Surface functionalisation of sol–gel derived aluminosilicates in simulated body fluids

Iron containing aluminosilicate systems obtained by sol–gel method are investigated as potential biomaterials for hyperthermia. The samples surface functionalisation in simulated body fluid enriched with bovine serum albumin (BSA) was studied by Fourier-transform infrared spectroscopy performed in reflectance mode and X-ray photoelectron spectroscopy (XPS). β-sheet/turns ratio estimated using the deconvolution of IR absorption band corresponding to amide I of adsorbed BSA on surface samples indicates a positive contribution to the biocompatibility of these materials. XPS results show an early attachment of albumin on sample surface that is weakly influenced by the protein concentration and prolonged immersion time in BSA–SBF solution.     

Microstructure and electro-optical properties of sol–gel derived Cd-doped ZnO films

The microstructure, and the electrical and optical properties of undoped zinc oxide (ZnO) and cadmium-doped ZnO (CZO) films deposited by a sol–gel method have been investigated. The films have a polycrystalline structure with hexagonal wurtzite ZnO. Scanning electron microscopy (SEM) images indicated that the films have a wrinkle network with uniform size distributions. The elemental analyses of the CZO films were carried out by energy dispersive X-ray analysis. The fundamental absorption edge changed with doping. The optical band gap of the films decreased with Cd dopant. The optical constants of the films such as refractive index, extinction coefficient and dielectric constants changed with Cd dopant. A two-probe method was used to investigate the electrical properties, and the effect of Cd content on the electrical properties was investigated. The electrical conductivity of the films was improved by incorporation of Cd in the ZnO film.     

Inorganic phosphors in lead–silicate glass for white LEDs

Using spectrophotometry and stationary and kinetic fluorimetry, we have shown that xanthene dye fluorescein forms complexes with polycationic derivative of fullerene in aqueous solutions mainly due to electrostatic interactions. It is found that efficient quenching of singlet excited states of dye occurs in the structure of these complexes due to the transfer of excitation or electron from dye to fullerene. As a result, the photodynamic activity of the newly formed complex is much higher than that of fluorescein and fullerene derivative. This effect makes it possible to predict the formation of new-generation hybrid photodynamic preparations using dyes excited only into a singlet state; as a result, directed searches for these dyes are significantly facilitated.     

Inverse magnetocaloric effect in sol–gel derived nanosized cobalt ferrite

The magnetocaloric properties of cobalt ferrite nanoparticles were investigated to evaluate the potential of these materials as magnetic refrigerants. Nanosized cobalt ferrites were synthesized by the method of sol–gel combustion. The nanoparticles were found to be spherical with an average crystallite size of 14 nm. The magnetic entropy change (ΔS _m) calculated indirectly from magnetization isotherms in the temperature region 170–320 K was found to be negative, signifying an inverse magnetocaloric effect in the nanoparticles. The magnitudes of the ΔS _m values were found to be larger when compared to the reported values in the literature for the corresponding ferrite materials in the nanoregime.     

Propylene oxide-assisted fast sol–gel synthesis of mesoporous and nano-structured LiFePO4/C cathode materials

LiFePO₄/C nanocomposites are synthesized by a propylene oxide-assisted fast sol–gel method using FeCl₃, LiNO₃, NH₄H₂PO₄, and sucrose as the starting materials. It was found that after adding propylene oxide into the solution containing the starting materials, a monolithic jelly-like FePO₄ gel containing lithium and carbon source is generated in a few minutes without controlling the pH value of the solution and a time-consuming heating process. Propylene oxide plays a key role in the fast generation of the precursor gel. The final products of LiFePO₄/C are obtained by sintering the dry precursor gel. The structures, micro-morphologies, and electrochemical properties of the LiFePO₄/C composites are investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption analysis, electrochemical impedance spectrum, and charge–discharge cycling tests. The results indicate that the LiFePO₄/C composite prepared by sintering the precursor gel at 680 °C for 5 h is about 30 nm in size with a meso-porous structure (the main pore size distribution is around 3.4 nm). It delivers 166.7 and 105.8 mAh g^?1 at 0.2 and 30 C, respectively. The discharge specific capacity is 97.8 mAh g^?1 even at 40 C. The cycling performance of the prepared LiFePO₄/C composite is stable. The excellent electrochemical performance of the LiFePO₄/C composite is attributed to the nano-sized and mesoporous structure of LiFePO₄/C and the in-situ surface coating of the carbon. It was also found that propylene oxide is crucial for the generation of mesoporous and nano-structured LiFePO₄/C.     

Large piezoelectric strain observed in sol–gel derived BZT–BCT ceramics

High performance lead (Pb)-free piezoelectric ceramics with excellent piezoelectric properties is in great demand for sensor and actuator applications. Barium zirconate titanate–barium calcium titanate [xBZT–(1 − x)BCT] (x = 0.5) is one such lead free system, which exhibits high piezoelectric properties similar to lead zirconate titanate (PZT). In this study we report the synthesis and characterization of this lead free [xBZT–(1 − x)BCT] (x = 0.5) via wet chemical sol–gel method. Calcination of the BZT–BCT precursor only at 1000 °C (against 1300 °C reported in the literature) for 4 h resulted in formation of single phase nanoparticles (<50 nm) as confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. Highly dense and homogenous microstructure with 95% of the theoretical density was obtained by solid-state sintering of the green pellets at 1550 °C. Remanent polarization (Pr) of 11.55 μC/cm² and relative permittivity of 20,020 at the Curie temperature of 95 °C were obtained. Electrically poled BZT–BCT ceramics samples exhibited high piezoelectric charge coefficients, d₃₃ ∼ 530 pC/N, d₃₃* ∼ 942 pm/V, large electromechanical coupling coefficient k_p ∼ 0.45 and a large strain of 0.15%, which are comparable to those of lead based piezoelectric ceramics. The excellent piezoelectric properties of this sol–gel derived BZT–BCT system has been analyzed and correlated to its structure in this report.     

Effect of the excimer laser irradiation on sol–gel derived tungsten–titanium dioxide thin films

A novel technique based on the excimer laser induced crystallization and modification of TiO₂ thin films is being reported. W⁺⁶ ions loaded TiO₂ (WTO) precursor films were prepared by a modified sol–gel method and spin-coated onto microscopic glass slides. Pulsed KrF (248 nm, 13 ns) excimer laser was used to irradiate the WTO amorphous films at various laser parameters. Mesoporous and nanostructured films consisting of anatase and rutile were obtained after laser irradiation at room temperature. The effect of varying W⁺⁶ ions concentrations on structural and optical properties the WTO films was analyzed by X-ray diffraction, field-emission scanning electron microscope, UV-Vis spectrophotometer and transmission electron microscope before and after laser treatment. Films irradiated for 10 pulses at 65–75 mJ/cm² laser fluence, exhibited anatase whereas higher parameters promoted the formation of rutile. XPS results revealed WO₃ along with minor proportion of WO₂ compounds after laser irradiation. Photo-absorbance of the WTO films was increased with increase in W⁺⁶ ions concentration in the film. TEM results exhibited a crystallite size of 15 nm which was confirmed from SEM results as well.     

Structural and optical characterization of sol–gel derived Tm-doped BaTiO3 nanopowders and ceramics

Nanocrystalline Tm³⁺(5%)-doped BaTiO₃ (BT-Tm) has been synthesized by the sol–gel method. The morphology, structure, and optical properties of powders and ceramics were characterized. The average grain size of the gel precursor annealed at 700 and 900 °C was 20 nm and 30 nm, respectively. These powders were single phase and crystallized with a cubic structure while the BT-Tm sintered ceramics were crystallized with the tetragonal BaTiO₃ structure. The photoluminescence spectra showed typical transitions of Tm³⁺ ions and a structure consistent with the Tm³⁺ ions incorporation in the BaTiO₃ crystalline lattice. Thermoluminescence peaks recorded at 300 °C (for annealed samples) or at 230 °C for the ceramic sample were assigned to the recombination of the Tm²⁺-electron traps located mainly at the surface of the nano-crystals or inside the microcrystals, respectively.     

Two-photon polymerization of titanium-containing sol–gel composites for three-dimensional structure fabrication

In this work, we have synthesized and characterized a novel, titanium-containing hybrid material that can be structured three-dimensionally using two-photon polymerization. We investigate the effect on the structurability of the increase of titanium isopropoxide and methacrylic acid in this photosensitive composite. We show that while it is possible to make transparent thin films with a titanium isopropoxide molar content as high as 90%, three-dimensional structures can be made only when the titanium isopropoxide molar content is less than 50%. We measure the refractive index of films with different titanium isopropoxide: methacrylic acid concentrations and we show that while the refractive index increases linearly with the titanium isopropoxide, the increase of the methacrylic acid content does not affect the refractive index of the material.     

Structure and site selective luminescence of sol–gel derived Eu:Sr2SiO4

Strontium silicate (Sr₂SiO₄) samples doped with varying Eu³⁺content were prepared via sol–gel route and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), dynamic light scattering (DLS) and photoluminescence (PL) techniques. The synthesis temperature could be brought down to 600 °C for formation of a singe phase sample. The concentration of the dopant ion and the temperature of annealing were optimized for maximum PL intensity. The critical energy-transfer distance for the Eu³⁺ ions was evaluated based on which the quenching mechanism was verified to be a multipole–multipole interaction. Based on the time-resolved emission data (TRES), it was inferred that, two different types of Eu³⁺ ions were present in the matrix. The first type was a long lived species (τ=4.7 ms) present at 10-coordinated ‘Sr’sites and the other was a short lived species (τ=1.2 ms) present at the 9-coordinated ‘Sr’sites which gets selectively excited at 296 nm. Judd–Ofelt (J–O) intensity parameters for both the species were evaluated. The trend observed for the two species in the J–O parameters, Ω₂ and Ω₄ were different confirming their existence in two different environments. The color coordinates of the system were evaluated and plotted on a CIE index diagram. Commercial utility of the phosphor was investigated by comparing it with commercial red phosphor.     

Growth of vertically aligned one-dimensional ZnO nanowire arrays on sol–gel derived ZnO thin films

Vertically aligned one-dimensional ZnO nanowire arrays have been synthesized by a hydrothermal method on sol–gel derived ZnO films. Sol–gel derived ZnO films and corresponding ZnO nanowire arrays have been characterized by X-ray diffraction and field-emission scanning electron microscopy. The effect of sol–gel derived ZnO film surface on the morphology of ZnO nanowire arrays has been investigated. The authors suggest from our investigation that sol–gel derived ZnO films affect the growth of one-dimensional ZnO nanostructures. Not only crystalline ZnO films but also amorphous ones can act as a scaffold for ZnO nucleus. Tilted ZnO micro-rods are grown on ZnO gel films, whereas vertically aligned ZnO nanowire arrays are grown on nanometer-sized ZnO grains. The average diameter of ZnO nanowire arrays are correlated strongly with the grain size of sol–gel derived ZnO films.     

Evolution of ZnO nanostructures in sol–gel synthesis

Evolution of the microstructure and optical properties of ZnO nanoparticles in a mild sol–gel synthesis process is studied. The ZnO nanostructures were prepared by reacting zinc acetate dihydrate with NaOH in water at 50−60 °C. Evolution of ZnO nanostructures with reaction time is studied using UV–Vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy techniques. During the process of Zn²⁺ hydroxylation, well defined rod-like crystals were formed within 15 min. Further hydroxylation leads to the formation of a gel-like structure within about 45 min. However, XRD, FT-IR and energy dispersive spectroscopy (EDS) confirmed that these initial products were zinc hydroxyl double salts (Zn-HDS), not ZnO. On ageing the reaction mixture, ZnO nanoparticles with wurtzite structure evolved.     

Effects of annealing rate and morphology of sol–gel derived ZnO on the performance of inverted polymer solar cells

The effects of annealing rate and morphology of sol–gel derived zinc oxide(ZnO)thin films on the performance of inverted polymer solar cells(IPSCs)are investigated.ZnO films with different morphologies are prepared at different annealing rates and used as the electron transport layers in IPSCs.The undulating morphologies of ZnO films fabricated at annealing rates of 10 C/min and 3 C/min each possess a rougher surface than that of the ZnO film fabricated at a fast annealing rate of 50 C/min.The ZnO films are characterized by atomic force microscopy(AFM),optical transmittance measurements,and simulation.The results indicate that the ZnO film formed at 3 C/min possesses a good-quality contact area with the active layer.Combined with a moderate light-scattering,the resulting device shows a 16%improvement in power conversion efficiency compared with that of the rapidly annealed ZnO film device.     

Structural studies and impedance spectroscopy of sol–gel derived Bi0.9Pr0.1FeO3 nanoceramics

Nano-crystalline Bi_0.9Pr_0.1FeO₃ (BPFO) ceramics have been synthesized by a sol–gel technique. The Rietveld refinement of the room temperature powder X-ray diffraction pattern confirms that the BPFO crystallizes in the rhombohedral R3c space group symmetry. SEM image of the sintered BPFO ceramic shows particles with same shape and fine grain morphology with the average grain size of 53±12 nm. The electrical properties of the ceramic are analysed by impedance spectroscopy. Grain and grain-boundary effect is observed in the material at lower temperature range which has been confirmed by electric modulus formalism. The ac conductivity spectrum obeys the Johnscher's power law. The activation energy calculated from dc conductivity is found to be 0.373 eV, which represents the conduction of small polaron over barrier between two sites of the lattice.     

Spectroscopic properties of Co2+: ZnAl2O4 nanocrystals in sol–gel derived glass–ceramics

Transparent glass–ceramics containing zinc–aluminum spinel (ZnAl₂O₄) nanocrystals doped with tetrahedrally coordinated Co²⁺ ions were obtained by the sol–gel method for the first time. The gels of composition SiO₂–Al₂O₃–ZnO–CoO were prepared at room temperature and heat-treated at temperature ranging 800–950 °C. When the gel samples were heated up to 900 °C, ZnAl₂O₄ nanocrystals were precipitated. Co²⁺ ions were located in tetrahedral sites in ZnAl₂O₄ nanocrystals. X-ray diffraction analysis shows that the crystallite sizes of ZnAl₂O₄ crystal become large with the heat-treatment temperature and time, and the crystallite diameter is in the range of 10–15 nm. The dependence of the absorption and emission spectra of the samples on heat-treatment temperature were presented. The difference in the luminescence between Co²⁺ doped glass–ceramic and Co²⁺ doped bulk crystal was analysed. The crystal field parameter D_q of 423 cm⁻¹ and the Racah parameters B of 773 cm⁻¹ and C of 3478.5 cm⁻¹ were calculated for tetrahedral Co²⁺ ions.     

Microwave sol–gel derived NaCaGd(MoO4)3:Er3+/Yb3+ phosphors and their upconversion photoluminescence properties

Ternary molybdate NaCaGd_1−x(MoO₄)₃:Er³⁺/Yb³⁺ phosphors with the proper doping concentrations of Er³⁺ and Yb³⁺ (x = Er³⁺ + Yb³⁺, Er³⁺ = 0, 0.05, 0.1, 0.2 and Yb³⁺ = 0, 0.2, 0.45) were successfully synthesized by microwave sol–gel method for the first time. Well-crystallized particles formed after heat-treatment at 900 °C for 16 h showed a fine and homogeneous morphology with particle sizes of 3–5 μm. The optical properties were examined comparatively using photoluminescence emission and Raman spectroscopy. Under excitation at 980 nm, the doped particles exhibited a strong 525-nm emission band, a weak 550-nm emission band in the green region, which correspond to the ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions, and a very weak 655-nm emission band in the red region, which corresponds to the ⁴F_9/2 → ⁴I_15/2 transition. The optimal Yb³⁺:Er³⁺ ratio was obtained to be 9:1, as indicated by the composition-dependent quenching effect of Er³⁺ ions. The pump power dependence of upconversion emission intensity and Commission Internationale de L’Eclairage chromaticity coordinates of the phosphors were evaluated in detail.     

Microwave behavior of ferrites prepared via sol–gel method

Ni-ferrites were prepared at different temperatures via sol–gel method. The electromagnetic properties of these materials, namely permittivity and permeability were measured in the 0.1–13 GHz frequency range. Following a mathematical procedure, microwave absorption diagrams were constructed including the dependence of the microwave absorption of ferrite layer on microwave frequency and layer thickness. The permeability spectra broaden and the microwave absorption improves at 9–10 GHz with increase of annealing temperature.