White light upconversion of nanocrystalline Er/Tm/Yb doped tetragonal Gd4O3F6

Er³⁺, Tm³⁺ and Yb³⁺ codoped gadolinium oxyfluoride nanoparticles were prepared in aqueous solution by a simple coprecipitation method, under alkaline conditions. After a suitable heat treatment at 500 °C, the nanocrystalline powders were found to be single phase tetragonal Gd₄O₃F₆ after a structural characterization using X-ray powder diffraction. Transmission electron microscopy images showed that the average size of the nanoparticles was approximately 50 nm. Following appropriate lanthanide ion doping, the nanocrystals show bright white light upconversion upon excitation at 980 nm using a diode laser as the excitation source.     

A simple route to prepare nanocrystalline titanium carbonitride

Nanocrystalline titanium carbonitride, TiC_0.7N_0.3, has been synthesized directly by a simple reaction route of TiCl₄ and C₃N₃C1₃ using sodium as the reductant at 600°C. The composition of the powders has been investigated by X-ray powder diffraction. Transmission electron microscopy image reveals that the average size of the obtained particles is about 30 nm.     

Synthesis and photoluminescence properties of CaSiO3:Eu spheres prepared by the reverse micelles soft template

We report here the successful synthesis of CaSiO₃:Eu³⁺ spheres using the reverse micelles soft template. The influence of the calcination temperature on the shape, crystallization and photoluminescence properties of the prepared spheres was investigated by DTA-TG, XRD, IR, SEM and PL. The results showed that the temperature of crystallization (from amorphous phase to β-CaSiO₃) is 668 °C. The temperature of phase transition (from β-CaSiO₃ to α-CaSiO₃) is 790 °C. The average size of CaSiO₃:Eu³⁺ spheres calcined at 700 °C was about 350 nm. The radiation was dominated by the red emission peak at 613 nm and the highest emission intensity was observed when the spheres were calcined at 700 °C. When calcined at 800 °C, the spheres are almost cracked and melted down, due to the high temperature.     

Continuous production of phosphor YAG:Tb nanoparticles by hydrothermal synthesis in supercritical water

Phosphor YAG:Tb ((Y_2.7Tb_0.3)Al₅O₁₂) nano particles were synthesized by a hydrothermal method at supercritical conditions (400 °C and 30 MPa) using a flow reactor. Hydroxide sol solutions formed by stoichiometric aluminum nitrate, yttrium nitrate, terbium nitrate and potassium hydroxide solutions. The relationship between particle size and experimental variables including pH, concentration of coexistent ions and hydroxide sol were investigated. Particles were characterized by XRD, TEM and photo-luminescence measurements. Particle size of YAG:Tb became finer as pH was increased or potassium nitrate concentration of the starting metal salt solution was increased. By removing the coexisting ions (NO₃⁻, K⁺) from the metal salt solution, single phase YAG:Tb particles with 20 nm particle size were obtained. The emission spectra of YAG:Tb particles of 14 nm shows a blue shift.     

Tin dioxide nanoparticles: Reverse micellar synthesis and gas sensing properties

Tin dioxide (SnO₂) nanoparticles have been synthesized by reverse micellar route using cetyltrimethyl ammoniumbromide (CTAB) as the surfactant. Monophasic tin dioxide (SnO₂) was obtained using NaOH as the precipitation agent at 60 °C, however, when liquor NH₃ was used as precipitating agent then crystalline SnO₂ nanoparticles are obtained at 500 °C. SnO₂ prepared using NaOH show crystallite size of 4 and 12 nm after heating at 60 and 500 °C respectively using X-ray line broadening studies. Transmission electron microscopy (TEM) studies show agglomerated particles of sizes 70 and 150 nm, respectively. The grain size was found to be 6-8 nm after heating the precursor obtained (using liquor NH₃) at 500 °C by X-ray line broadening and the TEM studies. Dynamic light-scattering (DLS) studies show the aggregates of SnO₂ nanoparticles with uniform size distribution. Mössbauer studies show an increase of s-electron density at the Sn sites compared to bulk SnO₂ and a finite quadrupole splitting indicative of lowering of symmetry around tin atoms. The gas sensing characteristics have also been investigated using n-butane which show high sensitivity and fast recovery time.     

Synthesis of nano-particles of anatase-TiO2 and preparation of its optically transparent film in PVA

Anatase-TiO₂ nano-particles have been synthesized by using long-carbon chain carboxylic acid and titanium tetrachloride (TiCl₄). As-prepared powder has been calcined at 500 °C to obtain highly crystalline TiO₂. Broad X-ray diffraction (XRD) pattern of as-prepared as well as calcined powder showed all prominent peaks for tetragonal crystal structure representing anatase-TiO₂. The particle diameter by applying Scherrer formula was found to be about 20 nm. It was possible to load as-prepared particles in poly vinyl alcohol (PVA) for optical studies. Optically transparent film showed sharp absorption band for TiO₂ nano-particles at ∼ 300 nm. Photoluminescence (PL) studies of the solution showed emission wavelength at about 330 nm. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) revealed that the particles in the film have uniform distribution and even for the powder no agglomeration was observed. Thermal analysis (TGA) showed that the stability of host polymer is enhanced. FTIR spectra showed presence of carboxylate functional group in the powder.     

Rapid synthesis of pure and narrowly distributed Eu doped ZnO nanoparticles by solution combustion method

Pure ZnO:Eu³⁺ nanoparticles (~ 50 nm) were prepared by a solution combustion method. ZnO and Eu₂O₃ were used as starting materials and dissolved in nitric acid. Citric acid was used as a fuel. The reaction mixture was heated at 350 °C resulting into a rapid exothermic reaction yielding pure nanopowders. The atomic weight concentration of Eu³⁺ doped in ZnO was 20%. Transmission electron microscopy (TEM) was used to study the particle size and morphology. The nanopowders were characterized for phase composition using X-ray diffractrometry (XRD). Particle size distribution (PSD) analysis of ZnO: Eu³⁺ showed particle sizes ranging from 30 to 80 nm.The photoluminescence emission spectra of ZnO:Eu³⁺ nanostructures showed a strong band emission around 618 nm when excited with 515 nm wavelength.     

Synthesis of uniformly porous NiO/ZrO2 particles

Porous NiO-ZrO₂ particles were successfully synthesized using a spray-drying method with polystyrene latex (PSL: 400 nm) as a template and starting materials that included NiO powder (7 nm) and ZrO₂ sol (1.2 nm). Porous particles with an average diameter of 4.5 μm and nearly spherical, narrow pores with an average size of ∼300 nm were obtained from the precursor at a pH of 3.7. The Brunauer, Emmett and Teller (BET) surface area of the prepared particles was relatively high—about 27 m²/g. When the solution pH was increased to 9.7, the particle morphology became completely spherical, indicating that the morphology of prepared particles can be controlled by adjusting the pH. Calcinations at 900 and 1200 °C were carried out to estimate the thermal stability of the prepared particles, which had shrinkage of less than 36%. The existence of these pores means that various applications, such as electrodes and catalysts, will be possible for the prepared particles.     

A novel method to low temperature synthesis of nanocrystalline forsterite

Nanocrystalline forsterite (Mg₂SiO₄) powder was synthesized using sucrose as a chelating agent and template material from an aqueous solution of magnesium nitrate and colloidal silica. The synthesized powders were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), simultaneous thermal analysis (STA), and scanning electron microscopy (SEM). The synthesized nano-powder had particle size smaller than 200 nm and average crystallite size of powders calcined at 800 °C for 3 h was in the range of 10-30 nm. Also the effect of addition 2 and 4 wt.% forsterite seed on nucleation temperature and crystallite size of forsterite was investigated. The presence of small amounts of Mg₂SiO₄ as seed obviously accelerated the crystallization of forsterite. According to DTA results the inceptive formation temperature of Mg₂SiO₄ without any seed was 760 °C, while this temperature for the specimen containing 4 wt.% seed was 700 °C.     

Synthesis of mesoporous hydroxyapatite using a modified hard-templating route

Mesoporous polycrystals of hydroxyapatite-calcium are synthesized via a modified hard-templating route. The structure properties of hydroxyapatite-calcium are characterized by means of X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and N₂ adsorption-desorption isotherms. Wide-angle X-ray diffraction and Fourier transform infrared spectroscopy measurements reveal that the crystalline grains consist of highly crystalline pure hydroxyapatite phases. Transmission electron microscopy results show that rod-like hydroxyapatite-calcium grains with an average diameter of about 100 nm long and about 20 nm wide are uniformly distributed, which are also observed with an average pore size of 2-3 nm. Based on N₂ adsorption-desorption isotherms investigation, the pore size, surface area and pore volume of mesoporous hydroxyapatite-calcium are 2.73 nm, 42.43 m² g⁻¹ and 0.12 cm³ g⁻¹, respectively.     

Synthesis and characterization of nanocrystalline MgAl2O4 spinel via sucrose process

Nanocrystalline MgAl₂O₄ spinel powder was synthesized using metal nitrates and a polymer matrix precursor composed of sucrose and polyvinyl alcohol (PVA). The precursor and the calcined powders were characterized by simultaneous thermal analysis (STA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to XRD results, the inceptive formation temperature of spinel via this technique was between 600 and 700 °C. The calcined powder at 800 °C for 2 h has faced shaped morphology and its crystallite size is in the range of 8-12 nm. Further studies also showed that the amount of polymeric matrix to metal ions has significant influence on the crystallite size of synthesized magnesium aluminate spinel powder.     

The hydrothermal synthesis of super-paramagnetic barium hexaferrite particles

Superparamagnetic Ba-hexaferrite nanoparticles were prepared using modified hydrothermal synthesis. The precursor and hydroxide [OH⁻] concentrations were optimized and the synthesis temperature and time were drastically reduced. The size and the morphology of synthesized nanoparticles was confirmed by transmission electron microscopy (TEM) images. The crystal structure of the nanoparticles was characterized by X-ray diffraction data. Powders synthesized at 160 °C exhibit a bimodal particle size distribution while those synthesized at T_S = 150 °C show a monomodal particle size distribution. Zero-field-cooling (ZFC) and field-cooling (FC) magnetization measurements were performed using a superconducting quantum interference device magnetometer from 2 to 300 K to investigate the magnetic properties of nanoparticles. The FC/ZFC magnetization measurements showed a typical superparamagnetic behavior. The synthesized superparamagnetic particles exhibit a disc-like shape, in average 11 nm wide and 3 nm thick with a room temperature magnetization of approximately 10 Am²/kg at 5 T.     

Synthesis of nanocrystalline Mn3O4 at 100 °C

A simple gel to crystal conversion route has been followed for the preparation of nanocrystalline tetragonal Mn₃O₄ powders at 80-100 °C under refluxing conditions. Freshly prepared manganese hydroxide gel is allowed to crystallize under refluxing and stirring conditions for 4-6 h. Formation of nano crystallites of Mn₃O₄ is confirmed by X-ray diffraction (XRD) study. Transmission electron microscope (TEM) investigations revealed that the average particle size is 50 nm for these powders.     

Wet chemical route to transparent BiFeO3 films on SiO2 substrates

BiFeO₃ nanoparticles were prepared by a wet chemical synthesis method. Transparent films were deposited on glass and quartz substrates by dip and spin coating processes from the synthesized sol. We obtained thicker films (~ 2 µm) by dip coating process and thinner films (~ 200 nm) by spin coating process. Transmission electron microscopy images confirmed that the particles are nanocrystalline in size. From the optical transmittance spectra the band gap of the BiFeO₃ nanoparticles was determined in the range of ~ 3.03-2.88 eV (~ 410-430 nm). Electrical resistivity, polarization, zero-field-cooled and field-cooled magnetizations versus temperature characteristics were also studied for these films.     

Synthesis of nanocrystalline xCuFe2O4-(1 − x)BiFeO3 magnetoelectric composite by chemical method

xCuFe₂O₄-(1 − x)BiFeO₃ spinel-perovskite nanocomposites with x = 0.1, 0.2, 0.3 and 0.4 were prepared using citrate precursor method. X-ray diffraction (XRD) analysis showed phase formation of xCuFe₂O₄-(1 − x)BiFeO₃ calcined at 500 °C. Transmission electron microscopy (TEM) shows formation of nanocrystallites of xCuFe₂O₄-(1 − x)BiFeO₃ with an average particle size of 40 nm. Variation of dielectric constant and dielectric loss with frequency showed dispersion in the low frequency range. Coercivity, saturation magnetization and squareness have been found to vary with concentration of ferrite phase and annealing temperature due to the increase in crystallite size. Squareness and coercivity increased with an increase in annealing temperature up to 500 °C and then decreased with a further increase in temperature to 600 °C. Magnetoelectric effect of the nanocomposites was found to be strongly depending on the magnetic bias and magnetic field frequency.     

Low temperature combustion synthesis of CoxMg1−xAl2O4 nano pigments using oxalyldihydrazide as a fuel

Oxalyldihydrazide as a fuel was used to prepare new nano size blue refractory ceramic pigments MgAl₂O₄: xCo²⁺ (0.00 ≤ x ≤ 0.10) using low temperature combustion synthesis (LCS) method. The synthesized and calcined powders were characterized by Fourier transform infra red (FTIR) spectrometry, electronic spectra, thermogravimetry, differential thermogravimetry, differential thermal analysis, X-ray diffraction (XRD) analysis, and transmission electron microscopy (TEM). Also, the color measurements of nano pigments are studied by diffuse reflectance spectroscopy (DRS) using CIE-L*a*b* parameter method. The FTIR spectra show frequency bands in range the 422–700 cm⁻¹ correspond to metal oxygen bonds through vibrations for the spinel structure compound. The average particle size of prepared samples as determined from XRD and TEM was 30 nm at 1100 °C. Also, the results revealed the varying bulk density, particle size, shape and color with different calcination times and temperatures.     

The effect of Tb doping on the structure and spectroscopic properties of MgAl2O4 nanopowders

In this paper, a modified sol-gel method was employed to prepare nanostructured MgAl₂O₄ spinel powders doped with Tb³⁺ ions and thermally treated at 700 and 1000 °C for 3 h. The structural properties of the prepared at 700 and 1000 °C powders where characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). According to obtained XRD patterns the formation of single-phase spinels after calcination was confirmed. The XRD analyses demonstrated that the powders were single-phase spinel nanopowders with high crystallite dispersion. The Rietveld method was applied to calculate lattice parameters. The averaged spinel particle size was determined to be ∼10 nm for calcination at 700 °C and ∼20 nm at 1000 °C. The emission and excitation spectra measured at room and low temperature (77 K) for the samples calcined at 700 and 1000 °C demonstrated characteristic spectra of Tb³⁺ ions. The effect of MgAl₂O₄:Tb³⁺ grain sizes on luminescence properties was noticed.     

Mixture of fuels approach for the solution combustion synthesis of Al2O3-ZrO2 nanocomposite

A modified solution combustion approach was used for the first time in the preparation of nanosize zirconia toughened alumina (ZTA) composite. ZTA-1 with an average particle size of ∼37 nm was prepared using corresponding metal nitrates and urea. ZTA-2 with an average particle size of <10 nm was prepared by using mixture of fuels such as ammonium acetate, urea and glycine. The products formed were characterised by powder X-ray diffractometry, Transmission electron microscopy and BET surface area analysis. By using mixture of fuels, the energetics of the combustion reaction and eventually the properties of the combustion product have been changed. A series of combustion reactions were carried out to optimise the fuel ratio combinations required to obtain <10 nm ZTA particles. The microstructure of ZTA consisted of crystallites of Al₂O₃ and ZrO₂ both of which were nanocrystalline as evident from TEM.     

Low temperature synthesis of h-BN nanoflakes

Boron nitride (BN) with flake-like morphology has been synthesized by reacting powder H₃BO₃, Mg and NH₄Cl in an autoclave at 600 °C for 10 h. X-ray diffraction (XRD) patterns show the sample has hexagonal phase with lattice parameters a = 2.506 and c = 6.692 Å. Transmission electron microscopy (TEM) and field emission scanning electron (FE-SEM) indicate the as-synthesized product is pure flake with a mean size of about 100 nm in thickness and 600 nm in width length. X-ray photoelectron spectra (XPS) give an average B/N atomic ratio of 0.98:1. Fourier transformation infrared spectroscopy (FTIR) has a strong B-N absorption at 1376 cm^− 1 and 814 cm^− 1.     

Synthesis of pure anatase TiO2 nanocrystals in SiO2 host and the determination of crystal planes by ImageJ

Anatase TiO₂ nanocrystals in the TiO₂- SiO₂ matrix were prepared by the ultra hydroylsis sol-gel route. The samples were heat treated at 350 °C and 500 °C. The structural analyses of the samples were carried out using X-ray diffraction technique, Raman spectroscopy and Transmission electron microscopy. The size of the nanocrystals from the XRD spectra (8.3 nm) and TEM (5-8 nm) is well in agreement. The spacing for the crystal planes was also determined using the ImageJ program. The Raman peaks further confirmed the formation of only the anatase phase within the matrix.