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Luminescence Spectroscopy (luminescence + spectroscopy)
Selected AbstractsPhotostabilization of styrene,ethylene,butylene,styrene block copolymer by hindered phenol and phosphite antioxidantsJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 1 2006Cristina Luengo The photostabilization of poly(styrene- b -ethylene- co -butylene- b -styrene) (SEBS), by hindered phenols and their combination with phosphite antioxidants has been studied by using a variety of spectroscopic methods including FTIR, UV, and luminescence spectroscopy coupled with crosslinking and hydroperoxide analysis. The addition of a hindered phenol was found to photostabilize the SEBS in terms of the inhibition of discoloration, and the formation of hydroperoxides, acetophenone, and oxidation products, as well as chain scission and disaggregation of the styrene units. Strong synergism was found with combinations of a hindered phenol and phosphite antioxidant, especially with an increase in the phosphite concentration. Residual titanium traces present as impurities in the material were found to play an important role in the photo-oxidation of SEBS. Molecular weight appeared to be a determining factor in the proportion of chain scission/crosslinking reactions that occured. Nevertheless, the addition of antioxidants and the reduction of titanium content also proved satisfactory in stabilizing the low-molecular-weight material. J. VINYL. ADDIT. TECHNOL. 12:2,7, 2006. © 2006 Society of Plastics Engineers [source] Synergistic profiles of chain-breaking antioxidants with phosphites and hindered amine light stabilizers in styrene,ethylene,butadiene,styrene (SEBS) block copolymerJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 1 2006Cristina Luengo The photostabilization of poly(styrene- b -ethylene- co -butylene- b -styrene) (SEBS) by phosphite/p -hydroxybenzoate antioxidants and hindered phenol/hindered amine light stabilizers (HALS) was studied by using a variety of spectroscopic methods, including FTIR, UV, and luminescence spectroscopy coupled with crosslinking and hydroperoxide analysis. The results were compared with those obtained for hindered phenols and their combinations with phosphite antioxidants. All the stabilizing packages stabilized the SEBS in terms of the inhibition of discoloration and the formation of hydroperoxides, acetophenone, and oxidation products, as well as chain scission and disaggregation of the styrene units. Although phosphite/p -hydroxybenzoate combinations appeared to reduce the formation of oxidation products, they did not show any remarkable enhancement in long-term stabilization with respect to phenolic/phosphite antioxidants. On the other hand, strong synergistic profiles were found with the HALS. Mobility and diffusion impediments in the polymeric material appeared to play an important role in the stabilizing activity of the HALS. J. VINYL. ADDIT. TECHNOL. 12:8,13, 2006. © 2006 Society of Plastics Engineers [source] Novel Light Emitting Diode Using Organic Electroluminescence MicrocapsulesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2003Jae-Seok Heo Abstract Novel light emitting diodes (LEDs) were prepared using electroluminescence (EL) material/polymer microcapsules (ELC). N-vinylcarbazole as a hole-transporting component and methyl methacrylate (MMA) were copolymerized for producing the seed particles using dispersion polymerization. An oxadiazole derivative, synthesized as a electron-transporting component, and tris(8-hydroxyquinolinato) aluminium(III) (Alq3) were incorporated into the polymer particles by using the solute co-diffusion method (SCM). The LEDs for the EL characterization were fabricated in a thin sandwich configuration: Al anode/ELC/ITO cathode. The surface imaging of the LED prepared using ELC was performed by atomic force microscopy (AFM). The EL characteristics of the ELC were investigated by UV, photoelectron and luminescence spectroscopy, and the current-voltage and the light-voltage characteristics for the LED were determined. Encapsulation procedure using solute co-diffusion method (SCM). [source] Photophysical Properties of Terbium Molecular-based Hybrids Assembled with Novel Ureasil LinkagesPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Bing Yan Three silica-based organic,inorganic hybrid systems composed of hydroxyl aromatic derivatives (2-acetylphenol [HAP], 2-hydroxy-3-methylbenzoic acid [HMBA], 3-hydroxy-meta-phthalic acid [HMPHTH] complexes) were prepared via a sol,gel process. The active hydroxyl groups of the three ligands grafted by 3-(triethoxysilyl)-propyl isocyanate (TESPIC) through hydrogen transfer addition reaction were used as multi-functional bridge components, which can coordinate to Tb3+ with carbonyl groups, strongly absorb ultraviolet light and effectively transfer energy to Tb3+ through their triplet excited state, as well as undergo polymerization or crosslinking reactions with tetraethoxysilane (TEOS), for anchoring terbium ions to silica backbone. NMR, FT-IR, UV,vis absorption, luminescence spectroscopy was used to investigate the obtained hybrid material. UV excitation in the organic component resulted in strong green emission from Tb3+ ions due to an efficient ligand-to-metal energy transfer mechanism. [source] Random lasing in nanocrystalline ZnO powdersPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2010Heinz Kalt Abstract We investigate the properties of random lasing in nanocrystalline ZnO powders. The lowest threshold for lasing occurs for average particle diameters of about 260,nm. Reproducible lasing features are achieved for reduced ensemble sizes. Spatially resolved luminescence spectroscopy is used to probe directly the degree of localization of random laser mode. We find that strongly confined and extended modes can co-exist in the same spatial area. However, localized modes appear for small optical gain while extended modes are only supported in the presence of large optical gain, as is expected from theory. Localized and extended random-laser modes co-exist in space but appear in spectral regions of low and high optical gain, respectively. [source] Peculiarities of ozone adsorption on a porous silicon surface at low temperaturePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2007V. B. Pikulev Abstract Interaction between ozone molecules and silicon nanocrystallites in porous silicon (por-Si) results in effective luminescence similar to optically excited emission but the mechanism still is not quite understood. To study the process the kinetics of both adsorption and oxidation of highly porous silicon surface under exposure to ozone (16O3 and 18O3) at low temperatures were measured using FTIR- and luminescence spectroscopy. It is shown that ozone chemisorption on por-Si surface takes place yet at liquid oxygen temperature. The oxide coat formed instantly after ozone admission inhibits further oxidation and results in the predominance of ozone physisorption. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical micro-characterization of group-III-nitrides: correlation of structural, electronic and optical propertiesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2003J. Christen Abstract For a detailed understanding of complex semiconductor heterostructures and the physics of devices based on them, a systematic determination and correlation of the structural, chemical, electronic, and optical properties on a micro- or nano-scale is essential. Luminescence techniques belong to the most sensitive, non-destructive methods of semiconductor research. The combination of luminescence spectroscopy with the high spatial resolution of a scanning electron microscope, as realized by the technique of cathodoluminescence microscopy, provides a powerful tool for the optical nano-characterization of semiconductors, their heterostructures as well as their interfaces. Additional access to the local electronic and structural properties is provided by micro-Raman spectroscopy, e.g. giving insight into the local free carrier concentration and local stress. In this paper, the properties of group-III-nitrides are investigated by highly spatially and spectrally resolved cathodoluminescence microscopy in conjunction with micro-Raman spectroscopy. Complex phenomena of self-organization and their strong impact on the microscopic and nanoscopic properties of both binary and ternary nitrides are presented. As the ultimate measure of device performance, the microscopic properties of light emitting diodes are assessed under operation. Using micro-electroluminescence mapping in the optical microscope as well as in the near field detection mode of a scanning near field optical microscope, the microscopic origin of the macroscopic spectral red shift in light emitting diodes is identified. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Quest for Environmentally Benign Ligands for Actinide Separations: Thermodynamic, Spectroscopic, and Structural Characterization of UVI Complexes with Oxa-Diamide and Related LigandsCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2009Guoxin Tian Dr. Abstract Complexation of UVI with N,N,N,,N, -tetramethyl-3-oxa-glutaramide (TMOGA) and N,N -dimethyl-3-oxa-glutaramic acid (DMOGA; see picture) was studied in comparison with their dicarboxylate analogue, oxydiacetic acid (ODA). The stability constants, enthalpy, and entropy of complexation all decrease in the order ODA> DMOGA>TMOGA, showing that the complexation is entropy driven and the substitution of a carboxylate group with an amide group reduces the strength of complexation with UVI due to the decrease in the entropy of complexation (see figure). Complexation of UVI with N,N,N,,N, -tetramethyl-3-oxa-glutaramide (TMOGA) and N,N -dimethyl-3-oxa-glutaramic acid (DMOGA) was studied in comparison with their dicarboxylate analogue, oxydiacetic acid (ODA). Thermodynamic parameters, including stability constants, enthalpy, and entropy of complexation, were determined by spectrophotometry, potentiometry, and calorimetry. Single-crystal X-ray diffraction, EXAFS spectroscopy, FT-IR absorption spectroscopy, and laser-induced luminescence spectroscopy were used to obtain structural information on the UVI complexes. Like ODA, TMOGA and DMOGA form tridentate UVI complexes, with three oxygen atoms (the amide, ether, and/or carboxylate oxygen) coordinating to the linear UO22+ ion through the equatorial plane. The stability constants, enthalpy, and entropy of complexation all decrease in the order ODA>DMOGA>TMOGA, showing that the complexation is entropy driven and the substitution of a carboxylate group with an amide group reduces the strength of complexation with UVI due to the decrease in the entropy of complexation. The trend in the thermodynamic stability of the complexes correlates very well with the structural and spectroscopic data obtained by single-crystal X-ray diffraction, FT-IR spectroscopy, and laser-induced luminescence spectroscopy. [source] Speciation of Rare-Earth Metal Complexes in Ionic Liquids: A Multiple-Technique ApproachCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2009Peter Nockemann Dr. Abstract The dissolution process of metal complexes in ionic liquids was investigated by a multiple-technique approach to reveal the solvate species of the metal in solution. The task-specific ionic liquid betainium bis(trifluoromethylsulfonyl)imide ([Hbet][Tf2N]) is able to dissolve stoichiometric amounts of the oxides of the rare-earth elements. The crystal structures of the compounds [Eu2(bet)8(H2O)4][Tf2N]6, [Eu2(bet)8(H2O)2][Tf2N]6,2H2O, and [Y2(bet)6(H2O)4][Tf2N]6 were found to consist of dimers. These rare-earth complexes are well soluble in the ionic liquids [Hbet][Tf2N] and [C4mim][Tf2N] (C4mim=1-butyl-3-methylimidazolium). The speciation of the metal complexes after dissolution in these ionic liquids was investigated by luminescence spectroscopy, 1H, 13C, and 89Y,NMR spectroscopy, and by the synchrotron techniques EXAFS (extended X-ray absorption fine structure) and HEXS (high-energy X-ray scattering). The combination of these complementary analytical techniques reveals that the cationic dimers decompose into monomers after dissolution of the complexes in the ionic liquids. Deeper insight into the solution processes of metal compounds is desirable for applications of ionic liquids in the field of electrochemistry, catalysis, and materials chemistry. [source] Tetraethylenepentamine-Directed Controllable Synthesis of Wurtzite ZnSe Nanostructures with Tunable MorphologyCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2008Baojuan Xi Dr. Abstract A novel tetraethylenepentamine (TEPA)-directed method has been successfully developed for the controlled synthesis of ZnSe particles with distinctive morphologies, including nanobelts, nanowires, and hierarchically solid/hollow spheres. These structures, self-assembled from nanobelts and nanorods, have been synthesized by adjusting the reaction parameters, such as the solvent composition, reaction temperature, and the aging time. Results reveal that the volume ratio of H2O and TEPA plays a crucial role in the final morphology of ZnSe products. The mechanisms of phase formation and morphology control of ZnSe particles are proposed and discussed in detail. The products have been characterized by means of X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy (TEM), selected area electron diffraction, high-resolution TEM, Raman spectra and luminescence spectroscopy. The as-prepared ZnSe nanoparticles display shape- and size-dependent photoluminescent optical properties. This is the first time to report preparation of complex hollow structures of ZnSe crystals with hierarchy through a simple solution-based route. This synthetic route is designed to exploit a new H2O/TEPA/N2H4,H2O system possibly for the preparation of other semiconductor nanomaterials. [source] Extraction of Lanthanides from Aqueous Solution by Using Room-Temperature Ionic Liquid and Supercritical Carbon Dioxide in ConjunctionCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2006Soufiane Mekki Dr. Abstract For the first time, the study of a three-step extraction system of water/ionic liquid/supercritical CO2 has been performed. Extraction of trivalent lanthanum and europium from an aqueous nitric acid solution to a supercritical CO2 phase via an imidazolium-based ionic liquid phase is demonstrated, and extraction efficiencies higher than 87,% were achieved. The quantitative extraction is obtained by using different fluorinated ,-diketones with and without the addition of tri(n -butyl)phosphate. The complexation phenomenon occurring in the room-temperature ionic-liquid (RTIL) phase was evidenced by using luminescence spectroscopy. [source] | |||||||||||||