Synthesis of Sr2CeO4: Eu-3 by citrate-gel method and its luminescence properties

A novel phosphor Sr2CeO4 was synthesized by the citrate-gel method. The results of XRD show that the temperature at which the crystallization starting is lowered and the soak time for complete crystallization is decreased. The values of pH of the precursor and the ratio( R) between the citrate and cation ions have an effect on the crystallization process. The host can transfer its exciting energy to rare earth ion Eu3+. The doped compound emits strong white light when the concentration of the doped Eu3+ is low. When that of Eu3+ is increased, it emits strong red light. The fluorescence from the higher excited states can be observed because the multiphonon relaxation probability between Eu3+ ions is low.

Determination of molecular weight and molecular sizes of polymers by high temperature gel permeation chromatography with a static and dynamic laser light scattering detector

Flow-mode static and dynamic laser light scattering (SLS/DLS) studies of polymers, including polystyrene, polyethylene, polypropylene and poly(dimethylsiloxane) (PDMS), in 1,2,4-trichlorobenzene (TCB) at 150 degreesC were performed on a high temperature gel permeation chromatography (GPC) coupled with a SLS/DLS detector. Both absolute molecular weight (M) and molecular sizes (radius of gyration, R-g and hydrodynamic radius, R-h) of polymers eluting from the GPC columns were obtained simultaneously. The conformation of different polymers in TCB at 150 degreesC were discussed according to the scaling relationships between R-g, R-h and M and the rho-ratio (p = R-g/R-h). Flow-mode DLS results of PDMS were verified by batch-mode DLS study of the same sample. The presented technique was proved to be a convenient and quick method to study the shape and conformation of polymers in solution at high temperature. However, the flow-mode DLS was only applicable for high molecular weight polymers with a higher refractive index increment such as PDMS.

Toluidine blue modified self-assembled silica gel coated gold electrode as biosensor for NADH

A toluidine blue modified gold electrode was constructed using self-assembled silica gel technique. Firstly, toluidine blue was encapsulated within 3D network of silica self-assembly monolayer on the surface of gold electrode. Secondly, another layer of silica sol was further assembled to protect from leaching of mediator or possible contamination. The electrochemical characteristics of toluidine blue immobilized within self-assembled silica gel were studied in detail. The modified electrode was applied for electrochemical oxidation of NADH with satisfactory results.

Sol-gel derived iridium composite glucose biosensor

Iridium powder is introduced into sol-gel process for the first time to fabricate a novel type of sol-gel derived metal composite electrode. The iridium ceramic electrode shows excellent electrocatalytic action for both oxidation and reduction of hydrogen peroxide. The glucose biosensor based on sol-gel derived iridium composite electrode was fabricated. The biosensor shows highly selectivity towards glucose because of the strong catalytic action of iridium composite matrix for enzyme-liberated hydrogen peroxide at low operating potential, at which common interferences cannot be sensed. The novel type of biosensor can be renewed by simply mechanical polishing with favorable reproducibility and long-term stability.

Effect of alkyl group length on the conductivity in the 2,3,7,8,12,13,17,18-octakis(alkyl-thio)tetraazaporphyrins and redox properties of the metallooctakis(hexyl-thio)tetraazaporphyrins

A series of 2,3,7,8,12,13,17,18-octakis(alkyl-thio)tetraazaporphyrins (H(2)OATTAP) with different alkyl chain lengths have been synthesized. Cyclic voltammetry and differential pulse voltammetry have been used to investigate the effect of the controlled lengths of the eight peripheral thioether tails on the redox behavior of the molecules. The electrochemical reduction of octakis(hexyl-thio)tetraazaporphyrins, MOHTTAP (where M = Cu, Ni), was studied in 1,2-dichloroethane at a platinum electrode. The Cu derivative was oxidized in one single-electron-transfer step to yield a pi-cation radical and reduced in three single-electron-transfer steps to yield a pi-anion radical, dianion and trianion, respectively. For the Ni derivative, electron transfer reactions involving both the central metal atom and the macrocyclic ring were observed. Electron transfer pathways are proposed based upon voltammetric and in situ spectroelectrochemical results.

Citrate-gel synthesis and luminescent properties of ZnGa2O4 doped with Mn2+ and EU3+

By using inorganic salts as raw materials and citric acid as complexing agent, spinel oxide ZnGa2O4 and Mn2+, Eu3+-doped ZnGa2O4 phosphor powders were prepared by a citrate-gel process. X-ray diffraction (XRD), TG-DTA, FT-IR. and luminescence excitation and emission spectra were used to characterize the resulting products. The results of XRD reveal that the powders begin to crystallize at 500 degreesC and pure ZnGa2O4 phase is obtained at 700 degreesC, which agrees well with the results of TG-DTA and FT-IR. In the crystalline ZnGa2O4, the Eu shows its characteristic red (615 nm, D-5(0)-F-7(2)) emission with a quenching concentration of 5 mol% (of Ga3+), and the Mn shows green emission (505 nm, T, A,) with a quenching concentration of 0.1 mol% (of Zn2+). The luminescence mechanism of ZnGa2O4:Mn2+/Eu3+ is presented.

Sol-gel derived iridium composite glucose biosensor

Iridium powder is introduced into sol-gel process for the first time to fabricate a novel type of sol-gel derived metal composite electrode. The iridium ceramic electrode shows excellent electrocatalytic action for both oxidation and reduction of hydrogen peroxide. The glucose biosensor based on sol-gel derived iridium composite electrode was fabricated. The biosensor shows highly selectivity towards glucose because of the strong catalytic action of iridium composite matrix for enzyme-liberated hydrogen peroxide at low operating potential, at which common interferences cannot be sensed. The novel type of biosensor can be renewed by simply mechanical polishing with favorable reproducibility and long-term stability.

Hybrid organic-inorganic compounds doped with terbium carboxyl complexes produced in situ via a sol-gel approach

In situ synthesis of terbium carboxyl complexes in an organic-inorganic hybrid matrix by a sol-gel process has been proposed. The formation of terbium carboxyl complexes in the hybrid matrix is confirmed by the luminescence spectra and IR spectra. It is observed that the location at the amino group in aminobenzoic acid has a large effect on the luminescence properties and lifetimes. Furthermore, the emission intensity decreases with increasing temperature.

Preparation of polymer/silica nanoscale hybrids through sol-gel method involving emulsion polymers. II. Poly(ethyl acrylate)/SiO2

Poly(ethyl acrylate) (PEA)/SiO2 hybrids with different compositions were prepared under different casting temperatures and pH values. Their morphology as investigated by transmission electron microscopy (TEM) shows that samples with different compositions have different morphologies. When the SiO2 content is lower, PEA is the continuous phase and SiO2 is the dispersed phase. At higher SiO2 content, the change in phase morphology takes place, nd PEA gradually dispersing in the form of latex particles in SiO2 matrix. Change in phase morphology depends mainly on the time the sol-gel transition occurs. At suitable casting temperature and pH value, PEA/SiO2 in 95/5 and 50/50 hybrids with even dispersion was obtained.

Luminescence properties of rare earth-polyoxometalate thin film deposited by sol-gel process

The rare earth (Eu3+, Dy3+)-polyoxometalate thin films were fabricated on quartz plate by the sol-gel method. The thin films were demonstrated by the luminescence spectra. The thin films exhibit the characteristic emission bands of the rare-earth ions. It is noticed that the yellow to blue intensity ratio (Y:B) of Dy3+ and the red to orange ratio (R:O) of Eu3+ in the films are different from that of the corresponding solids. Furthermore, the thin films present shorter fluorescence lifetime than the pure complexes. The reasons that were responsible for these results were also discussed.

Sol-gel derived silicate oxyapatite phosphor films doped with rare earth ions

Rare-earth (Eu3+, Tb3+)-doped Ca2Y8(SiO4)(6)O-2 luminescent thin films were dip-coated on silicon and quartz glass substrates through a sol-gel route. X-ray diffraction (XRD), scanning electron microscopy (SEM) and luminescence excitation and emission spectra as well as luminescence decays were used to characterize the resultant films. The results of XRD reveal that these films remain amorphous below 700 degreesC, begin to crystallize at 800 degreesC, and crystallize completely around 1000 degreesC with an oxyapatite structure. The grain structure of the film can be seen clearly from SEM micrographs, where particles with various shape and average size of 250 nm can be resolved. The Eu3+ and Tb3+ ions show their characteristic red (D-5(0)-F-7(2)) and green (D-5(4)-F-7(5)) emission in the films with a quenching concentration of 10 and 6 mol% (of Y3+), respectively. The lifetime of Eu-3divided by increases with the heat treatment temperature front 700 to 1100 degreesC.