ELECTROCHEMISTRY OF THE TRANSFER OF ISOPOLY AND HETEROPOLY ANIONS ACROSS THE WATER NITROBENZENE INTERFACE - ISOPOLYTUNGSTATE AND HETEROPOLYTUNGSTATE ANIONS

The transfer behavior of the heteropoly anion [H3PW11O39]4- and the isopoly anion [H2W12O39]4- across the water/nitrobenzene interface was investigated by cyclic voltammetry and chronopotentiometry with linear current scanning. The transfer processes were

DIRECT ELECTRON-TRANSFER REACTION OF HEMEPROTEINS PROMOTED BY METHYLENE-BLUE MODIFIED ELECTRODE

The heterogeneous electron transfer reaction of hemeproteins including hemoglobin, myoglobin and cytochrome C at Pt mesh electrode adsorbed methylene blue has been investigated. Thin-layer spectroelectrochemical technique was used for observing the electron transfer processes of three kinds of proteins, and the corresponding electrode rate constants were measured.

Tm3+/Er3+/Yb3+-codoped oxyhalide tellurite glasses as materials for three-dimensional display

Blue, green and red emissions through frequency upconversion and energy transfer processes in Tm3+/Er3+/Yb3+-codoped oxyhalide tellurite glass under 980 nm excitation are investigated. The intense blue (476 nm), green (530 and 545 nm) and red (656 nm) emissions are simultaneously observed at room temperature. The blue (476 nm) emission was originated from the (1)G(4)->H-3(6) transition of Tm3+. The green (530 and 545 nm), and red (656 nm) upconversion luminescences were identified from the H-2(11/2)->I-4(15/2), S-4(3/2)->I-4(15/2), and F-4(9/2)->I-4(15/2) transitions of Er3+, respectively. The energy transfer processes and possible upconversion mechanisms are evaluated. (C) 2005 Elsevier B.V. All rights reserved.

Broadband near-infrared emission in Er3+-Tm3+ codoped chalcohalide glasses

The near-IR emission spectra of Er3+-Tm3+ codoped 70GeS(2)-20In(2)S(3)-10CsI chalcohalide glasses were studied with an 808 nm laser as an excitation source. A broad emission extending from 1.35 to 1.7 mu m with a FWHM of similar to 160 nm was recorded in a 0.1 mol.% Er2S3, 0.5 mol.% Tm2S3 codoped chalcohalide glass. The fluorescence decay curves of glasses were measured by monitoring the emissions of Tm3+ at 1460 nm and Er3+ at 1540 nm, and the lifetimes were obtained from the first-order exponential fit. The luminescence mechanism and the possible energy-transfer processes are discussed with respect to the energy-level diagram of Er3+ and Tm3+ ions. (C) 2008 Optical Society of America

Localized exciton dynamics in AlInGaN alloy

Carrier recombination dynamics in AlInGaN alloy has been studied by photoluminescence (PL) and time-resolved PL (TRPL) at various temperatures. The fast red-shift of PL peak energy is observed and well fitted by a physical model considering the thermal activation and transfer processes. This result provides evidence for the exciton localization in the quantum dot (QD)-like potentials in our AlInGaN alloy. The TRPL signals are found to be described by a stretched exponential function of exp[(-t/,tau)13], indicating the presence of a significant disorder in the material. The disorder is attributed to a randomly distributed QDs or clusters caused by indium fluctuations. By studying the dependence of the dispersive exponent beta on temperature and emission energy, we suggest that the exciton hopping dominate the diffusion of carriers localized in the disordered QDs. Furthermore, the localized states are found to have 0D density of states up to 250 K, since the radiative lifetime remains almost unchanged with increasing temperature. (C) 2003 Elsevier Science Ltd. All rights reserved.

Multiple energy transfers in rare earth complex-doped SiO2 spheres

Silica spheres doped with Eu(TTFA)(3) and/or Sm(TTFA)(3) were synthesized by using the modified Stober method. The transmission electron microscope image reveals that the hybrid spheres have smooth surfaces and an average diameter of about 210 nm. Fluorescence spectrometer was used to analyze the fluorescence properties of hybrid spheres. The results show that multiple energy transfer processes are simultaneously achieved in the same samples co-doped with Eu (TTFA)(3) and Sm(TTFA)(3), namely between the ligand and Eu3+ ion, the ligand and Sm3+ ion, and Sm3+ ion and Eu3+, ion. Energy transfer of Sm3+-> Eu3+, in the hybrid spheres leads to fluorescence enhancement of Eu3+ emission by approximately an order of magnitude. The lifetimes of the hybrid spheres were also measured.

Optical properties of AIInGaN quaternary alloys

Carrier recombination dynamics in AlInGaN alloy has been studied by photoluminescence (PL) and time-resolved photoluminescence (TRPL). The fast redshift of PL peak energy is observed and well fitted by a physical model considering the thermal activation and transfer processes. This result provides evidence for the exciton localization in the quantum dot (QD)-like potentials in our AlInGaN alloy. The TRPL signals are found to be described by a stretched exponential function of exp[(-t/tau)(beta)], indicating the presence of a significant disorder in the material. The disorder is attributed to a randomly distributed quantum dots or clusters caused by indium fluctuations. By studying the dependence of the dispersive exponent 8 on the temperature and emission energy, we suggest that the exciton hopping dominate the diffusion of carriers localized in the disordered quantum dots. Furthermore, the localized states are found to have OD density of states up to 250 K, since the radiative lifetime remains almost unchanged with increasing temperature.

Optical characterization of the Ge/Si (001) islands in multilayer structure

We show that the observed temperature dependence of the photoluminescence (PL) features can be consistently explained in terms of thermally activated carrier transfer processes in a multilayer structure of the self-organized Ge/Si(001) islands. The type II (electron confinement in Si) behavior of the Ge/Si islands is verified. With elevated temperature, the thermally activated electrons and holes enter the Ge islands from the Si and from the wetting layer (WL), respectively. An involvement of the type I (spatially direct) into type II (spatially indirect) recombination transition takes place at a high temperature.

多电荷态硫离子与氦原子和氢分子碰撞中的多电子转移过程研究

本工作采用反冲离子飞行时间技术和散射离子位置灵敏探测技术，实验研究了Sq+离子与He、H2碰撞中的多电子转移过程和分子离子的碎裂现象。研究了转移电离截面与单电子俘获截面比值和入射离子损失一个电子和两个电子的情况下，靶原子双重电离与单重电离的截面比值随入射离子能量和入射离子电荷态的变化规律，并对不同的碰撞体系的结果进行了比较。研究发现：在本工作研究的入射离子能区，对于HZ分子靶，双电子俘获自电离反应道：S2+H2→S(q-l)+2H++e-。是转移电离过程的主要贡献，而直接转移电离的贡献可以忽略；随着入射离子电荷态的增加，双电子俘获自电离的贡献增加，直接转移电离的贡献逐渐减小，但双电子俘获自电离的贡献的增加比理论预言的要慢。建立了蒙特卡罗程序模拟离子与分子碰撞中产生的具有不同的初始动能的离子碎片的飞行时间谱，深入分析和研究了Sq＋与H2分子碰撞中产生的H2+的解离过程和库仑爆炸过程，以及H＋碎片的能量分布。模拟结果与实验测量到的TOF谱的分析比较说明：在Sq＋与H2分子碰撞实验中，库仑爆炸是产生H+的主要反应道，而氢分子离子H2+发生解离产生H+的反应道相对很弱。

Adsorption of 4,4 '-thiobisbenzenethiol on silver surfaces: surface-enhanced Raman scattering study

Adsorption of 4,4'-thiobisbenzenethiol (4,4'-TBBT) on a colloidal silver surface and a roughened silver electrode surface was investigated by means of surface-enhanced Raman scattering (SERS) for the first time, which indicates that 4,4'-TBBT is chemisorbed on the colloidal silver surface as dithiolates by losing two H-atoms of the S-H bond, while as monothiolates on the roughened silver electrode. The different orientations of the molecules on both silver surfaces indicate the different adsorption behaviors of 4,4'-TBBT in the two systems.

Direct electrochemistry of horseradish peroxidase immobilized in calcium carbonate microsphere doped with phospholipids

Protein electrochemistry affords a direct method to study the biological electron transfer processes. However, supplying a biocompatible environment to maintain the native state of protein is all-important and challengeable. Here, we chose vaterite, one of the crystalline polymorphs of calcium carbonate, with highly porous nature and large specific surface area, which was doped with phospholipids, as the matrix to immobilize horseradish peroxidase (HRP). The integrity of HRP was kept during the simple immobilization procedure. By virtue of this organic/inorganic complex matrix, the direct electrochemistry of HRP was realized, and the activity of HRP for catalyzing reduction of O-2 and H2O2 was preserved.

Electrooxidation of COad intermediated from methanol oxidation on polycrystalline Pt electrode

The poisonous intermediate of methanol oxidation on a Pt electrode was validated to be COad by electrochemical method. An approximate treatment to bimolecular elementary reactions on an electrode was advanced and then was applied to the stripping normal pulse voltammetry (NPV) for complex multistep multielectron transfer processes on plane electrodes to study the kinetics of completely irreversible process Of COad oxidation to CO2. The kinetic parameters for this process, such as standard rate constant (0) and anodic transfer coefficient (alpha) for this irreversible heterogeneous electron-transfer process at electrode/solution interface and apparent diffusion coefficient (D-app) for charge-transfer process within the monolayer of COad on electrode surface, were obtained with stripping NPV method. The effect of the approximate treatment on the kinetic parameters was also analyzed.

Copper hexacyanoferrate multilayer films on glassy carbon electrode modified with 4-aminobenzoic acid in aqueous solution

4-Aminobenzoic acid (4-ABA) was covalently grafted on a glassy carbon electrode (GCE) by amine cation radical formation during the electrooxidation process in 0.1 M KCl aqueous Solution. X-ray photoelectron spectroscopy (XPS) measurement proves the presence of 4-carboxylphenylamine on the GCE. Electron transfer processes of Fe(CN)(6)(3-) in solutions of various pHs at the modified electrode are studied by both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Changing the solution pH would result in the variation of the terminal group's charge state, based on which the surface pK(a) values were estimated. The copper hexacyanoferrate (CuHCF) multilayer films were formed on 4-ABA/GCE prepared in aqueous solution, and which exhibit good electrochemical behavior with high stability.

Photosensitization of TiO2 nanoparticulate thin film electrodes by CdS nanoparticles

Surface photovoltage spectra (SPS) measurements of TiO2 show that a large surface state density is present on the TiO2 nanoparticles and these surface states can be efficiently decreased by sensitization using US nanoparticles as well as by suitable heat treatment. The photoelectrochemical behavior of the bare TiO2 thin film indicates that the mechanism of photoelectron transport is controlled by the trapping/detrapping properties of surface states within the thin films, The slow photocurrent response upon the illumination can be explained by the trap saturation effect. For a TiO2 nanoparticulate thin film sensitized using US nanoparticles, the slow photocurrent response disappears and the steady-state photocurrent increases drastically, which suggests that photosensitization can decrease the effect of surface states on photocurrent response.

Interfacial characteristics of the self-assembly system of poly-L-lysine 3-mercaptopropionic acid gold electrode

The interfacial characteristics of poly-L-lysine (PL) attached on self-assembled monolayers (SAMs) of 3-mercaptopropionic acid (MPA) were studied by an electrochemical method. The results indicated that PL\MPA layer inhibited partly the diffusion process of redox species in solution, and the electrode surface behaved like a microelectrode array. Its permeation effect was also strongly affected by Mg2+. The more Mg2+ ions were added into the electrolyte solution, the greater the difficulty with which the electron transfer of potassium ferricyanide took place. The three different conformations of PL on the electrode surface had different influences on the electron transfer processes of ferricyanide. PL in random coil state hindered most strongly the electron transfer behavior of ferricyanide,while the alpha-helical PL had nearly no effect and the effect of the beta-sheet state PL was intermediate of these. (C) 1997 Elsevier Science S.A.