Synthesis and Judd-Ofelt analysis of a sol-gel material doped with a Ln2(Benzoate)6(Phen)2 (Ln = Er/Yb) complex

In this work, we have prepared a sol-gel derived hybrid material directly doped with Er_1.4Yb_0.6(Benzoate)₆(Phen)₂ (Phen = 1,10-phenanthroline) complex, which was reported with intramolecular Yb-Er energy-transfer process in our previous work. The infrared (IR) spectra of the pure complex and hybrid gel material were investigated. The NIR photoluminescence (PL) spectrum of hybrid gel material shows strong characteristic emission of Er³⁺ with broad full width at half-maximum (FWHM) of 70 nm. Judd-Ofelt theory was used in order to analyze the optical properties of Er³⁺ ions in the hybrid gel material.     

Microstructure and optical properties of (Pb,Ca)TiO3 films grown on Si(1 0 0) substrates by a simple sol-gel process

Amorphous and polycrystalline (Pb_0.76Ca_0.24)TiO₃ (PCT) thin films deposited on an Si(1 0 0) substrate have been prepared by a simple sol-gel process. The microstructure and surface morphologies of the thin films have been studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The polycrystalline PCT film on the Si(1 0 0) substrate has a tetragonal perovskite structure with grain size from 60 to 110 nm. AFM reveals smooth surfaces and root mean square (rms) roughness of 0.17 and 4.4 nm for amorphous and polycrystalline films, respectively. The refractive index n and extinction coefficient k of the amorphous and polycrystalline thin films was obtained by spectroscopic ellipsometry as a function of the photon energy in the range from 2.0 to 5.4 eV. The maximum n and direct bandgap energies of amorphous and polycrystalline thin films were 2.66 and 4.11 eV, 2.64 and 3.84 eV, respectively.     

Fabrication of two-dimensional lattices by using photosensitive sol-gel and four-beam laser interference

This work demonstrates a promising method to fabricate 2D lattices by using photosensitive sol-gel method combining with four-beam of a 350.7 nm Kr ion laser interference. Photosensitive TiO₂ gel films with chelate complexes as precursors are fabricated. The characteristics of UV and IR spectra of the films and their variations in the process of laser irradiation are investigated. The results show that the gel films had an absorption peak at about 358 nm due to the formation of chelate complex. This peak gradually decreases with irradiation in time, which indicates the photosensitive properties of the TiO₂ films. A flexible four-beam interference system is proposed. Given incident angles 20.5° and 44.5°, the lattices with pitch of 700 nm and 326 nm are fabricated, respectively. The diffraction phenomenon of the 700 nm lattices is investigated by inverse method. The results are fully consistent with the 2D crystal diffraction theory.     

Synthesis and characterization of visible light responsive N-TiO2 mixed crystal by a modified hydrothermal process

N doped TiO₂ with anatase and rutile mixed crystal were prepared by using tetrabutyl titanate as the precursor via a modified hydrothermal process and calcination at 320 °C. The microstructure and morphology of samples were characterized by XRD, UV-vis-DRS, FTIR and XPS. The results showed that N-TiO₂ particles were crystallized to anatase and rutile mixed crystal structure; they were presented narrow particle size distribution, and the average particle size was ca. 13.5 nm calculated from XRD results. It was found that the N-doped TiO₂ particles showed strong visible-light absorption and high photocatalytic activity for the mineralization of Rhodamine B under irradiation by visible light (400-500 nm). The high visible-light photocatalytic activity of the obtained N-doped TiO₂ might result from the synergetic effect of nitrogen doping and the mixed lattice structure of N-TiO₂. Possible mechanism of N-TiO₂ mixed crystal formed under hydrothermal conditions was discussed.     

Preparation and characterization of ZnO-TiO2 films obtained by sol-gel method

The sol-gel route has been applied to obtain ZnO-TiO₂ thin films. For comparison, pure TiO₂ and ZnO films are also prepared from the corresponding solutions. The films are deposited by a spin-coated method on silicon and glass substrates. Their structural and vibrational properties have been studied as a function of the annealing temperatures (400-750 °C). Pure ZnO films crystallize in a wurtzite modification at a relatively low temperature of 400 °C, whereas the mixed oxide films show predominantly amorphous structure at this temperature. XRD analysis shows that by increasing the annealing temperatures, the sol-gel Zn/Ti oxide films reveal a certain degree of crystallization and their structures are found to be mixtures of wurtzite ZnO, Zn₂TiO₄, anatase TiO₂ and amorphous fraction. The XRD analysis presumes that Zn₂TiO₄ becomes a favored phase at the highest annealing temperature of 750 °C. The obtained thin films are uniform with no visual defects. The optical properties of ZnO-TiO₂ films have been compared with those of single component films (ZnO and TiO₂). The mixed oxide films present a high transparency with a slight decrease by increasing the annealing temperature.     

Fabrication and characterization of photocurable inorganic-organic hybrid materials using organically modified colloidal-silica nanoparticles and acryl resin

Photocurable inorganic-organic hybrid materials were prepared from colloidal-silica nanoparticles synthesized through the sol-gel process and using acryl resin. The synthesized colloidal-silica nanoparticles had uniform diameters of around 20 nm and were organically modified, using methyl and methacryl functional silanes, for efficient hybridization with acryl resin. The organically modified and stabilized colloidal-silica nanoparticles could be homogeneously hybridized with acryl resin without phase separation. The successfully fabricated hybrid materials exhibit efficient photocurability and simple film formation due to the photopolymerization of the organically modified colloidal-silica nanoparticles and acryl resin upon UV exposure as well as an excellent optical transmission of above 90% in the visible region and an enhanced surface smoothness of around 1 nm RMS roughness. They likewise exhibit improved thermal and mechanical characteristics, much better than those of acryl resin. Lastly and most importantly, these photocurable hybrid materials fabricated through the synergistic combination of colloidal-silica nanoparticles with acryl resin are candidates for optical and electrical applications.     

Dielectric studies of segmental dynamics in poly(dimethylsiloxane)/titania nanocomposites

Differential scanning calorimetry, thermally stimulated depolarization currents and dielectric relaxation spectroscopy techniques, covering together a broad frequency range of 10⁻⁴ to 10⁶ Hz, were employed to investigate the effects of in situ synthesized titania nanoparticles on thermal transitions, segmental dynamics and interfacial interactions in poly(dimethylsiloxane)/titania nanocomposites. Titania particles (TiO₂, 20-40 nm in diameter) were prepared and well dispersed into the polymer network through sol-gel technique, aiming at stable and mechanically reinforced systems. The interactions between polymer and fillers were found to be strong, supressing crystallinity and affecting the temperature development of the glass transition. The segmental relaxation associated with the glass transition consists of three contributions, arising, in the order of decreasing mobility, from the bulk (unaffected) amorphous polymer fraction (α relaxation), from polymer chains restricted between condensed crystal regions (α_c relaxation), and from the semi-bound polymer in an interfacial layer with strongly reduced mobility due to interactions with hydroxyls on the nanoparticle surface (α? relaxation). The thickness of the interfacial layer was estimated to be in the range of 3-5 nm. Measurements using different thermal protocols proved very effective in analyzing the origin of each relaxation and the respective effects of filler addition.     

Spectroscopic characterization of intrinsic losses in an organic-inorganic hybrid waveguide synthesized by the sol-gel process

A promising way of fabricating integrated optics components is based on the sol-gel synthesis and photocuring of hybrid materials. However, the presence of OH groups in these materials is a major factor in optical amplification inhibition. In particular, high losses at 1550 nm are mainly due to non-condensed OH groups originating from the sol-gel process at low temperature. Thus, improvement of the final properties of these materials is correlated with the inhibition of OH group concentration. In this study, we used ²⁹Si NMR and near infrared spectroscopy to demonstrate the catalytic effect of zirconium (IV) n-propoxide on the condensation reactions of silanol groups. ²⁹Si NMR showed the absence of silanol species at the end of the synthesis. This result is attributed to the zirconate hydrophilic effect which consumes OH groups by catalysing the polycondensation of Si-OH bonds. In parallel, near-infrared experiments showed the presence of a high proportion of OH species at the end of the synthesis showing that the remaining OH groups are only present in the zirconium species.     

Development of optical nonlinearity, high dielectric constant and ferromagnetic behavior in a silicate glass nanocomposite by suitable heat treatment

We have explored the development of multifunctionalities viz, optical nonlinearity, high dielectric constant and ferromagnetic behavior in a nanostructured silica based glass of 14.0Na₂O, 26.0BaO, 26.0TiO₂, 16.0B₂O₃, 17.0SiO₂, 1.0NiO (mol%) composition. A heat treatment at 863 K for 4 h led to nonlinear refractive index and absorption coefficients at wavelength 800 nm of 0.11 × 10⁻¹⁹ m²/W and 1.15 × 10⁻³ cm/GW, respectively. A heat treatment at 1073 K for 2 h followed by 1113 K for 3 h increased the dielectric constant from 11 to 50, apparently due to the formation of nanocrystals of BaTiO₃ within the glass medium. Glass samples reduced at 923 K for 1 h exhibited ferromagnetic behavior due to the presence of nickel nanoparticles.     

Characterization and synthesis of Y0.9Ca0.1Ba1.8Sr0.2Cu3O7−δ via combining sol-gel and solid-state route

We applied the conventional sol-gel and solid-state reactions in this study to prepare double-substituted superconducting Y_0.9Ca_0.1Ba_1.8Sr_0.2Cu₃O_7−δ. The result and the effect of calcium and strontium doping on high-T_c compound Y-123 have been investigated. The precursor gel Ca-Ba-Sr-Cu-O was prepared by acetate-tartrate sol-gel route which involved hydrolysis and olation (polycondensation). Y_0.9Ca_0.1Ba_1.8Sr_0.2Cu₃O_7−δ was obtained by solid-state reaction between Y₂O₃ and Ca-Ba-Sr-Cu-O heated at 880 °C for 18 h with step cooling 50 °C/h until 450 °C. Without oxygen flow during the whole annealing process, the sample still showed good superconducting properties with T_c-zero close to 80 K. The presence of organic material in the sol-gel precursor Ca-Ba-Sr-Cu-O is nucleophile species, which is chemically reactive to Y₂O₃ during solid-state reaction thus enhance the diffusion rate. Moreover, -OH group in the precursor gel has ability to provide a sufficient amount of oxygen for the sample to stabilized the multicomponent superconductor.     

Sol-gel synthesis and characterization of adsorbent and photoluminescent nanocomposites of starch and silica

Using sol-gel method, mesoporous and photoluminescent silica nanocomposites of soluble starch have been synthesized and characterized. Different ratios of H₂O, TEOS and EtOH were used at fixed template (soluble starch) and catalyst (NH₄OH) concentrations to obtain materials of different performances in terms of heavy metal binding from a solution which has been monitored using Cd(II) as representative divalent heavy metal ion. Optimum material was obtained when H₂O, TEOS and EtOH were used in 14:1:2 ratio. This sample was not only an efficient metal ion adsorbent but also had an intense luminescence in ultra-violet region and potentially may be used in silicon-based UV-emitting devices. Metal binding by the material was further enhanced after calcination (at 800 °C in air) while its luminescence had a multipeak profile in UV-visible region. In a batch adsorption study, calcined hybrid composite (0.25 g/L) could remove 98.5% Cd(II) from 100 mg/L Cd(II) solution in 2 h. The chemical, structural and textural characteristics of the synthesized materials have been investigated using Fourier Transform Infrared Spectroscopy (FTIR), X-rays Diffraction (XRD), Thermal Analysis (TGA/DTA), Photoluminescence (PL), Brunauer-Emmett-Teller Analysis (BET) and Scanning Electron Microscopy (SEM).     

Surfactant effects on the particle size of iron (III) oxides formed by sol-gel synthesis

In this work, we probed the effects of a common surfactant, sodium dodecylbenzene sulfonate (NaDDBS), on the particle size of iron (III) oxides formed via a modified sol-gel synthesis. The goal was to create tunable nanosized particles via a method that combines the efficiency and advantages of the sol-gel process, but inhibits the formation of a gel. Two different metal salt precursors were used, ferric nitrate nonahydrate, Fe(NO₃)₃ · 9H₂O, and ferric chlorate hexahydrate, FeCl₃ · 6H₂O. The particle size of the dried gel was 4.5 nm for Fe(NO₃)₃ · 9H₂O and 3.6 nm for FeCl₃ · 6H₂O. In the presence of the surfactant FeCl₃ · 6H₂O formed a gel and Fe(NO₃)₃ · 9H₂O was unable to gel, but the new particle sizes were 4.9 nm and 3.2 nm, respectively. The addition of the surfactant in the later stages of the process afforded the stabilization of independent nanoparticles of the same size as those obtained in the systems that gelled.     

Ultralow density silica aerogels prepared with PEDS

This paper deals with the synthesis of ultralow density silica aerogels using polyethoxydisiloxanes (PEDS) as the precursor via sol-gel process followed by supercritical drying using ethanol solvent extraction. Ultralow density silica aerogels with 5 mg/cc of density were made for the molar ratio by this method. A remarkable reduction in the gelation time was observed by the effect of the catalyst NH₄OH at room temperature. The microstructure and morphology of the ultralow density silica aerogels were characterized by the specific surface area, S_BET, SEM, TEM and the pore size distribution techniques. The results show that the diameter of the silica particles is about 13 nm and the pore size of the silica aerogels is about several nm. The specific surface area of the silica aerogel is 339 m²/g and the specific surface area, pore volume and average pore diameter decrease with increasing density of the silica aerogel.     

Hydrothermal synthesis of organic hybrid BaTiO3 nanoparticles using a supercritical continuous flow reaction system

Barium titanate (BaTiO₃: BT) nanoparticles were synthesized by the hydrothermal method in the presence of dispersants using a continuous supercritical flow reaction system. The reactants of TiO₂ sol/Ba(NO₃)₂ mixed solution and KOH solution were used as starting materials and that was heated quickly up to 400 °C under the pressure of 30 MPa for 8 ms as reaction time. The dispersant solution such as polyacrylic acid (PAA) and polyoxyethylene(20) sorbitan monooleate (Tween 80) was injected in the cooling process after the reaction. The crystal phase of the obtained particles was identified as perovskite cubic BaTiO₃ by X-ray diffractometry (XRD) and Raman spectroscopy. Raman spectra and thermogravimetric data revealed that PAA and Tween 80 fabricated hybrid BT nanoparicles. Primarily particle size of the BaTiO₃ nanoparticle was determined by means of BET surface area, as small as less than 10 nm irrespective of dispersants. In contrast, dispersed particle size in solution measured by dynamic light scattering (DLS) technique decreased from 282 nm to less than 100 nm depending on the dispersant. Aggregation of BaTiO₃ nanoparticles might be depressed in the presence of dispersants, especially PAA is the most effective among the dispersants examined.     

Fluorescent compacts prepared by the entrapment of benzoxazole type dyes into a silica matrix at high pressure

We have produced silica-gel compacts doped with 2,5-Bis(benzoxazol-2^′-yl)-4-methoxyphenol dye using high-pressure processing of powders synthesized by the sol-gel technique. The high-pressure compaction of powders with three different dye concentrations was done at 4.5 GPa and room temperature. We have measured optical and mechanical properties of the obtained compacts. They were very stable, transparent, crack free, hard (3.56 ± 0.07 GPa) and dense (1.95 ± 0.03 g/cm³), being resistant to polishing and leaching, which enables its use in optical applications. The Stokes shift observed was higher than 100 nm indicating that the intramolecular proton-transfer in the electronically excited state (ESIPT) of this dye is maintained, even in an OH rich environment like silica. A shift to higher wavelength in the fluorescence spectra of the compacts, attributed to the increasing in the conjugation of the π system, was observed.     

Synthesis and characterization of monolithic Gd2O3 aerogels

In this thesis, we will elaborate on the synthesis and characterization of monolithic Gd₂O₃ aerogel. We conducted the experiment in the following procedure. Use gadolinium nitrate or gadolinium chloride, a kind of inorganic gadolinium salt as raw material, and polymerize it in ethanol with propylene oxide as gelation initiator in the way of sol-gel. After this step, we can obtain the wet gel. Then, dry the wet gel by supercritical CO₂, at last we will get aerogel. The product has strong transparency and also shows some thermal stability. XRD characterization shows that it is amorphous. Nitrogen adsorption/desorption analysis tells clearly its surface area (223 m²/g), average pore diameters (42 nm) and large pore volume (1.83 ml/g). It is also characterized by transmission electron microscopy and high-resolution transmission electron microscopy.     

Thermal stability and crystallization behavior of TiO2 doped ZBLAN glasses

ZBLAN glasses with the composition (in mol%) of (100 − x)(53 ZrF₄ + 19 BaF₂ + 5LaF₃ + 3AlF₃ + 20NaF) + xTiO₂ (x = 0, 1.0 and 2.0 mol%) were prepared using a conventional melting technique in dry nitrogen atmosphere. The thermal stability, glass-forming ability, and crystallization kinetics of the ZBLAN system as a function of the TiO₂ concentrations were investigated by Differential Scanning Calorimetry (DSC). Also, the crystalline phases were determined by X-ray Diffraction (XRD). Our study indicates that adding TiO₂ in a fluoride system improves the thermal parameters of the glass, which is interesting for applications as optical fiber.     

Characterization and optical properties of sol-gel processed PMMA/SiO2 hybrid monoliths

Organic-inorganic hybrid monoliths consisting of poly(methyl methacrylate) and SiO₂ were synthesized by the sol-gel process. Three PMMA/TEOS ratios by weight were prepared, namely PMMA/TEOS = 80/20, 50/50 and 20/80. The effects of the ratio of PMMA/TEOS on thermal stability, microstructure, morphology and optical properties were systematically studied. In particular, scanning electron microscopy (SEM) demonstrated morphological variation corresponding to the degree of miscibility between organic and inorganic components. Energy dispersive spectroscopy (EDS) clearly revealed that the SiO₂ was more uniformly distributed in the hybrids with increasing PMMA content. The refractive index could be adjustable in the range of 1.474-1.486. The 80/20 monolith had the similar transparency to pure PMMA in the visible region and lower absorption than PMMA in the near infrared region, suggesting its potential applications for optical devices.     

Optical and electrical properties of lithium doped nickel oxide films deposited by spray pyrolysis onto alumina substrates

Non-doped and lithium doped nickel oxide crystalline films have been prepared onto quartz and crystalline alumina substrates at high substrate temperature (600 °C) by the pneumatic spray pyrolysis process using nickel and lithium acetates as source materials. The structure of all the deposited films was the crystalline cubic phase related to NiO, although this crystalline structure was a little bit stressed for the films with higher lithium concentration. The grain size had values between 60 and 70 nm, almost independently of doping concentration. The non-doped and lithium doped films have an energy band gap of the order of 3.6 eV. Hot point probe results show that all deposited films have a p-type semiconductor behavior. From current–voltage measurements it was observed that the electrical resistivity decreases as the lithium concentration increases, indicating that the doping action of lithium is carried out. The electrical resistivity changed from 10⁶ Ω cm for the non-doped films up to 10² Ω cm for the films prepared with the highest doping concentration.     

Preparation, phase transformation and microstructure of ZrxTi1−xO2 (x = 0.1-0.9) fine fibers

Zr_xTi_1−xO₂ (x = 0.1-0.9) fibers were prepared by the sol-gel dry-spinning method. Polyacetylacetonatozirconium (PAZ) and tetrabutyl titanate (C₁₆H₃₆O₄Ti) were used as raw materials. The green fibers were obtained from the amorphous spinnable solution and then heat-treated to convert into polycrystalline fibers. The main phase changes from TiO₂ to zirconium titanate (ZT) and then tetragonal ZrO₂ with increasing ZrO₂ content. The crystallization temperature varied with the molar ratio of Zr:Ti. The heat-treated fibers at 1050 °C have few pores and no cracks with diameters of 10-20μm and lengths of 1-5 cm.