Preparation of α-Fe2O3 nanoparticles by high-energy ball milling

α-Fe₂O₃ nanoparticles were prepared by high-energy ball milling using α-FeOOH as raw materials. The prepared samples were characterized by transmission electron microscopy (TEM), Mössbauer spectroscopy, X-ray diffraction (XRD) and differential thermal analysis–thermogravimetric analysis (DTA–TGA). The results showed that after 90 h milling α-Fe₂O₃ nanoparticles were obtained, and the particle size is about 20 nm. The mechanism of reaction during milling is supposed that the initial α-FeOOH powder turned smaller and smaller by the high-speed collision during ball milling, later these particles turned to be superparamagnetic, at last these superparamagnetic α-FeOOH particles were dehydrated and transformed into α-Fe₂O₃.     

One-step solution synthesis of Fe2O3 nanoparticles at low temperature

A new synthesis method of α-Fe₂O₃ nanoparticles was developed, in which the ferrous and ferric salts as well as polyaniline acted as the precursor and dispersant, respectively. From the investigation of X-ray diffraction and FT-IR spectra, the α-Fe₂O₃ nanoparticles can be directly prepared by the co-precipitation method without high-temperature calcining. Transmission electron microscope (TEM) and scanning electron microscope (SEM) observation revealed that the α-Fe₂O₃ nanoparticles had average diameters ranging from 30.0 to 75.0 nm. Compared with previous methods, this present method shows an easy processing and can be applied on the large-scale produce of α-Fe₂O₃ nanoparticles in one step.     

Synthesis of Fe2O3 concentrations and sintering temperature on FTIR and magnetic susceptibility measured from 4 to 300 K of monolith silica gel prepared by sol–gel technique

Nano-crystalline ferric oxide was synthesized inside an amorphous silica matrix by the sol–gel method. The formation of ferric oxide can be detected, giving fine particles around 5–10 nm crystallite sizes calculated from win-fit program. This is associated with a specific role of the silica matrix, which facilitates the diffusion of the reacting cations, enhancing the ferric oxide formation. γ- to α- and/or ε-Fe₂O₃ transformations take place by increasing the Fe₂O₃ concentration for samples sintering at constant-heat treatment temperature. The dried monolith gel materials were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), as well as by scanning electron microscopy (SEM). The magnetic susceptibility at zero-field cooling (M_ZFC) of the prepared samples was evaluated using superconducting quantum interference device (SQUID) magnetometer in temperature range from 4 to 300 K at 1 T.     

Structural and optical properties of Ba(Ti1−x,Nix)O3 thin films prepared by sol–gel process

Ba(Ti_1−x,Ni_x)O₃ thin films were prepared on fused quartz substrates by a sol–gel process. X-ray diffraction and Raman scattering measurements showed that the films are of pseudo-cubic perovskite structure with random orientation and the change of lattice constant caused by Ni-doping with different concentrations is very small. Optical transmittance spectra indicated that Ni-doping has an obvious effect on the energy band structure. The energy gap of Ba(Ti_1−x,Ni_x)O₃ decreased linearly with the increase of Ni concentration. It indicates that the adjusting of band gap can be achieved by controlling the Ni-doping content accurately in Ba(Ti_1−x,Ni_x)O₃ thin films. This has potential application in devices based on ferroelectric thin films.     

Novel nanostructures of β-Ga2O3 synthesized by thermal evaporation

In this study, we report the novel β-Ga₂O₃ nanostructures synthesized by the thermal evaporation of Ga droplet in the presence of Au catalysts at 900 °C. The morphology and structure of the products were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The single-crystalline β-Ga₂O₃ nanosheets have lateral dimensions up to several tens of microns. Large arrays of column-like layered crystal β-Ga₂O₃ structures that consisted of many nanosheets were formed on the Au-coated silicon substrate under the suitable vapor concentration. These novel β-Ga₂O₃ nanostructures are expected to have potential application in functional nanodevices.     

Luminescence enhancement in (Nd+Ce) doped SiO2 : Al2O3 sol–gel glasses

An enhancement in NIR luminescence from Nd³⁺-doped Ce³⁺ co-doped SiO₂+Al₂O₃ sol–gel glasses has been observed. The lasing transition (⁴F_3/2→⁴I_11/2) at 1072 nm from the dual rare-earth Nd³⁺+Ce³⁺-doped glasses has shown an emission strength of about five times that of the single rare-earth ion Nd³⁺-doped glass. From the measurement of lifetimes of the transition at 1072 nm, the transfer rate (W_tr), critical distance (R₀) and energy transfer efficiency (η) of the neodymium glasses have been calculated.     

Synthesis and luminescence properties of nanocrystalline Gd2O3:Eu by combustion process

The nanocrystalline Gd₂O₃:Eu³⁺ powders with cubic phase were prepared by a combustion method in the presence of urea and glycol. The effects of the annealing temperature on the crystallization and luminescence properties were studied. The results of XRD show pure phase can be obtained, the average crystallite size could be calculated as 7, 8, 15, and 23 nm for the precursor and samples annealed at 600, 700 and 800 °C, respectively, which coincided with the results from TEM images. The emission intensity, host absorption and charge transfer band intensity increased with increasing the temperature. The slightly broad emission peak at 610 nm for smaller particles can be observed. The ratio of host absorption to O²⁻-Eu³⁺ charge transfer band of smaller nanoparticles is much stronger compared with that for larger nanoparticles, furthermore, the luminescence lifetimes of nanoparticles increased with increasing particles size. The effects of doping concentration of Eu³⁺ on luminescence lifetimes and intensities were also discussed. The samples exhibited a higher quenching concentration of Eu³⁺, and luminescence lifetimes of nanoparticles are related to annealing temperature of samples and the doping concentration of Eu³⁺ ions.     

Nanometric core-shell-shell γ-Fe2O3/SiO2/TiO2 particles

The preparation of core-shell-shell γ-Fe₂O₃/SiO₂/TiO₂ nanoparticles of few tens nanometers is performed by successively coating onto magnetic nanoparticles a SiO₂ layer and a TiO₂ layer, using sol–gel methods. The thickness of the two layers and the aggregation state of the particles can be controlled by the experimental conditions used for the two coatings. These composite nanoparticles may find application as magnetic photocatalysts, since they are characterized by their small diameters which allow a good accessibility to the TiO₂ shell. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Optical properties of Mg<Subscript>0.05</Subscript>Zn<Subscript>0.95</Subscript>O/SiO<Subscript>2</Subscript> nanocomposite films prepared by sol–gel technique

Mg_0.05Zn_0.95O/SiO₂ nanocomposite films in the molar ratio 25:75 consisting of Mg_0.05Zn_0.95O nanoparticles embedded in a dielectric matrix were prepared by sol–gel technique (spin coating). Optical transmittance, Raman effect and photoluminescence measurements of the composites indicated effective capping of the Mg_0.05Zn_0.95O nanoparticles (radii 1. 61–1.68 nm) in the host showing practically no variation of particle size with the post deposition annealing treatments. The blue shift of the band gap (4.29–4.23 eV) from that of bulk Mg_0.05Zn_0.95O indicated strong carrier confinement for samples annealed at T ≤ 873 K. Highly intense UV emission ( ∼ 4.14 eV) compared to that of defect related emission (2.59 eV) at room temperature was obtained by incorporating 5% Mg in ZnO.This revised version was published online in August 2005 with a corrected issue number.     

Synthesis and luminescent properties of nanoparticles LaSrAl3O7:Eu, Tb

Phosphors of nanoparticles LaSrAl₃O₇:RE³⁺(REEu, Tb) have been prepared by a sol–gel method. The structure and luminescent properties of LaSrAl₃O₇:Eu³⁺ and LaSrAl₃O₇:Tb³⁺ phosphors were characterized by X-ray diffraction and atomic force microscopy (AFM), photoluminescence excitation and emission spectra were utilized. From X-ray diffraction (XRD) patterns, it is indicated that the phosphor LaSrAl₃O₇ forms without impurity phase at 900 °C. From atomic force microscopy (AFM) images, it is shown that the crystal size of the phosphores are about 60–80 nm. Upon excitation with UV irradiation, it is shown that there is a strong emission at around 617 nm corresponding to the forced electric dipole ⁵D₀–⁷F₂ transition of Eu³⁺, and at around 545 nm corresponding to the ⁵D₄–⁷F₅ transition of Tb³⁺. The dependence of photoluminescence intensity on Eu³⁺(or Tb³⁺) concentration and annealing temperature were also studied in detail.     

New Synthesis of Ferrite–Silica Nanocomposites by a Sol–Gel Auto-Combustion

A sol–gel autocombustion method was used to synthesize nanometric metal-oxide powders, and was extended for the first time to prepare ferrite–silica nanocomposites. The gels obtained by mixing suitable amounts of citric acid, metal nitrates, ammonia (pure phases) and tetraethylortosilicate (nanocomposites) were converted directly to ferrite (either γ-Fe₂O₃ or CoFe₂O₄) or ferrite–silica composites through a rapid autocombustion reaction. The combustion involves a thermally induced autocatalytic oxidation–reduction reaction between the nitrate and the citrate ions. The sample characterization by X-ray diffraction, transmission electron microscopy and N₂ physisorption measurements revealed nanosized pure phase powders and nanocomposites in which small spherical nanoparticles (mean size 3.5 and 5.0nm, respectively for the γ-Fe₂O₃and CoFe₂O₄) are homogeneously dispersed over a mesoporous silica matrix.     

Effect of the synthesis route on the structural properties and shape of the indium oxide (In2O3) nano-particles

Nano-crystalline indium oxide (In₂O₃) particles have been synthesized by sol–gel and hydro-thermal techniques. A simple hydro-alcoholic solution consisting indium nitrate hydrate and citric acid (in sol–gel method) and 1, 4-butandiol (in hydro-thermal method) have been utilized. The structural properties of indium oxide nano-powders annealed at 450 °C (for both methods) have been characterized by the X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and specific surface area (SSA) analysis. Structural analysis of the samples shows cubic phase in sol–gel and cubic-hexagonal phase mixture in hydro-thermally prepared particles. The nano-particles prepared by sol–gel method have nearly spherical shape, whereas hydro-thermally-made ones display wire- and needle-like shape in addition to the spherical shape. The obtained In₂O₃ nano-particles surface areas were 23.2 and 55.3 in sol–gel and hydro-thermal methods, respectively. The optical direct band gap of In₂O₃ nano-particles were determined to be 4.32 and 4.24 eV for sol–gel and hydro-thermal methods, respectively. These values exhibit 0.5 eV blue shift from that the bulk In₂O₃ (3.75 eV), which is related to the particle size reduction and approaching the quantum confinement limit of nano-particles.     

Optical properties of Mg0.05Zn0.95O/SiO2 nanocomposite films prepared by sol–gel technique

Mg_0.05Zn_0.95O/SiO₂ nanocomposite films in the molar ratio 25:75 consisting of Mg_0.05Zn_0.95O nanoparticles embedded in a dielectric matrix were prepared by sol–gel technique (spin coating). Optical transmittance, Raman effect and photoluminescence measurements of the composites indicated effective capping of the Mg_0.05Zn_0.95O nanoparticles (radii 1. 61–1.68 nm) in the host showing practically no variation of particle size with the post deposition annealing treatments. The blue shift of the band gap (4.29–4.23 eV) from that of bulk Mg_0.05Zn_0.95O indicated strong carrier confinement for samples annealed at T ≤ 873 K. Highly intense UV emission ( ∼ 4.14 eV) compared to that of defect related emission (2.59 eV) at room temperature was obtained by incorporating 5% Mg in ZnO.     

Electric-field gradients at Ta donor impurities in Cr2O3(Ta) semiconductor

We report perturbed-angular-correlation (PAC) experiments on ¹⁸¹Hf(→¹⁸¹Ta)-implanted corundum Cr₂O₃ powder samples in order to determine the magnitude and symmetry of the electric-field gradient (EFG) tensor at Ta donor impurity sites of this semiconductor. These results are analyzed in the framework of ab initio full-potential augmented-plane wave plus local orbitals (FP−APW+lo) calculations. The results are also compared with EFG results coming from PAC experiments in isomorphous α-Al₂O₃ and α-Fe₂O₃ doped with ¹¹¹In→¹¹¹Cd and ¹⁸¹Hf→¹⁸¹Ta tracers. This combined analysis enables us to quantify the magnitude of the lattice relaxations induced by the presence of the impurity and to determine the charge state of the impurity donor level introduced by Ta in the band gap of the semiconductor.     

Anodization of aluminium thin films on pSi and annihilation of strong luminescence from Al2O3

Photoluminescence (PL) of Al₂O₃ films obtained by anodization of thermally evaporated and annealed thin Al films on p⁺⁺Si in 0.3 M oxalic acid has been investigated. Thermal annealing at 200–950 °C under the dry nitrogen atmosphere was used for deactivation of luminescence centres. Luminescence from as grown films was broad and located at 425 nm. This luminescence reached to highest level after annealing at 600 °C. Maximum 10 min was required for full optical activation and prolonged annealing up to 4 h did not change the luminescence intensity. Because of deep levels, absorption band edge of as grown films was shifted to the lower energy which is 3.25 eV. Annealing above 800 °C reduced the PL intensity and this observation was correlated with the blue shift of band edge as the defects annealed out. Disappearing PL intensity and blue shift of band edge absorption after annealing at 950 °C was mainly attributed to the oxygen-related defects and partly to impurities that may be originated from oxalic acid. AFM results did not show any hexagonally ordered holes but uniformly distributed nanosized Al₂O₃ clusters that were clearly seen. XRD measurements on as grown Al₂O₃ showed only [1 1 0] direction of α phase. Debye–Scherer calculation for this line indicates that cluster size is 35.7 nm. XRD and AFM pictures suggest that nanocrystalline Al₂O₃ are embedded in amorphous Al₂O₃.     

Luminescence studies on ZnO-P2O5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Zinc phosphate glasses doped with Gd₂O₃:Eu nanoparticles and Eu₂O₃ were prepared by conventional melt-quench method and characterized for their luminescence properties. Binary ZnO-P₂O₅ glass is characterized by an intrinsic defect centre emission around 324 nm. Strong energy transfer from these defect centres to Eu³⁺ ions has been observed when Eu₂O₃ is incorporated in ZnO-P₂O₅ glasses. Lack of energy transfer from these defect centres to Eu³⁺ in Gd₂O₃:Eu nanoparticles doped ZnO-P₂O₅ glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between the luminescent centre and Eu³⁺ ions. Both doped and undoped glasses have the same glass transition temperature, suggesting that the phosphate network is not significantly affected by the Gd₂O₃:Eu nanoparticles or Eu₂O₃ incorporation.     

An easy and novel approach for the decoration of graphene oxide by Fe3O4 nanoparticles

A new and relatively general route was developed to fabricate graphene oxide (GO)-Fe₃O₄ hybrid. X-ray diffraction, transmission electron morphology, X-ray photoelectron spectroscopy (XPS) and energy-dispersive spectrum were used to demonstrate the successful attachment of iron oxide nanoparticles to GO sheets. Transmission electron microscopy observation indicates that the size of the Fe₃O₄ nanoparticles was about 2.7 nm with narrow size distribution. Moreover, this hybrid shows superparamagnetic property and allows the rapid separation under an external-magnetic field. In addition, the method could be extended to further development of graphene-based nanoelectronics.     

Optical properties of (ZnO)0.5(P2O5)0.5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Binary (ZnO)_0.5(P₂O₅)_0.5 glasses doped with Eu₂O₃ and nanoparticles of Gd₂O₃:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO)_0.5(P₂O₅)_0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na₂O-SiO₂ glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu³⁺ ions leading to improved Eu³⁺ luminescence from such glasses. Based on the decay curves corresponding to the ⁵D₀ level of Eu³⁺ ions in both Gd₂O₃:Eu nanoparticles incorporated as well as Eu₂O₃ incorporated glasses, a significant clustering of Eu³⁺ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO)_0.5(P₂O₅)_0.5 glass doped with Gd₂O₃:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu³⁺ ions. Poor energy transfer from the defect centres to Eu³⁺ ions in Gd₂O₃:Eu nanoparticles doped (ZnO)_0.5(P₂O₅)_0.5 glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between luminescent centre and Eu³⁺ ions.     

A novel chemical synthesis and characterization of Mn3O4 thin films for supercapacitor application

Mn₃O₄ thin films have been prepared by novel chemical successive ionic layer adsorption and reaction (SILAR) method. Further these films were characterized for their structural, morphological and optical properties by means of X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), field emission scanning electron microscopy (FESEM), wettability test and optical absorption studies. The XRD pattern showed that the Mn₃O₄ films exhibit tetragonal hausmannite structure. Formation of manganese oxide compound was confirmed from FTIR studies. The optical absorption showed existence of direct optical band gap of energy 2.30 eV. Mn₃O₄ film surface showed hydrophilic nature with water contact angle of 55°. The supercapacitive properties of Mn₃O₄ thin film investigated in 1 M Na₂SO₄ electrolyte showed maximum supercapacitance of 314 F g⁻¹ at scan rate 5 mV s⁻¹.     

Infrared (IR) stimulated luminescence from αAl2O3:C

Infrared (IR) stimulated luminescence from α---Al₂O₃:C single crystals was investigated. The data show that the IR-stimulated luminescence curve contains at least two overlapping signals. One of the components was found to be both thermally and optically unstable whereas the second component was thermally stable and slowly decaying under constant stimulation. The slow decaying component was found to be very sensitive to radiation dose. It was found that doses smaller than 1 mGy could be measured and the luminescence could be read several times without significant depletion of the signal.