Aware of the difficulties in applying sol-gel technology on the preparation of thin films suitable for optical devices, the present paper reports on the preparation of crack-free erbium- and ytterbium-doped silica: hafnia thick films onto silica on silicon. The film was obtained using a dispersion of silica-hafnia nanoparticles into a binder solution, spin-coating, regular thermal process and rapid thermal process. The used methodology has allowed a significant increase of the film thickness. Based on the presented results good optical-quality films with the required thickness for a fiber matching single mode waveguide were obtained using the erbium- and ytterbium-activated sol-gel silica:hafnia system. The prepared film supports two transversal electric modes at 1550 nm and the difference between the transversal electric mode and the transversal magnetic mode is very small, indicating low birefringence. Photoluminescence of the I-4(13/2) -> I-4(15/2) transition of erbium ions shows a broad band centered at 1.53 mu m with full width at a half maximum of 28 nm. Up-conversion emission was carried out under different pump laser powers, and just one transition at red region was observed. (c) 2006 Elsevier B.V. All rights reserved.
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Er3+-doped glass-ceramic SiO2-ZrO2 Optical Planar waveguides were prepared by the sol-gel route using different SiO2:ZrO2 molar ratios (90:10, 85:15, 80:20 and 75:25). Multilayered films were deposited onto Si(100) substrates by the dip-coating technique. Structural characterization was performed using vibrational spectroscopy and X-ray diffraction. Some optical properties, densification and surface morphology of these films were investigated as a function of the SiO2:ZrO2 ratio. annealing temperature and time. Optical properties such as refractive index, number of propagating modes and attenuation coefficient were measured at 632.8, 543.5 and 1550 nm, by the prism coupling technique. Uniform surface morphology with roughness less than 0.5 nm. Low losses, less than 0.9 dB/cm at 612.8 nm in the TE0 mode, were measured for the planar waveguides containing up to 25 mol% zirconium oxide. Luminescence of Er3+ in the near infrared was observed for the active nanocomposite. (C) 2008 Elsevier B.V. All rights reserved.
Thin films of undoped and Sb-doped SnO2 have been prepared by a sol-gel dip-coating technique. For the high doping level (2-3 mol% Sb) n-type degenerate conduction is expected, however, measurements of resistance as a function of temperature show that doped samples exhibit strong electron trapping, with capture levels at 39 and 81 meV. Heating in a vacuum and irradiation with UV monochromatic light (305 nm) improve the electrical characteristics, decreasing the carrier capture at low temperature. This suggests an oxygen related level, which can be eliminated by a photodesorption process. Absorption spectral dependence indicates an indirect bandgap transition with Eg ≅ 3.5 eV. Current-voltage characteristics indicate a thermionic emission mechanism through interfacial states.
The magnetic and structural properties of sol-gel derived organic/inorganic nanocomposites doped with Fe(II), Fe(III), Nd(III) and Eu (III) ions are discussed. These hybrids consist of poly(oxyethylene)-based chains grafted onto siloxane nanodomains by urea cross-linkages. Small angle X-ray scattering data show the presence of spatial correlations of siloxane domains embedded in the polymer matrix. The magnetic properties of rare-earth doped samples are determined by single ion crystal-field-splitted levels (Eu3+ J=0; Nd3+ J=9/2) and the small thermal irreversibility is mainly associated to structural effects. Fe2+ -doped samples behave as simple paramagnet with residual antiferromagnetic interactions. Fe3+-doped hybrids are much more complex, with magnetic hysterisis, exchange anisotropy and thermal irreversibility at low temperatures. Néel temperatures increase up to 14K for the highest (∼5.5%) Fe3+ mass concentration.
A solid state system having the configuration WO 3/Ormolyte/CeO2-TiO2 has been assembled. Syntheses routes for tungsten oxide WO3, and cerium-titanium CeO 2-TiO2 oxide sols, were developed. A novel solid electrolyte - Ormolyte is reported, which were obtained by the sol-gel process, they have a chemical stability due to the covalent bonds between the inorganic and organic phase, and were prepared with different [O]/[L] ratios, being the best for [O]/[L]=15. The variation of transmittance of the electrochromic device using the ormolyte [O]/[L]=15 was 35% (colored state) and 77% (bleached state).
Erbium activated SiO2 -HfO2 planar waveguides, doped with Er3+ concentrations ranging from 0.01 to 4 mol%, were prepared by sol-gel method. The films were deposited on v-SiO2 and silica-on-silicon substrates using dip-coating technique. The waveguides show high densification degree, effective intermingling of the two film components, and uniform surface morphology. The waveguide deposited on silica-on-silicon substrates shows one single propagation mode at 1.5μm, with a confinement coefficient of 0.81 and an attenuation coefficient of 0.8 dB/cm at 632.8nm. Emission in the C-telecommunication band was observed at room temperature for all the samples upon continuouswave excitation at 980 nm or 514.5 nm. The shape of the emission band corresponding to the 4I13/2 → 4I15/2 transition is found to be almost independent both on erbium content and excitation wavelength, with a FWHM between 44 and 48 nm. The 4I13/2 level decay curves presented a single-exponential profile, with a lifetime ranging between 1.1 - 6.6 ms, depending on the erbium concentration. Infrared to visible upconversion luminescence upon continuous-wave excitation at 980 nm was observed for all the samples. Channel waveguide in rib configuration was obtained by etching the active film in order to have a well confined mode at 1.5 μm.
A alumina tem sido muito utilizada como catalisador ou suporte de catalisador em diversas áreas da química. Neste trabalho sintetizou-se aluminas pelo método sol-gel através da hidrólise de alcóxidos de alumínio e subseqüentes condensações em soluções ácidas. Foi utilizado como fonte de alumínio o tri(iso-propóxido) de alumínio e o tri(sec-butóxido) de alumínio, além dos ácidos nítrico e oxálico. Os materiais obtidos foram analisados por espectroscopia na região do infravennelho, difração de raios-X, TGA, BET. As aluminas sintetizadas, além da alumina comercial, foram testadas em alguns sistemas envolvendo epoxidação de cicloexeno e cicloocteno, utilizando-se peróxido de hidrogênio (aquoso e anidro em acetato de etila) como oxidante. Das aluminas sintetizadas, a alumina preparada com tri(sec-butóxido) de alumínio e ácido oxálico apresentou maior atividade catalítica, tanto para cicloexeno quanto para cicloocteno. Para uma análise detalhada desta alumina, foram feitos alguns testes variando-se a temperatura de calcinação (entre 70° e 1000°) e em seguida as amostras foram analisadas por XRD e BET. Alguns fatores como efeito da água no meio reacional e reciclagem dos catalisadores também foram avaliados. Verificou-se que água no sistema favoreceu a formação de epóxidos além de permitir uma reciclagem mais eficiente...
A indústria aeronáutica utiliza ligas de alumínio de alta resistência para o
fabrico dos elementos estruturais dos aviões. As ligas usadas possuem
excelentes propriedades mecânicas mas apresentam simultaneamente uma
grande tendência para a corrosão. Por esta razão essas ligas necessitam de
protecção anticorrosiva eficaz para poderem ser utilizadas com segurança. Até
à data, os sistemas anticorrosivos mais eficazes para ligas de alumínio contêm
crómio hexavalente na sua composição, sejam pré-tratamentos, camadas de
conversão ou pigmentos anticorrosivos. O reconhecimento dos efeitos
carcinogénicos do crómio hexavalente levou ao aparecimento de legislação
banindo o uso desta forma de crómio pela indústria. Esta decisão trouxe a
necessidade de encontrar alternativas ambientalmente inócuas mas
O principal objectivo do presente trabalho é o desenvolvimento de prétratamentos
anticorrosivos activos para a liga de alumínio 2024, baseados em
revestimentos híbridos produzidos pelo método sol-gel. Estes revestimentos
deverão possuir boa aderência ao substrato metálico, boas propriedades
barreira e capacidade anticorrosiva activa. A protecção activa pode ser
alcançada através da incorporação de inibidores anticorrosivos no prétratamento.
O objectivo foi atingido através de uma sucessão de etapas. Primeiro
investigou-se em detalhe a corrosão localizada (por picada) da liga de alumínio
2024. Os resultados obtidos permitiram uma melhor compreensão da
susceptibilidade desta liga a processos de corrosão localizada. Estudaram-se
também vários possíveis inibidores de corrosão usando técnicas
electroquímicas e microestruturais.
Numa segunda etapa desenvolveram-se revestimentos anticorrosivos híbridos
orgânico-inorgânico baseados no método sol-gel. Compostos derivados de
titania e zirconia foram combinados com siloxanos organofuncionais a fim de
obter-se boa aderência entre o revestimento e o substrato metálico assim
como boas propriedades barreira. Testes industriais mostraram que estes
novos revestimentos são compatíveis com os esquemas de pintura
convencionais actualmente em uso. A estabilidade e o prazo de validade das
formulações foram optimizados modificando a temperatura de armazenamento
e a quantidade de água usada durante a síntese. As formulações sol-gel foram dopadas com os inibidores seleccionados
durante a primeira etapa e as propriedades anticorrosivas passivas e activas
dos revestimentos obtidos foram estudadas numa terceira etapa do trabalho.
Os resultados comprovam a influência dos inibidores nas propriedades
anticorrosivas dos revestimentos sol-gel. Em alguns casos a acção activa dos
inibidores combinou-se com a protecção passiva dada pelo revestimento mas
noutros casos terá ocorrido interacção química entre o inibidor e a matriz de
The therapeutic use of biological molecules such as growth factors and monoclonal antibodies is challenging in view of their limited half-life in vivo. This has elicited the interest in delivery materials that can protect these molecules until released over extended periods of time. Although previous studies have shown controlled release of biologically functional BMP-2 and TGF-β from silica sol–gels, more versatile release conditions are desirable. This study focuses on the relationship between room temperature processed silica sol–gel synthesis conditions and the nanopore size and size distribution of the sol–gels. Furthermore, the effect on release of large molecules with a size up to 70 kDa is determined. Dextran, a hydrophilic polysaccharide, was selected as a large model molecule at molecular sizes of 10, 40 and 70 kDa, as it enabled us to determine a size effect uniquely without possible confounding chemical effects arising from the various molecules used. Previously, acid catalysis was performed at a pH value of 1.8 below the isoelectric point of silica. Herein the silica synthesis was pursued using acid catalysis at either pH 1.8 or 3.05 first, followed by catalysis at higher values by adding base. This results in a mesoporous structure with an abundance of pores around 3.5 nm. The data show that all molecular sizes can be released in a controlled manner. The data also reveal a unique in vivo approach to enable release of large biological molecules: the use more labile sol–gel structures by acid catalyzing above the pH value of the isoelectric point of silica; upon immersion in a physiological fluid the pores expand to reach an average size of 3.5 nm...
Exposure of benzyldimethylketal (BDK)-doped sol-gel hybrid glass films to ultra-violet light produces a refractive index increase up to 43 × 10-3 and an increase in thickness due to photolocking of the BDK into the sol-gel hybrid glass matrix. Thus, sing
8 pages, 6 figures, 3 tables.-- PMID: 18164194 [PubMed].-- Available online Nov 17, 2007.; Organically modified molecularly imprinted silicas (MIS) for nafcillin recognition were prepared using a simple sol–gel procedure. Molecular recognition of the template was observed by tuning the chemical and structural properties of the MIS. The relative amounts of organically modified alkoxysilane precursors were found to be key in the textural and morphological characteristics of the MIS as well as for developing an imprinting effect in the materials. The recognition properties of the imprinted materials were found to be strongly influenced by the hydrolytic stability of the alkoxysilanes and their inductive effects during sol–gel hydrolysis/condensation stages. The concept was to combine properties of organic groups with those of glass-like materials in order to develop synergetic properties through variations in the composition. Results from batch rebinding experiments as well as from the thorough study of the N2 adsorption properties and the textural and structural characteristics of the MIS revealed that an imprint effect could be attributed to the presence of the template during the synthesis of MIS.; Authors gratefully acknowledge financial support to the Spanish Science and Education Ministry (Projects #BQU2003-00853 and CTQ2006-14644-C02-01). L. Guardia thanks FICYT (Foundation for Scientific and Technological Research...
Sol-gel synthesis of organic-inorganic hybrid materials for planar waveguides and devices has received growing interest due to its low-cost processing and good suitability for doping. Titania is an important optical dopant, but homogeneous incorporation of titania in silica is difficult to be achieved by the conventional sol-gel process (aqueous system) because of the significant difference between the hydrolysis rates of the precursors. In this paper, we report an anhydrous sol-gel process for synthesising titania-doped siloxane polymers. The process consists of a hydrolysis of 3- methacryloxypropyltrimethoxysilane (MPS) with boric acid under anhydrous conditions, and a condensation with dimethyldimethoxysilane (DMDMS), diphenyldimethoxysilane (DPhDMS) and titanium ethoxide (TET). Optical characterisations for the produced titania-doped polymer were performed, and results showed that TET doping is useful for reducing the OH concentration of the synthesised polymer and is also effective for improving the optical quality of spin coatings. DMDMS and DPhDMS are favourable in reducing the birefringence and in increasing the thermostability of the material, and the methacryl groups of MPS are UV-polymerizable, which is useful for low cost fabrication of waveguides by photolithographic process. The results of ellipsometry scanning measurements show that titania is homogeneously incorporated in the hybrid matrix...
Incorporation of metal alkoxides (Ti, Zr, etc.) for tuning the optical properties of silica glasses by the sol-gel process is of significant interest for optical applications. In this paper, we report an anhydrous sol-gel process for preparation of photosensitive titania-doped hybrid glassy polymer with good homogeneity and high doping concentration (TiO2 up to 40mol%). The process consists of two steps: in the first step methacryloxypropyltrimethoxysilane (MPS) is hydrolyzed by boric acid through ligand exchange reaction (OH ↔ OR) under anhydrous conditions; and in the second step dimethyldimethoxysilane (DMDMS), diphenyldimethoxysilane (DPhDMS) and titanium ethoxide (TET) were added to condense with the silanols formed in the first step. The optical properties of the synthesized hybrid polymer were studied, and results showed that the hybrid material has low OH absorption, low optical losses (0.45dB/cm at 1550nm and 0.16dB/cm at 1310nm respectively), and good thermo-optical linearity with tuneable refractive index. The effect of TiO2 doping in reducing the OH concentration of the hybrid material was observed, and the mechanism for this effect is discussed.
Methacrylate-modified hybrid polymer with varied TiO2 concentrations was prepared by an anhydrous sol-gel process, and the effects of TiO2 on the photosensitivity of the hybrid polymer in the forms of wet films (before the polymerisation of the unsaturated CC bonds of methacrylate groups) and hard films (after the polymerisation of the unsaturated CC bonds with a pre-UV cross-linking and thermo-curing process) were studied. TiO 2 doping was found useful for enhancing the photosensitive response to UV light irradiation in both wet and hard films. In wet films, TiO 2 has a similar effect as a photo-initiator on accelerating the polymerisation of the unsaturated CC bonds of methacrylate groups, therefore TiO2 doping favours UV-patterning with photolithographic process for planar optical waveguides fabrication. In the fully polymerised TiO 2-doped hard films, photosensitivity with a refractive index increase as large as 0.01 was firstly observed. The structural changes of the hybrid polymer upon UV irradiation were investigated by FT-IR and energy dispersive X-ray spectroscopic (EDXS) techniques, and the mechanisms for the photosensitivity in hard films were proposed.
We investigated linear optical and second-order nonlinear optical (NLO) properties of films of poly(bisphenol A carbonate) resin, and a newly synthesised titania/silica/hybrid sol-gel polymer resin doped with Disperse Red 1 (DR1) molecular chromophore. DC electric field induced second harmonic generation (SHG) technique has been used to monitor in situ the polar alignment and relaxation of orientation of the guest molecules in the corona-poled films. The temporal behaviour of the second harmonic signal was remarkably different in these two polymers both during poling and when the poling field was turned off. A fast decay of the second harmonic intensity was observed at room temperature in 3 wt% DR1-doped sol-gel film, and a long relaxation time constant was found in 13 wt% DR1-doped polycarbonate film. Resonantly enhanced d eff coefficient of about 9 pm/V was found in the sol-gel film, and 25 pm/V in the polycarbonate film at the fundamental wavelength 1053 nm. The d 33 values were about 20 pm/V, and 60 pm/V in these films, respectively. The SHG results were used to estimate the average rotation mobility parameter of DR1 molecules in the host polymers.