Photoluminescence Characteristics of ZnCuInS-ZnS Core-Shell Semiconductor Nanocrystals

The photoluminescence （PL） characteristics of ZnCuInS quantum dots （Q, Ds） with varying ZnS shell thicknesses of O, 0.5, and 1.5 layers are investigated systemically by time-correlated single-photon counting measurements and temperature-dependent PL measurements. The results show that a ZnS shell thickness of 1.5 layers can effectively improve the PL quantum yield in one order of magnitude by depressing the surface trapping states of the core ZnCuInS QDs at room temperature. However, the PL measurements at the elevated temperature reveal that the core-shell nanocrystals remain temperature-sensitive with respect to their relatively thin shells. The temperature sensitivity of these small-sized single-layered core-shell nanocrystals may find applications as effective thermometers for the in vivo detection of biological reactions within cells.

Stability and band gap engineering of silica-confined lead halide perovskite nanocrystals under high pressure

SiO_(2)is the major mineral substance in the upper mantle of the earth.Therefore,studies of the silica-coated materials under high-pressure are essential to explore the physical and chemical properties of the upper mantle.The silica-confined CsPbBr_(3)nanocrystals(NCs)have recently attracted much attention because of the improved photoluminescence(PL)quantum yield,owing to the protection of silica shell.However,it remains considerable interest to further explore the relationship between optical properties and the structure of CsPbBr_(3)@SiO_(2)NCs.We systemically studied the structural and optical properties of the CsPbBr_(3)@SiO_(2)NCs under high pressure by using diamond anvil cell(DAC).The discontinuous changes of PL and absorption spectra occurred at~1.40 GPa.Synchrotron X-ray diffraction(XRD)studies of CsPbBr_(3)@SiO_(2)NCs under high pressure indicated an isostructural phase transformation at about 1.36 GPa,owing to the pressure-induced tilting of the Pb-Br octahedra.The isothermal bulk moduli for two phases are estimated about 60.0 GPa and 19.2 GPa by fitting the equation of state.Besides,the transition pressure point of CsPbBr_(3)@SiO_(2)NCs is slightly higher than that of pristine CsPbBr_(3)NCs,which attributed to the buffer effect of coating silica shell.The results indicate that silica shell is able to enhance the stabilization without changing the relationship between optical properties and structure of CsPbBr_(3)NCs.Our results were fascinated to model the rock metasomatism in the upper mantle and provided a new‘lithoprobe’for detecting the upper mantle.

Synthesis and fluorescence properties of CdTe:Eu3+ nanocrystals and core-shell SiO2-coated CdTe:Eu3+ nanospheres

Eu3+ doped-CdTe(CdTe:Eu3+)nanocrystals were prepared via a facile hydrothermal method,and Eu3+ was successfully incorporated into the crystal lattice of CdTe and measured by X-ray powder diffraction(XRD),transmission electron microscopy(TEM),ultraviolet-visible(UV-Vis) absorption spectroscopy and fluorescence emission.The CdTe:Eu^3+ nanocrystals still have a cubic crystal structure,and the corresponding XRD peaks of CdTe:Eu3+nanocrystals shift to larger angles compared with those of pure CdTe.The CdTe:Eu3+ nanocrystals are monodisperse and the particles size is about 2-4 nm.Compared with pure CdTe,the CdTe:Eu^3+ nanocrystals have larger band gap and thus exhibit blueshift in the emission spectra,which could be accounted for by the energy transfer between Eu^3+ and CdTe.To enhance the stability and functionality of CdTe:Eu3+nanocrystals,the CdTe:Eu3+nanocrystals were coated with SiO2 and the core-shell SiO2-coated CdTe:Eu3+nanocrystals(CdTe:Eu^3+@SiO2) were prepared via microemulsion method.TEM results show that CdTe:Eu3+nanocrystals are uniformly dispersed in the shell,and CdTe:Eu3+@SiO2 nanospheres are uniformly spherical with an average diameter of about 75 nm.The fluorescence emission of CdTe:Eu3+@SiO2(567 nm) shows a blueshift compared with that of CdTe:Eu^3+nanocrystals(632 nm),possibly because of altered surface properties after SiO2 coating.CdTe:Eu^3+and CdTe:Eu^3+@SiO2 with tunable photoluminescence are potentially useful in fabricating optical and bioimaging devices.

One-pot synthesis of Au@Pt star-like nanocrystals and their enhanced electrocatalytic performance for formic acid and ethanol oxidation

The current bottleneck facing further developments in fuel cells is the lack of durable electrocatalysts with satisfactory activity. In this study, a simple and fast one-pot wet-chemical method is proposed to synthesize novel Au@Pt star-like bimetallic nanocrystals （Au@Pt SLNCs） with a low Pt/Au ratio of 1：4, which show great electrocatalytic properties and outstanding stability toward the electro-oxidation reactions commonly found in fuel cells. The star-like Au core （90±20 nm） is partially coated with 5 nm Pt nanocluster shells, a morphology which creates a large amount of boundaries and edges, thus tuning the surface electronic structure as demonstrated by X-ray photoelectron spectroscopy and CO-stripping measurements. This promotes excellent electrocatalytic performance towards the formic acid oxidation reaction in acidic media and the ethanol oxidation reaction in alkaline media, compared to commercial Pt or Au@Pt triangular nanoprisms, in which the Au core is fully coated by a Pt shell. Au@Pt SLNCs have the highest current density within the dehydrogenation potential range, needing the least potential to achieve a certain current density as well as the highest long-term stability. Because of the small amount of Pt usage, very fast synthesis, excellent electrocatalytic activity and durability, the proposed Au@Pt SLNCs have a promising practical application in fuel cells.

Composition- and oxidation-controlled magnetism ternary FeCoNi nanocrystals

Ternary FeCoNi metallic nanostructures have attracted significant attention due to their high saturation magnetization, unique mechanical properties, and large corrosion resistance. In this study, we report a controlled synthesis of ternary FeCoNi nanocrystals using solution-based epitaxial core-shell nanotechnology. The thickness and stoichiometry of the FeCoNi nanocrystals affect their magnetic characteristics, which can be controlled by a phase transformation-induced tetragonal distortion. Furthermore, surface oxidation of the stoichiometry-controlled FeCoNi nanostructures can drastically enhance their magnetic coercivity （up to 8,881.60e for AuCu-FeCo）, and optimize the AuCu-FeCo08Ni0.2 performance corresponding to the saturated magnetization of 134.4 emu-g-1 and coercivity of 4,036.70e, which opens the possibility of developing rare-earth free high energy nanomagnets.

Organic polystyrene and inorganic silica double shell protected lead halide perovskite nanocrystals with high emission efficiency and superior stability

The practical application of all-inorganic semiconductor lead halide perovskite nanocrystals(LHP NCs)has been limited by their poor stability.Recently,a lot of research on core-shell structure has been done to improve the stability of perovskite NCs,but the effect was far from the application requirements.Herein,we,for the first time,report a convenient approach to synthesize organic-inorganic double shell CsPbBr_(3)@SiO_(2)@polystyrene(PS)NCs with an inter-core of CsPbBr_(3),the intermediate layer of SiO_(2)shell,and outmost PS shell.Particularly,the CsPbBr_(3)@SiO_(2)@PS NCs maintained more than 90%of their initial photoluminescence(PL)intensity under one month's ultraviolet lamp irradiation or in 85℃ and 85%relative humidity(RH)condition.The white-light-emitting-diodes(WLEDs)were fabricated by encapsulating commercial InGaN chip with CsPbBr_(3)@SiO_(2)@PS NCs and K2SiF6:Mn^(4+)(KSF:Mn^(4+))phosphor with a luminous efficacy of~100 lm/W at 20 mA current and a color gamut of 128%of the National Television Standards Committee(NTSC)standard.In addition,these WLEDs still maintain 91%of the initial luminous efficacy after 1200 h of continuous lighting.These results demonstrated that double shell-protected CsPbBr_(3)perovskite NCs have great potential in the field of WLEDs.

Multilayer core-shell nanostructures for enhanced 808 nm responsive upconversion

The construction of core-shell structure is an effective strategy for promoting the emission efficiency of upconversion nanocrystals(UCNCs). In this work, the UCNCs based on Nd-doping with a multilayer coreshell nanostructure are fabricated toward achieving efficient upconversion for 808 nm excitation, which have great potential for optical applications, especially photobiological applications.

Controlled one-pot synthesis of RuCu nanocages and Cu@Ru nanocrystals for the regioselective hydrogenation of quinoline

RuCu nanocages and core–shell Cu@Ru nanocrystals with ultrathin Ru shells were first synthesized by a one-pot modified galvanic replacement reaction. The construction of bimetallic nanocrystals with fully exposed precious atoms and a high surface area effectively realizes the concept of high atom-efficiency. Compared with the monometallic Ru/C catalyst, both the RuCu nanocages and Cu@Ru core–shell catalysts supported on commercial carbon show superior catalytic performance for the regioselective hydrogenation of quinoline toward 1,2,3,4-tetrahydroquinoline. RuCu nanocages exhibit the highest activity, achieving up to 99.6% conversion of quinoline and 100% selectivity toward 1,2,3,4-tetrahydroquinoline. [Figure not available: see fulltext.] © 2015, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

Electrospun Polyacrylonitrile Membrane In Situ Modified with Cellulose Nanocrystal Anchoring TiO_(2)for Oily Wastewater Recovery

With the increasingly urgent demand for clean water resources and the growing emission of oily wastewater,high-flux oil/water separation materials with the special wettability are progressively desired.Cellulose nanocrystal(CNC)from renewable biomass has been utilized to fabricate oil/water separation membranes,but it is limited to enhancing mechanical properties.Herein,a wrinkled structure with abundant–OH is constructed on polyacrylonitrile(PAN)nanofibers via the CNC hybridization process.And then,a super-hydrophilic nano-TiO_(2)shell is anchored tightly on the surface of the fiber by wrinkles and–OH.The CNC promotes significantly the in situ growth of TiO_(2),with the TiO_(2)loading ratio of up to 5.3%.The nano-TiO_(2)shell endows the obtained film with super-hydrophilicity and underwater super-oleophobicity,resulting in a visible increase of the permeation flux for the oil/water mixture from 1483 to 11,023 L m^(−2)h^(−1).Interestingly,the hierarchical structure facilitates the demulsification for oil-in-water emulsion stabilized by surfactant,allowing the obtained membrane to exhibit eminent antifouling property and high emulsion permeability of about 3,278 L m^(−2)h^(−1).This design strategy develops next-generation anchors for targeted modification on the non-reactive substrates and provides a novel pathway for fabricating oil/water separation membranes.

Engineering upconverting core–shell nano-probe for spectral responsive fluid velocimetry

Particle velocimetry based on the temporal feature of upconversion luminescent nanocrystals is a newly-raising fluid velocimetry.Exploiting the availability to low flow rate fluid and exempting redundance external calibration(achieving once calibration for all)are highly expected and challenging.Herein,an engineered core–shell nano-probe,NaYF4:Yb/Ho/Ce@NaGdF4,was proposed,in which the Ce3+ions were utilized to manipulate the upconversion dynamic of Ho3+.Through optimization,a superior sensitive against low-speed flow is achieved,and the external calibrations before each operation can be avoided.Application demonstrations were conducted on a fluid circulation system with controllable flow rate.The fluid velocity was monitored successfully,no matter it is permanent,or cyclically variating(imitating the in vivo arterial blood).Moreover,this velocimetric route is competent in spatial scanning for handling the spatially inhomogeneous velocity field.Such sensing nanomaterial and fluid velocimetric method exhibit promising application potential in human blood velocimetry,industrial control,or environmental monitoring.

Surface strain-enhanced MoS_(2)as a high-performance cathode catalyst for lithium-sulfur batteries

Lithium-sulfur batteries(LSBs)are one of the main candidates for the next generation of energy storage systems.To improve the performance of LSBs,we herein propose the use of strained MoS_(2)(s-MoS_(2))as a catalytically active sulfur host.The introduction of strain in the MoS_(2)surface,which alters its atomic positions and expands the S-Mo-S angle,shifts the d-band center closer to the Fermi level and provides the surface with abundant and highly active catalytic sites;these enhance the catalyst's ability to adsorb lithium polysulfides(LiPS),accelerating its catalytic conversion and promoting lithium-ion transferability.Strain is generated through the synthesis of core-shell nanoparticles,using different metal sulfides as strain-inducing cores.s-MoS_(2)nanoparticles are supported on carbon nanofibers(CNF/s-MoS_(2)),and the resulting electrodes are characterized by capacities of 1290 and 657 mAh g−1 at 0.2 and 5 C,respectively,with a 0.05%capacity decay rate per cycle at 8 C during 700 cycles.Overall,this work not only provides an ingenious and effective strategy to regulate LiPS adsorption and conversion through strain engineering,but also indicates a path toward the application of strain engineering in other energy storage and conversion fields.