Naisen Yu

Self-assembled 3D flower-shaped NaY(WO4)2:Eu3+ microarchitectures: Microwave-assisted hydrothermal synthesis, growth mechanism and luminescent properties

Three dimensional (3D) flower-shaped microarchitectures of NaY(WO4)2 were synthesized via a microwave-assisted hydrothermal process in the presence of trisodium citrate (Na3Cit) and a post-calcination process. The effects of reaction conditions on the morphology of precursor microstructures were studied. It was found that Na3Cit, as the chelating agent and shape modifier, plays a key role in the microstructure growth. A possible growth mechanism for the flower-shaped microarchitectures was proposed. The as-formed precursor can completely transform into NaY(WO4)2 with its original flower-shaped morphology via a heat treatment process. The concentration and temperature quenching behaviors of Eu3+ fluorescence in the flower-shaped NaY(WO4)2 were studied, and the optimal doping concentration was confirmed, meanwhile the activation energy was obtained. Judd-Ofelt parameters Ωλ (λ = 2, 4 and 6) of Eu3+ in the flower-shaped NaY(WO4)2 phosphor were obtained by using the emission spectrum of Eu3+, moreover the radiative transition properties were analyzed.

Hydrothermal synthesis and tunable luminescence of persimmon-like sodium lanthanum tungstate:Tb3+, Eu3+ hierarchical microarchitectures

Persimmon-like NaLa(WO(4))(2) microarchitectures were prepared via hydrothermal process with using trisodium citrate (Na(3)Cit) as chelated reagent and characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), photoluminescence (PL), and fluorescent dynamics. The influences of Na(3)Cit concentration, organic additivities, and reaction time on the morphologies of NaLa(WO(4))(2) phosphor were studied. The results revealed that Na(3)Cit species had double functions of strong ligand and structure-directing reagent that could efficiently control the formation of persimmon-like NaLa(WO(4))(2) microarchitectures. The possible mechanism for the growth of persimmon-like NaLa(WO(4))(2) microarchitectures was attributed to the Ostwald ripening mechanism. The energy transfer from Tb(3+) to Eu(3+) in the persimmon-like NaLa(WO(4))(2) phosphors was observed. The energy transfer efficiencies and emission colors can be tuned by changing the concentration of Eu(3+). Finally, it was deduced that the electric dipole-dipole interaction (D-D) is the main mechanism for energy transfer between Tb(3+) and Eu(3+) in the persimmon-like NaLa(WO(4))(2) phosphor.

Local and Remote Charge-Transfer-Enhanced Raman Scattering on One-Dimensional Transition-Metal Oxides

The one-dimensional (1D) transition-metal oxide MoO(3) belt is synthesized and characterized with X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. Charge-transfer-(CT) enhanced Raman scattering of 4-mercaptobenzoic acid (4-MBA) on a 1D MoO(3) belt was investigated experimentally and theoretically. The chemical enhancement of surface-enhanced Raman scattering (SERS) of 4-MBA on the MoO(3) belt by CT is in the order of 10(3). The SERS of 4-MBA was investigated theoretically by using a quantum chemical method. The remote SERS of 4-MBA along the 1D MoO(3) belt (the light excitation to one side of the MoO(3) belt, and the SERS spectrum is collected on the other side of the MoO(3) belt) is also shown experimentally, which provides potential applications of SERS. The incident polarization dependence of remote SERS spectra has also been investigated experimentally.

Lanthanide dopant-induced phase transition and luminescent enhancement of EuF3 nanocrystals

A novel strategy is proposed to prepare hexagonal EuF3 nanocrystals by doping lanthanide ions (Ln3+) with large ionic radius (such as La3+, Ce3+, Pr3+, Nd3+ and Sm3+). Complete phase transition from orthorhombic to hexagonal phase can be achieved with the increase of ionic radius or doping concentration of Ln3+ ions. Meanwhile, the size and self-assembly degree of the product can be reduced dramatically. The possible growth and phase transformation mechanism of EuF3 nanocrystals was proposed. Finally, Eu3+ ion was used as the structural probe to investigate the effect of phase transition on the luminescence. It was found that the emissions of the 5D0 level of Eu3+ are greatly enhanced with the phase transition from orthorhombic to hexagonal phase. The luminescent enhancement is attributed to the larger radiative transition rate of the 5D0 level in the environment with lower symmetry, which can be confirmed by Judd–Ofelt (J–O) theory.

InGaN-based light-emitting diodes grown and fabricated on nanopatterned Si substrates

InGaN-based light-emitting diodes (LEDs) were grown and fabricated on nanoscale patterned Si (111) substrates (NPSi). Using anodized aluminum oxide as the etch mask, the NPSi was prepared with an average nanopore diameter of 150 nm and interpore distance of 120 nm. LEDs grown on NPSi exhibit relaxed tensile stress relative to the ones grown on microscale patterned Si (111) substrates (MPSi). Nanoheteroepitaxial lateral overgrowth was significantly promoted on NPSi, which led to extensive dislocation bending and annihilation. The devices made on NPSi exhibit lower leakage current and higher light output power as compared with those on MPSi.

The control of the morphologies, structures and photoluminescence properties of C70 nano/microcrystals with different trichlorobenzene isomers

Trichlorobenzene isomers with different molecular structures (1,2,3-, 1,2,4- and 1,3,5-trichlorobenzene) were used as shape and luminescence tuners of C70 nano/microcrystals. C70 nano/microcrystals with different morphologies (nano/microrods, nano/microsheet clusters and nano/microballs) were synthesized. C70 nano/microballs fabricated using 1,3,5-trichlorobenzene have a simple cubic (sc) structure, and C70 nano/microcrystals obtained using other solvents have a face-centered-cubic (fcc) structure. Meanwhile, the introduction of different trichlorobenzenes in the C70 nano/microcrystals enhanced their PL intensities to different degrees. In particular, the PL intensities of the C70 nano/microcrystals doped with 1,3,5-trichlorobenzene were most highly enhanced, which is one order of magnitude higher than that for the pristine bulk C70 crystals.

Preparation of Tungsten-Doped VO2 (M) Nanoparticles through Sol-Gel Method and Hydrothermal Synthesis

A new process was developed for synthesizing tungsten-doped vanadium dioxide VO2(M) from ammonium metavanadate. The process includes obtaining V2O5 by pyrolysing NH4VO3, doping tungsten in V2O5 by sol-gel method, and reducing V2O5 to VO2(M) with hydrazine by hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were applied to characterizing the product. The experimental results indicated that tungsten doped VO2 (M) nanoparticles were successfully synthesized. The product VO2 (M) presents mainly rod-like and block-like morphology. The phase transition temperature decreases with tungsten doped amount increasing, the phase transition takes place over the range from 36.23°C to 62.16°C and the largest enthalpy of the phase transition is 16.24J/g.

Synthesis and local electrical characterization of ZnO microwalls grown on cracked GaN/Si(111) by aqueous method

ZnO microwalls have been grown on cracked GaN/Si(111) using aqueous method. The cracks of GaN direct ZnO grow and form two-dimensional microwall networks. Electrical characterization of individual upright standing ZnO microwall was performed by using conductive atomic force microscopy. Enhanced conductivity for the off-axis facet plane present on as-grown ZnO microwalls has been detected. Meanwhile, the local current-voltage characteristics shows that the sidewall has lower Schottky barrier height, it indicated that the off-axis sidewalls planes are more electrically active than c-plane ZnO. Furthermore, it will also provide a unique structure for surface-related applications, such as sensing, catalyzing, energy harvesting, etc.

Postsynthetic modification of single Pd sites into uncoordinated polypyridine groups of a MOF as the highly efficient catalyst for Heck and Suzuki reactions

A novel holmium(III) metal–organic framework (Ho-MOF), namely, [Ho(2-TriPP-COO)3] (2) has been hydrothermally obtained using 4′-(4-carboxyphenyl)-2,2′:6′,2′′-terpyridine (2-TriPP-COOH) and Ho(NO3)3·5H2O, and it is structurally characterized by single-crystal XRD, powder XRD as well as elemental analysis. The postsynthetic modification of Ho-MOF is based on the utilization of a strong coordination effect between Pd2+ ions and free polypyridine groups in the skeleton of Ho-MOF, which play a critical role to access the highly efficient Pd-HoMOF catalyst. Also, Pd-HoMOF exhibits very high activity in Heck and Suzuki–Miyaura cross-coupling reactions. Moreover, the MOF catalyst displays good thermal stability (up to 400 °C), and it can be recovered and reused for five reaction cycles. The bridging between the MOF structure and homogeneous molecular Pd catalyst represents a good example in designing highly efficient catalysts for various fine chemical transformations.

ZnO NANONEEDLES DEPOSITED ON CHEMICALLY ETCHED SILICON NANOWIRES VIA HYDROTHERMAL PROCESS

ZnO nanoneedles were deposited on the chemically etched silicon nanowires via simple low temperature hydrothermal process in this paper. The morphology, structure and optical properties were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL), and Raman spectrum, respectively. The XRD pattern reveals a wurtzite structure for the ZnO nanoneedles. And SEM results show that the ZnO nanoneedles have a length of ∼ 400 nm with an average tip diameter of ∼ 5 nm and a base diameter of ∼ 50 nm. Meanwhile, the PL results show that the nanoneedles have wide band emission. Furthermore, the Raman results confirmed that the ultrafine nanoneedles have high surface area and surface defects. The wide band emission of ZnO nanoneedles suggests that it might serve as a potential host for white-light-emitting materials.