Sol-Gel Processing and Luminescent Properties of Rare-Earth Oxyfluoride Materials

Luminescent rare-earth oxyfluoride materials were prepared by a sol-gel method using trifluoroacetic acid as a fluorine source. Crystalline (La, Eu)OF powders and thin films were obtained by heating gels at typically 600–800°C. Transparent SiO₂-LaOF glass-ceramic thin films were also prepared by mixing the trifluoroacetate sols and silica sols, spin-coating on silica glass substrates and heating at temperatures 600–900°C. Eu³⁺ ions doped in the oxyfluoride materials exhibited a strong red ⁵D₀ ⁷F₂ emission (611 nm) by a charge-transfer (O^2–-Eu³⁺) excitation with ultra-violet radiation (265 nm). It was strongly suggested that the Eu³⁺ activators were preferentially incorporated into the crystalline LaOF phase in the SiO₂-LaOF glass-ceramics.     

Influence of Sol-Gel Synthesis Parameters on the Microstructure of Particulate Silica Xerogels

The influence of key sol-gel synthesis parameters on the pore structure of microporous silica xerogels was investigated. The silica xerogels were prepared using an acid-catalyzed aqueous sol-gel process, with tetraethoxysilane (TEOS) as the silicon-containing precursor. At high H2O : TEOS ratios, sols synthesized at pH 2–3 yielded minimum values of mean micropore diameter and micropore volume. Analysis of the resulting Type I nitrogen adsorption isotherms and the equilibrium adsorption of N(C4F9)3 indicated micropore diameters for these xerogels of less than approximately 10 Å.Xerogel micropore volumes corresponding to sols prepared at pH 3 and an H2O : TEOS ratio of r = 83 were consistent with nearly close packing of silica spheres in the xerogel. Xerogel microstructure was only weakly dependent upon H2O : TEOS ratio during sol synthesis for r > 10. Xerogel micropore volume increased rapidly with sol aging time during an initial induction period of particle formation. However, the xerogel microstructure changed only slowly with time after this initial period, suggesting potential processing advantages for the particulate sol-gel route to porous silica materials.Surface adsorption properties of the silica xerogels were investigated at ambient temperature using N2, SF6, and CO2. CO2 adsorbed most strongly, SF6 also showed measurable adsorption, and N2 adsorption was nearly zero. These results were consistent with the surface transport of CO2, and to a lesser extent SF6, observed in gas permeation studies performed through thin membrane films cast from similarly prepared silica sols.     

Preparation and properties of SiO2-TiO2 thin films from silicic acid and titanium tetrachloride

The preparation of SiO₂-TiO₂ thin films by the sol-gel method using silicic acid and titanium tetrachloride as starting materials was studied. The homogeneous sols were obtained by the condensation reaction of silicic acid with titanium tetrachloride in methanol-tetrahydrofuran. The dipcoating of slide glasses and silicon wafers followed by heat treatment gave oxide thin films of 88–93% transmittance, 3000–4500 Å thickness, and 1.45–1.80 refractive index, depending on heat-treatment temperature and TiO₂ content. FT-IR measurement showed that the Si-O-Ti bond is formed even in the sol and films. The variations of film thickness and refractive index on transformation from the gels into the oxides were found to be quite low.     

Effect of hybrid phosphorus-doped silica thin films produced by sol-gel method on the thermal behavior of cotton fabrics

The aim of this work was to prepare hybrid organic-inorganic silica thin films to provide cotton fabrics with flame retardant properties and to investigate the films’ influence on the thermal and burning behavior of the treated samples. The fabrics were modified with three different sols in order to study the effect of pure silica sol-gel precursor, γ-aminopropyltriethoxysilane (APTES), and that of the hybrid sols consisting of the APTES and the phosphorus compound diethylphosphite. Furthermore, in order to improve the cross-linking degree and the phosphorus-nitrogen synergistic effect on flame retardancy of the P-doped silica thin film the melamine-based resin was added in the third sol. To evaluate the chemical structure of the coating material, pure xerogels of the treatment solutions were applied to glass slides and tested by ATR FT-IR spectroscopy. The cotton fabrics were impregnated with the sols by a padding-squeezing process and then dried. Thermal behavior of the treated cotton samples was investigated by thermogravimetric/differential scanning calorimetry analysis (TGA-DTG/DSC) and compared to the untreated one. The flame retardancy was tested according to the ASTM D 1230 standard method. The results showed a substantial enhancement of char-forming properties and flame retardancy for the fabrics modified with the thin films.     

Preparation and Spectroscopy of Aluminosilicate Films Deposited on Graphite Surfaces via an Anhydrous Sol-Gel Route

Anhydrous aluminosilicate sols with Al : Si molar ratio ranging from 1 : 10 to 1 : 5 were prepared by a two-step anhydrous sol-gel process, in which tetraethoxysilane (TEOS) is pre-hydrolysed by formic acid, followed by addition of aluminium ethoxide. Unlike the case of aqueous sol-gel routes, where the Si–O–Al network homogeneity is greatly restricted by precipitation of Al(OH)₃, this anhydrous route yields clear, homogeneous sols. The sol formation and densification processes were investigated by infrared spectroscopy and X-ray powder diffraction (XRD) techniques, and the existence of Al–O–Si linkages was confirmed. To demonstrate an application of the anhydrous sol-gel process, aluminosilicate films were deposited onto graphite surfaces by dip coating and densified at 800°C under nitrogen, and their protective effect was evaluated.     

Investigations of MgF2 Optical Thin Films Prepared from Autoclaved Sol

MgF₂ thin films with ultra low refractive indices were obtained by sol–gel method using sols prepared from magnesium acetate and hydrofluoric acid. The sols were autoclaved in a Teflon cell at 100–180°C for 24 h and then coated on SiO₂ glass or CaF₂ crystal substrates by spin coating. Subsequently, the samples were heat treated at 150°C for 1 h. The optical properties of the thin films, such as refractive index and transmittance, were investigated in the UV region, especially in the deep UV (DUV, below 250 nm) region. Though the coatings consist of single layers, both samples exhibited high transmittance. In addition, they exhibit such antireflection effect over a very wide range of wavelength. Such a good antireflection effect was produced only by low refractive indices. It has also been confirmed that, even in the range of vacuum UV (VUV, 200–150 nm), CaF₂ samples with antireflection coatings could keep such a good antireflection effect.     

Large Size Recyclable Colored Glass Plates Prepared from Organic Colorant Dispersed Silica Sols by the Dipping Method

We have prepared the recyclable colored glass plates of blue, green, or red by coating organic colorant dispersed silica sols. Phthalocyanine-type or diketopyrrolopyrrole-type compounds were used as colorants for colored coating and the sol coated glass plates were heat-treated at 300–400°C. The coating was done by using a dipping-withdrawing equipment designed originally for coating large sized glass plates with 2 m in length and 1 m in width. The colored coating films were uniform and transparent with low haze values less than 1.0% and with thickness of 120–540 nm. The visible light transmittance of the colored glass plates was controlled in the relatively wide range of 50–90% by changing the film thickness or the colorant concentration in the coating sols. The practical durabilities of the blue colored glass plate against abrasion, scratch, chemicals and UV-light were acceptable to the specification required for interior glass products.     

Effect of non-ionic surface active agents on TEOS-derived sols,gels and materials

The sol-gel process, starting from tetraethylorthosilicate precursor, is a suitable technique for the preparation of silica thin films. The use of specific organic additives, like non ionic surface-active agents, drastically modifies the gelation process and allows the preparation of microporous materials with a high microporous volume. The effects of additives on the sol, gel and material characteristics have been investigated by several methods such as ²⁹Si NMR, QELS, SAXS (for sols and gels), and N₂ adsorption, FESEM (for fired materials). It appears that the interactions of surface active agents with TEOS derived species limit condensation reactions and particle growing. A brittle gel structure is generated which leads to highly porous microporous silica after the elimination of organic chains by thermal treatment at 450°C. The material porous texture (specific surface area, pore size distribution and porous volume) can be varied especially by varying the surface active agent chain length and quantity. This kind of sol-gel system is suitable to prepare microporous silica membranes candidate for gas separation or catalytic reactor applications.     

Naphthenic Acid-Derived Nanocrystalline ZnO Films on Silica Substrate

Sol–gel-derived nanocrystalline ZnO thin films on silica glass substrates were prepared by using a zinc naphthenate precursor. As-deposited films were heat treated at 500, 600 and 700°C for 30 min in air. The ZnO films were analyzed by X-ray diffraction, field emission—scanning electron microscope, scanning probe microscope, and ultra violet—visible—near infrared spectrophotometer. With an increase in heat treatment temperature, the peak intensity of (002) plane increases. No evidently aggregated particles are present. All the films exhibit a high transmittance (>80%) in visible region and show a sharp fundamental absorption edge at about 0.38–0.40 m. The estimated energy band gap for all the films are within the range reported for films and single crystal.     

Rheological and Coating Properties of Modified Silica Sols

The rheological behavior of modified silica sols has been investigated by gel formation kinetics and dynamic flowing within the pH range 3–7 and the temperature range 20–50°C. The sols show pseudo-plastic behavior at low shear-rates, with Newtonian behavior below 100 s–1. Oscillation measurements reveal that gelation starts with a significant decrease of phase difference <10°, because of a strong increase in elastic behavior. After solidification the values of phase difference increase, indicating a partial destruction of the gel structure due to stress. The relationship between the viscosity of the modified silica sols and their coating parameters was compared for both dip coating and continuous coating with a slide coating unit.     

Study of the Lead Environment in Liquid and As-Dried Precursors of PZ, PT and PZT Thin Films

The environment of lead and zirconium atoms in liquid and as-dried precursors for PbZrO3 (PZ), PbTiO3 (PT) and Pb1.1Zr0.53Ti0.47O3 (PZT) thin film deposition were analyzed by EXAFS. The sols were prepared by 2-methoxyethanol route with lead acetate and lead oxide as lead sources. Pb—O—M (M = Zr and/or Ti, depending on the sol composition) linkages were determined in all sols. The choice of lead source weakly influences the lead environment, and strongly influences that of zirconium in both PZ and PZT sols. By drying lead oxide based sols the Pb–M correlation is moderately reduced in PZ, PT and is strongly reduced in PZT.     

SiO2 溶胶及其静电自组装薄膜的制备

Silica sols were prepared by hydrolysis of Si（OC2H5）4（TEOS）using HCl,NH3·H2O,HCl/NH3·H2O as catalyzers,and the different granularities of SiO2 sols which catalyzed by HCl first and then NH3·H2O have the same terminal pH value were prepared. The silica colloidal particles were investigated with Transmission Electron Microscope（TEM）. The results showed sol catalyzed by HCl possesses very little particle,catalyzed by NH3·H2O has particle configuration,catalyzed by HCl/NH3·H2O possesses consecutive configuration. Poly（diallyldimethylammonium chloride）（PDDA）and SiO2 nanoparticulate complex thin films were prepared by electrostatic self-assembly multiplayer（ESAM）method. After assembling films,thin films surface conformation was observed with Electron Microscope and their transmittance was tested with 721 Spectrophotometer. The results showed that the silica sol catalyzed with HCl is not good for the fabrication of ESAM films and the silica sol catalyzed with HCl first and then NH3·H2O or by NH3·H2O only are very suitable for ESAM film fabrication. TEM data indicate that the microstructure of PDDA/ SiO2 prepared from silica sol catalyzed with HCl first and then NH3·H2O is consecutive and that the microstructure of PDDA/ SiO2 prepared from silica sol catalyzed by NH3·H2O only is particulate-parking like. The dependence of the transmittance of assembled films on the bilayer number of the films and the anti-scratching properties of the films were investigated. The results show that PDDA/ SiO2 films prepared from silica sol catalyzed by NH3·H2O only possess higher transmittance but lower anti-scratching properties. The effect of granularity of sols on optical performances of the thin films was studied,results showed the less the granularity of sol,the better the optical performances. For the sake of improving the light transmittance of films,we can reduce the granularity of sol,but it may play down its mechanical damage resist intensity.     

Photocatalytic Activity and Characterization of the Sol-Gel Derived Pb-Doped TiO2 Thin Films

Photocatalytically active Pb-doped TiO₂ thin films were prepared on a soda-lime glass substrate by sol-gel dip-coating technique using TiO₂ sols containing lead(II) nitrate. The thin films were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), UV-VIS spectroscopy and X-ray diffraction (XRD). A shift of the UV-VIS absorption towards longer wavelengths was observed, which indicated a decrease in the band-gap of TiO₂ upon Pb doping. XRD results showed both pure and Pb-doped TiO₂ thin films were polycrystalline, anatase type, and oriented predominantly to the (101) plane. A slight shift in the d-spacing for the Pb-doped film indicated the incorporation of Pb into the TiO₂ lattice to form Pb _x Ti_1–x O₂ solid solution. AFM results showed Pb-doped TiO₂ thin films were composed of larger TiO₂ particles and had rougher surface, compared with un-doped TiO₂ thin films. XPS results showed that except for the enrichment of Pb near the surface, Pb exists in the forms of Pb _x Ti_1–x O₂ and PbO. Dimethyl-2,2-dichlorovinyl phosphate (DDVP) was efficiently degraded in the presence of the Pb-doped TiO₂ thin films by exposing the insecticide solution to sunlight. The mechanism of photocatalytic activity enhancement of the Pb-doped TiO₂ thin films was discussed.     

Nitro-Porphyrin Entrapped in a Silica Matrix by Sol-Gel Methodology

This work describes the preparation of the iron (III) porphyrin, FeTDCNO₂, entrapped in a silica matrix in the form of powder (FePD) or thin film using the sol-gel process. The films were obtained from sols using the dip-coating technique. The variables involved in the FePD preparation were analysed by a fractional factorial design with resolution 5, designated by 2 _V ^{5 – 1}. The variables which present a positive effect and maximise the loading of the studied ironporphyrin on the FePD material are solvent, water volume and reaction time. The utilization of pyridine or imidazole as template does not affect the preparation of the FePD material. The UV-visible absorption spectra of all prepared materials present the characteristic Soret band of ironporphyrins at 419–420 nm.The materials were analysed by thermogravimetric analysis, isotherm of nitrogen adsorption, ²⁹Si NMR and scanning electron micrograph. The catalytic performance of FePD-imidazole on the epoxidation of z-cyclooctene with iodosylbenzene is similar to that of FeTDCNO₂ in homogeneous solution (60 and 52%).     

Silica-Zirconia Sol–Gel Coatings Obtained by Different Synthesis Routes

Homogeneous xSiO₂-(1−x)ZrO₂ coatings have been prepared onto glass-slides, monocrystalline Si and stainless steel (AISI 304) using sols prepared via acid and basic catalysis. Zirconium tetrabutoxide (TBOZr), zirconium n-propoxide (TPZ), tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) were used as precursors of zirconia and silica, respectively. The different parameters involved in the synthesis procedure, as molar ratios H₂O/alkoxides, NaOH/alkoxides, and sintering temperature have been analysed, correlating the stability and rheological properties of the sols. The evolution and structure of the sols and coatings have been studied by FTIR. Coatings have been prepared by dipping from acid and basic sols. Electrophoretic Deposition (EPD) technique has also been used to prepare coatings onto stainless steel from basic particulate sols in order to increase the critical thickness. A maximum thickness of 0.5 μ m was reached by both dipping and EPD process for 75SiO₂: 25 ZrO₂ composition. The critical thickness decreases with ZrO₂ amount depending strongly of the drying conditions. Si–O–Zr bonds have been identified by FTIR, indicating the existence of mixed network Si–O–Zr in the coatings obtained by the different routes. Crystallisation of ZrO₂(t) was only observed at high sintering temperature (900^∘C) by FTIR and confirmed by DRX.     

Properties of proton-conducting materials formed by the sol-gel method

Proton-conducting materials produced by the sol-gel method were studied by spectroscopic methods. Films and xerogels were formed from silica sols modified with orthophosphoric and sulfuric acids, as well as with a mixture of these acids, with subsequent drying at room temperature and 150°C. The ionic conductivity of the xerogels and IR transmission of the films were examined.     

Preparation and Characterization of MgO Thin Films by a Novel Sol-Gel Method

MgO thin films have been prepared on Si substrates by a novel and simple sol-gel method using magnesium nitrate and collodion as starting material. Solutions consisting of magnesium nitrate in a mixture of collodion and ethanol were spin-coated onto silicon substrates. It was found that collodion was a necessary component to form stable sols and the crystallization and structures were clearly dependent on the amount of the collodion and the annealing temperature. The MgO thin films with good crystallization were obtained after annealing at 800°C. Meanwhile, the microstructure of the MgO films was examined by transmission electron microscopy and atomic force microscopy.     

Silver containing sol–gel derived silica thin films: effect of aluminum incorporation on optical,microstructural and bactericidal properties

Silver containing silica (Ag–SiO₂) thin films with and without aluminum (Al) were prepared on soda-lime-silica glass by spin coating of aqueous sols. The coating sol was formed through mixing tetraethyl orthosilicate [Si(OC₂H₅)₄]/ethanol solution with aqueous silver nitrate (AgNO₃) and aluminum nitrate nonahydrate [(AlNO₃)₃·9H₂O] solutions. The deposited films were calcined in air at 100, 300 and 500 °C for 2 h and characterized using x-ray diffraction, UV-visible and x-ray photoelectron spectroscopy. The effect of Al incorporation and calcination treatment on microstructure and durability of the films, and chemical/physical state of silver in the silica thin film have been reported. The bactericidal activity of the films was also determined against Staphylococcus aureus via disk diffusion assay studies before and after chemical durability tests. The investigations revealed that the optical, bactericidal properties and chemical durability of Ag–SiO₂ films can be improved by Al addition. The Al-modified Ag–SiO₂ thin films do not exhibit any coloring after calcination in the range of 100–500 °C, illustrating that silver is incorporated within the silica gel network in ionic form (Ag⁺). Al incorporation also improved the overall durability and antibacterial endurance of Ag–SiO₂ thin films.     

Preparation and Characterization of HgxCd1-xS and PbxCd1-xS Quantum Dots and Doped Thin Films

Thin silica and silica-titania films doped with sulfide nanocrystals of controlled size were fabricated by a method based on the preparation of colloidal particles and their introduction into a glassy matrix through the sol-gel method. Colloidal sols of composition Hg_xCd_1-xS and Pb_xCd_1-xS (with _x ranging from 0 to 1) were prepared and used to dope alkoxide solutions for the deposition of thin silica and silica-titania films. Optical absorption spectra were taken on both precursor colloidal sols and derived doped films. X-ray diffraction characterization gave structural information on the nature and size of particles in powders obtained by precipitation from colloidal sols and in doped films. The advantages and limits of the investigated systems are discussed in light of possible applications. The nonlinear properties of the most interesting PbS-doped planar waveguides have been investigated in the near-infrared, at 1.064 m. A reversible nonlinear effect was measured, with n ₂ values ranging from -5 to -20×10^-9 cm²/kW.     

Soluble Powders as Precursors for TiO<Subscript>2</Subscript> Thin Films

Amorphous precursor powders have proven to be highly advantageous for the sol–gel processing of TiO₂ thin films. Oxide yield, density, solubility, and thermal degradation of powders prepared under various conditions were determined; the thermoanalytical data could be assigned to the oxidative decomposition of different organic constituents. Certain powders are suitable for the preparation of alcohol-based sols, whereas also aqueous coating solutions can be prepared from others. Thin films prepared from both systems show excellent adhesion and optical properties when deposited on borosilicate glass substrates.