Counterion effects on the structure and solubilization properties of anionic detergents. Role of hydrophobic cations in stabilizing micelles and attenuating their solvent properties

A series of alkyl sulfate detergents has been investigated in the presence of the cations Na +, methylviologen(2+) (MV 2+), 4-(cyanomethyl)pyridinium(1+) (CMP +), and tetramethylammonium (TMA +). The binding of these ions to the aqueous micellar assemblies has been measured through studies of luminescence quenching with the extramicellar probe, RuL 34-, where L = 4,4′-dicarboxy-2,2′-bipyridine. A general comparison of the alkyl sulfate aggregates with the nonquenching cations Na + and TMA + shows that the latter ion reduces the critical micelle concentration but at the same time depresses the ability of the detergent assemblies to bind or solubilize the hydrophobic quencher cations MV 2+ or CMP +. The reduced binding ability of the TMA + aggregates compared to that of the corresponding Na + soaps shows up largely in the form of a reduced favorable ΔS° for the solubilization in the case of the former. The results are in accord with a picture of the TMA + micelle as being more stable and more disordered than the corresponding assembly with Na + as the counterion. © 1989 American Chemical Society.

QUIMILUMINESCENCIA: ASPECTOS QUIMICOS E FISICOS

The history, the chemistry and the physic aspects of luminescence phenomenon are approached, essentially in relation to chemiluminescence, chemical reactions which emit light, discussing about its importance, definition, classification and application.

Synthesis of lanthanide oxysulfides activated by Eu3+. A topochemical reaction

The oxysulfide compounds La2O2S:Eu and Y2O2S were obtained directly from thermodecomposition of the respective oxalate compounds under argon and sulfur vapor, the obtained compounds were analyzed by infrared spectroscopy, X ray diffraction and luminescence spectroscopy. The particle size distribution and crystalline habit of the compounds were observed by scanning electron microscopy. Although the particle size of the oxysulfide was found to be 30%-40% smaller than the precursor oxalates, the initial morphology was completely maintained, which indicates the occurrence of a topochemical reaction from oxalates to oxysulfides. © Gauthier-Villars.

Violet-blue emissions due to frequency up-conversion in Nd3+-doped fluoroindate glasses

We report the observation of intense frequency up-conversion in Nd3+-doped fluoroindate glasses pumped by the second harmonic of a cw mode-locked Nd: YAG laser. Mechanisms for generating the observed emissions are discussed.

Crystallization of fluorindate and fluorogallate glasses

Crystallization of binary InF3-MF2 and GaF3-MF2 (where M = Ba, Sr and Ca) glasses was studied. Characteristic temperatures and kinetic parameters E (activation energy) and n (Avrami exponent) were obtained. Stability against devitrification is discussed in terms of the above cited parameters and also of some others parameters proposed in literature. Optical properties (IR and upconversion emissions) are reported in different crystallized samples containing Nd3+. The main observation is that up conversion emission presents an enhanced sensibility to crystallization when compared to conventional emission. © 1997 Published by Elsevier Science B.V.

Preparation and characterization of uniform, spherical particles of Y2O2S and Y2O2S:Eu

The preparation of spherical Y2O2S and Y2O2S:Eu particles using a solid-gas reaction of monodispersed precursors with elemental sulfur vapor under an argon atmosphere has been investigated. The precursors, undoped and doped yttrium basic carbonates, are synthesized by aging a stock solution containing the respective cation chloride and urea at 82-84 °C. Y2O2S and Y2O2S:Eu were characterized in terms of their composition, crystallinity and morphology by chemical analysis, X-ray powder diffraction (XRD), IR spectroscopy, and scanning electron microscopy (SEM). The Eu-doped oxysulfide was also characterized by atomic absorption spectrophotometry and luminescence spectroscopy. The spherical morphology of oxysulfide products and of basic carbonate precursors suggests a topotatic inter-relationship between both compounds.

Study of the binding of Eu3+ and Tb3+ to L-phenylalanine and L-tryptophan

Trivalent europium and terbium ions have ionic radii similar to that of Ca2+. So they are employed as probes of calcium binding sites in biological molecules. These ions exhibit very useful spectroscopic characteristics, chiefly a pronounced luminescence. In protein bound lanthanide, visible light emission from the lanthanide excited states can be observed when UV light is absorbed by aromatic amino acids. Subsequently, the energy is transferred to the lanthanide ion. The present work was carried out to define the binding sites of Eu3+ and Tb3+ in complexes with the aromatic amino acids L-phenylalanine and L-tryptophan. The techniques utilized were infrared and C nuclear magnetic resonance spectroscopies. It was found that trivalent europium and terbium interact with the carboxylate group of both amino acids. With L-tryptophan, the imino group of the indole ring is also involved representing another coordination site.

Optical spectroscopy of Er3+ and Yb3+ co-doped fluoroindate glasses

Optical absorption, Stokes, and anti-Stokes photoluminescence were performed on Er3+-Yb3+ co-doped fluoroindate glasses. For compounds prepared with a fixed 2 mol % ErF3 concentration and YbF3 contents ranging from 0 to 8 mol %, important upconversion processes were observed as a function of temperature and photon excitation energy. Based on the experimental data, two mechanisms for the upconversion (or anti-Stokes photoluminescence) processes were identified and analyzed in detail. At high Yb contents, the upconversion mechanisms are mostly determined by the population of the 2F5/2 levels of Yb3+ ions (or 4I11/2 levels of Er3+ ions, by energy transfer) regardless of the photon excitation energy and temperature of measurement. Moreover, green and red light emission have similar intensities when a large Yb3+ content is present. © 1998 American Institute of Physics.

Energy transfer between Pr3+ ions in a fluoroindate glass

The efficiency of energy transfer (ET) between Pr3+ ions in a fluoroindate glass is determined. ET rates, WET, were determined for dilute samples and the results show a dependence of WET on the Pr3+ concentration. ET processes which contribute to resonance fluorescence and frequency upconversion emission were studied. The origin of the interaction energy among the Pr3+ ions was determined to be dipole - dipole. © 1998 Elsevier Science B.V. All rights reserved.

In(PO3)3 stabilised fluoroindate glasses

Results on thermal and optical characterization of new lanthanide containing fluoroindate glasses in the system InF3-BaF2-In(PO3)3 are presented. Good optical quality and very stable glasses presenting up to 5 mm in thickness could be prepared in this system. Thermal analysis, Raman scattering and Eu3+ luminescence were the techniques utilized. A novel method for In(PO3)3 synthesis is proposed and the dependence of physical properties and structural features on the polyphosphate content is stressed. © 1998 Elsevier Science S.A.

Preparation, characterization and spectroscopy of the europium diphenylphosphinate complex

The purpose of this work is to study the preparation and spectroscopic behavior of the europium diphenylphosphinate complex -Eu(DPP)3. Elemental and thermogravimetric analysis, powder X-ray diffractometry, and infrared spectroscopy were applied to characterize the formula of the final product and the sixfold coordination of the Eu3+ ion. Excitation and emission spectra have been recorded at liquid nitrogen and room temperatures. The 5D0→7F2 transition intensity decreases when T decreases in comparison to the 5D0→7F1 transition intensity. Molecular mechanic calculations were developed in order to obtain the spatial coordinates of the Eu3+ and ligand ions. The simple overlap model was used to calculate the total splitting of the 5D0→7F1 transition, 5D0→7F0/5D 0→7F2 ntensity ratio and the intensity parameters, Ωλ (λ=2 and 4). Good agreements between theoretical predictions and experimental results have been obtained with g=2/3 as the effective charge and α=0.8×10-24 cm3 as the isotropic polarizability of the oxygen. © 1998 Elsevier Science S.A.

Violet and blue light amplification in Nd3+-doped fluoroindate glasses

We report optical gain at 382 and 414 nm from Nd3+-doped fluroindate glasses after excitation with lasers operating either at 583 or 532 nm. Stimulated emission due to a frequency upconversion process results in increase of the emitted violet and blue light intensity and emission line narrowing. Large optical gain is measured by pump-probe spectroscopy using samples with various Nd3+ concentrations. © 1999 American Institute of Physics.

White light emission of Eu3+-based hybrid xerogels

The luminescence spectra and extended x-ray-absorption fine-structure (EXAFS) measurements of a series of Eu3+-based organic/inorganic xerogels were reported and related to the local coordination of the lanthanide cations. The hybrid matrix of these organically modified silicates, classed as U(2000) ureasils, is a siliceous network to which short organic chains containing oxyethylene units are covalently grafted by means of urea bridges. The luminescent centers were incorporated as europium triflate, Eu(CF3SO3)3, and europium bromide, EuBr3, with concentrations 200≥n≥20 and n=80, 40, and 30, respectively - where n is the number of ether oxygens in the polymer chains per Eu3+ cation. EXAFS measurements were carried out in some of the U(2000)nEu(CF3SO3)3 xerogels (n=200, 80, 60, and 40). The obtained coordination numbers N ranging from 12.8, n=200, to 9.7, n=40, whereas the average Eu3+ first neighbors distance R is 2.48-2.49 Å. The emission spectra of these multiwavelength phosphors superpose a broad green-blue band to a series of yellow-red narrow 5D0→7F0-4 Eu3+ lines and to the eye the hybrids appeared to be white, even at room temperature. The ability to tune the emission of the xerogels to colors across the chromaticity diagram is achieved by changing the excitation wavelength and the amount of salt incorporated in the hybrid host. The local environment of Eu3+ is described as a continuous distribution of closely similar low-symmetry network sites. The cations are coordinated by the carbonyl groups of the urea moieties, water molecules, and, for U(2000)nEu(CF3SO3)3, by the SO3 end groups of the triflate anions. No spectral evidences have been found for the coordination by the ether oxygens of the polyether chains. A mean radius for the first coordination shell of Eu3+ is calculated on the basis of the emission energy assignments. The results obtained for U(2000)nEu(CF3SO3)3, 2.4 Å for 90 ≥n≥40 and 2.6 and 2.5 Å for n=30 and 20, respectively, are in good agreement with the values calculated from EXAFS measurements. The energy of the intraconfigurational charge-transfer transitions, the redshift of the 5D0→7F0 line, with respect to the value calculated for gaseous Eu3+, and the hypersensitive ratio between the 5D0→7F2 and 5D0→7F1 transitions, point out a rather low covalency nature of the Eu3+ first coordination shell in these xerogels, comparing to the case of analogous polymer electrolytes modified by europium bromide. ©1999 The American Physical Society.

L-Histidine-europium(III) complex: A spectroscopical study

Chemical characterization as well as spectroscopical study of the L-histidine-europium(III) complex were developed both experimental and theoretically. Molecular mechanics (MM) simulation was performed in order to have indication of the compound structure and the Eu 3+ chemical environment. The Simple Overlap Model (SOM) was applied to predict spectroscopic quantities as 5D 0→ 7F 0/ 5D 0→ 7F 2 intensity ratio, 5D 0→ 7F 1 transition splitting and the intensity Ω λ parameters (λ = 2 and 4). Satisfactory results are obtained with 0.1 and 2/3 as the effective charges of the nitrogen (gN) and oxygen (gO) respectively, and their polarizabilities (α) depend on the distance. © 1999 Elsevier Science B.V. All rights reserved.

Photoluminescence in amorphous (PbLa)TiO3 thin films deposited on different substrates

Pb1-xLaxTiO3 thin films, (X=0.0; 13 and 0.27mol%) were prepared by the polymeric precursor method. Thin films were deposited on Pt/Ti/SiO2/Si(111), Si(100) and glass substrates by spin coating, and annealed in the 200-300°C range in an O2 atmosphere. X-ray diffraction, scanning electron microscopy and atomic force microscopy were used for the microstructural characterization of the thin films. Photoluminescence (PL) at room temperature has been observed in thin films of (PbLa)TiO3. The films deposited on Pt/Ti/SiO2/Si substrates present PL intensity greater than those deposited on glass and silicon substrates. The intensity of PL in these thin films was found to be dependent on the thermal treatment and lanthanum molar concentration. © 2002 Elsevier Science B.V. All rights reserved.