Chunsheng Liao

Fluorescence intensity and color purity improvement in nanosized YBO3:Eu

In order to improve the color purity of YBO3:Eu, which is practically used as a plasma phosphor, the lowering of the structural symmetry is proposed and subsequently realized in nanosized YBO3:Eu so as to increase the contribution of 5D0–7F2 transition of the luminescent centers, Eu3+ ions. Spherical YBO3:Eu nanocrystals were fabricated via thermal decomposition of complex precursors and could be crystallized at lower temperature than required by the bulks. The particle size could be controlled by adjusting the annealing temperature and time. Unlike the bulk YBO3:Eu synthesized by solid-state reaction, the quenching concentration increased with the decrease of the particle size. Furthermore, the fluorescence intensity and color purity were significantly improved in nanocrystals. Possible mechanisms responsible for these improvements were proposed.

ZnO nanowires fabricated by a convenient route

A convenient microemulsion-mediated hydrothermal process was employed to synthesize ZnO nanowires, which exhibited a strong ultraviolet emission and a relatively weak defect emission. X-Ray diffraction, scanning electron microscopy, transmission electron microscopy and fluorescence spectroscopy were used to characterize the as-prepared ZnO nanowires.

Nanophased CoFe2O4 prepared by combustion method

The combustion method has been utilized to prepare nanophased powders of cobalt spinel ferrite using glycine as fuel. Structural and magnetic properties of the products were investigated with an X-ray diffractometer, a surface analyzer, and an alternating gradient magnetometer, respectively. Cobalt spinel ferrite prepared by the present method can easily form the well-crystallized nanoscale particles with a large specific surface area. The magnetization and coercivity show a strong dependence on the G/N (glycine to nitrates) ratio in the range from 0.2 to 1.0.

MICROSTRUCTURE, MAGNETIC, AND MAGNETO-OPTICAL PROPERTIES OF CHEMICAL SYNTHESIZED CO-RE (RE=HO, ER, TM, YB, LU) FERRITE NANOCRYSTALLINE FILMS

The sol-gel synthesis of Co–RE (RE=Ho, Er, Tm, Yb, Lu) ferrite nanocrystalline films was accomplished on monocrystalline silicon substrates, and the influence of RE ions on structure, magnetic, and magneto-optical (MO) properties of the resultant ferrites was examined. The results obtained reveal that, when x⩽0.2, the CoFe2−xRExO4 ferrite films have pure spinel phase with slightly enlarged cell constants and lattice distortion due to the large radii of RE ions. The RE ions tend to decrease the room-temperature magnetization as well as the Curie point of products, and may have a certain contribution to coercive force except for a nonmagnetic Lu3+ ion. For the present optical structure in which MO layers are substrated on silica, Co–RE ferrite films show the peak Kerr rotation at a shorter wavelength than the CoFe2O4 film, and Er or Tm doped samples exhibit an interesting enhancement of the MO effect.

Rare earth activated nanosized oxide phosphors: synthesis and optical properties

Gd 2 O 3 :I Eu and (Gd,Y) 2 O 3 : Eu nanocrystals were prepared by the glycine assist combustion method. The as-prepared products are porous networks from the HTEM and isolated nanoparticles can be observed after further annealing From the luminescence spectra and XRD patterns, the prepared Gd 2 O 3 : Eu nanocrystals were found to be monoclinic. While Y 3+ doped into the Gd 2 O 3 to form the complex host, the structure changed from monoclinic to cubic when Y 3+ /Gd 3+ is 0.3. More interesting, the luminescent intensity of the (Gd,Y) 2 O 3 : Eu nanocrystals is higher than that of pure Y 2 O 3 : Eu or Gd 2 O 3 : Eu system Besides XRD pattern, the luminescence spectra, another powerful evidence in deducing the crystal structure, are used for analysis.

ZnS nanoparticles doped with Cu(I) by controlling coordination and precipitation in aqueous solution

A novel method for the synthesis of ZnS:Cu colloids has been studied in aqueous solution, in which the Cu + ions were incorporated into the ZnS matrix by the assistance of a sulfur-containing ligand, i.e. thiourea or thiosulfate. The optical properties of the colloids (absorption, emission and excitation spectra) were studied. Compared with the bulk materials, the absorption band-edge is blue-shifted, which is attributed to a quantum size effect. The average ZnS nanoparticle size, deduced from the absorption spectra by an effective mass approximation, is about 4 nm. Upon excitation at 325 nm, a broad green emission band is observed, while for samples doped with 0.2% Cu, a blue emission band at 450 nm is also observed, which is quenched at higher dopant concentrations. It is concluded that Cu + ions occupy Zn 2+ sites in the lattice of ZnS nanocrystals and act as both green and blue luminescent centers at different dopant concentrations. The sulfur-containing ligand (thiourea or thiosulfate) plays an important role in the synthesis as both ligand and surfactant; it stabilizes the Cu + ions, reduces the solubility difference between ZnS and Cu 2 S, and protects the particles surfaces.

Nanostructure magneto-optical thin films of rare earth (RE=Gd,Tb,Dy) doped cobalt spinel by sol–gel synthesis

Nanocrystalline CoFe1.9RE0.1O4 [rare earth (RE=Gd,Tb,Dy)] films have been prepared by the sol–gel route, and their polar magneto-optical (MO) Kerr rotation and ellipticity have been determined in the spectral range of 4000–8000 A. The films are composed of nanometer grains with the spinel structure. RE doped cobalt spinel ferrites are found to have dramatic changes in magnetic and MO properties, with increases in their coercive force and enhancement of the MO rotation in the Tb3+ doped sample.

Topological isomerism in the formation of a novel three-dimensional metal-organic polycatenane

The self-assembly of cadmium nitrate with sodium dicyanamide and 1,3-bis(4′-pyridyl)propane generates a kinetic 1D isomer and a thermodynamic 2D isomer, which presents an unusual pattern of 3D supramolecular entanglement.

Large enhancement in room-temperature magnetoresistance and dramatic decrease in resistivity in La0.7Ca0.3MnO3–Ag composites

A ferromagnet-metal-type composite, La0.7Ca0.3MnO3 (LCMO)–Ag, was fabricated by a two-step chemical route which can avoid the doping of Ag into the lattice of LCMO. The grain size of Ag can be reduced by increasing calcination temperature, which favors the penetration of Ag into LCMO matrices. A large enhancement in magnetoresistance (MR) near room temperature and a dramatic decrease in resistivity are observed for the samples calcined at above the melting temperature of Ag. We suggest that the shift of metal–insulator transition up to Curie temperature in melted-Ag-added LCMO and magnetic inhomogeneity are responsible for the enhanced MR.

Chemical synthesis and magnetic study of nanocrystalline thin films of cobalt spinel ferrites

The sol-gel method was introduced to prepare the nanocrystalline thin films of cobalt spinel ferrite, which presents a convenient approach to perform the doping of foreign ions. The dependence of morphology and grain sizes of thus-obtained thin films on the annealing temperature were observed. Nanocrystalline thin films of CoFe2O4 have relatively lower magnetization than bulk phase and negative interactions between magnetic grains, the latter of which may be of significance to reduce the media noise for polycrystalline materials.