Synthesis and Photoluminescent Properties of Rare Earth Doped ZnO Hierarchical Microspheres

Hierarchical ZnO microspheres constructed by mesoporous quasi-single-crystalline ZnO nanosheets were fabricated by pyrolysis of the microspheres of layered hydroxide zinc carbonate, Zn5(CO3)2(OH)6, which was the hydrothermal precipitate of zinc nitrate and urea. A growth mechanism of Zn5(CO3)2(OH)6 microspheres was proposed. During the pyrolysis process, single-crystalline Zn5(CO3)2(OH)6 nanosheets were transformed into mesoporous quasi-single-crystalline ZnO nanosheets. When the samples were doped with trivalent rare earth ion, RE3+ (RE = Pr, Sm, Tb, Ho, Tm), no ZnO → RE3+ energy transfer was observed. However, the ZnO:Eu3+ sample showed efficient Eu3+ emissions under UV photon excitation (λ < 365 nm), which is attributed to energy transfer from photon-generated electron−hole pairs to Eu3+ ions in the surface layer of the ZnO nanosheet

The Formation of Mesoporous TiO₂ Spheres via a Facile Chemical Process

The mesoporous TiO2 solid and hollow spheres have been synthesized via a controllable and simple chemical route. Structural characterization indicates that these TiO2 mesoporous spheres after calcined at 500 °C have an obvious mesoporous structure with the diameters of 200−300 nm for solid spheres and 200−500 nm for hollow spheres. The average pore sizes and BET surface areas of the mesoporous TiO2 solid and hollow spheres are 6.8, 7.0 nm and 162, 90 m2/g, respectively. Optical adsorption investigation shows that TiO2 solid and hollow spheres possess a direct band gap structure with the optical band gap of 3.68 and 3.75 eV, respectively. A possible formation mechanism for TiO2 solid and hollow spheres is discussed

Synthesis of Rare Earth Ions-Doped ZnO Nanostructures with Efficient Host−Guest Energy Transfer

Rare earth (RE) ions (Tb3+, Dy3+, and Er3+) are incorporated into ZnO nanostructures by a facile isocrystalline core−shell (ICS) protocol. Characteristic photoluminescence of rare earth ions has been observed for these doped nanocrystals. Effective doping has also been manifested by dramatic splitting and enhancement of intra-4f transitions in photoluminescence excitation spectra. Efficient energy transfer from ZnO host to guest RE ions has been revealed through the characteristic emissions of RE ions by direct excitation of ZnO host. The ICS protocol is universal in doping rare earth ions into ZnO nanocrystals with a spherical shape and shows a great potential for a variety of applications

Kinetics-Driven Growth of Orthogonally Branched Single-Crystalline Magnesium Oxide Nanostructures

Orthogonally branched single-crystalline magnesium oxide nanostructures were synthesized through a simple chemical vapor transport and condensation process in a flowing Ar/O2 atmosphere. Other morphologies, such as cubes and nanowires, can also be obtained under different controlled conditions. The formation of different types of nanostructures can be tuned by modifying oxygen partial pressure during the synthesis. All the nanostructures are cubic single-crystalline enclosed by low-index {100} facets. Growth mechanisms for the nanostructures are discussed in detail:  different supersaturation ratios, relatively high substrate temperatures, and surface defects in certain crystallographic planes cooperatively take important effects on determining the product morphologies. Structural defect-related blue light emission of the three types of MgO nanostructures was investigated. The MgO nanostructures with abundant morphologies may find applications in various nanodevices, and the kinetics-driven methodology might be exploited to synthesize similar nanostructures of other functional oxide materials

Synthesis of Rare Earth Ions-Doped ZnO Nanostructures with Efficient Host−Guest Energy Transfer

Rare earth (RE) ions (Tb3+, Dy3+, and Er3+) are incorporated into ZnO nanostructures by a facile isocrystalline core−shell (ICS) protocol. Characteristic photoluminescence of rare earth ions has been observed for these doped nanocrystals. Effective doping has also been manifested by dramatic splitting and enhancement of intra-4f transitions in photoluminescence excitation spectra. Efficient energy transfer from ZnO host to guest RE ions has been revealed through the characteristic emissions of RE ions by direct excitation of ZnO host. The ICS protocol is universal in doping rare earth ions into ZnO nanocrystals with a spherical shape and shows a great potential for a variety of applications

Synthesis of Eu₂O₃ Nanotube Arrays through a Facile Sol−Gel Template Approach

Eu2O3 nanotubes have been successfully fabricated by an improved sol−gel template method within the nanochannels of porous anodic alumina templates. The morphology, structure, and composition of the nanotubes were characterized by means of X-ray diffraction techniques, scanning electron microscope, transmission electron microscopy, and selected-area electron diffraction. The results show that the Eu2O3 nanotubes are polycrystalline with a cubic structure. The outer diameter of nanotubes is 50−80 nm, and the thickness of the tube wall is about 5 nm. The mechanism of nanotube formation was discussed

Periodically Twinned Nanowires and Polytypic Nanobelts of ZnS: The Role of Mass Diffusion in Vapor−Liquid−Solid Growth

There are two mass diffusion processes regarding the vapor−liquid−solid (VLS) growth of nanostructures:  one is inside the catalyst droplet toward the liquid−solid interface; the other is along the side surface planes of the growing nanostructures. In this letter, microscale, modulated mass diffusion scenarios are exhibited through the synthesis of two types of ZnS nanostructures in an Au-catalyzed VLS process:  periodically twinned nanowires originated from periodical fluctuation between diffusion rate inside the catalytic droplet and the growth rate on the liquid−solid interface; the formation of asymmetrically polytypic nanobelts is related to one certain side surface bounded by high surface-energy plane, which serves as a preferential diffusion direction of reactant adatoms. The results may have important impact on the understanding of the physical and chemical process of the VLS mechanism. These longitudinally and latitudinally tunable crystalline structures enrich the family of one-dimensional nano-building blocks, and may find potential applications in nanotechnology

Electronic Transport Behavior of Bismuth Nanotubes with a Predesigned Wall Thickness

Bismuth nanotubes (BiNTs) were synthesized by electrodeposition inside the nanochannels of an anodic aluminum oxide template coated with a thin mesh-like Au layer onto one planar surface side. By tuning the Au layer thickness and current density during electrodeposition, BiNTs with a predesigned wall thickness and with a wall thickness variation along the axis were achieved. Measurements of resistance−temperature demonstrate that BiNTs show a semiconducting electronic transport behavior, and the resistance of BiNTs with thinner walls shows a larger temperature dependence than that of BiNTs with thick walls. Our approach could be used to build other materials that can be obtained via electrodeposition into nanotubes with a designed wall thickness that might have potential in future nanotechnology

Controlled Growth and Phase Transition of Silver Nanowires with Dense Lengthwise Twins and Stacking Faults

Large-scale face-centered cubic (FCC)-Ag nanowires with dense (111) stacking faults and (111)/[112] growth twins were prepared by the electrodeposition in the holes of porous alumina template. The obtained twins and stacking faults in Ag nanowires are parallel to the axis of the nanowire and persist along the whole wire length. Importantly, novel 4H-Ag nanowires can form spontaneously after aging or heating this kind of FCC-Ag nanowire. This study contributes to the understanding of planar defect formation in the electrodeposition process and could be used to control the crystalline structure of Ag nanowires

Micro-Nano-Structured Fe₂O₃:Ti/ZnFe₂O₄ Heterojunction Films for Water Oxidation

Iron­(III) oxide photoelectrodes show promise in water oxidation applications. In this study, micro-nano-structured hematite films are synthesized, and Ti ions are doped to improve photoelectric conversion efficiency. The photocurrent increases for enhanced electrical conductivity. Further enhanced photocurrent is achieved for Fe₂O₃:Ti/ZnFe₂O₄ heterojunction electrodes. Cyclic voltammograms combined with optical absorbance examinations demonstrate that the conduction and valence band edges of ZnFe₂O₄ shift from those of Ti doped Fe₂O₃ to the negative direction, which facilitates the efficient separation of electron–hole pairs at the Fe₂O₃:Ti/ZnFe₂O₄ interface. These findings demonstrate that, by doping hematite and by engineering the interface between the hematite and the electrolyte, charge separation can be effectively promoted and photocurrent density can be dramatically increased