Xiufeng Song

Two-dimensional antimonene single crystals grown by van der Waals epitaxy

Unlike the unstable black phosphorous, another two-dimensional group-VA material, antimonene, was recently predicted to exhibit good stability and remarkable physical properties. However, the synthesis of high-quality monolayer or few-layer antimonenes, sparsely reported, has greatly hindered the development of this new field. Here, we report the van der Waals epitaxy growth of few-layer antimonene monocrystalline polygons, their atomical microstructure and stability in ambient condition. The high-quality, few-layer antimonene monocrystalline polygons can be synthesized on various substrates, including flexible ones, via van der Waals epitaxy growth. Raman spectroscopy and transmission electron microscopy reveal that the obtained antimonene polygons have buckled rhombohedral atomic structure, consistent with the theoretically predicted most stable β-phase allotrope. The very high stability of antimonenes was observed after aging in air for 30 days. First-principle and molecular dynamics simulation results confirmed that compared with phosphorene, antimonene is less likely to be oxidized and possesses higher thermodynamic stability in oxygen atmosphere at room temperature. Moreover, antimonene polygons show high electrical conductivity up to 104u2009Su2009m−1 and good optical transparency in the visible light range, promising in transparent conductive electrode applications.

Intercrossed Carbon Nanorings with Pure Surface States as Low-Cost and Environment-Friendly Phosphors for White-Light-Emitting Diodes

As an important energy-saving technique, white-light-emitting diodes (W-LEDs) have been seeking for low-cost and environment-friendly substitutes for rare-earth-based expensive phosphors or Pd(2+)/Cd(2+)-based toxic quantum dots (QDs). In this work, precursors and chemical processes were elaborately designed to synthesize intercrossed carbon nanorings (IC-CNRs) with relatively pure hydroxy surface states for the first time, which enable them to overcome the aggregation-induced quenching (AIQ) effect, and to emit stable yellow-orange luminescence in both colloidal and solid states. As a direct benefit of such scarce solid luminescence from carbon nanomaterials, W-LEDs with color coordinate at (0.28, 0.27), which is close to pure white light (0.33, 0.33), were achieved through using these low-temperature-synthesized and toxic ion-free IC-CNRs as solid phosphors on blue LED chips. This work demonstrates that the design of surface states plays a crucial role in exploring new functions of fluorescent carbon nanomaterials.

Monolayer MoS2-Graphene Hybrid Aerogels with Controllable Porosity for Lithium-Ion Batteries with High Reversible Capacity.

Monolayer MoS2 nanosheets (NSs) are promising anode materials for lithium-ion batteries because all redox reactions take place at the surface without lithium-ion diffusion limit. However, the expanded band gap of monolayer MoS2 NSs (∼1.8 eV) compared to their bulk counterparts (∼1.2 eV) and restacking tendency due to the van der Waals forces result in poor electron transfer and loss of the structure advantage. Here, a facile approach is developed to fabricate the MoS2-graphene aerogels comprising controlled three-dimensional (3D) porous architectures constructed by interconnected monolayer MoS2-graphene hybrid NSs. The robust 3D architectures combining with the monolayer feature of the hybrid NSs not only prevent the MoS2 and graphene NSs from restacking, but also enable fast electrode kinetics due to the surface reaction mechanism and highly conductive graphene matrix. As a consequence, the 3D porous monolayer MoS2-graphene composite aerogels exhibit a large reversible capacity up to 1200 mAh g(-1) as well as outstanding cycling stability and rate performance, making them promising as advanced anode materials for lithium-ion batteries.

Photoluminescent properties of SrSi2O2N2 : Eu2+ phosphor: concentration related quenching and red shift behaviour

Highly efficient green phosphors SrSi2O2N2 : Eu2+, suitable for white light emitting diodes (LEDs), was synthesized by solid-state reaction and their photoluminescence properties were investigated. SrSi2O2N2 : Eu2+ phosphors can be effectively excited by ultraviolet (UV)–Vis light (300–460 nm) and yield green emission with a single, intense, broad band centred at around 540 nm. Concentration quenching occurs in the phosphors when the Eu2+ concentration exceeds 2 at%. The mechanism of concentration quenching is confirmed to be dipole–dipole interaction of Eu2+. With an increase in the Eu2+ concentration, the emission band of Eu2+ shifts to a longer wavelength due to the 5d-orbit hybridization of Eu2+ with the host crystal and the energy transfer between adjacent Eu2+ ions. All the results indicate that SrSi2O2N2 : Eu2+ is a promising green phosphor for UV or blue chip based white LEDs.

Optimizing Hybridization of 1T and 2H Phases in MoS2 Monolayers to Improve Capacitances of Supercapacitors

We report on a 100-fold capacitance increase in MoS2-based supercapacitors achieved via optimizing the in-plane 1T-2H phase hybridization of the monolayers. Chemically exfoliated MoS2 monolayers were annealed at low temperature to tune their 1T content from 2% to 60%. The obtained hybridization states were confirmed by X-ray photoelectron and Raman spectroscopies. After optimizing the hybridization degree, the electrode based on MoS2 monolayers with 40% of the 1T phase exhibited outstanding performance with a resistance as low as 0.68u2005kΩu2005sq−1, specific capacitance of 366.9u2005Fu2005g−1, and retention ratio of 92.2% after 1000 cycles at current densities of 0.5u2005Au2005g−1. GRAPHICAL ABSTRACT

Photoluminescence properties of Eu2+-activated CaSi2O2N2: Redshift and concentration quenching

Highly efficient CaSi2O2N2:Eu2+ green phosphors were synthesized via solid-state reaction method. The produced phosphors are effectively excited with UV-vis light of wavelength between 300 and 460 nm and emit a single, intense, and broad emission band centered at 538 nm. The experimental results and their analysis suggest that the energy transfer mechanism should occur due to dipole-dipole interactions among Eu2+ ions, resulting in a shift in emission spectrum toward longer wavelengths with increasing Eu2+ concentration. The quenching concentration of Eu2+ (i.e., where the emission intensity maximizes) is approximately 2 at.u2009%. Accordingly, the produced CaSi2O2N2:Eu2+ green phosphors are qualified for further consideration and experimentation for potential use in white light emitting diodes.

Li(2)SrSiO(4):Eu(2+) phosphor prepared by the Pechini method and its application in white light emitting diode

Eu 2+ -doped Li 2 SrSiO 4 phosphors were prepared by two different synthesis processes, the Pechini sol-gel route and solid-state reaction (SSR) method. Their morphology, crystal structure, and luminescence properties have been characterized. Li 2 SrSiO 4 :Eu 2+ phosphors show broad and intensive excitation in the range of 390–480 nm and emit yellow-orange light extending from 500 to 700 nm. The luminescence efficiency of Li 2 SrSiO 4 : Eu 2+ phosphors synthesized through the Pechini route is much better than that of phosphors prepared by solid-state reaction method. The application of phosphors from the Pechini route in white light emitting diodes (LEDs) has been investigated. The Commission Internationale de L’Eclairage (CIE) chromaticity coordinates and the correlated color temperature of these white LEDs have been calculated; they are comparable to corresponding values of commercial Y 3 Al 5 O 12 :Ce 3+ converted white LEDs.

Luminescence and Energy-Transfer Mechanism in SrSi2O2N2 : Ce3 + , Eu2 + Phosphors for White LEDs

A series of Ce 3+ and Eu 2+ co-doped SrSi 2 O 2 N 2 phosphors, whose features qualify them for consideration in white-light UV or blue light-emitting diodes (LEDs), was synthesized via a high temperature solid-state reaction under a reductive atmosphere. The dependence of luminescence properties of the produced powders on the concentration of an activator (Eu 2+ ) and a coactivator (Ce 3+ ) was investigated. The experimentally recorded luminescence spectra and the calculations of the efficiency of energy transfer from Ce 3+ to Eu 2+ and the critical distance between Ce 3+ and Eu 2+ suggest a resonance-type energy-transfer mechanism from Ce 3+ to Eu 2+ due to dipole-dipole interactions.

Flexible quantum dot–PVA composites for white LEDs

Integration of blue light-emitting diode (LED) chips with yellow phosphors has been the most practical way to achieve white lighting, but finding a low-cost alternative for Y3Al5O12:Ce3+ (YAG:Ce) phosphors, which are expensive and lack red emission, is still a great challenge. The present report documents a strategy of combining quantum dot–polyvinyl alcohol (PVA) composites and blue chips for white LEDs. Cadmium-free and water-soluble ZnSe:Mn/ZnS quantum dots (QDs) were synthesized through a nucleation doping strategy, and then embedded in PVA. The flexible composite contains well-dispersed QDs and exhibits highly efficient photoluminescence at 590–635 nm, and hence is available for resin-free white LEDs. Besides excellent stability, the assembled white LEDs possess promising color characteristics, including a color rendering index (CRI) value of 93.5, a correlated color temperature (CCT) of 2913 K at Commission Internationale de lEclairage (CIE) color coordinates of (0.41,0.37), and a luminous efficacy (LE) of 18.9 lm W−1 under 300 mA current excitation. This work demonstrates that such a silica-coated QD–PVA composite plate, as a reliable color converter, would be promising for the next-generation QD-based LEDs.

Low-Voltage Photodetectors with High Responsivity Based on Solution-Processed Micrometer-Scale All-Inorganic Perovskite Nanoplatelets

All-inorganic photodetectors based on scattered CsPbBr3 nanoplatelets with lateral dimension as large as 10 µm are fabricated, and the CsPbBr3 nanoplatelets are solution processed governed by a newly developed ion-exchange soldering mechanism. Under illumination of a 442 nm laser, the photoresponsivity of photodetectors based on these scattered CsPbBr3 nanoplatelets is as high as 34 A W-1 , which is the largest value reported from all-inorganic perovskite photodetectors with an external driven voltage as small as 1.5 V. Moreover, the rise and fall times are 0.6 and 0.9 ms, respectively, which are comparable to most of the state-of-the-art all-inorganic perovskite-based photodetectors. All the material synthesis and device characterization are conducted at room temperature in ambient air. This work demonstrates that the solution-processed large CsPbBr3 nanoplatelets are attractive candidates to be applied in low-voltage, low-cost, ultra highly integrated optoelectronic devices.