Spindlelike Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> nanorod bundles: hydrothermal synthesis and photoluminescence properties

Uniform spindlelike Y(OH)₃ nanorod bundles were successfully prepared for the first time via a simple hydrothermal method at 200 °C for 12 h with the presence of Na₂H₂EDTA · 2H₂O (EDTA). Scanning electron microscope (SEM) images show that the obtained Y(OH)₃ spindlelike nanorod bundles have a length of about 11 μm and a diameter of about 2 μm in the middle part. The nanorod bundles are composed of numerous nanorods, and all these nanorods are orientationally aligned and grow uniformly along the bundles. The individual nanorod is with typical width of about 100 nm, thickness of about 40 nm, and length longer than 1 μm. The effects of reaction temperature, reaction time, and the concentration of NaOH and EDTA on the sizes and morphologies of the products have been investigated. The possible formation mechanism of the nanorod bundles was suggested. Spindlelike Y₂O₃ nanorod bundles were obtained after thermal treatment of the as-obtained Y(OH)₃ nanorod bundles at 700 °C for 4 h. X-ray powder diffraction (XRD) results demonstrate that the as-prepared Y(OH)₃ and Y₂O₃ are attributed to hexagonal phase and cubic phase, respectively. Eu³⁺ doped Y₂O₃ nanorod bundles were also prepared and their photoluminescence (PL) properties were investigated.     

Preparation of Gd2O2S:Pr Scintillation Ceramics by Pressureless Reaction Sintering Method

Fabrication of Gd₂O₂S:Pr scintillation ceramics by pressureless reaction sintering was investigated. The 2Gd₂O _3˙(Gd,Pr)2(SO ₄)_3˙mH₂O precursor was made by hydrothermal reaction using commercially available Gd₂O₃, Pr₆O₁₁ and H₂SO₄ as the starting materials. Then single phase Gd₂O₂SO₄:Pr powder was obtained by calcining the precursor at 750°C for 2 h. The Gd₂O₂SO₄:Pr powder compacts can be sintered to single phase Gd₂O₂S:Pr ceramics with a relative density of 99% and mean grain size of 30 μm at 1750°C for 2 h in flowing hydrogen atmosphere. Densification and microstructural development of the Gd₂O₂S:Pr ceramics were examined. Luminescence spectra of the Gd₂O₂S:Pr ceramic under 309 nm UV excitation and X-ray excitation show a green emission at 511 nm as the most prominent peak, which corresponds to the ³P₀-³H₄ transition of Pr³⁺ ions.     

Structural and phase dependent thermo and photoluminescent properties of Dy(OH)3 and Dy2O3 nanorods

Hexagonal Dy(OH)₃ and cubic Dy₂O₃ nanorods were prepared by hydrothermal method. Dy(OH)₃ nanorods was directly obtained at 180 °C for 20 h after hydrothermal treatment whereas subsequently heat treatment at 750 °C for 2 h gives pure cubic Dy₂O₃. SEM micrographs reveal that needle shaped rods with different sizes were observed in both the phases. TEM results also confirm this. The TL response of hexagonal Dy(OH)₃ and cubic Dy₂O₃ nanorods have been analyzed for γ-irradiation over a wide range of exposures (1–5 kGy). TL glow peak intensity increases with γ dose in both the phases. The activation energy (E), order of kinetics (b), and frequency factor (s) for both the phases have been determined using Chen's peak shape method. The simple glow curve shape, structure and linear response to γ-irradiation over a large span of exposures makes the cubic Dy₂O₃ as a useful dosimetric material to estimate high exposures of γ-rays.     

Synthesis and characterization of polyaniline nanorods/Ce(OH)3-Pr2O3/montmorillonite composites through reverse micelle template

Polyaniline (PANI) nanorods/Ce(OH)₃-Pr₂O₃/montmorillonite (MMT) nanocomposites were synthesized via in situ polymerization of aniline monomer through reverse micelle template (RMT) in the presence of montmorillonite and Ce(OH)₃, Pr₂O₃. In the experiment, sulphosalicylic acid was used as dopant, aniline was designated as oil phase and the aqueous solution comprising Ce³⁺ and Pr³⁺ as water phase. The nanocomposites were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) analysis, Fourier transform infrared (FT-IR) spectroscopy and thermogravimetry-differential thermal analysis (TG-DTA). The results showed that PANI nanorods were synthesized in the interlayer spaces of MMT with uniform spherical rare earth nanoparticles. The thermal stability of the nanocomposites prepared was enhanced drastically compared with pure polyaniline.     

Synthesis and characterization of bundle-like structures consisting of single crystal Ce(OH)CO3 nanorods

Bundle-like structures consisting of single crystal cerium hydroxide carbonate (Ce(OH)CO₃) nanorods have been synthesized successfully by a hydrothermal method at 100 °C using cerium nitrate (Ce(NO₃)₃·6H₂O) as the cerium source, aqueous carbamide both as an alkaline and carbon source and cetyltrimethylammonium bromide (CTAB) as surfactant. X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were used to characterize such bundle-like structures. SEM and TEM images show that Ce(OH)CO₃ bundle-like structures were composed of nanorods with diameters of ∼ 100 nm. The XRD pattern and electron diffraction (ED) pattern indicate that Ce(OH)CO₃ has a pure orthorhombic single crystal structure.     

Thermoelectric properties of porous zinc oxide ceramics doped with praseodymium

We evaluated praseodymium (Pr) doping effects on thermoelectric properties of porous zinc oxide (ZnO) ceramics. The low density ceramics composed of ZnO and an additive of Pr (0.5 and 0.1 mol%) oxide were prepared by sintering processes in different atmospheres (air and oxygen), where the additives were Pr₆O₁₁ known for phase transformations and the trioxide Pr₂O₃ with low valence state different from Pr₆O₁₁. Thermoelectric properties of the samples were measured between 313 K and 903 K. At high-temperature around 590 K, some samples showed a maximum of electrical resistivity. We discussed the origin of the maximum on the basis of carrier transport model on gas sensor and varistor. From the results, The maximum appearance was attributable to an interchange of carriers through defects complex closely related with enhanced zinc vacancies acceptor-like in the vicinity of grain boundaries (GB), where the defect complex seemed to be caused by Pr with valence state between 3+ and 3.78+ around GB. The doping Pr into ZnO matrix is expected to be advantageous to improve thermoelectric power.     

Wavelength dependence of Verdet constant of Pr doped terbium gallium garnet crystal

Samples of the magneto-active material – Pr³⁺: Tb₃Ga₅O₁₂ crystals with Pr³⁺ ion concentration of 1%, 2%, 3% and 5%. The Verdet constant measurement has been carried out at room temperature in the 400–1500 nm range for all crystal samples and was compared with a pure Tb₃Ga₅O₁₂ material. A high value of the Verdet constant for 5% Pr³⁺: Tb₃Ga₅O₁₂ crystal was obtained at room temperature – namely, 324.5, 200.1 and 68.7 rad/(T·m) for 532, 632.8 and 1064 nm, respectively. The Verdet constant of Pr doped TGG crystal at 1064 nm is much more higher than that of TGG. The superior performance of the materials indicates that Pr³⁺: Tb₃Ga₅O₁₂ crystals have great potential to meet the increasing demand for magneto-optical devices in the VIS-NIR wavelength.     

Thermal decomposition behavior of praseodymium oxides,hydroxides, and carbonates

Thermal decomposition behavior was studied for Pr₆O₁₁, Pr₂O₃, Pr(OH₃), and Pr₂(CO₃)₃ · xH₂O. In the course of transformation, the intermediate species were different for each starting material, as well as the surface area and morphology of the final thermal decomposition products. During thermal decomposition in the temperature range of 200°C up to 1400°C, mass losses for each species were attributed to the removal of hydroxide and carbonate species based on changes in the infrared bands for each powder for hydroxide groups at ≃3600 cm⁻¹ and carbonate groups at ≃1300–1500 cm⁻¹. X-ray diffraction analysis identified the final decomposition product at 1400°C for each species as Pr₆O₁₁ regardless of the starting material. A decrease in surface area and increase in equivalent particle radius for each final Pr₆O₁₁ product is attributed to sintering. The presence of hydroxyl and carbonate groups in the Pr₆O₁₁, Pr₂O₃, Pr(OH₃), and Pr₂ (CO₃)₃ · xH₂O precursor dictate the morphology of thermally decomposed Pr₆O₁₁.     

Preparation and characterization of In2O3 nanorods

In₂O₃ nanorods were prepared by sol–gel technique with polyethylene octyl phenyl ther (OP-10) controlling their morphology and were characterized by TEM, TG-DSC and XRD. The results indicated that In₂O₃ nanorods had the length of about 120 nm and the diameter of about 20 nm. The precursor was In₂O(OH)₄ dry gelatin which was formed by partly dehydrating of In(OH)₃ molecules. The influencing factors and growth mechanism were discussed. The geometry arrangement parameter P of OP-10 was in 1/3–1/2 through calculating, which conformed the shape of claviform micelle.     

Morphological and magnetic properties of the hydrothermally prepared α-Fe2O3 nanorods

α-Fe₂O₃ nanorods were synthesized via hydrothermal method. X-ray powder diffraction revealed the formation of rhombohedral α-Fe₂O₃ single crystal phase with fiber texture. Scanning and transmission electron micrographs analyses showed that the rhombohedral α-Fe₂O₃ has nanorods in shape with diameters of 40–85 nm and lengths of 150–45,000 nm. Isothermal magnetization vs. applied magnetic field curves measured at room and liquid nitrogen temperatures displayed a variation on magnetic ordering: from weak ferromagnetism at room temperature to not hysteretic behavior at liquid nitrogen temperature that is well described by a Langevin function. Moreover, the zero field cooling-field cooling curves under applied magnetic field of 100 Oe confirms the decreasing of Morin temperature transition due to nanometric size of the samples.     

Porous network of Y2O3 nanorods prepared by electrogeneration of base in chloride medium

A porous network of Y₂O₃ nanorods was successfully prepared by an easy two-step and template-free process. Firstly, Y(OH)₃ was galvanostatically grown on steel cathode by electrogeneration of base in chloride medium. Then it was thermally converted to oxide via heat treatment. Phase transformations during the heat treatment of deposit were proposed. Morphological studies showed that the obtained oxide has a porous network, composed of intercrossed nanorods. The nanorods are 200–300 nm in length and 50–70 nm in diameter. The mechanism of base electrogeneration in chloride medium, the deposition of Y(OH)₃ nanorods on the cathode surface and their thermal conversion to Y₂O₃ have been discussed.     

PEG-directed hydrothermal synthesis of alumina nanorods with mesoporous structure via AACH nanorod precursors

Al₂O₃ nanorods with mesoporous structures are successfully synthesized from a hydrothermal and thermal decomposition process via the ammonium aluminum carbonate hydroxide (denoted as AACH) precursors. TEM images show that the average diameter of Al₂O₃ nanorods is about 60 nm, and the length is around 1–2 μm. The experimental results show that well-crystallized mesopores with hierarchically distributed pore sizes are embedded in the Al₂O₃ nanorods. The N₂ adsorption–desorption experiment indicates that the as-synthesized alumina nanorods have large surface area (ca. 176 m²/g) and narrow pore-size distributions. At the same time, the as-prepared Al₂O₃ nanorods exhibit strong photoluminescent properties at room temperature. A plausible surfactant-induced nanorod formation mechanism using the poly ethylene glycols as the template agent for the nanorod assembly is also proposed.     

Preparation,structure and optical properties of Pr:Gd2O3 phosphor

Pr³⁺-doped Gd₂O₃ phosphor powders were prepared by co-precipitation method. Their structures during heat-treatments were studied by XRD and IR methods. The pH was optimized to be 8 in the co-precipitation process and the hydroxide precursors were transformed into pure phase cubic Gd₂O₃ at 500 °C for 1 h. Optical properties of Pr:Gd₂O₃ phosphor powders were reported. The main emission bands are assigned to ¹D₂ → ³H₄, ³P₀ → ³H₆, ³P₀ → ³F₂ transition of Pr³⁺ under excitation at 255 and 488 nm. The emission intensities increase with increasing sintering temperature. Concentration quenching appears as the Pr³⁺ doping-concentration up to 1 at.%.     

Microstructure and current-voltage characteristics of praseodymium-doped zinc oxide varistors containing MnO2, Sb2O3 and Co3O4

The effects of the oxide additives MnO₂, Sb₂O₃ and Co₃O₄ commonly incorporated in commercial Bi₂O₃-doped ZnO varistors on the microstructure and the current-voltage characteristics of 0.5 mol% Pr₆O₁₁-doped ZnO varistors have been studied. A 1 mol% addition of Co₃O₄ to the ZnO-Pr₆O₁₁ binary system does not produce any additional secondary phases in addition to Pr oxides. In contrast to this, the addition of 1 mol% MnO₂ complicates the simple two-phase microstructure of the 0.5 mol% Pr₆O₁₁-doped material by forming the perovskite-type structure Pr(Mn_{1 – x} Zn _x )O₃. The addition of Sb₂O₃ produces the pyrochlore Pr₃Zn₂Sb₃O₁₄ and spinel Zn₇Sb₂O₁₂ phases. Application of the Fresnel fringe technique and the diffuse dark field technique showed that there was an amorphous Pr-rich layer of thickness <2 nm residing between adjacent ZnO grains in all the samples studied.     

Synthesis of ultrafine lanthanum hydroxide nanorods by a simple hydrothermal process

Lanthanum hydroxide (La(OH)₃) nanorods with 6–15 nm in width and 200–400 nm in length have been prepared by a simple hydrothermal process. X-ray diffraction (XRD) shows that the nanorods are of hexagonal structure, and furthermore, high-resolution transmission electron microscopy (HRTEM) identifies that the lanthanum hydroxide nanorods are highly crystalline. Moreover, the mechanism for the hydrothermal synthesis of lanthanum hydroxide nanorods has been preliminarily presented.     

Structural transformation from Mn3O4 nanorods to nanoparticles and band gap tuning via Zn doping

Synthesis of undoped and Zn doped hausmannite Mn₃O₄ nanorods was achieved through a simple hydrothermal route. Scanning electron microscopic studies showed that due to in situ Zn doping a structural deformation from Mn₃O₄ nanorods to a mixture of Mn₃O₄ nanorods and nanoparticles occurred. The amount of nanoparticles in the mixture increased with the increase of doping percentage. X-ray diffraction studies, transmission electron microscopy and selected area electron diffraction pattern revealed that both the nanorods and the nanoparticles were hausmannite Mn₃O₄. X-ray photoelectron spectroscopic studies confirmed successful zinc doping in Mn₃O₄. Microscopic studies revealed that the average diameters of Mn₃O₄ nanorods and nanoparticles were of 200 nm and 70 nm, respectively. The possible growth mechanism and the reasons behind the formation of nanoparticles along with nanorods are discussed briefly. UV–vis spectroscopic studies showed a continuous increase in the energy bandgap of Mn₃O₄ with the increase in Zn doping percentage.     

Facile route to the synthesis of porous α-Fe2O3 nanorods

The requirements of simple and reliable protocols for the synthesis of anisotropic structures with controlled morphology continue to be a major challenge in nanoscience. In this paper we describe the facile synthesis of porous hematite (α-Fe₂O₃) nanorods using anionic surfactant as a rod-like template. α-FeOOH nanorods with diameters of 170–210 nm and lengths up to 3–5 μm were synthesized in high yield via hydrothermal method using sodium dodecyl sulphate as a template. The porous α-Fe₂O₃ was obtained after solvent extraction and calcining the as-obtained α-FeOOH nanorods at 500 °C for 6 h. Even after removal of template by solvent extraction and calcination the shape of the nanorods was intact except the generation of pores on the nanorods. The porous nanorods were analysed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission and high-resolution transmission electron microscopy (TEM & HRTEM), scanning electron microscopy (SEM) and superconducting quantum interference device (SQUID) measurements. SEM and TEM images showed that the morphology of hematite nanostructure is homogeneous in the shape of rods and full of porosity and magnetization measurements of the porous α-Fe₂O₃ nanorods showed weak ferromagnetic behavior. The surfactant SDS (sodium dodecyl sulphate) plays a key role in controlling the nucleation and growth of the nanorods and their use as a new class of inorganic scaffolds for the synthesis of nanomaterials are salient features of the work with implications in crystal engineering and nanocomposites design for various applications.     

Synthesis of α-Sb2O4 nanorods by a facile hydrothermal route

α-Sb₂O₄ nanorods with diameter of 50–150 nm and length of 100–300 nm have been successfully synthesized by a hydrothermal method using SbCl₃ and I₂ as reaction reagents. The obtained sample is characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and selected-area electron diffraction. The results confirm that the product is pure single-crystalline α-Sb₂O₄ nanorods with few dislocations and defects. The vibrational property of the nanorods is investigated by Raman spectroscopy. Raman spectrum of α-Sb₂O₄ nanorods has a small red shifts compared with that of the bulk α-Sb₂O₄ powders. A possible growth mechanism of α-Sb₂O₄ nanorods is proposed as three stages: the hydrolyzation of SbCl₃ under strong acid condition, the oxidation of Sb₄O₅Cl₂ and the growth of α-Sb₂O₄ nanorods with the aid of iodine transport.     

Green hydrothermal synthesis and optical absorption properties of ZnO2 nanocrystals and ZnO nanorods

A green hydrothermal method was proposed for the controllable synthesis of ZnO₂ nanocrystals and ZnO nanorods, using the common and cost-effective 2ZnCO₃·3Zn(OH)₂ powder and 30 mass% H₂O₂ aqueous solution as the raw materials. The characterization results from X-ray diffraction, high resolution transmission electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy indicated that the products synthesized at 100-120 °C for 6 h or at 170 °C for 0 h were cubic phase ZnO₂ nanocrystals; while those synthesized at 170 °C for 3-6 h were hexagonal phase ZnO nanorods. The UV-vis absorption spectra showed that the as-synthesized ZnO₂ nanocrystals and ZnO nanorods had optical band gaps of about 4.1 and 3.3 eV, respectively.     

Photo-initiated growth of zinc oxide (ZnO) nanorods

A photo-initiated process via femtosecond pulse-induced heterogeneous nucleation in zinc ammine complex (Zn(NH₃)₄²⁺)-based aqueous solution without catalyst and surfactant, followed by hydrothermal treatments for crystal growth into zinc oxide (ZnO) nanorods, was investigated. Flat-top hexagonal ZnO nanorods with smooth planes of diameter ≥ 100 nm and length ≤ 1 μm were grown with laser irradiation, compared to porous rod-like structures without irradiation. The flat-top planes indicate slow growth rate, due to the intermediate step of Zn(NH₃)₄²⁺ decomposition to Zn(OH)₄²⁻, before dehydration to ZnO. Prolonged hydrothermal treatment produced nanotubes and lateral splits due to OH⁻ erosion of the crystal faces. XRD analysis showed a hexagonal crystal structure while photoluminescence study indicated a peak at about 380 nm.