Advanced Materials Research Vols. 306-307

Abstract: Temperature dependent photoluminescence of ZnO nanorods synthesized by hydrothermal method is studied. According to fifteen photoluminescent curves which were measured from 78 K to 288 K with an interval of 15 K, peak energy of exciton emissions, integral intensity of exciton emission peaks and integral intensity of deep-level emission peaks as a function of temperature were studied. The experimental data were fitted by Bose-Einstein relation and thermal activation function. By fitting, some important parameters were obtained and compared, such as the Einstein temperature for the excitons, the thermal activation energy of excitons or deep-level defects etc.

Abstract: Carbon nanofibers with various morphologies were synthesized by the catalytic pyrolysis of acetylene using nickel catalyst nanoparticles at different reaction temperatures. Experimental results demonstrate that temperature is a critical parameter for controlling the size and morphology of carbon fibers. Twin coiled fibers and linearly bifurcating fibers emanating from nickel particles were formed at 400 °C; whereas, only linear carbon nanofibers were obtained at reaction temperatures of 450 °C, 500 °C, and 550 °C. At low temperatures, nickel nanoparticles remain in the middle of two fibers, while nickel particles are positioned at one end of the linear fibers at high temperatures.

Abstract: A series of PAM/silica nanocomposite (NC) gels using silica sol as the inorganic component were prepared by in situ free-radical polymerization. The addition of silica sol was first used to bring silica nanoparticles to form organic (polymer)/inorganic system. Results from the swelling experiment indicated that the effect of silica particle was nevertheless rather complex as polymer/particle binding. Additionally, it revealed that the swelling ratio of the NC gels with a certain silica content increased with the increasing pH value. Moreover, it exhibited absorption of the polymer onto silica because the chemical cross-linked PAM has changed to the organic/inorganic system. The spectroscopic results showed that the silica nanoparticles formed by silica sol promoted high degree of attachment to the polymer chain. The AFM micrographs displayed that silica particles were of nano degree and in the monodisperse. Both evidences proved that the organic/inorganic system was effectively formed through the addition of silica sol.

Abstract: Nanocrystalline Fe³⁺-doped La₂Zr₂O₇ series solid solutions were prepared by a convenient salt-assisted combustion process using glycine as fuel. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The results showed the La ion can be partially replaced by Fe ion. The partial substituted products were still single-phase solid solutions and the crystal form remained unchanged. TEM images reveal that the products are composed of well-dispersed square-shaped nanocrystals. The method provides a convenient and low-cost route for the synthesis of nanostructures of oxide materials. The fluorescence of La_1.8Fe_0.2Zr₂O₇ nanocrystals was evaluated by the UV-visible absorption spectra and the fluorescence spectra. The results indicate that (La_xFe_1-x)₂Zr₂O₇ nanocrystals prepared by this method are a kind of potential fluorescent-emitted material.

Abstract: An environmentally friendly synthesis was developed to fabricate aqueous CdTe quantum dots (QDs) using thilglycolic acid (TGA) as a capping agent. Optimal preparation conditions including pH (11.2) and TGA/Cd molar ratio (1.5:1) resulted in CdTe QDs with high photoluminescence (PL) quantum yield up to 56%. The TGA-capped CdTe QDs exhibited tunable PL from green to red. Lifetime measurement indicated that the average lifetime of the TGA-capped QDs increased with increasing their sizes (27.5 and 37.2 ns for the QDs with PL peak wavelength of 607 and 636 nm, respectively). The PL of the QDs revealed the dependence of temperature, in which the QDs exhibited a red-shifted PL peak with increasing temperature. Such PL behavior depended strongly on the QD sizes.

Abstract: In this paper, the fabrication and characterization of free-standing titanium dioxide nanorods array film with pure anatase-phase are presented. Highly oriented TiO₂ nanorods array was firstly prepared by hydrothermal method with metal Ti foil, and then the free-standing film can be obtained through selective-dissolution of the metallic Ti substrate by Br₂ steam with preserving the original array structure. The crystal structural, morphological, lattice structural and optical information of the free-standing array film were studied. In addition, photo-degradation of crystal voilet in aqueous solution was used as a probe to assess the photo-catalytic activity of the free-standing array film under UV irradiation.

Abstract: This article proposed a liquid phase method to synthesize the small, even sized nano lead sulfide sol in high power (2KW) pulse ultrasonic reactor, which is designed by our research group. The characteristics of this method are the short time, the small granularity, the equal particle size and the mild synthesis condition. The particle size of lead sulfide sol is about 7～8 nanometer and the size distribution is narrow. Ultraviolet and visible spectroscopy shows that the absorption limit of this lead sulfide sol is about 670nm. Compared with the normal sized lead sulfide, the absorption limit is greatly blue shifted because of the quantum size effect.

Abstract: We first synthesized gadolinium oxide (Gd2O3) by a modified “polyol” strategy and then embedded it into mesoporous silica by a simple self-assembly sol-gel reaction. Scanning electron microscope (SEM) results show that the samples have good sphericity and good dispersibility. The structure of mesoporous silica was characterized by transmission electron microscopy (TEM) and small-angle X-ray diffraction (SAXRD). Results show that the mesoporous structure has not been destroyed after gadolinium oxide imbedding. The ratio of gadolinium and silica was determined by the mean of energy dispersive spectroscopy (EDS).

Abstract: In this paper, crystallinic FeB nanoflowers were successfully prepared at 500°C for 8h with FeCl₃ and NaBH₄ as the reactants. Field-emission scanning electronic microscope (FESEM) and transmission electronic microscope (TEM) images showed that the flowers composed of thin flakes are in the thickness of about 30 nm. More significantly, this is the first time to synthesize crystallinic FeB nanoflowers self-assembled by thin flake. Magnetic measurement showed that the flowers were a kind of soft magnetic materials (Hc = 600 Oe, Mr = 34.6 emu/g).

Abstract: A novel method with two steps for preparing high efficiency fluorescence nanocrystals (NCs)-encoded microspheres was developed. First, a series of polystyrene (PS) microspheres from 1 μm to 5 μm in diameter were prepared by dispersion polymerization; then, after a swelling process with CdSe NCs of different size the PS microspheres were encoded quantitatively. This method for fluorescence-encoding of microspheres was shown to have the following outstanding characteristics: (1) An emulsion containing CdSe NCs and swelling agents (chloroform) are firstly used for introduction of NCs into microspheres. (2) The embedded nanocrystals remain their original properties and they are not simply absorbed onto the surface of the microspheres but being carried into the inner of microspheres and so the NCs cannot be released or leaked out easily. As-prepared fluorescence-encoded microspheres could conjugate with proteins by some further surface modification, so they have a great potential to be applied to such fields as biochemistry, molecular biology, cell biology, immunology, etc. In addition, the method could be operated easily and reproducibly.