水热法制备ZnO及其光致发光

以氯化锌做为原料,氢氧化钠为矿化剂,在温度180℃、反应15h的条件下,利用水热法制备ZnO粉体。通过X射线衍射、扫描电镜和光致发光谱表征其晶体结构、微观形貌和光学性能。表征结果表明,随着反应溶液pH值的增大,ZnO的微观结构逐渐由一维棒状变成三维花状。对三维花状ZnO的形成机理进行了讨论,研究了pH对ZnO粉体的光致发光的影响。     

稀土掺杂钨钼酸盐类荧光粉水热法合成及结构与性能的研究

利用水热法制备了A0.925(MoO4)0.5(WO4)0.5∶Dy03.+05(A=Ca、Sr、Ba)固溶体微晶。通过X射线衍射(XRD)、扫描电镜(SEM)、荧光分析(FA)等测试手段对微晶结构、形貌和发光性能进行了表征。结果表明A0.925(MoO4)0.5(WO4)0.5∶Dy03+.05(A=Ca、Sr、Ba)复合钨钼酸盐微晶均呈现典型的四方晶相白钨矿结构。荧光光谱中的480nm处的偶合双峰和575nm处的锐而强的黄发射峰,分别对应于稀土离子Dy3+的4F9/2→6 H15/2和4F9/2→6 H13/2跃迁。其中具有球状颗粒(尺寸为0.7μm)形貌的Ca0.925(MoO4)0.5(WO4)0.5∶Dy03.+05微晶的发射峰强度最强,在光学材料中具有潜在应用。     

Hydrothermal synthesis,characterisation and photocatalytic properties of BiOIO3 nanoplatelets

In this work, BiOIO₃ nanoplatelets were successfully prepared by a simple hydrothermal method. The as-prepared samples were characterised by energy-dispersive spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray powder diffraction and ultraviolet visible diffuse reflectance spectroscopy. The photocatalytic activities of the as-prepared BiOIO₃ nanoplatelets were evaluated by photodegradation of rhodamine B (RhB) under simulated solar light. The results showed that the change of temperature within a certain range has almost no influence on the morphology and size of BiOIO₃ nanoplatelets. However, it had an obvious effect on the photocatalytic performance of BiOIO₃ nanoplatelets. The results showed that the BiOIO₃ sample synthesised at 130 °C exhibited the highest photocatalytic activities compared to others, with RhB completely decomposed in 80 min. The products with proper crystallinity formed at 130 °C have the optimal rate of RhB photodegradation. It indicated that the most favourable crystallinity made it beneficial to improve the photocatalytic activity. The possible mechanism of the photocatalytic reaction based on deep analysis and the experimental results was discussed in detail.     

EDTA-assisted phase conversion synthesis of (Gd0.95RE0.05)PO4 nanowires (RE = Eu,Tb) and investigation of photoluminescence

Abstract

Hexagonal (Gd_0.95RE_0.05)PO₄·nH₂O nanowires ~300 nm in length and ~10 nm in diameter have been converted from (Gd_0.95RE_0.05)₂(OH)₅NO₃·nH₂O nanosheets (RE = Eu, Tb) in the presence of monoammonium phosphate (NH₄H₂PO₄) and ethylene diamine tetraacetic acid (EDTA). They were characterized by X-ray diffraction, thermogravimetry, electron microscopy, and Fourier transform infrared and photoluminescence spectroscopies. It is shown that EDTA played an essential role in the morphology development of the nanowires. The hydrothermal products obtained up to 180 °C are of a pure hexagonal phase, while monoclinic phosphate evolved as an impurity at 200 °C. The nanowires undergo hexagonal→monoclinic phase transformation upon calcination at ≥600 °C to yield a pure monoclinic phase at ~900 °C. The effects of calcination on morphology, excitation/emission, and fluorescence decay kinetics were investigated in detail with (Gd_0.95Eu_0.05)PO₄ as example. The abnormally strong ⁵D₀→⁷F₄ electric dipole Eu³⁺ emission in the hexagonal phosphates was ascribed to site distortion. The process of energy migration was also discussed for the optically active Gd³⁺ and Eu³⁺/Tb³⁺ ions.     

Controlled synthesis and photoluminescence properties of hierarchical BaXO4 (X = Mo, W) nanostructures at room temperature

Controlled synthesis of hierarchical Barium molybdate (BaMoO₄) nanostructures with different morphologies, such as peanut-like, cube-like and flower-like, was successfully achieved in aqueous solution at room temperature. The obtained products were characterized by a scanning electron microscope (SEM) and an X-ray power diffractometer (XRD). The morphologies of the obtained products were found to be greatly dependent on reaction time, EDTA concentration and the [Ba²⁺]/[MoO₄²⁻] ratio. This controllable method could be readily extended to produce hierarchical Barium tungstate (BaWO₄) nanostructures with peanut-like, dumbbell-like, sphere-like and flower-like morphologies. The photoluminescence (PL) properties of the obtained BaMoO₄ and BaWO₄ nanostructures exhibited strong dependence on the morphologies and sizes, respectively.     

Facile hydrothermal crystallization of NaLn(WO4)2 (Ln=La-Lu,and Y), phase/morphology evolution,and photoluminescence

Abstract

Hydrothermal reaction of Ln nitrate and Na₂WO₄ at pH=8 and 200 °C for 24 hours, in the absence of any additive, has directly produced the scheelite-type sodium lanthanide tungstate of NaLn(WO₄)₂ for the larger Ln³⁺ of Ln=La-Dy (including Y, Group I) and an unknown compound that can be transformed into NaLn(WO₄)₂ by calcination at the low temperature of 600 °C for the smaller Ln³⁺ of Ln=Ho-Lu (Group II). With the successful synthesis of NaLn(WO₄)₂ for the full spectrum of Ln, the effects of lanthanide contraction on the structural features, crystal morphology, and IR responses of the compounds were clarified. The temperature- and time-course phase/morphology evolutions and the phase conversion upon calcination were thoroughly studied for the Group I and Group II compounds with Ln=La and Lu for example, respectively. Unknown intermediates were characterized by elemental analysis, IR absorption, thermogravimetry, and differential scanning calorimetry to better understand their chemical composition and coordination. The photoluminescence properties of NaEu(WO₄)₂ and NaTb(WO₄)₂, including excitation, emission, fluorescence decay, and quantum efficiency of luminescence, were also comparatively studied for the as-synthesized and calcination products.     

The effect of pH value on the synthesis and photocatalytic performance of MnWO4 nanostructure by hydrothermal method

In this study MnWO₄ nanocrystals with different morphologies were synthesised by a simple hydrothermal method with MnCl₂?·?4H₂O and Na₂WO₄?·?2H₂O as source materials. The products were characterised by X-ray powder diffraction, field-emission scanning electron microscopy, Raman spectroscopy and fluorescence spectroscopy. The results reveal that pH value plays an important role in the morphology and phase of samples. A simple reaction mechanism for the formation of MnWO₄ was presented. The photodegradation of acetone was employed as a probe reaction to test the photoactivities of the as-prepared samples.     

Facile synthesis and magnetic properties of manganese dioxide nanowires

A large number of MnO₂ nanowires were fabricated by a facile hydrothermal method. The nanowires have a tetragonal pyrolusite structure and a smooth surface. The common bulk defects such as dislocations, twinnings and stacking faults are not detected by HRTEM measurement. The magnetisation dependence of temperature indicates that the magnetisation, linearly and monotonically, increases with decreasing temperature in the range 300–80?K, revealing the paramagnetic properties of the nanowires. The first discharge capacity reaches 223.5?mA?h?g^?1, and the value of capacity steadily decreases during the following cycles, down to an acceptable 122.3?mA?h?g^?1 after 25 cycles. The high surface ratio of nanowires is the main reason for the excellent discharge cycle property of the MnO₂ nanowires.     

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.     

CaMoO4:Eu3+纳米荧光粉的尺寸调控及光学性能研究

采用水热法制备了CaMoO₄:Eu³⁺纳米荧光粉.研究了反应温度、反应时间和Eu³⁺掺杂浓度对CaMoO₄:Eu³⁺纳米晶的颗粒尺寸以及光学性能的影响.利用XRD、SEM、FT-IR、UV-Vis和PL对所得样品的相结构、形貌、光学吸收以及发光性能进行了表征.研究结果表明：所合成样品均为四方晶系白钨矿结构的CaMoO₄纳米晶;一方面,随着水热反应温度的降低或者反应时间的缩短,CaMoO₄:Eu³⁺纳米晶都表现出尺寸减小的趋势,荧光强度逐渐减弱,样品的紫外可见光吸收带边发生蓝移;另一方面,随着Eu³⁺掺杂浓度的增加,CaMoO₄:Eu³⁺纳米晶的颗粒尺寸逐渐减小,样品的紫外可见光吸收带边出现红移.同时,在275 nm的光激发下,CaMoO₄:Eu³⁺荧光粉在614 nm处的⁵D₀→⁷F₂跃迁具有最高的荧光强度,观察到红光发射,且发现其荧光猝灭摩尔浓度为6%.     

Controlled synthesis and photoluminescence properties of BaXO4 (X = W, Mo) hierarchical nanostructures via a facile solution route

Shape-controlled synthesis of BaWO₄ hierarchical nanostructures has been achieved in a mixed solvent of water and ethanol at room temperature. By simply adjusting the volume ratio of C₂H₅OH and H₂O (R ratio), the size and shape of BaWO₄ nanostructures, such as shuttle-like and ellipsoid-like, are successfully controlled. This simple method has been extended to synthesize BaMoO₄ hierarchical nanostructures. Both BaWO₄ and BaMoO₄ hierarchical nanostructures exhibited new green emission peaks at 558 and 560 nm, respectively.     

The effects of preparation conditions on the structural and up-conversion properties of NaYF4:Yb, Er nano powders

The NaYF₄:Yb³⁺, Er³⁺ powders were prepared by a co-precipitation method. The relationship between the phase ratio of cubic to hexagonal phase and the emission intensity ratio of red to green was investigated. This concluded that the cubic phase dominantly contributed to the red emission, while the green emission was mainly ascribed to the hexagonal phase. The effects of Al³⁺ doping on UC emission were investigated first. The red emission intensity of the cubic phase was drastically enhanced when 10 mol% Al was added.     

Hydrothermal synthesis of magnetite nanoparticles via sequential formation of iron hydroxide precipitates

A novel method for preparing fine magnetite nanoparticles without using any additives and organic solvents has been developed. In this method, a sequential precipitates formation method, ferrous and ferric hydroxides are not coprecipitated but sequentially formed in an alkaline solution, and then the resulting suspension is subjected to a hydrothermal treatment. The obtained magnetite nanoparticles were characterised through scanning electron microscopy observation and X-ray diffraction analysis, and the particle size and magnetic properties were measured with a dynamic light scattering particle size analyser and a superconducting quantum interference device magnetometer, respectively. In order to prepare fine magnetite nanoparticles with a uniform size, both the formation sequence of ferrous and ferric hydroxide precipitates and the supersaturation of ferric hydroxide in the solution were essential. The ferromagnetic magnetite nanoparticles with a median size 8.5?nm were relatively easily obtained in the formation process in which a ferric sulphate solution was rapidly poured into a suspension of ferrous hydroxide particles prepared beforehand using ferric chloride and sodium hydroxide, whereas the median size of magnetite nanoparticles prepared via conventional coprecipitation route was 38.6?nm.     

Polymer-assisted synthesis and luminescence properties of MgAl2O4:Tb nanopowder

In the present work, terbium doped magnesium alluminate (MgAl₂O₄:Tb) nanopowder was synthesized by a polyacrylamide gel method. Structure, morphology and luminescence spectra were investigated by X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), and photoluminescence spectroscopy (PL) measurements. The results showed that the single-phase MgAl₂O₄ could be formed at a relatively low temperature about 800 °C without unreacted Al₂O₃ and MgO phases. Powders with nanosized microstructures were formed. The polyacrylamide gel method resulted in a powder with smaller particle size and fewer agglomerates than the conventional sol-gel method. Luminescence analysis indicated that, the prepared MgAl₂O₄:Tb powders had strong green emission with ⁵D₄-⁷F₅ as the most prominent group. The emission intensity increased with increasing the calcination temperature.     

Facile synthesis of amine-functionalized graphene quantum dots with highly pH-sensitive photoluminescence

Graphene quantum dots (GQDs) as promising materials have gained increasing attention due to their optical and chemical properties, but the complicated synthetic procedures restrict their large-scale application. Here we report a novel one-pot hydrothermal method to synthesize the GQDs with bifunctional groups (-OH and -NH₂) using a polycyclic aromatic hydrocarbon as the precursor, in which 1,5-dinitronaphthalene was graphitized in aqueous ammonium solution. The as-synthesized GQDs with single-layer structures have a size distribution of 1–3 nm and an average value of 1.5 nm. The alkaline species play a crucial role in the formation of amine-functionalized GQDs. More importantly, the as-synthesized GQDs exhibit a distinct pH-sensitive photoluminescence and the fluorescence colors vary from bluish green to yellow with pH value from 5 to 10, which can be attributed to the protonation and deprotonation of the amine-groups in acid or alkaline solution.     

Nanorods of white light emitting Sr2SiO4:Eu2+: microemulsion-based synthesis,EPR, photoluminescence,and thermoluminescence studies

White light emitting Sr₂SiO₄:Eu²⁺ nanoparticles were prepared using reverse micellar route using Tergitol as a surfactant. The systems were characterised by X-ray diffraction, scanning electron microscopy (SEM), photoluminescence, thermoluminescence (TL), and electron paramagnetic resonance (EPR) spectroscopy. SEM shows the formation of silicate nanorods. Two emission bands of bluish-green at 490 nm (S(I)) and of orange-red at 605 nm (S(II)) were observed. The two emission bands are assigned to the 4f–5d transition of Eu²⁺ ions in two different cation sites in α′-Sr₂SiO₄ orthorhombic lattices. Gamma-irradiated Sr₂SiO₄:Eu showed the presence of three TL glow peaks at 437, 487 K and weak peak at 540 K; however, no glow was observed in the undoped sample. Reduction of Eu³⁺ to Eu²⁺ is confirmed by EPR spectroscopy.     

二硫化钼花状微球的水热合成及其微观结构表征

以钼酸铵作为钼源,硫脲作为硫源和还原剂,采用简便的水热法合成二硫化钼花状微球。采用X射线衍射仪、拉曼光谱仪、扫描电子显微镜和透射电子显微镜对二硫化钼样品的形貌和结构进行表征。考察了钼硫比、反应时间、反应温度对二硫化钼花状微球形貌和结构的影响。结果表明,当钼硫物质的量比为1∶2.25,反应温度为220℃,反应时间为18h时合成了结晶性好的纳米片(厚度为10nm)组装而成的二硫化钼花状微球,其具有较大的比表面积,是一种性能优异的锂离子电池电极材料。     

Hydrothermal synthesis of W and Mo co-doped VO2(B) nanobelts

W and Mo co-doped VO₂(B) nanobelts which used formic acid as reduction acid, NH₄VO₃ as vanadium source, (NH₄)₆W₇O₂₄?·?6H₂O and (NH₄)₆Mo₇O₂₄?·?4H₂O as doped sources were synthesised by the hydrothermal method. The samples were characterised by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). TEM and HRTEM images showed the samples had a length of 1?µm and a width of 100?nm. XRD, FTIR and XPS spectra revealed that Mo⁶⁺ and W⁶⁺ incorporated into the VO₂(B) lattice and formed solid-solution phases with VO₂(B).     

Hydrothermal synthesis of CeO2 nano-octahedrons

CeO₂ nano-octahedrons were synthesized with a facile hydrothermal synthesis process where Ce(NO₃)₃·6H₂O and urea were used as a cerium resource and mineralizer respectively and no surfactant or template was applied. The effects of synthesis parameters such as reaction temperature, reaction time, as well as the dosages of Ce (NO₃)₃·6H₂O and urea were studied. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis were conducted to characterize the crystalline and morphology of the obtained CeO₂ powders. The optimal reaction condition to prepare the CeO₂ of the desired fluorite structure was established. The possible mechanism of synthesis of CeO₂ with a nano-octahedron morphology was illustrated.     

Self-assembled 3D flower-like NaY(MoO4)2:Eu microarchitectures: Hydrothermal synthesis, formation mechanism and luminescence properties

Self-assembled 3D flower-like NaY(MoO₄)₂:Eu³⁺ microarchitectures were successfully synthesized by a glycine-assisted hydrothermal method at 180 °C. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) were employed to characterize the as-obtained products. It was found that morphology modulation could be easily realized by changing the time of hydrothermal reaction system. 3D flower-like NaY(MoO₄)₂:Eu³⁺ microarchitectures were formed with 72 h reaction time. The formation mechanism for flower-like architecture was proposed on the basis of a series of time-dependent experiments. The NaY(MoO₄)₂:Eu³⁺ powders obtained can be effectively excited by 396 nm light, and exhibit strong red emission around 615 nm, attributed to the Eu³⁺⁵D₀ → ⁷F₂ transition. An investigation on the photoluminescence (PL) properties of NaY(MoO₄)₂:Eu³⁺ obtained revealed that the luminescence properties were correlated with the morphology and size.