Influence of fuels on the morphology of undoped Y3Al5O12 and photoluminescence of Y3Al5O12:Eu prepared by a combustion method

Undoped and Eu-doped yttrium aluminum garnet nano-powders were prepared by a facile combustion method with citric acid/ethylene diamine tetraacetic acid (EDTA) as fuels and nitrates as oxidizers. The precursors and powders calcined at 1030 °C were investigated using thermogravimetric (TG), differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscope (SEM), and Brunauer-Emmett-Teller (BET) surface area measurements. It was found that the powders could be indexed with a garnet structure. The grains were in shape of hemispherical with sizes between 60 nm and 100 nm. With decreasing the citric acid/EDTA ratio, the crystallite size decreased steadily and the specific surface area increased. Investigations of photoluminescence (PL) revealed that as-synthesized YAG:Eu³⁺ phosphor samples exhibited an orange emission band with a main peak at 591 nm under the excitation of 394 nm. As citric acid amounts increased, the quality of crystallinity became higher and the luminescent properties were monotonously enhanced.     

Low-temperature synthesis and characterization of yttrium-gallium garnet Y3Ga5O12 (YGG)

To obtain yttrium-gallium garnet (Y₃Ga₅O₁₂, YGG) a simple “chimie douce” method has been developed. This sol-gel method yielded excellent starting gel precursor for the fabrication of YGG phase, which could be used as host material for optical applications. The pattern of X-ray diffraction analysis of the ceramic sample sintered for 10 h at 1000 °C showed the formation of monophasic Y₃Ga₅O₁₂ phase. The phase transformations, composition and micro-structural features in the gels and polycrystalline sample were studied by thermoanalytical methods (TGA/DTA), powder X-ray diffraction analysis (XRD), infrared spectroscopy (IR) and scanning electron microscopy (SEM). The quality of the resulting products (homogeneity, crystallisation temperature, grain size, grain size distribution, etc.) is discussed.     

Preparation and characterization of porous ultrafine Fe2O3 particles

Porous ultrafine Fe₂O₃ particles were prepared by homogeneous precipitation method. Fe³⁺ and urea were chosen as starting materials and anionic surfactant as the template. It is shown that the reaction results in the precipitation of a gelatinous hydrous iron oxide/surfactant mixture, which gives ultrafine Fe₂O₃ particles after drying and calcinations. The products were characterized by XRD, TEM, TG/DTA and BET. Conventional XRD patterns show that the products are mixture of γ-Fe₂O₃ and α-Fe₂O₃ phase after being sintered at 350 °C, and γ-Fe₂O₃ transforms entirely to α-Fe₂O₃ when sintered at 650 °C. The low-angle XRD patterns indicate that the mesostructure can only exist between 350 and 400 °C. TEM results show that the Fe₂O₃ particles have diameters of about 30 nm and lengths ranging from 100 to 120 nm; in each particle, there are several vermiculate-like mesopores with diameter of about 20-25 nm. The BET surface areas in excess of 50 m²/g are obtained after calcinations at 350 °C. The BJH desorption average pore width is around 22 nm, which is in agreement with the TEM results. The results show that anionic surfactant and sintering temperature are important to obtain this special morphology.     

Growth of Yb-doped Y2O3 single crystal rods by the micro-pulling-down method

The rare-earth sesquioxides (RE₂O₃, RE = Lu, Y and Sc) are very promising host crystals for advanced laser diode (LD)-pumped Yb³⁺-doped solid-state lasers due to unusual combination, almost unique of favourable structural, thermal and spectroscopic properties which are described. In spite of these favourable properties, the bulk single crystal growth technology for the rare-earth sesquioxides has not been established yet. The extremely high melting temperature at around 2400 °C has prevented it. However, we shall show that yttrium oxide crystals (Yb_xY_1−x)₂O₃, x = 0.0, 0.005, 0.05, 0.08 and 0.15 of cylindrical shape as laser rods with 4.2 mm in diameter and 15-20 mm in length have been grown from rhenium crucibles by the micro-pulling-down method. The crystal quality characterisation of undoped Y₂O₃ crystal was determined using X-ray rocking curve (XRC) analysis. Yb were homogeneously distributed in Y₂O₃ host crystal.     

Synthesis and formation mechanism of Cu3V2O7(OH)2·2H2O nanowires

Cu₃V₂O₇(OH)₂·2H₂O nanowires have been synthesized in high yield through a simple and facile low-temperature hydrothermal approach without any template or surfactants. XRD, TG, FE-SEM, TEM and HRTEM were used to characterize the product. The results indicated that the product consisted of wirelike crystals about 80 nm in diameter and length up to several micrometers. The formation of wirelike structure of Cu₃V₂O₇(OH)₂·2H₂O depended crucially on the reaction time and pH value of the precursor suspensions. The optical absorption spectrum indicates that the Cu₃V₂O₇(OH)₂·2H₂O nanowires have a direct band gap of 1.94 eV.     

Hydrothermal synthesis of nanocrystalline VO2 from poly(diallyldimethylammonium) chloride and V2O5

Novel vanadium dioxide nanorods were fabricated from V₂O₅ in the presence of a reducing agent, the poly(diallyldimethylammonium chloride) (PDDA) via a hydrothermal method at 180 °C for 48 h. The samples produced were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared spectroscopy (FTIR), nitrogen adsorption (BET) and thermogravimetry (TG/DTG). The nanorods obtained are approximately 50 nm wide and from 300 to 500 nm long and presents high surface area (42 m² g⁻¹). The nanocrystalline B phase VO₂ is not produced by hydrothermal treatment in the absence of the PDDA polyelectrolyte.     

Controlled synthesis of Mn3O4 and MnCO3 in a solvothermal system

Controlled synthesis of Mn₃O₄ nanocrystals and MnCO₃ aggregates was achieved by a facile solvothermal method using different divalent manganese source in the solvent of N,N-dimethylformamide (DMF) with/without the introduction of poly(vinylpyrrolidone) (PVP). PVP was used as a co-reducing reagent in the controlled formation of MnCO₃ crystal. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED), Fourier transform infrared (FTIR) spectra, Raman spectrum and magnetic measurement. Higher process temperature and longer solvothermal time were favorable for the formation of MnCO₃ single phase using MnCl₂ as the manganese source. Mn₃O₄ nanocrystals were prepared at a relatively lower temperature. MnCO₃ aggregates consisted by small nanoparticles have a certain orientation, showing that the nanocrystals formed earlier through oriented aggregation. The size of Mn₃O₄ nanocrystals was 22.5 ± 7.3 nm and 7.3 ± 1.4 nm prepared using MnCl₂ and Mn(CH₃COO)₂, respectively, at 160 °C for 24 h. Raman spectra showed size-dependent characteristics. Smaller Mn₃O₄ nanoparticle resulted in a red-shift in Raman spectra. Magnetic property of the prepared Mn₃O₄ nanoparticle was influenced by the size distribution and crystallinity.     

Low-temperature sintering characteristics of nano-sized BaNd2Ti5O14 and Bi2O3–B2O3–ZnO–SiO2 glass powders prepared by gas-phase reactions

Nano-sized BaNd₂Ti₅O₁₄ (BNT) powders were prepared by spray pyrolysis from solutions containing ethylenediaminetetraacetic acid and citric acid. Treatment at temperatures ≥900 °C and subsequent milling resulted in nanoparticle powders with orthorhombic crystal structures. The mean particle size of the powder post-treated at 1000 °C was 160 nm. Nano-sized Bi₂O₃–B₂O₃–ZnO–SiO₂ glass powder with 33 nm average particle size was prepared by flame spray pyrolysis and used as a sintering agent for the BNT. BNT pellets sintered at 1100 °C without the glass had porous structures and fine grain sizes. Those similarly sintered with the glass had denser structures and larger grains.     

Synthesis of submicron-sized spherical Y2O3 powder for transparent YAG ceramics

Spherical monodispersed, submicron-sized Y₂O₃ powder was prepared via a homogeneous precipitation method using nitrate and urea as raw materials. The structure, phase evolution and morphology of Y₂O₃ precursor and the calcined powder were studied by FTIR, TG/DTA, XRD and SEM methods. The sphere size of the precursor was about 250 nm and that of Y₂O₃ powder calcined at 800 °C for 2 h was about 200-210 nm. With the spherical Y₂O₃ powder and a commercial Al₂O₃ ultrafine powder, high transparent YAG ceramics was fabricated by vacuum sintering at 1780 °C for 6 h through a solid-state reaction method. The in-line transmittances of the as-fabricated YAG ceramics at the wavelength of 1064 nm and 400 nm were 82.8% and 79.5%, respectively, which were much higher than that of the YAG ceramics with a commercial Y₂O₃ powder and a commercial Al₂O₃ ultrafine powder directly. The superior properties are attributed to the good morphology, dispersibility and uniform grain size of the as-prepared spherical Y₂O₃ powder, which matches that of the commercial Al₂O₃ powder.     

Preparation and characterization of sol-gel derived ZnTiO3 nanocrystals

Nanometer scale cubic ZnTiO₃ has been synthesized by sol-gel method at a lower temperature (600 °C). X-ray diffraction (XRD) analysis shows that the average crystalline size of the sample is ∼8-10 nm. The cubic to hexagonal phase transition of ZnTiO₃ is clearly observed from the XRD patterns of the sample. The thermal behavior of the sample was characterized by the thermogravimetric/differenthermal analysis (TG/DTA), XRD patterns, and the infrared spectra (IR). Transmission electron microscope (TEM) observations of the sample reveal a high microstructural uniformity.     

Preparation of Y2O3-Al2O3-SiO2 glasses by combustion synthesis melt-casting under high gravity

Y₂O₃-Al₂O₃-SiO₂ glasses were prepared by combustion synthesis melt-casting under high gravity. The properties of the glasses strongly depended on the starting compositions and preparation conditions. With a higher SiO₂ content in the starting compositions, the glass-forming ability of the melt was improved, but the density and hardness of the prepared glasses decreased. Crystallization occurred more frequently for larger samples and by using quartz crucibles instead of graphite ones. By increasing the high-gravity factors, both the density and hardness of the samples were improved. It is proposed that enhancing the high-gravity field facilitates the removal of bubbles from the melt.     

Preparation and properties of nickel ferrite (NiFe2O4) nanoparticles via sol-gel auto-combustion method

Using nickel and ferric nitrates and citric acid, NiFe₂O₄ nanoparticles are prepared by a simple and cost-effective polyvinylpyrrolidone (PVP) assisted sol-gel auto-combustion method. The synthesised nanoparticles consist of single phase inverse spinel structure of NiFe₂O₄. The particles are in spherical shape with an average size of ∼8 nm. The vibrational properties show tetrahedral and octahedral sites of NiFe₂O₄ nanoparticles. The super-paramagnetism is observed with magnetic saturation (M_s) of 50.4 emug^−1.     

Low-temperature synthesis,phonon and luminescence properties of Eu doped Y3Al5O12 (YAG) nanopowders

This contribution presents two simple and cost-effective routes for the low-temperature and large-scale production of pure and Eu-doped Y₃Al₅O₁₂ (yttrium aluminum garnet YAG) nanopowders. The proposed methodologies combine a mechanically assisted metathesis reaction or coprecipitation from solution followed by crystallization of the obtained precursors from molten sodium nitrate/nitrite. Both procedures allow obtaining pure and/or doped YAG nanopowders at remarkably low temperatures, i.e. already at 350 °C although firing at 500 °C is needed in order to get single phase and fully crystalline materials. As-obtained samples were characterized by XRD, TEM, Raman, IR and luminescence methods. These methods showed that the mean crystallite size is near 23–31 and 51 nm, when crystallization is performed from the amorphous precursor obtained by a mechanically assisted metathesis reaction and coprecipitation, respectively. Raman and IR spectra indicated better crystallinity of the powders prepared at 500 °C. The emission study showed that the intensity ratio between hypersensitive ⁵D₀ → ⁷F₂ and magnetic-dipole ⁵D₀ → ⁷F₁ transitions of Eu³⁺ is significantly larger than expected for well-crystallized YAG. Origin of this behavior is discussed.     

Preparation of KMgF3 and Eu-doped KMgF3 nanocrystals in water-in-oil microemulsions

In this study, KMgF₃:Eu²⁺ luminescent nanocrystals (NCs) were prepared in water/cetyltrimethylammonium bromide (CTAB)/2-octanol microemulsions. The KMgF₃:Eu²⁺ NCs were characterized by transmission electron microscopy (TEM), X-ray diffractometer (XRD), fluorescence spectrum, infrared spectroscopy (IR) and elementary analysis. The results showed that the size of the KMgF₃:Eu²⁺ NCs was hardly affected by water content and surfactant (CTAB) concentration. The emission spectrum showed that the position of the 362 nm peak is due to the K⁺ sites substituted Eu²⁺. Two emission peaks located at 589 and 612 nm can be attributed to Eu³⁺, which exist at two different types of Eu³⁺ centers: one is Eu³⁺ at a K⁺ site, the other is clustering of Eu³⁺ ions in the interstices of KMgF₃ host lattice.     

Polyol method for the preparation of nanosized Gd2O3, boehmite and other oxides

A modified microwave-assisted polyol method was applied to prepare nanoparticulate ceramic powders of different oxides, i.e. Gd₂O₃, AlO(OH) (boehmite) and TiO₂. Due to the good dielectric properties of the utilised solvents, such as ethylene glycol, diethylene glycol and 1,4 butanediol, a significant decrease in reaction time was achieved under microwave heating. In the case of AlO(OH) and Gd₂O₃, <5 nm primary particle size were obtained. Boehmite was found to be intercalated with the solvent. The general applicability of the process is shown and the advantages in terms of properties and processibility are described. The powders thus prepared were investigated using X-ray diffractometry, electron microscopy and physisorption.     

Synthesis and high-pressure sintering of (W0.5Al0.5)C

A new solid solution of Al in WC, which can be expressed by the chemical formula (W_0.5Al_0.5)C, has been synthesized directly by reaction milling (RM) of a W_0.5Al_0.5 alloy and the proper amount of carbon. The total reaction time is about 50 h. The ESEM photograph shows that the prepared (W_0.5Al_0.5)C powders are spherical, and the average particle size is about 40 nm. (W_0.5Al_0.5)C has been identified to crystallize in the hexagonal space group P-6m2 (No.187) and belongs to the WC structure type. The lattice parameter of (W_0.5Al_0.5)C is calculated to be a = 2.908(1) Å, c = 2.836(1) Å. This nanocrystalline powder can be well sintered at the high temperature (1600 °C) under the high pressure (4.5 GPa), and the relative density reaches 99.1%. The hardness of the sintered (W_0.5Al_0.5)C is tested to be 1500 ± 50 kg mm⁻², while the density is about 9.417 ± 0.003 g cm⁻³, which is far lower than that of WC.     

Microwave-assisted synthesis of cobalt oxalate nanorods and their thermal conversion to Co3O4 rods

Cobalt oxalate nanorods have been successfully synthesized by a simple microwave-assisted solution approach using an ionic liquid 1-n-butyl-3-methyl imidazolium tetrafluoroborate. Upon thermal decomposition at 400 °C, cobalt oxalate nanorods could be converted to Co₃O₄ rods consisting of nanoparticles. The products were characterized using X-ray powder diffraction, transmission electron microscopy, thermogravimetric analysis and differential scanning calorimetric analysis.     

Synthesis and photoluminescence of nano-Y2O3:Eu phosphors

We report nano-Y₂O₃:Eu³⁺ phosphors with particle size of about 50 nm and relatively high photoluminescence (PL) intensity which is close to the standard for application. The influences of the dope amount, the surfactant and the precipitation pH on the PL intensity, the particle size and the dispersion have been studied. It has been found that 4% is the best Eu³⁺ molar concentration to get the highest PL intensity for both nano- and micro-Y₂O₃:Eu³⁺. The addition of butanol as a surfactant inhibits the grain growth and the agglomeration of particles efficiently by reducing the oxygen bridge bonds. As the pH rises, the PL intensity and the particle size increase due to the formation of oxygen bridge bonds.     

High sensitivity chlorine gas sensors using CdIn2O4 thick film prepared by co-precipitation method

Gas-sensing properties to dilute Cl₂ have been investigated for CdIn₂O₄ thick film sensors prepared by co-precipitation method. Cadmium nitrate and indium nitrate were mixed in de-ionized water. The 0.1 M NaOH was added to the mixed solution. The co-precipitate obtained was washed, filtered, dried, and calcined at 600-900 °C for 4 h. The CdIn₂O₄ sensor prepared using the powder calcined at 600 °C showed high sensitivity (S=R_g/R_a) to dilute Cl₂ at 250 °C. In particular, the CdIn₂O₄ sensor showed the sensitivity as high as 1200 even to 0.2 ppm Cl₂. The crystal structure and surface morphology were examined by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively.     

Heterostructured Fe3O4/Bi2O2CO3 photocatalyst: Synthesis,characterization and application in recyclable photodegradation of organic dyes under visible light irradiation

Heterostructured Fe₃O₄/Bi₂O₂CO₃ photocatalyst was synthesized by a two-step method. First, Fe₃O₄ nanoparticles with the size of ca. 10 nm were synthesized by chemical method at room temperature and then heterostructured Fe₃O₄/Bi₂O₂CO₃ photocatalyst was synthesized by hydrothermal method at 180 °C for 24 h with the addition of 10 wt% Fe₃O₄ nanoparticles into the precursor suspension of Bi₂O₂CO₃. The pH value of synthesis suspension was adjusted to 4 and 6 with the addition of 2 M NaOH aqueous solution. By controlling the pH of synthesis suspension at 4 and 6, sphere- and flower-like Fe₃O₄/Bi₂O₂CO₃ photocatalysts were obtained, respectively. Both photocatalysts demonstrate superparamagnetic behavior at room temperature. The UV–vis diffuse reflectance spectra of the photocatalysts confirm that all the heterostructured photocatalysts are responsive to visible light. The photocatalytic activity of the heterostructured photocatalysts was evaluated for the degradation of methylene blue (MB) and methyl orange (MO) in aqueous solution over the photocatalysts under visible light irradiation. The heterostructured photocatalysts prepared in this study exhibit highly efficient visible-light-driven photocatalytic activity for the degradation of MB and MO, and they can be easily recovered by applying an external magnetic field.