Photoluminescence properties of an oligo-phenylkene vinylene derivative doped in polymer/silica hybrid sol–gel matrix

An oligo-phenykene vinylene derivative 4,4′-(1,4-phenylene dithenylene)-bis-(N-methyl pyridinium iodide) (OPVD) was introduced into poly(hydroxyethyl methacrylate) (PHEMA)-impregnated silica composite film by the sol–gel process. The X-ray diffraction and UV–VIS reveal that this method can restrict the crystallization of OPVD and OPVD molecules tend to form J-aggregates in the composite film. The results of photoluminescence of OPVD in the composite film indicate that as compared with OPVD itself, the emission peak of OPVD in the composite film undergoes a blue shift about 80 nm, fluorescence intensity enhances and the photostability is much better, which make such composite film of more practical significance.     

Dye-doped sol–gel materials for two-photon absorption induced fluorescence

Two-photon absorption (TPA) and subsequent fluorescence properties of laser dyes are retained when doped into solid state sol–gel materials. These properties were demonstrated to be applicable in true 3D displays.     

Photorefractive gratings in DR1-doped hybrid sol–gel films

Photorefractive gratings have been obtained with 632.8 nm writing beams in organic–inorganic SiO₂-based films. The hybrid glass is prepared by a sol–gel technique, starting from organic Si precursors, and contains Disperse Red 1 (DR1), carbazole units and 2,4,7-trinitro-9-fluorenone (TNF). The photorefractive gain, which has been found unexpectedly even without poling field, has been determined through an asymmetric energy exchange by two-beam coupling measurements. The effects of the polarization of the writing beams and of a circularly polarized photoisomerizing radiation during the erasure of the grating have been interpreted in terms of an orientational contribution to the grating formation.     

Holographic gratings in DR1-doped sol–gel silica and ORMOSILs thin films

Holographic diffraction gratings have been obtained in Disperse Red 1 (DR1)-doped silica and ORganically MOdified SILanes thin films (ORMOSILs), produced by tetraethylorthosilicate (TEOS) and 3-(triethoxysilyl)propyl isocyanate (ICPTEOS) as precursors for the sol–gel process. For the DR1 + TEOS film, the grating is associated to an irreversible bleaching of the dye and may be detected by a Raman micro-spectroscopy mapping. For films based on ICPTEOS, a transient phase diffraction grating is created by the photoinduced birefringence. Two characteristic relaxation times of the birefringence grating have been measured.     

Development of photo-patternable organo-mineral hybrid films from the sol–gel condensation of alkoxysilanes

We describe the synthesis and refractive index characterisation of four organo-siloxanes materials, applicable to the fabrication of photo-patternable channel waveguides. By combining aliphatic, aromatic and vinylic alkoxysilane precursors, organically modified silicates materials have been synthesised using the sol–gel process. Control of the refractive index was achieved through the variation of aliphatic and aromatic alkoxide content within the materials. It is clearly demonstrated that the presence of aromatic groups significantly increases the refractive index to 1.562. Conversely, the addition of vinylic groups decreases the value to 1.490. These findings are attributed to the atypical polarisability exhibited by aromatic and aliphatic precursors, which strongly affect the overall molar refraction.     

Reliability analysis of transparent conductive tracks embossed in ZnO and Al-ZnO sol–gel materials

In this paper, we present a low-cost rapid replication approach to fabricate ZnO and Al-doped ZnO Transparent Conductive Oxide electrode structures using both hard UV curable polyurethane acrylate and soft thermal curable polydimethylsiloxane moulds. The thin films of the ZnO and Al-ZnO sol–gel precursor solution prepared from zinc acetate monoethanolamine and isopropanol were cast into a polydimethylsiloxane or polyurethane acrylate mould containing the electrode design. For soft mould embossing, the sol–gel coated substrate and polydimethylsiloxane mould were dried under vacuum at 70 °C for 3h. While for hard mould embossing, the system was heated at 150 °C for 30 min with 100 N applying force and then demoulded at 80 °C. The formed electrode patterns can be further densified or annealed giving a stable film that retains the embossed shape. The difference of surface profile obtained by soft and hard moulding is detailed and the hard mould is shown to be more suitable for low aspect ratio conductors. And the reliability study on embossed ZnO and Al-ZnO conductive tracks prepared with hard moulds shows that the embossed structure still retains good quality.     

Indium-doped ZnO thin films deposited by the sol–gel technique

Conducting and transparent indium-doped ZnO thin films were deposited on sodocalcic glass substrates by the sol–gel technique. Zinc acetate and indium chloride were used as precursor materials. The electrical resistivity, structure, morphology and optical transmittance of the films were analyzed as a function of the film thickness and the post-deposition annealing treatments in vacuum, oxygen or argon. The obtained films exhibited a (002) preferential growth in all the cases. Surface morphology studies showed that an increase in the films' thickness causes an increase in the grain size. Films with 0.18 μm thickness, prepared under optimal deposition conditions followed by an annealing treatment in vacuum showed electrical resistivity of 1.3 × 10^− 2 Ωcm and optical transmittance higher than 85%. These results make ZnO:In thin films an attractive material for transparent electrodes in thin film solar cells.     

Low temperature synthesis and structural characterization of nanocrystalline YAG prepared by a modified sol–gel method

Nanocrystalline yttrium aluminum garnet, Y₃Al₅O₁₂ or YAG, was synthesized by means of a modified glycolate or sol–gel method that consists of a mixture of salts in an aqueous media. The monophasic nanocrystalline YAG was obtained at 800 °C, which is much lower than others prepared by wet-chemical methods and little higher than alkoxide sol–gel process. The structural evolution features of the nanocrystalline powder were studied by XRD, FT-IR, ²⁷Al MAS NMR, AFM, SEM and TEM. The crystallite sizes range from 26 to 95 nm for 800 and 1150 °C, respectively, suggesting the possibility to be controlled by the annealing temperature. The experimental results indicate the existence of oxygen defects and Al atoms with distorted or incomplete coordination sphere. The feasibility of the modified glycolate method for the preparation of nanocrystalline YAG is discussed.     

Preparation and optical properties of sol–gel derived photo-patternable organic–inorganic hybrid films for optical waveguide applications

Photo-patternable TiO₂/organically modified silane hybrid films were prepared by combining a low-temperature sol–gel technique with a spinning–coating process. A ridge waveguide pattern was fabricated by ultraviolet light irradiation through a mask placed contact with the hybrid film in direct. Optical properties and photochemical activity of the hybrid film, including refractive index, thickness, propagation mode, and propagation loss, were studied and monitored by a prism coupling technique and Fourier transform infrared spectroscopy. The change of transmittance with exposure time was also observed by ultraviolet–visible spectroscopy. These results indicate that the hybrid film is potential application for fabrication of photonic devices by ultraviolet light irradiation. The structure of ridge waveguide pattern was characterized and studied by scanning electron microscope and surface profiler. The fabrication process of the as-prepared photosensitive hybrid film as compared with traditional binary mask has a great amount of advantages of cost-effective, simple, and smooth surface over non-photosensitive material methods.     

UV-induced permanent gratings in sol–gel germanosilicate thin films

Germanosilicate thin films have been elaborated by the sol–gel process and the dip-coating technique. Pulsed or continuous wave UV laser (244 nm) was used to write permanent gratings in these films. In the case of exposure to cw laser, the grating diffraction efficiencies were measured using a focused beam from a He–Ne laser at 633 nm and photo-induced changes in refractive index as high as 4×10⁻³ have been obtained. The thermal behaviour of these gratings has been investigated showing a good stability up to 400°C. Exposure to pulsed fringe pattern led to a glass photo-expansion modulated by a strong corrugation which can be due mainly to photo-ablation at the places of the bright fringes. The waveguide surface at the grating places was investigated through Atomic Force Microscopy (AFM) and microscopic profilometry techniques. Preliminary results on the kinetics of the grating growths are also reported.     

Formation of CdS nanoparticles by gas-diffusion method in sol–gel derived ureasilicate matrix

CdS nanoparticles (NPs) were prepared by exposing a hybrid ureasilicate gel containing cadmium (II) ions to H₂S gas at room temperature. Additional component (tetraethoxysilane) was introduced during the synthesis in order to improve the mechanical properties of the host matrix. The obtained material was subsequently subjected to an annealing treatment under an argon atmosphere at temperatures that varied from 43 to 102 °C. The size of the embedded NPs increased with thermal annealing. The optical absorption spectroscopy, photoluminescence (PL) and transmission electron microscopy (TEM) measurements confirmed the formation of CdS nanoparticles (NPs) exhibiting quantum confinement effect.     

Preparation and optical properties of sol–gel derived organic–inorganic hybrid waveguide films doped with disperse red 1 azoaromatic chromophores

We report here on TiO₂/organically modified silane (ormosil) organic–inorganic hybrid waveguide films doped with disperse red 1 (DR1) azoaromatic chromophores and derived by a low-temperature sol–gel process for photonic applications. Acid-catalyzed solutions of γ-glycidoxypropyltrimethoxysilane and methyltrimethoxysilane mixed with tetrabutyl titanate are used as matrix precursor for the hybrid films. Third-order nonlinear and photo-responsive properties of the hybrid films are studied by using a z-scan technique and a UV–vis absorption spectroscopy. Results indicate that the hybrid films have a large third-order nonlinear susceptibility and an obvious trans-to-cis photoisomerization under UV light irradiation. The planar waveguide and structural properties of the hybrid films are also characterized by a prism coupling technique, thermal gravimetric analysis, and Fourier-transform infrared spectroscopy. These results indicate that the as-prepared hybrid films are promising candidates for integrated optics and photonic applications, which allow directly integrating on the same chip waveguide devices with the functionalized devices.     

Synthesis and microstructure of boron-doped alumina membranes prepared by the sol–gel method

Pure and boron-doped γ-Al₂O₃ membranes have been synthesized by the sol–gel method. The thermal stability of the unsupported alumina membrane was studied by determining the pore structure (including average pore size, pore volume and BET surface area). The average pore size of the pure alumina membrane increased sharply after sintering at temperatures higher than 1000°C. Addition of 16% boron can considerably stabilize the pore structure of the unsupported alumina membrane. The pore diameter for the B-doped membrane was stabilized within 13 nm after sintering at 1200°C for 5 h. The substantial increase in the pore size for the pure alumina membrane at the sintering temperature of 1000–1200°C was accompanied by the phase transformation from γ-Al₂O₃ to -Al₂O₃. The addition of boron can raise the temperature of this phase transformation significantly and, thus, improves the thermal stability of the membranes.     

Preparation of uniform titania nanocoating on ZnS-based phosphors by a sol–gel process

A sol–gel process has been developed to coat micron-sized ZnS:Cu,Au,Al phosphors with a smooth and uniform layer of amorphous titania having nanosize thickness. The titania nanocoating is based on the hydrolysis and condensation of titanium tetrabutoxide Ti(OBu)₄. Acetylacetone was used to decrease the reactivity of Ti(OBu)₄. The experimental variables such as water concentration, the amount of ZnS particles, and reaction time were investigated. The thickness of the titania nanocoating was homogeneous and can easily be controlled from 20 to 54 nm by adjusting the experimental variables. The as-prepared titania nanocoating was amorphous phase and could be crystallized to anatase phase upon heating at 500 °C in Ar atmosphere.     

Structural and optical properties of vanadium pentoxide sol–gel films

The V₂O₅ films were obtained using sol–gel procedure. The composition and mesostructure of the layers were investigated with the UV and Raman spectroscopy, as well as with electron microscopy. We showed that the changes in the properties of thin layers accompanying the variation of film thickness are connected with the changes in the microstructure of the film rather than with changes in its composition. The thin V₂O₅ layers obtained in the present study are composed of disordered clusters; their mean size is 4–13 nm.     

Inhomogeneous distribution of organic molecules adsorbed in sol–gel glasses

The effects of the porous matrix upon the radiative characteristics of quinine sulphate doped sol–gel glasses are investigated. The broadenings of the absorption and fluorescence spectra are explained by the attachment of the molecules on distorted sites or in a non-planar fashion, creating an inhomogeneous distribution of adsorbed molecules. For this reason, each emitting center relaxes with its own characteristics. This inhomogeneous distribution is also supported by the non-exponential and the wavelength dependence of the fluorescence decay.     

Fabrication of alumina ceramics from powders made by sol–gel type hydrolysis in microemulsions

The engineering aspects of the preparation of nanostructured alumina ceramic precursors by alcoholate hydrolysis using microemulsions as reaction media are investigated here. The precipitate was subjected to several treatment steps. Although the properties of the primary precipitated powders are independent of the chemical or reaction engineering parameters of the precipitation procedure, the structure of treated powders and sintered, dense ceramics strongly depends on thermal and mechanical handling like crystallization or grinding of the alumina ceramic precursor. Strong differences are manifested in relative densities and sintering kinetics and can be observed by SEM analysis.     

Ferroelectric properties of BiFeO3 films grown by sol–gel process

Several methods have been used to prepare ferroelectromagnetic BiFeO₃ films. In this paper, we adopted a sol–gel process to fabricate BiFeO₃ films on indium tin oxide (ITO)/glass substrates. X-ray diffraction pattern indicated that the samples are randomly oriented. Cross section scanning microscopy showed that the thicknesses of both films were about 1.2 μm and no apparent diffusion between the BiFeO₃ films and ITO/glass substrates. Remnant polarization of 2.0 and 1.75 μC/cm² were identified by the measuring of electric hysteresis loops for the films annealed at 500 and 600 °C respectively at an applied field of 108 kV/cm. Dielectric property and loss factor were investigated as a function of frequency. In addition, magnetism was detected at 77 K.     

Behavior of thymol blue analytical pH-indicator entrapped into sol–gel matrix

The preparation of transparent monolithic silica doping with thymol blue has been carried out by the acid catalyzed sol–gel reaction of tetraethylorthosilicate in the presence of thymol blue. The immobilized thymol blue pH-indicator shows similar behavior as its solution counterpart. The UV/VIS spectra indicate that the thymol blue retains its structure during the sol–gel reactions in terms of response to pH. Thymol blue can be regarded as uniformly distributed in the sol–gel matrix, and the use of SDS surfactant has positive effects on the immobilized thymol blue monolithic disk by homogenizing the polymerizing system. This research shows that thymol blue indicator can be used as solid pH sensor.