Low-temperature Synthesis Method Research Articles

Synthesis of Nano-Phosphor By Water Assisted Room Temperature Solid State Reaction (WASSR) Method

A solid-state reaction method has been usually used as a basis synthesis processing technique to obtain the ceramic materials, including phosphor materials, because of its very simple and easy. However, ceramic materials are generally synthesized at high temperature when the solid state reaction method used as synthesis method. Because ionic-diffusion in ionic crystal is very slow at room temperature, high temperature is essential for solid state reaction. The high temperature synthesis leads to increase in the processing cost and irregular particle morphology of the obtained powder. In contrast, we have proposed the two novel solid phase synthesis technique to synthesize the ceramic materials at low temperature below 100 °C without after any chemical or physical treatment. We refer to these synthesis techniques as water assisted room temperature solid state reaction (WASSR) method and solid hydratethermal reaction (SHR) method.1-3 We successfully synthesized the functional ceramic materials including phosphors. Furthermore, we demonstrated that the reaction mechanism of novel low temperature synthesis methods is different from the conventional solid state reaction and solution reaction. In this study, we present the practicability of our original novel solid state reaction methods on an industrial application in the ceramic oxide materials synthesis processing. References K. Toda, M. Sato, K. Uematsu, and T. Ishigaki, Japanese Unexamined Patent Application Publication No. 2011-16670 (2009).S.W. Kim, T. Kaneko, K. Toda, K. Uematsu, M. Sato, J. Koide, M. Toda, and Y. Kudo, IDW'2014, PH1-3 (2014).T. Kaneko, S.W. Kim, A. Toda, K. Uematsu, T. Ishigaki, K. Toda, M. Sato, J. Koide, M. Toda, Y. Kudo, T. Masaki, and D.H. Yoon, Sci. Adv. Mater., (2015) in press. doi:10.1166/sam.2015.2364.

Effect of growth time and annealing on the structural defect concentration of hydrothermally grown ZnO nanowires

As a low temperature and low cost synthesis method, the hydrothermal deposition is widely used to grow ZnO nanowire arrays. Their optical properties are closely related to concentration of the structural defects in the ZnO nanowires. In this work we report on investigation on the evolution of the structural defects of ZnO nanowire arrays for different growth time, before and after post-annealing. The photo-emission properties of the ZnO nanowire arrays have been investigated in detail by using photoluminescence (PL) spectroscopy both on the as-grown nanowires and on the annealed ones. The PL analysis results showed an increasing intensity in the visible emission band with the growth time which is closely related to the change of the concentration of the structural defects in the ZnO nanowires regarding to the UV near-edge emission. The visible PL emission band can be deconvoluted into three Gaussians components, which correspond to the green, yellow-orange and red emissions, respectively. It is further revealed that the intensity of the orange and red emission bands increase with the increase of the growth time, which are ascribed to the interstitial oxygen and/or hydroxide groups and adsorbed oxygen, respectively. The correlation between energy-dispersive X-ray spectroscopy (EDS) analysis and PL measurements revealed that the excess zinc can be formed in the nanowires during the hydrothermal process.

Low-temperature synthesis of CuFeO2 (delafossite) at 70 °C: A new process solely by precipitation and ageing

This study presents a new low temperature synthesis method to obtain pure delafossite (Cu1+Fe3+O2) at a temperature of 70°C within 24h. For the first time delafossite is synthesized solely by precipitation and subsequent ageing process and without usage of any additives controlling the oxidation state of copper. The synthesized material, called LT-delafossite, consists of pure Cu1+Fe3+O2 exclusive of any side products. Rietveld analysis confirms the presence of both 3R (space group (SG): R-3m) and 2H (SG: P63/mmc) polytypes in LT-delafossite. Electron microscopy images show nanometer-sized hexagonal plates with a diameter <500nm and a thickness of <30nm. Measurements of the magnetic susceptibility from 2K to 350K in zero-field show one peak ∼18.5K, which is attributed to an AFM phase transition. Zero-field-cooled magnetization data between −14T and +14T at 2K revealed an s-shape form around the origin having no remanent magnetization.

Incorporation of Cr 3+ ions in tuning the magnetic and transport properties of nano zinc ferrite

Cost effective and low temperature synthesis methods namely solution combustion and hydrothermal methods were used to prepare chromium incorporated nanocrystalline zinc ferrites. The effect of incorporation of low concentration Cr3+ ions on the structural, morphological, magnetic and transport properties of the zinc ferrite compounds were investigated. The crystalline nature and size variation with chromium content were valid from powder x-ray diffraction. Particles size and crystallite size variation were valid from scanning electron microscopy and transmission electron microscopy respectively. With the increase in chromium incorporation, the crystallite and particles sizes were decreased. Fourier transform infrared spectroscopy (FTIR) studies confirmed the presence of strong metal-oxygen bonds. The elastic properties of the materials in both the methods were estimated by FTIR studies. Magnetic properties namely saturation magentization, remanent magnetization and coercivity values were decreased with increase in Cr3+ ions concentration. The dielectric properties of the samples decreased with increase in the Cr3+ ions. The dielectric constant was observed to be of the order of 106 at low frequency and almost 1 at higher frequency range. The activation energy estimated using Arrhenius plots was of the order of 0.182 eV and 0.368 eV respectively for the compounds prepared by solution combustion and hydrothermal methods. The emission spectra of the samples excited at 344 nm were reported using photoluminescence (PL) spectroscopy. Further, the approximate energy band gap(Eg) was estimated from PL studies. The Eg of the materials were lie in the range of 2.11–1.98 eV.

Study on the formation of Co1−xZnxFe2O4 system using two low-temperature synthesis methods

This paper deals with the synthesis of cobalt–zinc ferrite Co1−xZnxFe2O4 (x = 0.5), by two different synthesis methods: thermal decomposition of carboxylate complex, and co-precipitation. The effect of temperature on the characteristics of the obtained powders was investigated by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and magnetic measurements. Thermal analysis was used to investigate metal carboxylate complex formation and their thermal stability. The mixture of Co(II), Zn(II), and Fe(III) carboxylates (precursor) decomposed at 300 °C was annealed at 350, 500, and 1000 °C. The XRD patterns revealed that all powders consist of the spinel phase Co1−xZnxFe2O4. As the annealing temperature increased, the crystallite size, lattice parameter, and saturation magnetization were increased. Co-precipitation method was used to synthesize samples at different temperatures: 25, 40, 60, and 80 °C. X-ray diffractometry proved that cobalt–zinc ferrite was formed starting with 25 °C, while the ferritization process was almost completed at 80 °C. The precipitate obtained at 80 °C was annealed at 500 and 1000 °C. At 80 and 500 °C, the powders have similar crystallite size (~9 nm) and similar lattice parameter (a = 8.37 A) and show a super-paramagnetic behavior. Powders obtained by both methods, at 1000 °C, have close values for the saturation magnetization σ (~60 emu g−1) and tend to have super-paramagnetic behavior (coercive field H c = 0.08 kOe). The lattice parameter has also similar values, corresponding to the Co0.5Zn0.5Fe2O4 composition (a = 8.40 A). Thermal decomposition of carboxylate complexes is a new method for the obtaining of Co0.5Zn0.5Fe2O4 ferrite. The results are comparable to those obtained by co-precipitation, starting from the same reagents (metal nitrates). The magnetic behavior makes this nanoferrite suitable for applications such as preparation of ferrofluids and hyperthermia for cancer treatment.

A modified sol–gel method for low-temperature synthesis of homogeneous nanoporous La1−x Sr x MnO3 with large specific surface area

A modified sol–gel (MSG) method was developed to synthesize perovskite La1−x Sr x MnO3 (x = 0.2, 0.4, 0.6, 0.8) with large specific surface area that allows for control of their particle size from the micrometer level to the nanometer level with novel nanoporous structure. The MSG method utilized carbon black (Vulcan XC-72R) as a pore-forming material during the preparation process. Two important process parameters, the calcination temperature and the pore former material addition, were investigated to control the size of the La1−x Sr x MnO3 particles. The phase evolution of La1−x Sr x MnO3 powders was investigated by thermogravimetric analysis (TG/DSC) and X-ray diffraction pattern. The results showed that the pure La0.6Sr0.4MnO3 phase has been obtained at about 550 °C in air, which is lowered around 150 °C comparing to conventional sol–gel method. In scanning electron microscope studied, it presented novel homogeneous nanoporous morphology with the average particle size from 30 to 100 nm. Based on the Brunauer–Emmett–Teller method analysis, the specific surface area of La1−x Sr x MnO3 was significantly influenced by the calcination temperature, the pore former material addition and the strontium content. The largest specific surface area of La0.2Sr0.8MnO3 reached 114.3 m2/g.

A facile low-temperature synthesis of TiO2 nanoparticles with excellent polymorph control

A facile low-temperature synthesis method of crystalline titanium dioxide nanoparticles has been developed, and the effect of temperature and acidity on polymorph selectivity has been systematically investigated. The crystal polymorph of titanium dioxide could be tuned by carefully controlling the condensation rate of titania. Conditions providing high condensation rate favoured the formation of the anatase and brookite phases, while lowering the condensation rate yielded higher rutile content. The reaction was found to proceed either in liquid state for reactions performed at low temperatures and high acidity or in a sol–gel manner for higher temperatures and lower acidity. The aggregation behaviour was found to be strongly affected by the employed synthesis conditions and by the crystal polymorph formed. The design of a facile low-temperature synthesis system with predictive control of polymorph selectivity is important for further development of titania-based materials for applications where type of polymorph is vital, such as photocatalytic and photonic.

Synthesis of Phosphor Materials By New Low-Temperature Solid-State Reaction Method Showing Abnormally High Diffusion

A solid-state reaction method has been usually used as a basis synthesis processing technique to obtain the ceramic materials, including phosphor materials, because of its very simple and easy. However, ceramic materials are generally synthesized at high temperature when the solid state reaction method used as synthesis method. Because ionic-diffusion in ionic crystal is very slow at room temperature, high temperature is essential for solid state reaction. The high temperature synthesis leads to increase in the processing cost and irregular particle morphology of the obtained powder. On the other hand, we recently proposed the novel low-temperature synthesis methods, such as water assisted room temperature solid state reaction (WASSR) method and solid hydratethermal reaction (SHR) method, to synthesize the ceramic materials in a single phase form at low temperature,1-3 and we successfully synthesized the functional ceramic materials including phosphors. Furthermore, we demonstrated that the reaction mechanism of novel low temperature synthesis methods is different from the conventional solid state reaction and solution reaction. In this study, we present the practicability of our original novel solid state reaction methods on an industrial application in the ceramic oxide materials synthesis processing. References K. Toda, M. Sato, K. Uematsu, and T. Ishigaki, Japanese Unexamined Patent Application Publication No. 2011-16670 (2009).S.W. Kim, T. Kaneko, K. Toda, K. Uematsu, M. Sato, J. Koide, M. Toda, and Y. Kudo, IDW'2014, PH1-3 (2014).T. Kaneko, S.W. Kim, A. Toda, K. Uematsu, T. Ishigaki, K. Toda, M. Sato, J. Koide, M. Toda, Y. Kudo, T. Masaki, and D.H. Yoon, Sci. Adv. Mater., (2015) in press. doi:10.1166/sam.2015.2364.

Influence of Structural Properties on the Performance of Dye-Sensitized Solar Cells Based on Electrodeposited ZnO

ZnO is an interesting material for application in the dye-sensitized solar cell (DCS) related to the large variety of low-temperature synthesis methods that allow for easy manipulation of the morphology and texture of the material. In particular, electrodeposition of crystalline ZnO can be achieved at room temperature, making it an excellent method for the preparation of solar cells based on flexible plastic substrates. We will present results on the performance of dye-sensitized solar cells based on electrodeposited ZnO, describing the electrodeposition method in detail, and compare the results to ZnO-based solar cells prepared using sol-gel synthesis and CVD. The morphology and texture are expected to influence the performance of the dye solar cell via a variety of effects. For instance, the exposed crystal facets may affect the dye bonding, dye coverage, and injection efficiency, the electron transfer kinetics to the solution, and the trap state distribution [1]. Using these materials, we have compared the electron transport and recombination properties using small-signal perturbation techniques [2]. We have also addressed the influence of solution additives on the performance of ZnO-based dye-sensitized solar cells and rationalized the results. The influence of surface facet exposure on dye bonding is highlighted.

Infrared spectroscopy and luminescence spectra of Yb3+ doped ZrO2 nanophosphor

The present paper reports infrared spectroscopy and luminescence spectra of Yb3+ doped ZrO2 nanophosphor. Sample was prepared by combustion synthesis method (CSM) for the variable concentration of ytterbium. The low temperature synthesis method was suitable for large scale production present method is an eco-friendly method as well as less time taking method as compared to other methods. The synthesized samples were characterized by X-ray diffraction (XRD) technique; scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) technique. The crystal size was calculated by Scherer's formula. The particle size distribution in prepared sample was determined by SEM and TEM study. The photoluminescence spectra was recorded under the 980 nm laser excitation with the variable concentration of ytterbium. Here the PL intensity increases with increasing the concentration of ytterbium. No concentration quenching were observed. The PL emission spectra shows intense emission peaks at 987, 998 and 1021 nm all in infrared regions.

Enhancement in the structure quality of ZnO nanorods by diluted Co dopants: Analyses via optical second harmonic generation

We report a systematic study about the effect of cobalt concentration in the growth solution over the crystallization, growth, and optical properties of hydrothermally synthesized Zn1−xCoxO [0 ≤ x ≤ 0.40, x is the weight (wt.) % of Co in the growth solution] nanorods. Dilute Co concentration of 1 wt. % in the growth solution enhances the bulk crystal quality of ZnO nanorods, and high wt. % leads to distortion in the ZnO lattice that depresses the crystallization, growth as well as the surface structure quality of ZnO. Although, Co concentration in the growth solution varies from 1 to 40 wt. %, the real doping concentration is limited to 0.28 at. % that is due to the low growth temperature of 80 °C. The enhancement in the crystal quality of ZnO nanorods at dilute Co concentration in the solution is due to the strain relaxation that is significantly higher for ZnO nanorods prepared without, and with high wt. % of Co in the growth solution. Second harmonic generation is used to investigate the net dipole distribution from these coatings, which provides detailed information about bulk and surface structure quality of ZnO nanorods at the same time. High quality ZnO nanorods are fabricated by a low-temperature (80 °C) hydrothermal synthesis method, and no post synthesis treatment is needed for further crystallization. Therefore, this method is advantageous for the growth of high quality ZnO coatings on plastic substrates that may lead toward its application in flexible electronics.

Synthesis and luminescent properties of two different Y2WO6:Eu3+ phosphor phases

In this paper, two different Y2−xEuxWO6 phases were synthesized. The monoclinic phase was prepared via a conventional solid-state reaction, whereas the orthorhombic phase was obtained via a facile, low-temperature combustion synthesis method. X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and photoluminescence (PL) spectroscopy were used to characterize the resulting phosphors. The XRD results indicate the orthorhombic phase crystallized isostructurally with the Aurivillius Bi2WO6 phase, whereas the other polymorph crystallized isostructurally with Yb2WO6 in the monoclinic system. The SEM studies revealed both phases had a strong tendency to form agglomerates averaging nanometers in size. The photoluminescence emission spectra confirmed all of the samples were efficiently excited by near UV light and were dominated by the electric dipole transition 5D0→7F2. The orthorhombic Y2−xEuxWO6 excitation spectrum possessed a broad band across the entire UV region (220–400nm); therefore, Y1.86Eu0.14WO6 could be considered an efficient spectral converter material for use in dye-sensitized solar cells.

Schottky junction study for electrodeposited ZnO thin films and nanowires

ZnO thin films and well-aligned nanowire arrays have been synthesized via electrochemical deposition method, a low temperature and low cost synthesis method. For the ZnO nanowires growth, the electrodeposition consists of two steps: the ZnO buffer layer was firstly deposited on the substrate using galvanostatic method at room temperature following by the ZnO nanowires growth under potentiostatic method at 80 °C. This second step has also used for the ZnO thin films growth directly on substrate. The morphological and microstructural properties of the as-deposited ZnO have been characterized using scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), as well as photoluminescence spectroscopy (PL). The electrical transport of the ZnO thin films and nanowire arrays have been studied at room temperature both in the symmetrical Al/ZnO/Al electrode configuration guarantying a good Ohmic contact and in the asymmetrical Al/ZnO/Au electrode configuration demonstrating a typical Schottky contact at the interface ZnO/Au. The feature parameters such as the series resistance, the Schottky barrier height, and the ideality factor, have been systematically analyzed. Comparing the diode parameters between thin films and nanowire arrays, we deduced that about 1/3 of the ZnO nanowires come into effective contact with the top Al electrode.

Ferrous sulfate based low temperature synthesis and magnetic properties of nickel ferrite nanostructures

We report a simple, low temperature and surfactant free co-precipitation method for the preparation of nickel ferrite nanostructures using ferrous sulfate as the iron precursor. The products obtained from this method were compared for their physical properties with nickel ferrites produced through conventional co-precipitation and hydrothermal methods which used ferric nitrate as the iron precursor. X-ray diffraction analysis confirmed the synthesis of single phase inverse spinel nanocrystalline nickel ferrites at temperature as low as 110°C in the low temperature method. Electron microscopy analysis on the samples revealed the formation of nearly spherical nanostructures in the size range of 20–30nm which are comparable to other conventional methods. Vibrating sample magnetometer measurements showed the formation of superparamagnetic particles with high magnetic saturation 41.3emu/g which corresponds well with conventional synthesis methods. The spontaneous synthesis of the nickel ferrite nanoparticles by the low temperature synthesis method was attributed to the presence of 0.808kJmol−1 of excess Gibbs free energy due to ferrous sulfate precursor.

EPR and optical investigations of LaMgAl11O19:Cr3+ phosphor

The LaMgAl11O19:Cr3+ phosphor has been prepared by a low-temperature combustion synthesis method. As-prepared combustion synthesized powder was characterized using powder X-ray diffraction (XRD), diffuse reflectance (DRS), electron paramagnetic resonance (EPR) and photoluminescence (PL) studies. The X-ray diffraction pattern reveals crystalline hexagonal phases. The UV–vis diffuse reflectance spectrum exhibits three broad bands characteristic of Cr3+ ions in octahedral symmetry. The EPR spectrum exhibits several resonance signals. The signals with the effective g values at g=4.84, 3.64 and 2.26 have been attributed to the isolated Cr3+ ions. The signal with the effective g value at g=1.94 has been attributed to exchange coupled Cr3+–Cr3+ ion pairs. The PL studies exhibit several bands characteristic of Cr3+ ions in octahedral symmetry.

One‐step hydrothermal synthesis of the Ag/AgI heterojunction with highly enhanced visible‐light photocatalytic performances

The Ag/AgI heterojunction was prepared by a facile, one-step and low-temperature hydrothermal synthesis method with P, I 2 and Ag 2 O. The approach proves a green and simple route to the products, which avoided multiple-step synthesis and the subsequent time-consuming photoreduction. The samples were carefully characterised by X-ray diffraction, X-ray photoelectronic spectra, scanning electron microscopy, transmission electron micrographs and ultraviolet-visible-light techniques. The results show that Ag nanoparticles were uniformly distributed on the surface of AgI and the heterostructure was formed. Under visible light, the photocatalytic activity of the Ag/AgI composites for the degradation of rhodamine B (RhB) was efficient and much higher than that of pure AgI. In particular, the Ag/AgI composites (at 120°C for 4 h) exhibited the best photocatalytic activity, and nearly 98% of RhB was degraded within 20 min. Remarkably, the photocatalytic degradation followed the pseudo-first-order reaction model and the corresponding apparent first-order rate constant of 0.157 min -1 which is five times more than that of pure AgI. The enhanced photocatalytic activity of Ag/AgI can be attributed to the strong surface plasmon resonances.

Facile Liquid-phase Synthesis and Optical Properties of Small Silver Iodide Quantum Dots

Abstract We report a low-temperature liquid-phase synthesis method of small AgI quantum dots with a diameter of 3.0 nm. The synthesized AgI quantum dots were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and powder X-ray diffraction measurements. In the UV–visible spectrum, the AgI quantum dots had a large blue shift in the absorption band compared to bulk one because of the quantum size effect.

An electron paramagnetic resonance and optical study of Cr doped BaAl12O19 powders

The BaAl12O19 powders doped with Cr3+ ions have been prepared by a low-temperature combustion synthesis method. As prepared combustion synthesized powder was characterized using powder X-ray diffraction and energy dispersive analysis of X-ray methods. The diffuse reflectance spectrum exhibits three bands characteristic of Cr3+ ions in distorted octahedral symmetry. The EPR spectra exhibit signals with the effective g values at g=1.96, 2.27 and 4.85. The signals with the effective g values at g=2.27 and 4.85 have been attributed to the isolated Cr3+ ions. The signal at g=1.96 has been attributed to the exchange coupled Cr3+ ions. The excitation spectrum exhibits bands characteristic of Cr3+ ions in distorted octahedral symmetry. The ligand field parameter Dq and the Racah interelectronic repulsion parameters B and C have been evaluated from the excitation spectrum. The emission spectrum exhibits an intense band centered at 700nm (14,286cm−1) and this band has been attributed to 2Eg→4A2g transition.

Optimization of the low temperature combustion synthesis of Er3+ doped lead–natrium–yttrium–fluoride phosphor

The low-temperature combustion synthesis (LCS) method is the most popular method for the synthesis of ultrafine oxides and compound oxides. A kind of Er - Y - Pb - Na quaternary fluoride sensitive to 1.55 μm was synthesized by the LCS method and the synthesis conditions were optimized with orthogonal experiments. Intense upconversion emissions at 522 nm, 541.4 nm and 654.7 nm corresponding to the 2 H 11/2, 4 S 3/2 and 4 F 9/2 transitions to the 4 I 15/2 ground state were observed when excited by CW laser radiation at 1.55 μm. The effect of the carbamide amount on the phase formation and the luminescence intensity was analyzed. The product is of uniform particle size of ca. 40 nm, which is very outstanding for its reutilization in the infrared detection field.

Preparation and millimeter wave attenuation properties of NiFe2O4/expanded graphite composites by low-temperature combustion synthesis

Abstract In this paper, NiFe 2 O 4 /expanded graphite (EG) composites are successfully prepared by low-temperature combustion synthesis method. The morphology, structure and millimeter wave (MMW) attenuation properties of the NiFe 2 O 4 /EG composites are investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) and MMV radar measurement device. The effects of fuel and stoichiometric ratio on the composites are also investigated. The results show that NiFe 2 O 4 /EG composites are uniform and have a good crystallinity. The composites possess better MMW attenuation properties than EG. The 3 and 8 MMW attenuation performances of NiFe 2 O 4 /EG composites are 8.5 dB and 14.6 dB, respectively.