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Au-and Ag-ZnO composite nanocrystals having a dumbbell-like structure were successfully synthesized through the nucleation and decomposition of zinc hydroxide at the surface of pre-existing Au and Ag nanoparticles, respectively. The average size of the Au and Ag nanoparticles used was ∼4 nm and that of the ZnO nanocrystals was ∼10 nm. The composite nanocrystals show strong crystallinity of face-centered cubic and wurztite structures from Au or Ag and ZnO, respectively. The composite nanocrystals show enhanced UV light emission due not only to the surface electron transfer from the Au or Ag to the ZnO by the surface plasmon resonance (SPR) but also to the extension of the Fermi energy level to the ZnO. The Au-ZnO composite nanocrystals showed significantly suppressed visible light luminescence, while the Ag-ZnO did not show any apparent difference compared to the ZnO nanocrystals.

Straight-stranded anatase TiO2 nanotubes were produced by anodic oxidation on a pure titanium substrate in an aqueous solution containing a 0.45 wt % NaF electrolyte (pH 4.3 fixed). The average length of the TiO2 nanotubes was approximately 3 μm, which had an effect on the level of dye adsorption in the dye-sensitized solar cells. The anodic TiO2 nanotubes were applied as a working electrode in a solid-state dye-sensitized solar cell. An approximately 1 nm ZnO shell was coated on the TiO2 nanotube to improve the open-circuit voltage (V oc) and conversion efficiency of the solar cell, and to retard any back reaction. Although the V oc and short-circuit current (J sc) of the cell were improved, there was a low fill factor as a result of the formation of a thick TiO2 barrier layer in the anodic TiO2/Ti substrate. A parameter on the degradation of fill factor (37%) is related to the formation of a thick TiO2 barrier layer in the anodic TiO2/Ti substrate interface. A hydrogen peroxide treatment was performed in an attempt to narrow the TiO2 barrier layer. This treatment was found to influence not only fill factor (37−49%) but also the conversion efficiency (0.704−0.906%) of the cell by eliminating the remnant after anodic reaction and barrier narrowing through an etching effect. This result was confirmed by X-ray photoelectron spectroscopy (XPS) and photocurrent-voltage measurements. The longer electron lifetime on the ZnO coated TiO2 film was measured by the open-circuit voltage decay. The improvement in the electron lifetime from the thin ZnO coating affects the number of electrons collected on the Ti substrate and the retardation of charge recombination. Therefore, the ZnO coating on the TiO2 nanotube film improves the efficiency of dye-sensitized TiO2 solar cells from the extended V oc from ZnO coating confirmed by the Mott−Schottky plots and the increased J sc through the inhibition of charge recombination confirmed by IPCE measurements.

White light was obtained by mixing blue light from the emission of a gallium nitride ͑GaN͒ chip and yellow light from the fluorescence of a Y 3 Al 5 O 12 :Ce 0.05 yellow phosphor. A uniform coating and an optimized thickness of yellow phosphor layer on a GaN chip were necessary for achieving an efficient white light emitting diode. The phosphor particles were coated on a GaN chip or indium tin oxide by several methods including the slurry method, the settling method, and electrophoretic deposition ͑EPD͒. The properties of the phosphor layers prepared by these methods were examined using scanning electron microscope and photoluminescence. The chromaticity of white light was dependent upon the thickness of the phosphor layer. The properties of the phosphor layer prepared by EPD such as packing density, thickness, and uniformity could be more easily controlled than those by the slurry and settling methods. Further high packing density of the EPD could compensate for the typical thick phosphor layer, allowing the thin layer to be fabricated. To overcome the weak adhesion strength of phosphor particles by the EPD, an aqueous solution including poly͑vinyl alcohol͒ ϩ ammonium dichromate was coated on the phosphor layer and cured by exposure to ultraviolet light.Yttrium aluminum garnet (Y 3 Al 5 O 12 , YAG͒ materials have been widely studied for their applications to fluorescent and solid state lasers, since YAG is a hard material which is not easily damaged under conditions of high irradiation. 1-4 The Y 3 Al 5 O 12 -Ce phosphor shows a bright yellow emission under excitation with a blue radiation ͑460 nm͒, and, thus, it is potentially applicable to a white light emitting diode ͑LED͒ by combining it with a blue gallium nitride ͑GaN͒ LED. 5 To improve the luminescence efficiency, the combinatorial method and an application of BaF 2 flux were used for the phosphor synthetic process.Advantages of LEDs include high brightness, reliability, low power consumption, and a long life. 6,7 The use of a blue LED for a white light prevents the generation of ultraviolet ͑UV͒ light by a fluorescent lamp. Applications of white LEDs can be found in general lighting including illuminations, displays, and signage. 7 The uniformity, optimized thickness, and packing density of a yellow phosphor layer on a GaN chip are important for achieving a highly efficient white LED. The adhesion strength of the phosphor layer on a GaN chip is also critical, since the weak adhesion strength of the phosphor layer may result in the dislodging of the phosphor during processing or a short lifetime of the fabricated white LED. For the coating of a yellow phosphor on a GaN chip, several methods such as slurry, settling, and electrophoretic deposition ͑EPD͒ are available.The slurry method is based on coating such as flowing, dipping, spinning, and photodevelopment of a phosphor suspension in a photoresist. A photochemical reaction such as the oxidation of poly͑vinyl alcohol͒ ͑PVA͒ and the reduction of ammonium dichromate ͑ADC͒ occurs and results in cross-linki...

Various kinds of nanostructured materials have been extensively investigated as lithium ion battery electrode materials derived from their numerous advantageous features including enhanced energy and power density and cyclability. However, little is known about the microscopic origin of how nanostructures can enhance lithium storage performance. Herein, we identify the microscopic origin of enhanced lithium storage in anatase TiO 2 nanostructure and report a reversible and stable route to achieve enhanced lithium storage capacity in anatase TiO 2 . We designed hollow anatase TiO 2 nanostructures composed of interconnected ∼5 nm sized nanocrystals, which can individually reach the theoretical lithium storage limit and maintain a stable capacity during prolonged cycling (i.e., 330 mAh g −1 for the initial cycle and 228 mAh g −1 for the 100th cycle, at 0.1 A g −1 ). In situ characterization by X-ray diffraction and X-ray absorption spectroscopy shows that enhanced lithium storage into the anatase TiO 2 nanocrystal results from the insertion reaction, which expands the crystal lattice during the sequential phase transition (anatase TiO 2 → Li 0.55 TiO 2 → LiTiO 2 ). In addition to the pseudocapacitive charge storage of nanostructures, our approach extends the utilization of nanostructured TiO 2 for significantly stabilizing excess lithium storage in crystal structures for long-term cycling, which can be readily applied to other lithium storage materials.