Synthesis of Eu3+-Doped NaGd9Si6O26 Sub-Microcrystals from a NaGdF4@SiO2 Structure.

Rare earth silicate phosphors of high quantum efficiency with a stable performance are promising materials in the fields of display and illumination. The grain sizes of products synthesized via the conventional solid-state reaction method are usually too large to satisfy the requirements of color cast and extraction efficiency in high-resolution light-emitting devices (LEDs). We designed a synthetic route and successfully fabricated rare earth silicate NaGd9Si6O26 (NGSO) sub-microcrystals with a size ranging from 550 to 1200 nm. The reaction mechanism and optical properties were systematically investigated. The quantum efficiency of Eu3+-activated NGSO sub-microcrystals was about 36.6%. The LED encapsulated with these sub-microcrystals showed lower color deviation and higher lumen efficiency and lumen flux compared to that with NGSO fabricated using the conventional solid state reaction method.

Efficient Near-Infrared Luminescence Based on Double Perovskite Cs2SnCl6.

Cs2SnCl6 double perovskite has attracted wide attention as a promising optoelectronic material because of its better stability and lower toxicity than its lead counterparts. However, pure Cs2SnCl6 demonstrates quite poor optical properties, which usually calls for active element doping to realize efficient luminescence. Herein, a facile co-precipitation method was used to synthesize Te4+ and Er3+-co-doped Cs2SnCl6 microcrystals. The prepared microcrystals were polyhedral, with a size distribution around 1-3 µm. Highly efficient NIR emissions at 1540 nm and 1562 nm due to Er3+ were achieved in doped Cs2SnCl6 compounds for the first time. Moreover, the visible luminescence lifetimes of Te4+/Er3+-co-doped Cs2SnCl6 decreased with the increase in the Er3+ concentration due to the increasing energy transfer efficiency. The strong and multi-wavelength NIR luminescence of Te4+/Er3+-co-doped Cs2SnCl6 originates from the 4f→4f transition of Er3+, which was sensitized by the spin-orbital allowed 1S0→3P1 transition of Te4+ through a self-trapped exciton (STE) state. The findings suggest that ns2-metal and lanthanide ion co-doping is a promising method to extend the emission range of Cs2SnCl6 materials to the NIR region.

Controlling Molecular Orientation of Small Molecular Dopant-Free Hole-Transport Materials: Toward Efficient and Stable Perovskite Solar Cells.

Perovskite solar cells (PSCs) have great potential for future application. However, the commercialization of PSCs is limited by the prohibitively expensive and doped hole-transport materials (HTMs). In this regard, small molecular dopant-free HTMs are promising alternatives because of their low cost and high efficiency. However, these HTMs still have a lot of space for making further progress in both efficiency and stability. This review firstly provides outlining analyses about the important roles of molecular orientation when further enhancements in device efficiency and stability are concerned. Then, currently studied strategies to control molecular orientation in small molecular HTMs are presented. Finally, we propose an outlook aiming to obtain optimized molecular orientation in a cost-effective way.

Lead-Free Cesium Thulium Halide Perovskite Microcrystals for Near Ultraviolet Luminescence.

Lead halide perovskites attract tremendous research attention due to excellent optoelectronic properties. However, realizing efficient near ultraviolet (NUV) luminescence with these materials is still a big challenge. Herein, a novel rare-earth perovskite cesium thulium chloride (CsTmCl3 ) with high crystallinity has been synthesized via a simple hot-injection method. The obtained CsTmCl3 microcrystals have a size distribution of around 1-5 µm, and demonstrate a highly efficient NUV emission at 337 nm with a full width at half maximum (FWHM) of 68 nm. The determined band gap of CsTmCl3 microcrystals is ≈3.92 eV, which is supported by theoretical calculations. Moreover, a high photoluminescence quantum yield (PLQY) of up to 12% in NUV region has been achieved in such a lead-free perovskite. The findings suggest that CsTmCl3 perovskite microcrystal is a promising low-toxic material for applications in NUV optoelectronic devices.

A Centrifugal-Force-Driven Nano-Replication Strategy.

The replication of nano-patterns is a significant means of nanomanufacturing. However, there is still a dearth of nano-replication methods that meet the requirements of both high precision and low cost. Therefore, a new strategy to achieve the replication of nano-patterns, namely centrifugal-force-driven nano-replication (CFDNR), is proposed here. An easily obtained centrifugal force which is perpendicular to the plane of a nanostructured template is designed as a driving power, to compel the dynamic polymer to fully fill the space of the template; then, the nano-pattern can be replicated on a polymer film. Anodic aluminum oxide (AAO) templates with nanohole periods of ~450 nm and ~100 nm were employed as the original masters to investigate the nano-replication behaviors. The results of morphology measurements demonstrate excellent precision. The size deviations between the nanohole in the template and the nanopillar on the polymer film are less than 4%. Furthermore, a vacuum-assisted CFDNR scheme is proposed to prevent the formation of cavitation on the polymer replica. This work provides new possibilities and choices for facile, inexpensive and high-precision nanomanufacturing.

Constructing Co3O4/La2Ti2O7 p-n Heterojunction for the Enhancement of Photocatalytic Hydrogen Evolution.

Layered perovskite-type semiconductor La2Ti2O7 has attracted lots of attention in photocatalytic hydrogen evolution, due to the suitable energy band position for water splitting, high specific surface area, and excellent physicochemical stability. However, the narrow light absorption range and the low separation efficiency of photogenerated carriers limit its photocatalytic activity. Herein, plate-like La2Ti2O7 with uniform crystal morphology was synthesized in molten NaCl salt. A p-n heterojunction was then constructed through the in situ hydrothermal growth of p-type Co3O4 nanoparticles on the surface of n-type plate-like La2Ti2O7. The effects of Co3O4 loading on photocatalytic hydrogen evolution performance were investigated in detail. The results demonstrate that composite Co3O4/La2Ti2O7 possesses much better photocatalytic activity than the pure component. The composite photocatalyst with 1 wt% Co3O4 exhibits the highest hydrogen evolution rate of 79.73 µmol·g-1·h-1 and a good cycling stability. The photoelectrochemistry characterizations illustrate that the improvement of photocatalytic activity is mainly attributed to both the enhanced light absorption from the Co3O4 ornament and the rapid separation of photogenerated electron-hole pairs driven by the built-in electric field close to the p-n heterojunction. The results may provide further insights into the design of high-efficiency La2Ti2O7-based heterojunctions for photocatalytic hydrogen evolution.

Intrinsic peroxidase-like activity of Cu2ZnSn(SxSe1-x)4 nanocrystals, and their application to the colorimetric detection of H2O2.

Nanocrystals (NCs) of type Cu2ZnSn(SxSe1-x)4 (CZTSSe) were prepared via a solvothermal approach. They are shown to be highly efficient peroxidase (POx) mimics for colorimetric detection of H2O2. By varying the molar ratio of S and Se during preparation, the NCs showed different crystal structures, morphologies, surface properties, and POx-like activities. Among them, the type CZTSSe-0.25 NCs exhibit the strongest POx-like activities towards the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine in the presence of H2O2 to generate a blue product. The enhanced activity is attributed to its more negative potential and larger specific surface of the NCs. Based on these findings, a rapid and ultrasensitive method was developed for the visual and colorimetric determination of H2O2. The method is selective, and the NCs are reusable and long-term stable. The detection limit of H2O2 is 50 nM. Kinetic and active species trapping experiments were performed to elucidate the POx-like mechanism of the NCs. Graphical abstract Schematic presentation of the process of Cu2ZnSn(SxSe1-x)4 nanocrystals catalyzing the oxidation of peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2 to induce a typical blue color reaction, which can be applied in colorimetric detection of H2O2.

Enhanced Peroxidase-Like Activity of MoS2 Quantum Dots Functionalized g-C3N4 Nanosheets towards Colorimetric Detection of H2O2.

MoS2 quantum dots (QDs) functionalized g-C3N4 nanosheets (MoS2@CNNS) were prepared through a protonation-assisted ion exchange method, which were developed as a highly efficient biomimetic catalyst. Structural analysis revealed that uniformly-dispersed MoS2 QDs with controllable size and different loading amount grew in-situ on the surface of CNNS, forming close-contact MoS2@CNNS nanostructures and exhibiting distinct surface properties. Compared to MoS2 QDs and CNNS, the MoS2@CNNS nanocomposites exhibited a more than four times stronger peroxidase-like catalytic activity, which could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2 to generate a blue oxide. Among the MoS2@CNNS nanocomposites, MoS2@CNNS(30) was verified to present the best intrinsic peroxidase-like performance, which could be attributed to the more negative potential and larger specific surface area. A simple, rapid and ultrasensitive system for colorimetric detection of H2O2 was thus successfully established based on MoS2@CNNS, displaying nice selectivity, reusability, and stability. The detection limit of H2O2 could reach as low as 0.02 µM. Furthermore, the kinetic and active species trapping experiments indicated the peroxidase-like catalytic mechanism of MoS2@CNNS. This work develops a novel, rapid, and ultrasensitive approach for visual assay of H2O2, which has a potential application prospect on clinical diagnosis and biomedical analysis.

Ag2S nanoparticle-decorated MoS2 for enhanced electrocatalytic and photoelectrocatalytic activity in water splitting.

In this article, a novel Ag2S nanoparticle-decorated MoS2 composite (A@M) was synthesized through a facile in situ growth of the monoclinic crystallographic Ag2S on MoS2 nanosheets. The A@M composite was used as a catalyst in water splitting which exhibits higher electrocatalytic and photoelectrocatalytic activity than the respective pure MoS2 and Ag2S counterparts. Experimental results indicate that the as-prepared A@M composite with an optimal Ag2S/MoS2 molar ratio of 16.30% (16%A@M) shows the best catalytic performance with low overpotentials (110 mV for Voc, 190 mV for onset overpotential, 208 mV for the current density of 20 mA cm-2), a small Tafel slope (42 mV dec-1), and a high photocurrent (82 µA cm-2 under an applied potential of 0.4 V). The enhanced electrocatalytic activity is associated with the improved electrical conductivity resulting from the stretched MoS2 nanosheets and the enriched active sites due to the decorated Ag2S particles. The formation of a type II heterojunction structure at the interface between Ag2S and MoS2 facilitates the separation of photogenerated charge carriers, and thus is responsible for the enhanced photoelectrocatalytic activity and photocatalytic H2 production rate (628 µmol h-1 g-1). This work suggests a promising choice to overcome the intrinsic drawbacks of MoS2 nanostructures for the application in hydrogen evolution.

Synthesis of EDTA-assisted CeVO4 nanorods as robust peroxidase mimics towards colorimetric detection of H2O2.

In this paper, CeVO4 materials were developed as highly efficient biomimetic catalysts for the first time to detect H2O2. These CeVO4 materials were prepared by a facile hydrothermal method with the assistance of EDTA, exhibiting different morphologies, surface properties, and distinct peroxidase mimetic activities. Among them, CeVO4-2 nanorods (NRs) were proved to display the best intrinsic peroxidase-like property compared to other CeVO4 samples due to their more negative potential and larger BET specific surface area, which could efficiently catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2 to generate a blue oxide. Based on the excellent peroxidase mimetic catalytic activity of CeVO4-2 NRs, a simple, convenient and visual H2O2 detection system was successfully established. The detection limit of H2O2 could reach as low as 0.07 µM. Moreover, the CeVO4-2 NR-based assay system presented an excellent selectivity, practicability, long-term stability, and reusability. The peroxidase-like catalytic mechanism of CeVO4-2 NRs was proposed on the basis of active species trapping experiments. This work provides a novel, convenient, rapid, and ultrasensitive system for the colorimetric detection of H2O2, which has a bright prospect in H2O2 detection and biomedical analysis.

Tunable photoluminescence and spectrum split from fluorinated to hydroxylated graphene.

Tunable control over the functionalization of graphene is significantly important to manipulate its structure and optoelectronic properties. Yet the chemical inertness of this noble carbon material poses a particular challenge for its decoration without forcing reaction conditions. Here, a mild, operationally simple and controllable protocol is developed to synthesize hydroxylated graphene (HOG) from fluorinated graphene (FG). We successfully demonstrate that under designed alkali environment, fluorine atoms on graphene framework are programmably replaced by hydroxyl groups via a straightforward substitution reaction pathway. Element constituent analyses confirm that homogeneous C-O bonds are successfully grafted on graphene. Rather different from graphene oxide, the photoluminescence (PL) emission spectrum of the obtained HOG becomes split when excited with UV radiation. More interestingly, such transformation from FG facilitates highly tunable PL emission ranging from greenish white (0.343, 0.392) to deep blue (0.156, 0.094). Additionally, both experimental data and density function theory calculation indicate that the chemical functionalization induced structural rearrangement is more important than the chemical decoration itself in tuning the PL emission band tail and splitting energy gaps. This work not only presents a new way to effectively fabricate graphene derivatives with tunable PL performance, but also provides an enlightening insight into the PL origin of graphene related materials.