Low temperature reduction route to synthesise bismuth telluride (Bi2Te3) nanoparticles: structural and optical studies

Herein, we report the synthesis of highly yielded bismuth-telluride (Bi₂Te₃) nanoparticles at 50 °C by direct wet chemical route in which the bismuth and tellurium precursors have been dissolved in deionised water, ethylene glycol and hydrazine hydrate. This method is very facile, inexpensive and less hazardous and ensures almost complete yield of the precursors. The powder product was well characterised by powder X-ray diffraction, UV-Vis spectroscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray diffraction, transmission electron microscopy and scanning electron microscopy. It is investigated that the synthesised powder has a rhombohedral structure of Bi₂Te₃ with average diameters of the particles about 35 nm. Thus, the synthesis process has been modified to design nanostructures of thermoelectric materials with related crystal structures.     

Shape controlled synthesis and photoluminescence properties of Eu3+-doped REVO4 nanophosphors

Eu3+-doped REVO4 nanphosphors were controllably synthesized by an EDTA-mediated hydrothermal method at 180 degrees C using RE(NO3)3 and Na3VO4 as precursors. The obtained products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectra (XPS), and photoluminescence spectroscopy (PL). The XRD results showed that the products were pure tetragonal structure and no other impurity phase appeared. The PL studies demonstrated Eu3+ ions doping effectively enhanced luminescent properties of LaxRE(1-x)VO4 and YxRE(1-x)VO4 nanoparticles, but EU3+ ions doping did not enhance luminescent properties of CexRE(1-x)VO4 (x not equal 0) nanoparticles. The prepared phosphors showed well-defined red luminescence due to radiative transitions from 5D0 to 7F(J) (J = 1,2) levels of Eu3+ ions, respectively. Furthermore, we reported Eu3+-doped CexRE(1-x)VO4 (x not equal 0) phases represented a new class of optically inactive materials.     

Hydrothermal synthesis of Eu3+-doped Y2Sn2O7 nanocrystals

Fine powders of Y₂Sn₂O₇ nanocrystals with pyrochlore structure have been successfully synthesized by the hydrothermal method in an alkaline system. The samples were characterized by X-ray diffraction, Fourier transform infrared and Raman spectroscopy. Furthermore, photoluminescence characterization of the Y₂Sn₂O₇ nanocrystals doped with 5 mol% Eu³⁺ was carried out, and the results show that there were some intense and prevailing emission peaks located at 580–635 nm.     

Structural,optical and magnetic characterisation of bifunctional core shell nanostructure of Fe3O4/CdS synthesised using a room temperature aqueous route

An aqueous route for the synthesis of bifunctional iron oxide hybrid core shell using CdS as the shell materials has been described. The as-grown particles have been characterised using X-ray diffraction, high resolution transmission electron microscopy (HRTEM), superconducting quantum interference device, optical absorbance and photoluminescence spectroscopy. HRTEM images demonstrated successful formation of the core–shell structure. The as-grown core shell structures have been shown to be strongly photoluminescent while retaining the room temperature superparamagnetic behaviour of the ferric oxide core.     

Hydrothermal synthesis and luminescent properties of GdVO4 : Eu3+ nanophosphors

Eu³⁺-doped GdVO₄ has been synthesised via hydrothermal method by altering the hydrothermal temperature, reaction time and surfactant. The microstructure and morphology information of the phosphors were investigated via the techniques of X-ray powder diffraction and scanning electronic microscopy, which show that the phosphors wear tetragonal phase and the products present various regular morphologies under different reaction conditions such as bulk and nanoparticle. Moreover, the morphologies of the products have been controlled by altering reaction temperature. In addition, the surfactant was also included to control the morphologies of the products and the phosphors present different morphologies. All the phosphors exhibit the characteristic fluorescence of Eu ion (⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₂). The electric dipole transition ⁵D₀ → ⁷F₂ of Eu³⁺ is dominant indicating that most sites of Eu³⁺ ions in GdVO₄ have no inversion centre. Furthermore, we found that the reaction time and the morphologies have great influence on optical properties.     

Optical properties and luminescence dynamics of Eu3+-doped terbium orthophosphate nanophosphors

The development of luminescent inorganic nanocrystals (NCs) doped with rare-earth (RE) ions has attracted increasing interest owing to their distinct optical properties and versatile applications in time-resolved bioassays, multiplex biodetection, DNA hybridization and bioimaging. Hexagonal TbPO4:Eu3+ NCs (10-30 nm) were synthesized via a facile hydrothermal method assisted with oleic acid (OA) surfactants, which exhibit tunable emissions from green to red by varying the concentration of Eu3+. The Tb3+-to-Eu3+ energy transfer efficiency observed reaches up to 94%. Different from their bulk counterparts, a new interface-state band (316 nm) in addition to the commonly observed spin-forbidden 4f-5d transition band (265 nm) of Tb3+ was found to be dominant in the excitation spectrum of NCs due presumably to the formation of surface TbPO4/OA complexes, which provides an additional excitation antenna in practical utilization. Two kinds of luminescence sites of Eu3+ in TbPO4 NCs, with the site symmetry of C2 or C1, were identified based on the emission spectra at 10 K and room temperature. Furthermore, the photoluminescence (PL) dynamics of Tb3+ ions in pure TbPO4 NCs have been revealed. Compared to the exponential PL decay in bulk counterparts induced by very fast energy migration, the non-exponential decay from 5D4 of Tb3+ in TbPO4 NCs is mainly attributed to the diffusion-limited energy migration due to more rapid energy transfer from Tb3+ to defects than the energy migration among Tb3+.     

Controlled fabrication of SrMoO4 hierarchical nanosheets in a surfactant-assisted nonaqueous system

Various hierarchical architectures of SrMoO₄ nanosheets (thickness of 8-9 nm) have been successfully prepared in nonaqueous system by a surfactant-assisted solvothermal method. X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy were employed to study the crystal structure and morphologies of the products. Experiments showed that the solvent, surfactant, reaction temperature and reaction time were crucial for the oriented aggregation of the SrMoO₄ nanosheets. Morphological control of these parameters resulted in platelet, column, interlaced multilayer and nest of nanosheets. A possible growth mechanism for these hierarchical architectures has also been proposed according to the morphological evolution with the reaction time. The optical properties of the products were also examined by means of photoluminescence and excitation spectroscopy. Photoluminescence studies revealed that these SrMoO₄ nanocrystals exhibited a greatly strong blue emission under 325-nm excitation with different intensities but centered at the same position of 474 nm.     

Europium-doped yttrium silicate nanophosphors prepared by flame synthesis

Europium-doped yttrium silicate (Y₂SiO₅:Eu³⁺) nanophosphors were successfully synthesized by flame spray pyrolysis method. The effect of silicon concentration on the crystal structure and morphology of the Y₂SiO₅:Eu³⁺ phosphors were investigated. As-prepared phosphor consists of spherical nanoparticles with filled morphology, high crystallinity, narrow size distribution, and intense photoluminescence. The crystal structure and photoluminescence intensity of Y₂SiO₅:Eu³⁺ nanophosphors are strongly affected by the ratio of silicon to yttrium in the precursor solution, and the maximum photoluminescence intensity is obtained from particles prepared from the silicon to yttrium ratio of 1.25. A concentration quenching limit is observed at 30 mol% Eu of yttrium. The photoluminescence intensity also increases with the increase of the concentration of precursor solution. This work demonstrates the advantages of flame spray pyrolysis method for the preparation of multi-component nanophosphor, which can be found potential application in lamp and display industries.     

A novel single-step synthesis of N-doped TiO2 via a sonochemical method

A novel single-step synthetic method for the preparation of anatase N-doped TiO₂ nanocrystalline at low temperature has been devoleped. The N-doped anatase TiO₂ nanoparticles were synthesized by sonication of the solution of tetraisopropyl titanium and urea in water and isopropyl alcohol at 80 °C for 150 min. The as-prepared sample was characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and UV–vis absorption spectrum. The product structure depends on the reaction temperature and reaction time. The photocatalytic activity of the as-prepared photocatalyst was evaluated via the photodegradation of an azo dye direct sky blue 5B. The results show that the N-doped TiO₂ nanocrystalline prepared via sonication exhibit an excellent photocatalytic activity under UV light and simulated sunlight.     

Gd2O2S:Tb3+X-射线纳米荧光粉的燃烧法合成

采用燃烧法,以稀土硝酸盐和二硫代乙二酰胺为反应物,在点燃温度为300-350℃时,制备了Gd2O2S:Tb3 X-射线纳米荧光粉.分别以X-射线衍射(XRD)、扫描电子显微镜(SEM)、光致发光(PL)光谱及X-射线激发的发光(XEL)光谱对样品进行了表征.XRD分析表明,当焙烧温度小于500℃时,可得到单一相的Gd2O2S:Tb3 X-射线纳米荧光粉;当温度为700℃时,样品完全转变为Gd2O2SO4相.SEM照片给出荧光粉具有疏松和多孔的块状及连续的三维的网络结构.PL和XEL光谱均呈现出激活剂Tb3 离子的较强的特征发射,但它们的峰位略有差别.此外,本实验Tb3 离子的最佳掺杂浓度是0.35mol%.     

A facile preparation and the luminescent properties of Eu3+-doped Y2O2SO4 nanopieces

The europium(III)-doped yttrium oxysulfate (Y₂O₂SO₄:Eu³⁺) nanopieces have been prepared via electrospinning followed by calcination at 1000 °C in mixed gas of sulfur dioxide and air. Based on the experimental results, a possible formation mechanism for the nanopieces is that the nanopieces are determined by the directing template of electrospun nanoribbons and the multilayer crystal structure of Y₂O₂SO₄. Besides, the nanopieces show excellent luminescent properties with emissions at 581, 589, 597, 653, 619, and 697 nm resulting from the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transition of Eu³⁺. The peaks of charge transfer and ⁵D₀ → ⁷F₂ transition of Eu³⁺ obviously have red shifts comparing to those of both Y₂O₃:Eu³⁺ nanoribbons and commercial Y₂O₃:Eu³⁺. Moreover, the nanopieces exhibit stronger intensities than the Y₂O₃:Eu³⁺ in excitation and emission spectra. Concentration quenching in the nanopieces occurs when Eu³⁺ concentration is 11 mol%, indicating that the nanopieces have an optimum luminescent intensity under this doping concentration.     

Tunable emission and excited state absorption induced optical limiting in Tb2(MoO4)3: Sm3+/Eu3+ nanophosphors

Photoluminescence properties and optical limiting behavior of pure and Sm³⁺/Eu³⁺ doped Tb₂(MoO₄)₃ nanophosphors are investigated. The prepared nanophosphors exhibit excellent emission when excited by UV light. Color-tunable emissions in Tb_2−xSm_x(MoO₄)₃ and Tb_2−xEu_x(MoO₄)₃ are realized by employing different excitation wavelengths or by controlling the doping concentration of Sm³⁺ and Eu³⁺. Luminescence quantum yield and CIE chromatic coordinates of the prepared phosphors were also presented. Optical limiting properties of the samples are investigated by open aperture Z-scan technique using 5 ns laser pulses at 532 nm. Numerical fitting of the measured Z-scan data to the relevant nonlinear transmission equations reveals that the nonlinear absorption is arising from strong excited state absorption, along with weak absorption saturation and it is found that the optical nonlinearity of Tb₂(MoO₄)₃ increases with Sm³⁺/Eu³⁺doping. Parameters such as saturation fluence, excited state absorption cross section and ground state absorption cross section of the samples have been determined numerically, from which the figure of merit for nonlinear absorption is calculated. The excited state absorption cross-section of the samples is found to be one order of magnitude higher than that of the ground state absorption cross-section, indicating strong reverse saturable absorption. These results indicate that Sm³⁺/Eu³⁺ doped Tb₂(MoO₄)₃ nanophosphors are efficient media for UV/n-UV pumped LEDs, and are also potential candidates for designing efficient optical limiting devices for the protection of human eyes and sensitive optical detectors from harmful laser radiation.     

Large-scale preparation of powder composites xNiO/(1-x)Al2O3 in reactions of solution combustion synthesis

The conditions for the production of composites by Solution Combustion Synthesis (SCS) from reaction solutions of aluminum and nickel nitrates of various concentrations with glycine have been studied. The concentration of reaction solutions increases the product yield and the productivity of SCS process. The effect of the presence of Al³⁺ cations in reaction solutions on the combustion reaction intensity reduction has been established. The SCS precursors contained metallic nickel, nickel oxide and amorphous alumina. The phase composition of the samples changed in the process of annealing: nickel oxidation, crystallization of γ-Al₂O₃ (600 °C) and formation of NiAl₂O₄ spinel (600–800 °C) were observed. The maximal specific surface area value recorded after annealing at 800 °C was 59–63 m²/g. In samples obtained with a lower fuel content, γ-Al₂O₃ or a mixture of γ-Al₂O₃ and NiAl₂O₄ crystallize on the surface of composite particles. The concentration of NiO on the surface of composites obtained from precursors synthesized from concentrated solutions at φ = 1.4 is close to the nominal composition.     

红色蓄光材料Y2O2S:Eu3+的硫熔法制备及其发光性能

用硫熔法制备了系列红色蓄光材料Y2O2S ：Eux^3＋（0．01≤x≤0．10）的多晶粉末样品并系统研究了其发光特性。XRD结果表明,晶胞参数c随着Eu^3＋含量的逐渐增大而增大,而晶胞参数α没有明显的线性变化关系,这与Y2O2S ：Eu^3＋的晶体结构有关。Y2O2S ：Eux^3＋（0．01≤x≤0．10）的激发光谱相似,在626nm发射光监控下最大激发波长约在330nm附近。在330nm激发下,随着Eu^3＋含量逐渐增大,发射光谱最强发射峰位置从540nm右移至626nm,观察到红色特征发射峰626nm的强度逐渐增大,在Eu^3＋含量为0．09时,其强度达到最大。在最佳合成条件及最佳Eu^3＋含量下,正在进行掺杂Mg^2＋和Ti^4＋及其发光特性的研究。     

Synthesis and characterization Y2O3:Eu3+ nanocrystals prepared via solvothermal refluxing route

Y₂O₃:Eu³⁺ nanocrystals were prepared via co-precipitation–solvothermal refluxing–calcination method using three kinds of organic solvents, propylene glycol, 1,3-butanediol and polyethylene glycol and yttrium chloride hexahydrate and europium chloride as starting materials. The Y₂O₃:Eu³⁺ nanocrystals with diameter of 20–50 nm prepared by refluxing in polyethylene glycol followed by calcinations at 800–1000 °C exhibited the strongest luminescence at 611 nm under the excitation wavelength of 254 nm than the reference sample prepared via conventional co-precipitation method. The photoluminescence spectra of the samples were recorded at room temperature. The effect of concentration of Eu³⁺ (Eu³⁺/Y³⁺ atomic ratio: 0.01–0.1) on the photoluminescence intensity was also investigated. The samples with the Eu³⁺/Y³⁺ atomic ratio of 0.07 exhibited the strongest emission at 611 nm and quenching effect was observed above 0.10.     

Low temperature synthesis of Ga-doped Li7 La3 Zr2 O12 garnet-type solid electrolyte by mechanical method

Synthesis of Li_6.25 Ga_0.25 La₃ Zr₂ O₁₂ (LLZO-Ga) solid electrolyte powder granule for all solid-state battery was investigated by applying mechanical processing of the raw powder materials adding LiF-BaF₂ as a flux. The LLZO-Ga of highly crystalline was synthesized by the mechanical method using an attrition-type mill without any extra-heat assistance. When 10 mass% of LiF-BaF₂ was added to the raw powder materials and 28 min processed, LLZO-Ga powder was favorably synthesized and granulated at the chamber temperature of 284 °C. The ionic conductivity of the sintered body of the LLZO-Ga granules was evaluated by impedance measurement. It revealed the high ionic conductivity of σ_total 1.0 × 10⁻³ S/cm. It suggests that the formation of LLZO-Ga/BaZrO₃ grain boundary contributes to higher ionic conductivity adding to the high crystalline phase of LLZO-Ga.     

Photophysical properties of Eu3+ and Tb3+-doped ZnAl2O4 phosphors obtained by combustion reaction

Europium- and terbium-doped zinc aluminate oxide nanocrystals with a spinel structure were successfully prepared by a combustion method, using urea as fuel. The samples thus obtained were characterized by X-ray diffraction, scanning electron microscopy and luminescence spectroscopy. X-ray diffraction results confirmed the formation of ZnAl₂O₄ spinel phase and a minor amount of ZnO. Our SEM results revealed agglomerates in the shape of irregular plates composed of nanoparticles with dispersed points of second phase in the surface. Powders containing Eu³⁺ and Tb³⁺ ions displayed red and green photoluminescence, respectively.     

Synthesis of nanocrystalline TiO<Subscript>2</Subscript> by tartarate gel method

A gel was formed when a mixture of TiOCl₂ and tartaric acid was heated on a water bath. Ultrafine powders of TiO₂ in the anatase phase were formed, when the gel was decomposed at 623 K and the mole ratio of tartaric acid to titanium was 2. The anatase phase was converted into rutile phase on annealing at higher temperatures, > 773 K. When initial ratio of titanium to tartaric acid was < 2, the decomposition of gel leads to the formation of mixed phases of rutile and anatase. However, pure rutile phase was not formed by the decomposition of gel for any ratio of tartaric acid and titanium. These powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and surface area measurements. The average particle size obtained for anatase phase was 3 nm whereas it was 30 nm for rutile phase. Raman scattering experiments were also performed to confirm both anatase and rutile phases.