General and Facile Method To Prepare Uniform Y2O3:Eu Hollow Microspheres

Well-shaped Y2O3:Eu hollow microspheres have been successfully prepared on a large scale via a urea-based homogeneous precipitation technique in the presence of colloidal carbon spheres as hard templates followed by a subsequent heat treatment process. XRD results demonstrate that all the diffraction peaks of the samples can be well indexed to the pure cubic phase Of Y2O3. TEM and SEM images indicate that the shell of the uniform hollow spheres, whose diameters are about 250 nm, is composed of many uniform nanoparticles with diameters of about 20 nm, basically consistent with the estimation of XRD results. Furthermore, the main process in this method was carried out in aqueous condition, without the use of organic solvents or etching agents. The as-prepared hollow Y2O3:Eu microspheres show a strong red emission corresponding to the D-5(0)-F-7(2) transition of the Eu3+ ions under ultraviolet or low voltage excitation, which might find potential applications in fields such as light phosphor powders, advanced flat panel displays, field emission display devices, and biological labeling.

Highly uniform and monodisperse beta-NaYF4 : Ln(3+) (Ln = Eu, Tb, Yb/Er, and Yb/Tm) hexagonal microprism crystals: Hydrothermal synthesis and luminescent properties

beta-NaYF4:Ln(3+) (Ln = Eu, Tb, Yb/Er, and Yb/Tm) hexagonal microprisms with remarkably uniform morphology and size have been synthesized via a facile hydrothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra as well as kinetic decays were used to characterize the samples. It is found that sodium citrate as a shape modifier introduced into the reaction system plays a critical role in the shape evolution of the final products. Furthermore, the shape and size of the products can be further manipulated by adjusting the molar ratio of citrate/RE3+ (RE represents the total amount of Y3+ and the doped rare earth elements such as Eu3+, Tb3+, Yb3+/Er3+, or Yb3+/Tm3+). Under the excitation of 397 nm ultraviolet light, NaYF4:xEu(3+) (x = 1.5, 5%) shows the emission lines of Eu3+ corresponding to D-5(0-3) -> F-7(J) (J = 0-4) transitions from 400 to 700 nm (whole visible spectral region) with different intensity, resulting in yellow and red down-conversion (DC) light emissions, respectively.

Large-scale, uniform DNA network on 11-mercaptoundecanoic acid modified gold (111) surface: Atomic force microscopy study

Large-scale, uniform plasmid deoxyribonucleic acid (DNA) network has been successfully constructed on 11-mercaptoundecanoic acid modified gold (111) surface using a self-assembly technique. The effect of DNA concentration on the characteristics of the DNA network was investigated by atomic force microscopy. It was found that the size of meshes and the height of fibers in the DNA network could be controlled by varying the concentration of DNA with a constant time of assembly of 24 h.

Large scale, templateless, surfactantless route to rapid synthesis of uniform poly(o-phenylenediamine) nanobelts

We reported the interesting finding that large scale uniform poly(o-phenylenediamine) nanobelts with several hundred micrometers in length, several hundred nanometers in width, and several ten nanometers in height can be rapidly yielded from an o-phenylenediamine-HAuCl4 aqueous solution without the additional introduction of other templates or surfactants at room temperature.

Carboxyl-cored dendrimer and toluene-assisted fabrication of uniform platinum nanodendrites at a water/oil interface and their potential application as a catalyst

Uniform platinum nanodendrites have been prepared at a water/oil interface by a facile catalyst-free method at room temperature. This is carried out by introducing NaBH4 into the platinum precursor solution in the presence of the second generation of carboxyl-cored dendrimer ([G-2]-CO2H dendrimer) and toluene to act as a protective agent and a linker, respectively. The average fractal dimension of 1.61 of the obtained platinum nanodendrites is calculated by analysing the transmission electron micrographs using the programs Fractal Dimension Version 1.1 and Fractal Dimension Calculator. Control experiments show that the fabrication of platinum nanodendrites can be operated with a wide parameter window, which undoubtedly raises the degree of control of the synthesis process. The potential application of such a nanostructure as a catalyst is investigated, and the results reveal that they show highly efficient catalytic properties for the typical redox reaction between hexacyanoferrate (III) and thiosulfate ions at 301 K.

CRYSTALLINITY OF UNIFORM OLIGO(OXYETHYLENE) MONO-N-ALKYL ETHERS STUDIED BY X-RAY-DIFFRACTION AND DIFFERENTIAL SCANNING CALORIMETRY

The crystallinity of two series of uniform oligo(oxyethylene) mono-n-alkyl ethers has been investigated: alpha-alkyl,omega-hydroxyoligo(oxyethylene)s, H(CH2)n(OCH2CH2)mOH, and alpha-alkyl,omega-methoxyoligo(oxyethylene)s, H(CH2)n(OCH2CH2)mOCH3. The hydroxy-ended oligomers formed bilayer crystals, and the methoxy-ended oligomers formed monolayer crystals. The helical oxyethylene blocks were oriented normal to the layer-crystal end-group plane, whilst the trans-planar alkyl blocks were generally tilted at an angle delta = 60-degrees. The melting temperature and enthalpy of fusion were higher for hydroxy-ended oligomers than for corresponding methoxy-ended oligomers.

Strongly nonlinear long interfacial waves in uniform basic flows and their dispersion relationship

In this paper, long interfacial waves of finite amplitude in uniform basic flows are considered with the assumption that the aspect ratio between wavelength and water depth is small. A new model is derived using the velocities at arbitrary distances from the still water level as the velocity variables instead of the commonly used depth-averaged velocities. This significantly improves the dispersion properties and makes them applicable to a wider range of water depths. Since its derivation requires no assumption on wave amplitude, the model thus can be used to describe waves with arbitrary amplitude.

Second-order solutions for random interfacial waves under steady uniform currents

In the present research, the study of Song (2004) for random interfacial waves in two-layer fluid is extended to the case of fluids moving at different steady uniform speeds. The equations describing the random displacements of the density interface and the associated velocity potentials in two-layer fluid are solved to the second order, and the wave-wave interactions of the wave components and the interactions between the waves and currents are described. As expected, the extended solutions include those obtained by Song (2004) as one special case where the steady uniform currents of the two fluids are taken as zero, and the solutions reduce to those derived by Sharma and Dean (1979) for random surface waves if the density of the upper fluid and the current of the lower fluid are both taken as zero.

Second-order solutions for random interfacial waves in N-layer density-stratified fluid with steady uniform currents

In the present paper, the random inter facial waves in N-layer density-stratified fluids moving at different steady uniform speeds are researched by using an expansion technique, and the second-order a symptotic solutions of the random displacements of the density interfaces and the associated velocity potentials in N-layer fluid are presented based on the small amplitude wave theory. The obtained results indicate that the wave-wave second-order nonlinear interactions of the wave components and the second-order nonlinear interactions between the waves and currents are described. As expected, the solutions include those derived by Chen (2006) as a special case where the steady uniform currents of the N-layer fluids are taken as zero, and the solutions also reduce to those obtained by Song (2005) for second-order solutions for random interfacial waves with steady uniform currents if N=2.

XRD and XPS studies on the ultra-uniform Raney-Ni catalyst prepared from the melt-quenching alloy

We present a novel method for preparing an ultra-uniform Raney-Ni catalyst, which includes melt-quenching, hydrogen treatment and leaching in an alkali solution. The resultant catalyst shows superior activity in the reaction of cyclohexanone hydrogenation. X-ray diffraction (XRD) and XPS have been employed to characterize the catalysts. As demonstrated, the pretreatment with hydrogen caused a distinct phase transfer of the Ni-Al alloys, forming more of the Ni2Al3 component. In the subsequent leaching process, the Ni2Al3 component shows high activity and the resultant catalyst exhibits high surface areas and small pores. Moreover, metallic Al in the hydrogen-pretreated alloy appeared to be leached more easily and thus the aluminium species remaining on the catalyst surface is aluminium oxide predominantly, which serves as a matrix to stabilize active Ni species on the surface. Copyright (C) 2001 John Wiley & Sons, Ltd.

Controlled growth of uniform silver clusters on HOPG

We have investigated growth of silver clusters on three different, i.e. normally cleaved, thermally oxidized and Ar+ ion sputtered highly oriented pyrolytic graphite (HOPG), surfaces. Scanning tunneling microscopy (STM) observations reveal that uniformly sized and spaced Ag clusters only form on the sputtered surface. Ar+ sputtering introduces relatively uniform surface defects compared to other methods. These defects are found to serve as preferential sites for Ag cluster nucleation, which leads to the formation of uniform clusters. (c) 2005 Elsevier B.V. All rights reserved.