O₂Se single crystal domains with thicknesses down to one monolayer is reported. The VS‐grown 2D Bi₂O₂Se has good crystalline quality, chemical uniformity, and stoichiometry. Field‐effect transistors (FETs) are fabricated using this material and they show a small contact resistivity of 55.2 Ω cm measured by a transfer line method. Upon light irradiation, a phototransistor based on the Bi₂O₂Se FETs exhibits a maximum responsivity of 22 100 AW^?1, which is a record among currently reported 2D semiconductors and approximately two orders of magnitude higher than monolayer MoS₂. The Bi₂O₂Se phototransistor shows a gate tunable photodetectivity up to 3.4 × 10¹⁵ Jones and an on/off ratio up to ≈10⁹, both of which are much higher than phototransistors based on other 2D materials reported so far. The results of this study indicate a method to grow large 2D Bi₂O₂Se single crystals that have great potential for use in optoelectronic applications.     

High Efficiency White Organic Light‐Emitting Devices Incorporating Yellow Phosphorescent Platinum(II) Complex and Composite Blue Host

A new class of charge neutral, strongly luminescent cyclometalated platinum(II) complexes supported by dianionic tetradentate ligand are synthesized. One of these platinum(II) complexes, Y‐Pt , displays a high photoluminescence quantum yield of 86% and electroluminescence efficacy (η_power) of up to 52 lm W^?1, and is utilized as a yellow phosphorescent dopant in the fabrication of white organic light‐emitting devices (WOLEDs). WOLEDs based on conventional structures with yellow emission from Y‐Pt in combination with blue emission from bis(4,6‐difluorophenyl‐pyridinato‐N,C²′) (picolinate) iridium(III) (FIrpic) show a total η_power of up to 31 lm W^?1. A two‐fold increase in η_power by utilizing a modified WOLED structure comprising of a composite blue host is realized. With this modified device structure, the total η_power and driving voltage at a luminance of 1000 cd m^?2 can be improved to 61 lm W^?1 and 7.5 V (i.e., 10 V for control devices). The performance improvement is attributed to an effectively broaden exciton formation‐recombination zone and alleviation of localized exciton accumulation within the FIrpic‐doped composite host for reduced triplet‐triplet annihilation, yielding blue light‐emission with enhanced intensity. The modified device structure can also adopt a higher concentration of Y‐Pt towards its optimal value, leading to WOLEDs with high efficiency.     

In Situ Carbon Homogeneous Doping on Ultrathin Bismuth Molybdate: A Dual‐Purpose Strategy for Efficient Molecular Oxygen Activation

Solar‐driven activation of molecular oxygen, which harnesses light to produce reactive oxygen species for the removal of pollutants, is the most green and low‐cost approach for environmental remediation. The energy coupling between photons, excitons, and oxygen is the crucial step in this reaction and still remains a challenge. In this study, a dual‐purpose strategy for enhanced molecular oxygen activation is established by in situ carbon homogeneous doping on ultrathin Bi₂MoO₆ nanosheets for the first time. The C‐doped ultrathin 2D material exhibits an enlarged bandgap straddling the electrochemical potential of O₂ /?O₂^? and H₂O /?OH, without any attenuation of light absorption. An internal electric field and shortened carrier‐transportation distance are also found in the longitude orientation of the nanosheets ([001] axis), leading to a higher density of effective photogenerated carriers localized on the exposed {001} surface. As applied for the nitric oxide removal, the reactive rate over the ultrathin C‐doped Bi₂MoO₆ nanosheets is 4.3 times higher than that over the bulk counterparts as a result of the increasing reactive oxygen species. This new proof‐of‐concept strategy not only realizes the band structure engineering and charge transportation regulation but also paves a new way to construct highly efficient photocatalytic materials.     

Giant Pressure-Induced Spectral Shift in Cyan-Emitting Eu2+-Activated Sr8Si4O12Cl8 Microspheres for Ultrasensitive Visual Manometry

To address the unsatisfactory pressure sensitivity of luminescent manometers, Eu²⁺-activated supersensitive microspheres operating in the visible range are developed. A series of Eu²⁺-doped Sr₈Si₄O₁₂C_l8 materials are synthesized as microspheres, and their structural and spectroscopic properties are studied theoretically and experimentally. Excited at 350 nm, the samples emit a bright cyan luminescence at ambient conditions that, upon pressure, changes to green emission and finally to yellow light above 7 GPa. Most importantly, a huge red-shift of the emission band from 497.3 to 568.8 nm is observed as the pressure increases, leading to an ultrahigh-pressure sensitivity of 9.69 nm/GPa, which is the highest sensitivity ever reported. The designed microspheres with polychromatic emissions and high-pressure sensitivity are suitable for visual optical pressure sensing, and the applied strategy provides some important guidelines for the development of new optical manometers, allowing pressure monitoring with unprecedented accuracy.