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CsPb2Br5 is a new member of the all-inorganic lead halide perovskite family with unique structures and optoelectronic properties for various applications. As an indirect band gap semiconductor, the photoluminescence (PL) mechanism of CsPb2Br5 is still under debate. To resolve this issue, CsPb2Br5 microplates with strong green PL have been prepared by a hot-injection method. Characterization by transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis and ultraviolet-visible (UV-vis) absorption spectroscopy indicates the existence of a small amount of embedded CsPbBr3 phase. The removal of the embedded CsPbBr3 phase by treatment with water containing ethanol solvent resulted in complete PL quenching, suggesting the origin of PL due to the embedded CsPbBr3 phase. Spatially resolved PL and time-resolved PL mapping have been further employed to directly visualize the spatial distribution of different emission centers. Our single particle spectroscopic studies indicated the existence of three different emission centers with different PL lifetimes: two types of embedded CsPbBr3 phases (clumped and randomly distributed CsPbBr3 nanocrystals) and intrinsic defects of CsPb2Br5. The embedded CsPbBr3 phases with fast and intermediate PL lifetimes are the primary contributors to PL of the CsPb2Br5 microplates while their intrinsic defects with slow PL lifetimes make only a minor contribution. These studies have unambiguously clarified the PL mechanisms of the CsPb2Br5 microplates and provided the direct mapping of different emission centers, which resolve the contradictory explanation and debate about the PL mechanism of the CsPb2Br5 microplates.

Tungsten disulfide monolayers have attracted extensive attention in nanoelectronics and optoelectronics applications due to their remarkable electronic and optical properties. High-quality WS2 monolayers with a scalable size and uniform thickness can be synthesized by a chemical vapor deposition method (CVD). However, they commonly contain intrinsic structural defects and different populations of charge carriers, which are responsible for different contributions of excitons, trions, and biexcitons to their photoluminescence (PL) emission. Here, we adopt sodium sulphide (Na2S) solution to chemically treat CVD-grown WS2 monolayers by a simple immersing method. The results show that WS2 monolayers have a significantly enhanced PL emission by a factor of 25-fold and an obvious red-shift of the PL wavelength, resulting from the different excitonic states induced by effective n-type doping after Na2S treatment. This work provides a simple but promising chemical doping route to significantly improve the optical properties of WS2 monolayers and paves the way for the realization of practical WS2 monolayer based optoelectronic applications.

Recent experimental and theoretical studies have demonstrated that two-dimensional (2D) transition metal dichalcogenide (TMDC) nanoflakes are one of the most promising candidates for non-noblemetal electrocatalysts for hydrogen evolution reaction (HER). However, it is still challenging to optimize their conductivity and enrich active sites for highly efficient electrochemical performance. Herein, we report a chemical vapor deposition (CVD) and thermal annealing two-step strategy to controllably synthesize hybrid electrocatalysts consisting of metallic NbS 2 nanoflake backbones and a highly catalytic active MoS x nanocrystalline shell on polished commercial glass carbon (GC). In addition, the amount of MoS x in the hybrids can be easily adjusted. We first demonstrate that a small amount of MoS x significantly promotes the HER activity of 2D NbS 2 nanoflakes, which is in good agreement with the density functional theory (DFT) calculation results. Moreover, the optimized MoS x @NbS 2 /GC electrocatalyst displays superior HER activity with overpotential of -164 mV at -10 mA cm -2 , a small Tafel slope of 43.2 mV dec -1 , and prominent electrochemical stability. This study provides a new path for enhancing the HER performance of 2D TMDC nanoflakes.

Recently, MoS2 nanosheets were demonstrated to be able to spontaneously adsorb single-stranded DNA, acting as efficient dye quenchers. We herein report a novel microfluidic biosensor for fluorescent DNA detection based on single-layered MoS2 nanosheets. The proposed platform is simple, rapid and visible with high sensitivity and selectivity.

Hybrid urchin-like nanostructures composed of a spherical onion-like carbon (OLC) core and MoS2 nanoleaves were synthesized by a simple solvothermal method followed by thermal annealing treatment. Compared to commercial MoS2 powder, MoS2/OLC nanocomposites exhibit enhanced electrochemical performance as anode materials of lithium-ion batteries (LIBs) with a specific capacity of 853 mA h g(-1) at a current density of 50 mA g(-1) after 60 cycles, and a moderate initial coulombic efficiency of 71.1%. Furthermore, a simple pre-lithiation method based on direct contact of lithium foil with MoS2/OLC nano-urchins was used to achieve a very high coulombic efficiency of 97.6% in the first discharge/charge cycle, which is at least 26% higher compared to that of pristine MoS2/OLC nano-urchins. This pre-lithiation method can be generalized to develop other carbon-metal sulfide nanohybrids for LIB anode materials. These results may open up a new avenue for the development of the next-generation high-performance LIBs.