Naifeng Zhuang

Growth and spectrum properties of Yb:GdVO4 single crystal

Abstract In this paper, the non-doped and doped Yb 3+ of GdVO 4 crystals whose polycrystalline material was synthesized by the liquid-phase reaction method were grown by the Czochralski method. The sinter temperature can be concluded by thermal analysis. The influence of the thermal gradient on the crystal quality, the segregate coefficient of Yb 3+ ion in the crystal, the transparence spectrum of the non-doped GdVO 4 crystal and the effect of lattice structure on the absorption spectra and the fluorescence spectra are discussed.

A study on the growth of Yb:YVO4 single crystal

Abstract The Yb:YVO 4 crystals with various dopant concentrations of Yb 3+ were grown using the Czochraski method. The preparation technique of polycrystalline materials, changes in the lattice parameters with various dopant concentrations of Yb 3+ , laser damage threshold values, growth protective atmosphere, as well as the influence of slight amount of water vapor on the crystallization are described.

Clean unzipping by steam etching to synthesize graphene nanoribbons.

A simple, clean method of steam etching carbon nanotubes is reported for the synthesis of graphene nanoribbons. The chemical mechanism of carbon nanotube unzipping is also discussed. As an anode catalyst, as-prepared graphene nanoribbons combined with Pt exhibit quite a high catalytic activity for ethanol electro-oxidation in fuel cells.

A new technique to grow incongruent melting Ga:YIG crystals: the edge-defined film-fed growth method

Crystalline yttrium iron garnet (YIG) is an important magneto-optical material. However, this crystal is an incongruent melting compound. As is well known, compared to the crystal growth of a congruent melting compound by using the Czochralski method, the crystal growth of an incongruent melting compound is more difficult. In this work, a system for growing Ga:YIG single crystals by the edge-defined film-fed growth (EFG) method was designed and constructed, and the mechanism of crystal growth was also preliminarily studied. The Ga3+ dopant concentration, the Curie temperature and the transmission spectra of as-grown crystals were investigated to evaluate their potential application in magneto-optical devices. The success of growing Ga:YIG crystals by the EFG method provides a new way to grow other incongruent melting compounds.

GROWTH, OPTICAL AND MAGNETIC PROPERTIES OF Co-DOPED TiO2 CRYSTAL

Co-doped TiO2 crystals (Co:TiO2) were grown by Czochralski growth (CZ) method and the edge-defined film-fed growth (EFG) method, respectively. Therein, EFG was an effective method to grow a higher quality Co:TiO2 crystal without the reverse flow of the melt. This as-grown crystal reaches a larger dimension of 10 mm × 15 mm × 18mm. XRD analysis confirms that as-grown crystal is isostructural with TiO2 rutile phase. Moreover, this crystal has ferromagnetism at room temperature and the magnetic moment of Co ion is 1.25 × 10-2 μB/Co. After annealed at 1273 K, Co:TiO2 crystal enhances obviously its optical transmittance, while this crystal shows diamagnetism due to the disappearance of the ferromagnetic signal.

Enhanced electrochemical performance of vanadium dioxide (B) nanoflowers with graphene nanoribbons support

Specific VO2 (B) nanoflowers and their composite hybridized with graphene nanoribbons (GNRs) are prepared using a moderate H2C2O4 reductant to reduce V2O5 with the molar ratio of H2C2O4:V2O5 as 3:1. The discharge specific capacities and the cycling stabilities of the VO2 (B) cathode material for lithium-ion batteries can be improved by graphenes support. In particular, GNRs support can improve the dispersibility and the electrical conductivity of the VO2 (B) nanoflowers. Thus, VO2 (B)/GNRs (32.2 wt%) composite exhibits excellent electrochemical performance with the high specific capacity of 471.5 mA h g−1 and the preferable cycling stability.

Growth, Faraday and inverse Faraday characteristics of Tb 2 Ti 2 O 7 crystal

Tb2Ti2O7 (TTO) single crystal with dimensions of 20 × 20 × 16 mm3 was grown by the Czochralski method. Rietveld structure refinement of X-ray diffraction (XRD) data confirms that the compound crystallizes in the cubic system with pyrochlore structure. Transmission spectra, Magnetic circular dichroism (MCD) spectra, Faraday and inverse Faraday characteristics of TTO crystal have been measured and analyzed in detail. The results demonstrate that TTO crystal has high transmittance at 700-1400 nm waveband and a larger Verdat constant than that of TGG reported. Magnetic circular dichroism (MCD) spectra showed that the 4f→4f transitions of Tb3+ have significant contributions to the magneto-optical activity (MOA). In the time-resolved pump-probe spectroscopy, the rotation signals of the probe beam based on the inverse Faraday effect in magneto-optical crystal were observed at zero time delay, the full width at half maximum of the rotation and ellipticity signals can be as fast as ~500 fs, which indicates that TTO crystal can be a promising material for ultrafast all-optical magnetic switching.

Crystal growth, spectroscopic characterization and laser performance of Nd:Lu0.33Y0.36Gd0.3VO4 crystal

A new three-matrix mixed vanadate crystal Nd:Lu0.33Y0.36Gd0.3VO4 (Nd:LuYGdVO4) crystal was grown by the Czochralski method. Room temperature absorption and fluorescence spectra of the Nd:LuYGdVO4 crystals were measured and the spectroscopic parameters were calculated by the Judd-Ofelt theory. The intensity parameters of the Nd:LuYGdVO4 crystal were Ω2 = 9.736 × 10−20 cm2, Ω4 = 4.179 × 10−20 cm2, Ω6 = 8.020 × 10−20 cm2 and the stimulate emission cross section was 5.3 × 10−19 cm2. Diodepumped actively Q-switched and passively Q-switched Nd:LuYGdVO4 and Nd:Lu0.14Y0.86VO4 lasers at 1.06 μm were demonstrated. The results indicate that, for both actively and passively Q-switched lasers, the Nd:LuYGdVO4 lasers can generate shorter pulse width with higher peak power than the Nd:Lu0.14Y0.86VO4 lasers at the same cavity conditions.

High electrochemical properties of graphene nanoribbons-hybridized manganese dioxide as cathode material for lithium battery

Manganese dioxide crystallite and its composite hybridized with graphene nanoribbons (GNRs) are prepared by hydrothermal method. The effects of reaction temperature and time, surfactant, and reducing Mn resource are discussed. As the cathode material for Li battery, γ-MnO2 nanowire/nanorod hybridizing with (GNRs) (γ-MnO2/GNRs) shows a higher discharge specific capacity than it covering with carbon nanotubes or graphene sheets. In addition, the discharge specific capacity of γ-MnO2/GNRs is much higher than those of pure β-MnO2 and compact β-MnO2/GNRs. The effects of crystal size, morphology, and GNR hybrid on the discharge specific capacity are discussed.

One-step oxidation preparation of unfolded and good soluble graphene nanoribbons by longitudinal unzipping of carbon nanotubes

A simple one-step method to prepare graphene nanoribbon (GNR) is reported in this paper. Compared with water steam etching, the oxidation and co-etching of dilute sulfuric acid can result in the more complete longitudinal unzipping of carbon nanotube, although there is no other strong oxidant. As-prepared GNRs are more flat and have more oxygenated functional groups along the edge. Moreover, they can steadily disperse in a water system. These make them suitable as a carrier for supporting palladium (Pd) nanoparticles. The Pd/GNR composite exhibits a superior electrocatalytic activity for ethanol oxidation.