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21.
R.A. Sá Ferreira L.D. Carlos V. de Zea Bermudez C. Molina K. Dahmouche Y. Messaddeq S.J.L. Ribeiro 《Journal of Sol-Gel Science and Technology》2003,26(1-3):315-319
The photoluminescence features and the energy transfer processes of Nd3+-based siloxane-poly(oxyethylene) hybrids are reported. The host matrix of these materials, classed as di-ureasils, is formed by a siloxane backbone covalently bonded to polyether chains of two molecular weights by means of urea cross-links. The room-temperature photoluminescence spectra of these xerogels show a wide broad purple-blue-green band (350–570 nm), associated with the emitting centres of the di-ureasil host, and the typical near infrared emission of Nd3+ (700–1400 nm), assigned to the 4F3/2 4I9/2,11/2,13/2 transitions. Self-absorptions in the visible range, resonant with intra-4f3 transitions, indicate the existence of an energy conversion mechanism of visible di-ureasil emission into near infrared Nd3+ luminescence. The existence of energy transfer between the di-ureasil's emitting centres and the Nd3+ ions is demonstrated calculating the lifetimes of these emitting centres. The efficiency of that energy transfer changes both with the polymer molecular weight and the Nd3+ concentration. 相似文献
22.
A. P. Rizzato C. V. Santilli S. H. Pulcinelli Y. Messaddeq P. Hammer 《Journal of Sol-Gel Science and Technology》2004,32(1-3):155-160
Tin oxide nanoparticles prepared by an aqueous sol–gel method were deposited by dip-coating on fluorozirconate glass, ZBLAN (53%ZrF4-20%BaF2-4%LaF3-3%AlF3-20%NaF) to improve its resistance against wet corrosion. The aqueous leaching of uncoated and SnO2-coated fluorozirconate glass was studied by X-ray photoemission spectroscopy (XPS) and it was shown that even an ultra thin tin dioxide film provides good protection of the glass surface against the bulk propagation of the hydrolytic attack. 相似文献
23.
A new class of tungstate fluorophosphate glasses was identified in the NaPO3-BaF2-WO3 ternary system. The variation of several physical properties was determined with respect to chemical composition. Characteristic temperatures, density and refractive index increase as tungsten oxide content increases. The optical transmission range and specially the energy bandgap depend of the WO3 amount. No crystallization could be observed for the most WO3 concentrated vitreous samples (?20% molar). Color and optical properties of the glasses depend of the melting time because of the presence of reduced tungsten species like W5+ and W4+. In addition, photodarkening is observed in tungsten rich glass samples under UV laser illumination and this phenomenon can be reversible by heat treatment near the glass transition temperature. 相似文献
24.
Y. Ledemi S.H. Messaddeq I. Skhripachev S.J.L. Ribeiro Y. Messaddeq 《Journal of Non》2009,355(37-42):1884-1889
To study the influence of Ga addition on photoinduced effect, GaGeS glasses with constant atomic ratio S/Ge = 2.6 have been prepared. Using Raman spectroscopy, we have reported the effect of Ga on the structural behavior of these glasses. An increase of the glass transition temperature Tg, the linear refractive index and the density have been observed with increasing gallium content. The photoinduced phenomena have been examined through the influence of time exposure and power density, when exposed to above light bandgap (3.53 eV). The correlation between photoinduced phenomena and Ga content in such glasses are shown hereby. 相似文献
25.
J. R. J. Delben A. A. S. T. Delben K. Miazato S. L. Oliveira Y. Messaddeq 《Journal of Thermal Analysis and Calorimetry》2004,75(2):637-642
New fluorindate glass compositions have been investigated in order to improve optical transmission as well as thermal properties.
Chloride inclusion extends transmission of a fluoride matrix to longer wavelength in infrared region. In the present work
thermal parameters of an IZnBS composition, based on InF3, ZnF2, BaF2 and SrF2, with various amounts of alkaline chlorides were investigated by differential scanning calorimetry. The chloride presence
decreased all characteristic temperatures and increased both thermal stability and glass forming ability up to 10% of MCl
content, where M=Li, Na, K and Rb. The presence of NaCl promoted glass phase separation. For samples containing same concentration of NaCl,
this effect is accentuated for increasing the contents of SrF2.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
26.
R. Bonzanini E.M. Girotto M.L. Baesso Y. Messaddeq A.C. Bento 《Journal of luminescence》2006,117(1):61-67
Spectroscopic properties of blends formed by bisphenol-A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) doped with Europium (III) acetylacetonate [Eu(acac)3], have been studied by photoacoustic spectroscopy (PAS) and photoluminescent (PL) spectroscopy. Emission and excitation spectra, excited state decay times, and quantum efficiency have been evaluated as well. PAS studies evidenced chemical interactions between the Europium complex and the PC/PMMA blend, which presented typical percolation threshold behavior regarding the Eu3+ content. PL spectra evidenced the photoluminescence of the Eu3+ incorporated into the blend. Photoluminescence property enhancement was observed for the composite in comparison with the precursor compound. Optimized emission quantum efficiency was observed for the 60/40 blend doped with 2% and 4% Europium (III) acetylacetonate. 相似文献
27.
José Maurício A. Caiut Lucas A. Rocha Fernando A. Sigoli Younes Messaddeq Jeannette Dexpert-Ghys Sidney J.L. Ribeiro 《Journal of Non》2008,354(42-44):4795-4799
Boehmite–GPTS (GPTS-glycidoxypropyltrimethoxysilane) hybrids (BGS) have been prepared by the sol–gel methodology. Spectroscopic properties and structural features have been evaluated from the initial sols to xerogels as a function of composition. Eu3+-containing BGS samples were also prepared, and the Eu3+ 5D0 state emission quantum efficiency was observed to depend on the boehmite–siloxane interactions. Boehmite–siloxane heterocondensation was inferred from vibrational spectroscopy and 13C, 29Si, and 27Al nuclear magnetic resonance results. Unreacted epoxi groups could be identified in the final material being an important characteristic for the future applications. Good optical quality and mechanical properties lead to the preparation of thin films deposited on glass substrates by dip and spin-coating. Refractive index could be tuned by the relative boehmite and GPTS content. Waveguide properties have also been studied by m-lines spectroscopy and guided modes together with attenuation measurements suggest potential application of the prepared films in integrated optics. 相似文献
28.
Hernane S. Barud Adalberto M. de Araújo Júnior Daniele B. Santos Rosana M.N. de Assuno Carla S. Meireles Daniel A. Cerqueira Guimes Rodrigues Filho Clvis A. Ribeiro Younes Messaddeq Sidney J.L. Ribeiro 《Thermochimica Acta》2008,471(1-2):61-69
Cellulose acetate (CA) is one of the most important cellulose derivatives and its main applications are its use in membranes, films, fibers, plastics and filters. CAs are produced from cellulose sources such as: cotton, sugar cane bagasse, wood and others. One promissory source of cellulose is bacterial cellulose (BC). In this work, CA was produced from the homogeneous acetylation reaction of bacterial cellulose. Degree of substitution (DS) values can be controlled by the acetylation time. The characterization of CA samples showed the formation of a heterogeneous structure for CA samples submitted to a short acetylation time. A more homogeneous structure was produced for samples prepared with a long acetylation time. This fact changes the thermal behavior of the CA samples. Thermal characterization revealed that samples submitted to longer acetylation times display higher crystallinity and thermal stability than samples submitted to a short acetylation time. The observation of these characteristics is important for the production of cellulose acetate from this alternative source. 相似文献
29.
Santagneli SH Schneider J Skripachev I Ribeiro SJ Messaddeq Y 《The journal of physical chemistry. B》2008,112(16):4943-4947
Glasses having the composition (100 - x)As2P2S8-xGa2S3 with x ranging from 0 to 50% were investigated to determine the compositional effect on properties and local structure. The glass transition temperature (Tg) and the stability parameter against crystallization (Tx - Tg) increased with the addition of Ga2S3. The structure of these glasses was probed by Raman scattering, Fourier transform infrared (FT-IR) and 31P nuclear magnetic resonance. On the basis of the observed vibrations and the strength of the 31P-31P homonuclear magnetic dipolar coupling, two scenarios can be proposed for the structural evolution induced by the addition of Ga2S3. For x or= 30% we have depolymerization of the As2P2S8 units and the formation of a network of GaPS4 units with each PS 4/2 unit (Q4) species carrying a single positive formal charge. 相似文献
30.
Santagneli SH de Araujo CC Strojek W Eckert H Poirier G Ribeiro SJ Messaddeq Y 《The journal of physical chemistry. B》2007,111(34):10109-10117
Vitreous samples were prepared in the (100 - x)% NaPO(3)-x% MoO(3) (0 相似文献