Synthesis and characterization of monodisperse spherical core-shell structured SiO2@Y3Al5O12 : Ce3+/Tb3+ phosphors for field emission displays

Nanocrystalline Y3Al5O12: Ce3+/Tb3+ ( average crystalline size 30 nm) phosphor layers were coated on non-aggregated, monodisperse and spherical SiO2 particles by the sol-gel method, resulting in the formation of core-shell structured SiO2@Y3Al5O12:Ce3+/Tb3+ particles. X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, photoluminescence, cathodoluminescence spectra, as well as lifetimes were utilized to characterize the core-shell structured SiO2@Y3Al5O12: Ce3+/Tb3+ phosphor particles. The obtained core-shell structured phosphors consist of well-dispersed submicron spherical particles with a narrow size distribution. The thickness of the Y3Al5O12:Ce3+/Tb3+ shells on the SiO2 cores ( average size about 500 nm, crystalline size about 30 nm) could be easily tailored by varying the number of deposition cycles (100 nm for four deposition cycles). Under the excitation of ultraviolet and low-voltage electron beams (1-3 kV), the core-shell SiO2@Y3Al5O12:Ce3+/ Tb3+ particles show strong yellow-green and green emission corresponding to the 5d-4f emission of Ce3+ and D-5(4)-F-7(J) ( J = 6, 5, 4, 3) emission of Tb3+, respectively.

The influence of core-shell structured modifiers on the toughness of poly (vinyl chloride)

The core-shell structured grafted copolymer particles of polybutadiene grafted polymethyl methacrylate (PB-g-PMMA, MB) were prepared by emulsion polymerization. The MB particles were used to modify poly (vinyl chloride) (PVC) by melt blending. The mechanical properties of the PVC blends were investigated. The micro-morphology of the PVC blends was observed by scanning electron microscopy (SEM). The results indicated that the samples with the best impact strength could be obtained when the core-shell weight ratio of PB to PMMA is lower than 93:7, the mechanical properties correlated well with SEM morphologies, the addition of modifier with the ratio core to shell of 93:7 could reduce the domain size of the dispersed phase. Furthermore, the compatibility and properties of the blends were greatly enhanced and improved. The modifier particles could be well dispersed in the PVC matrix.

PolydA and polyrA self-structured by a europium and amino acid complex

Different DNA selectivity was found for the newly synthesized europium-L-valine complex. Unexpected DNA and RNA selection results showed that europium-L-valine complex can cause single-stranded polydA and polyrA to self-structure. The sigmoidal melting curve profiles indicate the transition is cooperative, similar to the cooperative melting of a duplex DNA. This is different from another europium amino acid complex, europium-L-aspartic acid complex which can induce B-Z transition under the low salt condition. To our knowledge, there is no report to show that a metal-amino acid complex can cause the self-structuring of single-stranded DNA and RNA.

Sol-gel synthesis and characterization of SiO2@CaWO4, SiO2@CaWO4 : Eu3+/Tb3+ core-shell structured spherical particles

Nanocrystalline CaWO4 and Eu3+ (Tb3+)-doped CaWO4 phosphor layers were coated on non-aggregated, monodisperse and spherical SiO2 particles by the Pechini sol-gel method, resulting in the formation of SiO2@CaWO4, SiO2@CaWO4:Eu3+/Tb3+, core-shell structured particles. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), time-resolved PL spectra and lifetimes were used to characterize the core-shell structured materials. Both XRD and FT-IR indicate that CaWO4 layers have been successfully coated on the SiO2 particles, which can be further verified by the FESEM and TEM images. The PL and CL demonstrate that the SiO2@CaWO4 sample exhibits blue emission band WO42- with a maximum at 420 nm (lifetime = 12.8 mu s) originated from the 4 groups, while SiO2@CaWO4:Eu3+ and SiO2@CaWO4:Tb3+ show additional red emission dominated by 614 nm (Eu3+:D-5(0)-F-7(2) transition, lifetime = 1.04 ms) and green emission at 544 nm (Tb3+:D-5(4)-F-7(5) transition, lifetime = 1.38 ms), respectively.

Monodisperse spherical core-shell structured SiO2-CaTiO3 : Pr3+ phosphors for field emission displays

Nanocrystalline CaTiO3:Pr3+ phosphor layers were coated on nonaggregated, monodisperse, and spherical SiO2 particles by the sol-gel method, resulting in the formation of core-shell structured SiO2-CaTiO3:Pr3+ particles. X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, cathodoluminescence spectra, as well as lifetimes were utilized to characterize the core-shell structured SiO2-CaTiO3:Pr3+ phosphor particles. The obtained core-shell structured phosphors consist of well dispersed submicron spherical particles with a narrow size distribution. The thickness of the CaTiO3:Pr3+ shell could be easily controlled by changing the number of deposition cycles (about 70 nm for four deposition cycles). The core-shell SiO2-CaTiO3:Pr3+ particles show a strong red emission corresponding to D-1(2)-H-3(4) (612 nm) of Pr3+ under the excitation of ultraviolet (326 nm) and low voltage electron beams (1-5 kV). These particles may be used in field emission displays.

Fabrication and photoluminescence properties of core-shell structured spherical SiO2@Gd2Ti2O7 : Eu3+ phosphors

A sol-gel technique was used to prepare Gd2Ti2O7:Eu3+-coated submicron silica spheres (SiO2@Gd2Ti2O7:Eu3+). The resulted SiO2@Gd2Ti2O7:Eu3+ core-shell particles were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive x-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, as well as kinetic decays. The XRD results demonstrate that the Gd2Ti2O7:Eu3+ layers begin to crystallize on the SiO2 spheres after annealing at 800 degrees C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have perfect spherical shape with narrow size distribution (average size similar to 620 nm), non-agglomeration, and smooth surface. The thickness of the Gd2Ti2O7:Eu3+ shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (60 nm for four deposition cycles). Under the irradiation of 310 nm ultraviolet, the SiO2@GdTi2O7:Eu3+ samples show strong emission of Eu3+.

Core-shell structured SiO2@YVO4 : Dy3+/Sm3+ phosphor particles: Sol-gel preparation and characterization

Spherical SiO2 particles have been coated with YVO4:Dy3+/Sm3+ phosphor layers by a Pechini sol-gel process, leading to the formation of core-shell structured SiO2@YVO4:Dy3+/Sm3+ particles. X-ray diffraction (XRD), Fourier-transform IR spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting SiO2 @YVO4:Dy3+/Sm3+ core-shell phosphors. The obtained core-shell phosphors have perfect spherical shape with narrow size distribution (average size ca. 300 nm), smooth surface and non-agglomeration. The thickness of shells could be easily controlled by changing the number of deposition cycles (20 nm for one deposition cycle). The core-shell particles show strong characteristic emission from Dy3+ for SiO2@YVO4:Dy3+ and from Sm3+ for SiO2@YVO4:Sm3+ due to an efficient energy transfer from YVO4 host to them. The PL intensity of Dy3+ and Sm3+ increases with raising the annealing temperature and the number of coating cycles.

Fabrication and optical properties of core-shell structured spherical SiO2@GdVO4 : Eu3+ phosphor via sol-gel process

Europium-doped nanocrystalline GdVO4 phosphor layers were coated on the surface of preformed submicron silica spheres by sol-gel method. The resulted SiO2@Gd0.95Eu0.05VO4 core-shell particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, low voltage cathodoluminescence (CL), time resolved PL spectra and kinetic decays. The XRD results demonstrate that the Gd0.95Eu0.05VO4 layers begin to crystallize on the SiO2 spheres after annealing at 600 C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have spherical shape, narrow size distribution (average size ca. 600 nm), non-agglomeration. The thickness of the Gd0.95Eu0.05VO4 shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). PL and CL show that the emissions are dominated by D-5(0)-F-7(2) transition of Eu3+ (618 nm, red).

Oriented nano-structured hydroxyapatite from the template

Natural bone is one kind of compounds consisting of hydroxyapatite (HAp) nano-rods, which are embedded in the template of collagen matrix in vivo with the same crystallographic organization. Herein HAp nano-rods precursors were synthesized via wet chemical method. Large-scale HAp nano-wires with the same crystallographic organization as the template of anodic aluminum oxide (AAO) were obtained by the electrophoretic deposition and the technology of the template. It provides a meaningful method to study and understand the information of biological molecules' mineralization process.

Sol-gel preparation and luminescence properties of nano-structured hybrid materials incorporated with europium complexes

Microporous silica gel has been prepared by the sol-gel method utilizing the hydrolysis and polycondensation of tetraethylorthosilicate (TEOS). The gel has been doped with the luminescent ternary europium complex Eu(TTA)(3)(.)phen: where HTTA=1-(2-thenoyl)-3,3,3-trifluoracetone and phen=1,10-phenanthroline. By contrast to the weak f-f electron absorption bands of Eu3+, the complex organic ligand exhibits intense near ultraviolet absorption. Energy transfer from the ligand to Eu3+ enables the production of efficient, sharp visible luminescence from this material. Utilizing the polymerization of methyl methacrylate, the inorganic/polymer hybrid material containing Eu(TTA)(3)(.)phen has also been obtained. SEM micrographs show uniformly dispersed particles in the nanometre range. The characteristic luminescence spectral features of europium ions are present in the emission spectra of the hybrid material doped with Eu(TTA)(3)(.)phen.

Preparation and luminescent properties of inorganic polymer nano - Structured hybrid films doped with rare earth complexes

The inorganic/polymer hybrid films with good luminescent properties have been obtained by the sol - gel process via incorporating the polymer component doped with rare earth complexes. These films exhibit good toughness and transparency. Their fluorescence spectra and lifetimes indicate that they all have the characteristic luminescence of the central rare earth ions. The lifetimes of these films are longer than those of pure complexes. TEM have showed that the rare earth complexes are dispersed homogeneously in SiO2/PVB interpenetratiny networks, and the dispersed size is between 20 and 30 nn.

HIGHLY SENSITIVE AND SELECTIVE DETERMINATION OF RIBOFLAVIN BY FLOW-INJECTION ANALYSIS USING PARALLEL DUAL-CYLINDER MICROELECTRODES

A novel wall-jet cell with parallel dual cylinder (PDC) microelectrodes was constructed and used for flow injection analysis (FLA). The detector takes the advantages of ''redox recycling'' between bipotentiostated microcylinder electrodes (- 0.4 V/SCE an

THEORY OF STEADY-STATE CURRENT AT MULTIPLE MICROCYLINDER ELECTRODES COUPLED WITH A PARALLEL PLANAR ELECTRODE

A novel device of multiple cylinder microelectrodes coupled with a parallel planar electrode was proposed. The feedback diffusion current at this device was studied using bilinear transformation of coordinates in the diffusion space, where lines of mass flux and equiconcentration are represented by orthogonal circular functions. The derived expression for the steady-state current shows that as the gap between cylindrical microelectrodes and planar electrode diminishes, greatly enhanced currents can be obtained with high signal-to-noise ratio. Other important geometrical parameters such as distance between adjacent microcylinders, cylinder radius, and number of microcylinders were also discussed in detail.

DETERMINATION OF THE RATE-CONSTANT OF A CATALYTIC REACTION USING A PARALLEL INCIDENT SPECTROELECTROCHEMICAL CELL

The possibility of determining the rate constant of a catalytic reaction using a parallel incident spectroelectrochemical cell was investigated in this work. Various spectroelectrochemical techniques were examined, including single-potential-step chronoabsorptometry, single-potential-step open-circuit relaxation chronoabsorptometry and double-potential-step chronoabsorptometry. The values determined for the kinetics of the ferrocyanide-ascorbic acid system are in agreement with the reported values. The parallel incident method is much more sensitive than the normal transmission method and can be applied to systems which have smaller molar absorptivities, larger rate constants or lower concentrations.