Optical Nanocomposite Planar Waveguides Doped with Rare-Earth and Noble Metal Elements

The present paper is focused on multilayer Er³⁺-doped silica-titania planar waveguides, co-doped with silver, which were prepared by spin-coating on silica glass, or buffered single crystal silicon substrates. The single layer thickness (0.4 m) and refractive index (1.60–1.63) were measured by spectroscopic ellipsometry at 715 nm. The thickness of the waveguides (measured by mechanical profilometry) was 1 m and their optical propagation losses were measured at different laser wavelengths (488 nm, 514 nm and 633 nm), exhibiting an approximately Rayleigh-like behavior. The thermal precipitation of silver nanocrystallites was achieved, both in air and under a controlled atmosphere (dry nitrogen) and these were characterized by visible absorption spectroscopy, which clearly showed the development of a plasmon absorption band near 415 nm, by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). The Er³⁺ metastable level lifetimes for the emission at ca. 1.54 m were found to be ca. 4–6 ms, for Er³⁺ concentrations varying between 0.2–2.0 mol% (or (0.4–4.4) × 10²⁰ ions/cm³), but no significant variation was observed with the Ag concentration added (up to 2.5 mol%).     

Complexing equilibria and redox potentials of the Ag(II)/Ag(I) system in the presence of 2,2′:6′,2″-terpyridine in water

Summary The conditional protonation constants (=0.1) for 2,2:6,2-terpyridine, logK ₁=4.93, logK ₂=3.69, were determined by thepH-metric method. The compositions of complexes of Ag²⁺ and Ag⁺ ions with 2,2:6,2-terpyridine (tp) were studied and equilibria of the complex formation process were described. The values of conditional complex formation constants are as follows: for Ag(tp) ₂ ⁺ :log₀₁=5.79, log₀₂=9.68, for Ag(tp) ₂ ²⁺ :log₀₂=25.31, while the conditional constant of the Ag(tp)NO₃ precipitate formation is:K _SO=2.45·10⁴. Using coulometric and chronovoltamperometric measurements, the redox systems being formed in the complex solutions of Ag(II) and Ag(I) were determined and described including their formal potentials.

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Komplexibildungsgleichgewichte und Redoxpotentiale des Systems Ag(II)/Ag(I) in Gegenwart von 2,2:6,2-Terpyridin in Wasser

Zusammenfassung Mit Hilfe derpH-metrischen Methode wurden die konditionalen Protonationskonstanten (=0.1) von 2,2:6,2-Terpyridin bestimmt: logK ₁=4.93, logK ₂=3.69. Es wurde auch die Zusammensetzung der Komplexe von Ag(II) und Ag(I) mit 2,2:6,2-Terpyridin(tp) bestimmt sowie die Gleichgewichte der komplexbildung beschrieben. Die Werte der Konditionalkomplexbildungskonstanten sind: für Ag(tp) ₂ ⁺ :log₀₁=5.79, log₀₂=9.68, für Ag(tp) ₂ ²⁺ :log₀₂=25.31 und für das Löslichkeitsprodukt Ag(tp)NO₃:K _SO ^–1 =4.08·10^–5. Die in Komplexlösungen von Ag(II) und Ag(I) vorliegenden Redoxsysteme wurden mittels cyclischer Voltametrie und Coulometrie untersucht und die Formalpotentialwerte dieser Systeme in Wasser bestimmt.

     

一步法合成吲哚用Ag／SiO2催化剂的失活及其抑制

 用简单浸渍法制备了Ag／SiO2催化剂．该催化剂对苯胺和乙二醇一步合成吲哚表现出很高的催化活性，但同时存在明显的失活．TG，XRD和TEM表征结果表明，催化剂失活的主要原因是反应过程中催化剂表面的积碳和银粒子的烧结．向反应体系中通入氢和水蒸气能够减少催化 剂表面的积碳；向催化剂体系加入ZnO助剂能较大程度地提高银的分散度，并能有效抑制反应过程中银粒子的烧结．     

Construction of database of effective energy‐loss functions

Effective energy‐loss functions for Al, Cu, Ag and Au were derived from the reflection electron energy‐loss spectroscopy (REELS) spectra for 1 keV electrons using extended Landau theory. Features of the obtained effective energy‐loss functions are close to those of optical surface energy‐loss functions, revealing the significant contribution of the low energy loss below a few tens of electron‐volts in the REELS spectrum for Cu, Ag and Au. The REELS spectra were reproduced using the newly derived effective energy‐loss functions, leading to the confirmation that this type of database of the effective energy‐loss function is very useful not only for more comprehensive understanding of the measured spectrum of surface electron spectroscopies but also for practical background subtraction in surface electron spectroscopy. Copyright © 2003 John Wiley & Sons, Ltd.     

Electrocatalytic activity of dispersed platinum and silver alloys and manganese oxides for the oxygen reduction in alkaline electrolyte

This work reviews the studies conducted in this laboratory of the oxygen reduction reaction (ORR) on electrocatalysts formed by Pt-M/C (M = V, Cr, Co) and Ag-Pt/C alloys and on different Mn oxides (MnO/C, Mn₃O₄/C, MnO₂/C) in KOH electrolyte. The physical and electronic properties of the materials are investigated by in situ XAS (x-ray absorption spectroscopy) in the XANES (x-ray absorption near edge structure) region. The electrocatalytic activity for the ORR on the different catalysts is compared through mass-transport-corrected Tafel plots. The XANES results for the Pt-M/C and Ag-Pt/C composites at high electrode potentials show lower vacancy of the Pt 5d band compared to pure Pt/C, while for the results indicate a chance of the Mn oxidation state as a function of the electrode potential. The electrochemical measurements evidence increased electrocatalytic activity of the Pt alloys compared to pure Pt and this is attributed to a lowering of the adsorption strength of adsorbed oxygen species caused by the reduced Pt reactivity. An activity enhancement of the Ag atoms on the Ag-Pt/C alloys compared to pure Ag is ascribed to an electronic effect induced by the presence of Pt, increasing the Ag-O adsorption strength. In the case of the Mn_yO_x/C materials, the electrochemical results show low activity for MnO/C and higher activity for MnO₂/C and Mn₃O₄/C. This is explained based on the activation for the ORR, which is higher for the material with higher MnO₂ contents and the occurrence of a mediation processes involving the reduction of Mn(IV) to Mn(III), followed by the electron transfer of Mn(III) to oxygen. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 12, pp. 1417–1426. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22, 2005, Moscow. The text was submitted by the authors in English.     

Photogeneration of Silver Particles in PVA Fibers and Films

Fibers and films prepared from blends of poly(vinyl alcohol) and poly(acrylic acid) were found to be suitable matrices for the solid-state photoreduction of silver ions in the presence of air. Fast generation of nanometer-sized silver crystallites was observed when fibers of polymer blends crosslinked with dimethyl sulfoxide were irradiated with 350nm light. Optical determinations of the formation kinetics were carried out using thin films of noncrosslinked as well as lightly and heavily crosslinked polymer blends. Small Ag clusters were detected initially, which were stable in the dark but transformed into larger metal particles upon further illumination. Both formation processes occurred only under high light intensity illumination and the kinetic data were inconsistent with monophotonic mechanisms.     

阴离子导向组装：两个具有不同阳离子的多维Ag(I)配合物的晶体结构

Assembly of [Ag（CN）2]^- units with M（Ⅱ）-diamine complex cations [Cu（LN-N）2]^2＋, where LN-N represents L2-diaminopropane （pn） and ethylenediamine （en）, afforded two complexes, [Cu（pn）2][Ag2（CN）4] （1） and [Cu（en）2][Ag3（CN）5] （2）, which were characterized by elemental analysis, IR, UV-Vis and ESR spectra. Single crystal X-ray analyses show that these complexes have 2D and 3D architectures through silver-silver interactions and other weak interactions. The luminescence behaviors of the two complexes were also studied by means of emission spectra.     

The catanionic system dodecyltrimethylammonium hydroxide–n-dodecanephosphonic acid–water. Triangular phase diagram

 The triangular phase diagram of the system dodecyltri-methylammonium hydroxide (DTAOH)–dodecanephosphonic acid (H₂DP)–water was studied by several techniques. The DTAOH-rich zone could not be studied because DTAOH decomposed when it was dried. Pure H₂DP only forms lamellar mesophases with water. The inclusion of DTAOH in the system produces the appearance of cubic and hexagonal mesophases. The gradual increase in DTAOH proportion lead to the gradual reduction in the existence of the lamellar mesophase domain, and increase of the hexagonal liquid crystal domain. At high DTAOH content, the lamellar mesophase disappeared. This behavior was explained by the gradual destruction of the hydrogen-bonded structure in the polar headgroup layer of liquid crystal aggregates. H₂DP-rich anhydrous crystals were triclinic. Received: 8 September 1997 Accepted: 17 February 1998     

Zum Reaktionsverhalten der Tris(dialkylthiophosphinyl)phosphane – Die Kristallstruktur von [Ag{O[P(S)Me2]2}2] [AsF6]

Reactivity of Tris(dialkylthiophosphinyl)phosphines – Crystal Structure of [Ag{O[P(S)Me₂]₂}₂][AsF₆] In contrast to tris(dialkylphosphoryl)phosphines the reaction of tris(dimethylthiophosphinyl)phosphine with transition metal hexafluoroarsenates of the type [M(SO₂)_m [AsF₆]_n (M = Ag, m = 0, n = 1; M = Fe, Cd, m = n = 2) forms no molecular 2 : 1-complexes but polymeric products. The silver polymer is transformed into [Ag{O[P(S)Me₂]₂}₂][AsF₆], which is also formed by the reaction of Ag[AsF₆] with O[P(S)Me₂]₂. It crystallizes in the space group P1 with a = 862.5(2), b = 1 241.4(2), c = 1 254.0(3)pm, α = 80.34(1), β = 101.99(6), γ= 73.75(1)° (at 20°C) and Z = 2. The central silver atom is surrounded by four sulphur atoms in a slighly distorted tetrahedron. The average (Ag? S) and (P? S) bond lengthes are 259.4(2) pm and 194.9(2)pm, respectively.     

From Weakly Coordinating to Non‐Coordinating Anions? A Simple Preparation of the Silver Salt of the Least Coordinating Anion and Its Application To Determine the Ground State Structure of the Ag(η2‐P4)2+ Cation

The unexpected but facile preparation of the silver salt of the least coordinating [(RO)₃Al‐F‐Al(OR)₃]^? anion (R=C(CF₃)₃) by reaction of Ag[Al(OR)₄] with one equivalent of PCl₃ is described. The mechanism of the formation of Ag[(RO)₃Al‐F‐Al(OR)₃] is explained based on the available experimental data as well as on quantum chemical calculations with the inclusion of entropy and COSMO solvation enthalpies. The crystal structures of (RO)₃Al←OC₄H₈, Cs⁺[(RO)₂(Me)Al‐F‐Al(Me)(OR)₂]^?, Ag(CH₂Cl₂)₃⁺[(RO)₃Al‐F‐Al(OR)₃]^? and Ag(η²‐P₄)₂⁺[(RO)₃Al‐F‐Al(OR)₃]^? are described. From the collected data it will be shown that the [(RO)₃Al‐F‐Al(OR)₃]^? anion is the least coordinating anion currently known. With respect to the fluoride ion affinity of two parent Lewis acids Al(OR)₃ of 685 kJ mol^?1, the ligand affinity (441 kJ mol^?1), the proton and copper decomposition reactions (?983 and ?297 kJ mol^?1) as well as HOMO level and HOMO–LUMO gap and in comparison with [Sb₄F₂₁]^?, [Sb(OTeF₅)₆]^?, [Al(OR)₄]^? as well as [B(R^F)₄]^? (R^F=CF₃ or C₆F₅) the [(RO)₃Al‐F‐Al(OR)₃]^? anion is among the best weakly coordinating anions (WCAs) according to each value. In contrast to most of the other cited anions, the [(RO)₃Al‐F‐Al(OR)₃] anion is available by a simple preparation in conventional inorganic laboratories. The least coordinating character of this anion was employed to clarify the question of the ground state geometry of the Ag(η²‐P₄)₂⁺ cation (D_2h, D₂ or D_2d?). In agreement with computational data and NMR spectra it could be shown that the rotation along the Ag‐(P‐P‐centroid) vector has no barrier and that the structure adopted in the solid state depends on packing effects which lead to an almost D_2h symmetric Ag(η²‐P₄)₂⁺ cation (0 to 10.6° torsion) for the more symmetrical [Al(OR)₄]^? anion, but to a D₂ symmetric Ag(η²‐P₄)₂⁺ cation with a 44° twist angle of the two AgP₂ planes for the less symmetrical [(RO)₃Al‐F‐Al(OR)₃]^? anion. This implies that silver back bonding, suggested by quantum chemical population analyses to be of importance, is only weak.