Synthesis of barium fluoride nanoparticles from microemulsion

The cetyltrimethylammonium bromide (CTAB)/2-octanol/water microemulsion system was used to synthesize barium fluoride nanoparticles. X-ray powder diffraction (XRD) analysis showed that the products were single phase. The results of scanning electron microscopy and calculations using the Scherrer equation from the line widths of the XRD have been used to estimate the average particle sizes of the powder products. The results showed that the nanoparticle size was affected by water content and surfactant (CTAB) concentration. As water content decreases from 14.2 to 9.47% (w/w), the particle size decreases from 75 to 40 rim. In addition, increasing the reaction times from 5 to 120 min increases the particle size from 75 to 150 rim, and increasing the amount of surfactant decreases the size of the particle. Luminescence spectra of the BaF2:Ce nanoparticles are also discussed.

Synthesis and fluorescence properties of Eu2+-doped KMgF3 nanoparticles

The phase diagram of a cetyltrimethyl ammonium bromide( CTAB)/n-butanol/n-octane/KNO3-Mg( NO3)(2) system was drawn. Nanoparticles of Eu2+-doped KMgF3 were prepared from the quaternary microemulsions of cetyltrimethyl ammonium bromide(CTAB), n-butanol, n-octane and water. The X-ray diffraction(XRD) patterns were indexed to a pure KMgF3 cubic phase. The environmental scanning electron microscopic (ESEM) images show the presence of spherical Eu2+-doped KMgF3 nanoparticles with a diameter of ca. 20 nm. The emission of KMgF3: Eu2+ nanoparticles peaks at 360 mn. The excitation band was observed at 250 nm with a blue shift of ca. 70 nm compared with that of KMgF3: Eu2+ single crystal. The preparation method of nano-KMgF3: Eu2+/PMMA composite films was inquired into.

An in situ ionic-liquid-assisted synthetic approach to iron fluoride/graphene hybrid nanostructures as superior cathode materials for lithium ion batteries

A tactful ionic-liquid (IL)-assisted approach to in situ synthesis of iron fluoride/graphene nanosheet (GNS) hybrid nanostructures is developed. To ensure uniform dispersion and tight anchoring of the iron fluoride on graphene, we employ an IL which serves not only as a green fluoride source for the crystallization of iron fluoride nanoparticles but also as a dispersant of GNSs. Owing to the electron transfer highways created between the nanoparticles and the GNSs, the iron fluoride/GNS hybrid cathodes exhibit a remarkable improvement in both capacity and rate performance (230 mAh g^-1 at 0.1 C and 74 mAh g^-1 at 40 C). The stable adhesion of iron fluoride nanoparticles on GNSs also introduces a significant improvement in long-term cyclic performance (115 mAh g^-1 after 250 cycles even at 10 C). The superior electrochemical performance of these iron fluoride/GNS hybrids as lithium ion battery cathodes is ascribed to the robust structure of the hybrid and the synergies between iron fluoride nanoparticles and graphene. © 2013 American Chemical Society.

氟化物无机纳米粒子的制备及其稀土掺杂体系的光谱性质

对于纳米复合材料来说，首要解决的问题就是光散射。光散射现象主要是粒子尺寸以及粒子与基质材料折射率的差异引起的。对于小粒子（＜25nm），纳米粒子与基质材料之间的折射率差异不会造成明显的光散射现象，但对于较大粒子来说，为避免明显的光散射现象的发生，二者之间的折射必须吻合。由瑞利散射公式计算得知，当粒子直径大到100nm时，粒子与基质之间的折射率差值必须在0.02之内。因此，解决复合材料光散射问题有两种途径：尽量减小纳米粒子尺寸；选择折射率匹配良好的氟化物和聚合物分别作光学活性组分的基质和材料的基底材料。由于微乳液法合成纳米粒子条件温和、设备简单，所合成纳米粒子尺寸可控。本文首先研究了微乳液结构和性质，采用微乳液法合成氟化物纳米粒子，并研究了其稀土掺杂体系的光学性质。对于微乳液结构和性质的研究，本文绘制了十六烷基三甲基嗅化钱（CTAB）／正丁醇（n-C_4H_9OH）／正辛烷（n-C_8H_(18)）／水（或NH4F溶液、或Ba(NO_3)_2溶液、或KNO_3-Mg(NO_3)_2混合溶液）四组分微乳体系的三元相图，观察了电导率随水（或豁溶液）含量变化的规律，很好地印证了微乳液体系的相行为。实验发现，在这四个四元体系的相图中，Ba(NO_3)_2溶液体系的油包水区域面积最大，纯水体系水包油微乳区面积最小，我们分析认为水包油微乳区面积的变化是由于体系中加入离子后对表面活性剂阳离子的静电作用所引起的。采用十六烷基三甲基澳化按（CTAB）／正丁醇／正辛烷／水体系合成了KMgF_3以及KMgF_3:Eu~(2+)纳米粒子。XRD分析表明所合成纳米粒子为立方KMgF_3单相；环境扫描电子显微镜（ESEM）分析得到所合成KMgF_3:Eu~(2+)纳米粒子粒径约为20nm。KMgF_3:Eu~(2+)纳米粒子光谱研究发现其发射峰位于360nm附近，其激发峰位于250nm附近，较KMgF_3:Eu~(2+)单晶的激发峰峰蓝移了约80nm。对KMgF_3:Eu~(2+)纳米粒子激发峰蓝移的机理进行了初步探讨。采用CTAB/2-丁醇／水微乳体系合成出球形BaF_2纳米粒子，XRD和ICP数据显示样品为纯BaF_2相；FTIR谱图证明体系中没有有机物质的存在。将由纳米粒子分散到水中所形成的胶体滴到铜网上，干燥后发现所合成粒子有自组装的特性摘要且粒子自组装形状因粒子尺寸以及样品制备过程而异。粒子的自组装完全是自发的，没有任何的化学试剂对粒子进行包覆，也没对粒子施加除超声分散之外的任何外力。当将一滴胶体溶液直接滴到铜网上，干燥后我们得到粒子的圆形自组装，较大粒子分布在外围形成一个圆，较小粒子分布在圆的内部形成环；我们将一滴BaF_2纳米粒子胶体溶液滴加到铜网上，待干燥后滴加第二滴，重复此操作两次，这样铜网上共滴加的胶体溶液为3滴，此时我们得到粒子的双平行线型组装；直接滴加3滴BaF_2纳米粒子胶体溶液到铜网上，干燥后得粒子的桶状自组装。采用CTAB／正丁醇／正辛烷／水体系于35℃下合成带有枝晶的BaF_2纳米立方。这些枝晶生长在纳米立方的两个相邻面之间呈片状弧形。粉末XRD分析表明，体系为BaF_2单相且结晶良好；用扫描电子显微镜（SEM）对粒子进行分析发现，所得纳米立方边长为400-450nm；FTIR分析表明，经处理后样品中没有有机物质残存；对枝晶的能谱分析（EDS）分析表明，枝晶中只有Ba和F两种元素而未发现C元素存在。这说明，立方上所生长的枝晶为纯BaF_2产物而非有机物质所形成的。试验发现，所合成粒子的尺寸和形状依赖于反应温度和反应时间。采用士一述体系，于25℃下反应，可得到横截面边长40nm，长200nm的立方柱状纳米粒子，并且未见枝晶。从不同反应时间所合成粒子的形状上我们可以估计纳米立方以及枝晶的住：长过程。采用CTAB／正丁醇／正辛烷／水体系首次合成了BaF_2:Er纳米粒子，并研究了掺杂浓度对粒子红外发光的影响，XRD分析表明所合成BaF_2:Er纳米粒子为BaF_2立方相，物相纯净，结晶良好；TEM分析表明在掺杂浓度为6mol％时，粒子尺寸为15-20nm，士曾大粒子的掺杂浓度（8，10和12mol％）下，其尺寸和形状无明显改变，但粒子团聚现象严重。粒子在氢离子激光器488nm激发下的荧光（PL）光谱显示，随粒子掺杂浓度的增大，其发光强度增强，半峰宽加宽。研究了BoF_2:Er纳米粒子尺寸对其发光强度的影响，通过调节体系中水含量以达到控制粒子尺寸的目的。在体系中水含量。分别为5，8，15的条件「分别合成出平均粒径约为8，10和20.5nm的粒子。从粒子的激光粒度分布图中我们可得到粒子的平均尺寸。从粒子的XRD图中我们可以发现，随粒子粒径的减小，粉末的衍射峰出现偏移的情况。对于不同种纳米粒子，粒子粒径越小，衍射峰偏移越严重；对于相同的粒子，衍射角度越大，衍射峰偏移的越严重。从三种粒子的红峰的半峰宽和有效半峰宽越宽，对于8nm粒径的粒子，我们得到其最大半峰宽为145nm或有效半峰宽173nm。而且随粒子粒径的减小，其发射峰出现红移的现象。采用CTAB／正丁醇／正辛烷／水体系首次合成了CeF_3以及掺杂浓度为17，25，30，42和50mol％的CeF_3:Lu纳米粒子。XRD分析表明，所合成纳米粒子为CeF_3六角相，物相纯净，结晶良好，即使在高的掺杂浓度下（50mol％）体系中一也无其他杂质相的存在。环境扫描电子显微镜（ESEM-FEG）分析表明，所合成CeF_3纳米粒子粒径为巧一20nm，Lu的掺入对粒子的形状和尺寸影响不明显，但在较高的掺杂浓度下粒子团聚现象严重。粒子的荧光光谱表明，CeF_3以及Lu：CeF_3纳米粒子在254nm的激发波长下的发射光谱从290nm到400nm的宽带发射，发射峰位于325nm，较单晶体的发射峰红移约30nm；Lu的掺入有利于提高CeF_3纳米粒子的发光强度，随Lu掺入量的增大，粒子的发光强度出现先增后减的情况，在掺杂浓度为30mol％时，我们得到CeF_3纳米粒子的最大发射，但在50mol％的掺杂浓度下的粒子的发射强度仍要比未掺杂体系的发光强度要强。325nln监测粒子的激发光谱是从200nm到350nm的宽带吸收，激发峰峰位于260nm左右。比CeF_3单晶体的280nm激发峰蓝移了20nm左右。而且粒子的激发光谱中未见长波方向上的肩峰，说明粒子中CeF_3纳米粒子结晶良好，且体系中氧含量低。采用自创建一步原位聚合的方法合成了聚合物包覆的纳米粒子，并采用本体聚合的方法合成复合材料。综上所述，本文采用微乳液法合成了不同的氟化物纳米粒子，并研究了其稀土掺杂体系的光学特性，为聚合物基复合材料的制备以及应用奠定了可靠的实验基础。

Shape and Phase-Controlled Synthesis of KMgF3 Colloidal Nanocrystals via Microwave Irradiation

In this paper, we present a facile one-step route to controlled synthesis of colloidal KMgF3 nanocrystals via the thermolysis of metal trifluoroacetate precursors in combined solvents (OA/OM) using microwave irradiation. X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared (FT-IR) spectra, and photoluminescence (PL) spectra were employed to characterize the samples. Only through the variation of the OA/OM ratio, can the phase and shape of nanocrystals be readily controlled, resulting in the formation of well-defined near-spherical nanoparticles, and nanoplates of cubic-phased KMgF3, as well as nanorods of tetragonal-phased MgF2, and a possible mechanism has been proposed to elucidate this effect. Furthermore, all these samples in this system can be well dispersed in nonpolar solvents such as cyclohexane to form stable and clear colloidal solutions, due to the successful coating of organic surfactants (OA/OM) on the nanocrystal surface.

Synthesis of mesoporous YF3 nanoflowers via solvent extraction route

Mesoporous YF3 nanoflowers were successfully prepared via solvent extraction route. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations indicated that these nanoflowers with uneven porous architectures had a spherical shape and were consisted of many YF3 nanosheets with a thickness of about 15 not. Energy-dispersive spectroscopy (EDS) analysis was used to check the chemical composition and purity of the products. YF3 nanoflowers had bimodal mesoporous distribution and Brunauer-Emmett-Teller (BET) surface area of 116 m(2)/g.

Sonochemical synthesis and luminescence properties of single-crystalline BaF2:Eu3+ nanospheres

BaF2 nanocrystals doped with 5.0 mol% Eu3+ has been successfully synthesized via a facile, quick and efficient ultrasonic solution route employing the reactions between Ba(NO3)(2), Eu(NO3)(3) and KBF4 under ambient conditions. The product was characterized via X-ray powder diffraction (XRD), scanning electron micrographs (SEM), transmission electron microscopy (TEM), high-resolution transmission electron micrographs (HRTEM), selected area electron diffraction (SAED) and photoluminescence (PL) spectra. The ultrasonic irradiation has a strong effect on the morphology of the BaF2:Eu3+ particles. The caddice-sphere-like particles with an average diameter of 250 nm could be obtained with ultrasonic irradiation, whereas only olive-like particles were produced without ultrasonic irradiation. The results of XRD indicate that the obtained BaF2:Eu3+ nanospheres crystallized well with a cubic structure. The PL spectrum shows that the BaF2:Eu3+ nanospheres has the characteristic emission of Eu3+ D-5(0)-F-7(J) (J = 1-4) transitions, with the magnetic dipole D-5(0)-F-7(1) allowed transition (590 nm) being the most prominent emission line.

Surprising arching sheet-like dendrites growing from BaF2 nanocubes

BaF2 nanocubes were prepared from quaternary reverse micelles of cetyl trimethyl ammonium bromide (CTAB), n-butanol, n-octane, and water. Interestingly, there are arching sheet-like dendrites growing between two neighbouring sides of these cubes. X-ray powder diffraction (XRD) analysis showed that the products were BaF2 single phase. Scanning electron microscopy (SEM) or transition electron microscopy (TEM) was used to estimate the size of the final products. The results showed that the shape and size of particles were strongly dependent on the reaction conditions, such as the temperature and reaction time. When the reaction temperature was 25 degreesC, we obtained cuboid-like particles with 'clean' surfaces (no dendrites growing on them), and when the temperature was 35 degreesC, we obtained nanocubes with dendrites growing from them between the neighbouring sides. The influence of reaction time at a temperature of 35 degreesC is also discussed.

Flame Synthesis of Complex Fluoride-Based Nanoparticles as Upconversion Phosphors

Recent improvements in precursor chemistry, reactor geometry and run conditions extend the manufacturing capability of traditional flame aerosol synthesis of oxide nanoparticles to metals, alloys and inorganic complex salts. As an example of a demanding composition, we demonstrate here the one-step flame synthesis of nanoparticles of a 4-element non-oxide phosphor for upconversion applications. The phosphors are characterized in terms of emission capability, phase purity and thermal phase evolution. The preparation of flame-made beta-NaYF4 with dopants of Yb, Tm or Yb, Er furthermore illustrates the now available nanoparticle synthesis tool boxes based on modified flamespray synthesis from our laboratories at ETH Zurich. Since scaling concepts for flame synthesis, including large-scale filtration and powder handling, have become available commercially, the development of industrial applications of complex nanoparticles of metals, alloys or most other thermally stable, inorganic compounds can now be considered a feasible alternative to traditional top-down manufacturing or liquid-intense wet chemistry.

Poly(vinylidene fluoride)-Based Flexible and Lightweight Materials for Attenuating Microwave Radiations

Two unique materials were developed, like graphene oxide (GO) sheets covalently grafted on to barium titanate (BT) nanoparticles and cobalt nanowires (Co-NWs), to attenuate the electromagnetic (EM) radiations in poly(vinylidene fluoride) (PVDF)-based composites. The rationale behind using either a ferroelectric or a ferromagnetic material in combination with intrinsically conducting nanoparticles (multiwall carbon nanotubes, CNTs), is to induce both electrical and magnetic dipoles in the system. Two key properties, namely, enhanced dielectric constant and magnetic permeability, were determined. PVDF/BT-GO composites exhibited higher dielectric constant compared to PVDF/BT and PVDF/GO composites. Co-NWs, which were synthesized by electrodeposition, exhibited saturation magnetization (M-s) of 40 emu/g and coercivity (Hc) of 300 G. Three phase hybrid composites were prepared by mixing CNTs with either BT-GO or Co-NWs in PVDF by solution blending. These nanoparticles showed high electrical conductivity and significant attenuation of EM radiations both in the X-band and in the Ku-band frequency. In addition, BT-GO/CNT and Co-NWs/CNT particles also enhanced the thermal conductivity of PVDF by ca. 8.7- and 9.3-fold in striking contrast to neat PVDF. This study open new avenues to design flexible and lightweight electromagnetic interference shielding materials by careful selection of functional nanoparticles

New physical insights into the electromagnetic shielding efficiency in PVDF nanocomposites containing multiwall carbon nanotubes and magnetic nanoparticles

This work attempts to bring critical insights into the electromagnetic shielding efficiency in polymeric nanocomposites with respect to the particle size of magnetic nanoparticles added along with or without a conductive inclusion. To gain insight, various Ni-Fe (NixFe1-x; x = 10, 20, 40; Ni: nickel, Fe: iron) alloys were prepared by a vacuum arc melting process and different particle sizes were then achieved by a controlled grinding process for different time scales. Poly(vinylidene fluoride), PVDF based composites involving different particle sizes of the Ni-Fe alloy were prepared with or without multiwall carbon nanotubes (MWNTs) by a wet grinding approach. The Ni-Fe particles were thoroughly characterized with respect to their microstructure and magnetization; and the electromagnetic (EM) shielding efficiency (SE) of the resulting composites was obtained from the scattering parameters using a vector network analyzer in a broad range of frequencies. The saturation magnetization of Ni-Fe nanoparticles and the bulk electrical conductivity of PVDF/Ni-Fe composites scaled with increasing particle size of NiFe. Interestingly, the PVDF/Ni-Fe/MWNT composites showed a different trend where the bulk electrical conductivity and SE scaled with decreasing particle size of the Ni-Fe alloy. A total SE of similar to 35 dB was achieved with 50 wt% of Ni60Fe40 and 3 wt% MWNTs. More interestingly, the PVDF/Ni-Fe composites shielded the EM waves mostly by reflection whereas, the PVDF/Ni-Fe/MWNT shielded mostly by absorption. A minimum reflection loss of similar to 58 dB was achieved in the PVDF/Ni-Fe/MWNT composites in the X-band (8-12 GHz) for a particular size of Ni-Fe alloy nanoparticles. This study brings new insights into the EM shielding efficiency in PVDF/magnetic nanoparticle based composites in the presence and absence of conducting inclusion.

Tailor-Made Distribution of Nanoparticles in Blend Structure toward Outstanding Electromagnetic Interference Shielding

Engineering blend structure with tailor-made distribution of nanoparticles is the prime requisite to obtain materials with extraordinary properties. Herein, a unique strategy of distributing nanoparticles in different phases of a blend structure has resulted in >99% blocking of incoming electromagnetic (EM) radiation. This is accomplished by designing a ternary polymer blend structure using polycarbonate (PC), poly(vinylidene fluoride) (PVDF), and poly(methyl methacrylate) (PMMA) to simultaneously improve the structural, electrical, and electromagnetic interference shielding (EMI). The blend structure was made conducting by preferentially localizing the multi-wall nanotubes (MWNTs) in the PVDF phase. By taking advantage of pp stacking MWNTs was noncovalently modified with an imidazolium based ionic liquid (IL). Interestingly, the enhanced dispersion of IL-MWNTs in PVDF improved the electrical conductivity of the blends significantly. While one key requisite to attenuate EM radiation (i.e., electrical conductivity) was achieved using MWNTs, the magnetic properties of the blend structure was tuned by introducing barium ferrite (BaFe) nanoparticles, which can interact with the incoming EM radiation. By suitably modifying the surface of BaFe nanoparticles, we can tailor their localization under the macroscopic processing condition. The precise localization of BaFe nanoparticles in the PC phase, due to nucleophilic substitution reaction, and the MWNTs in the PVDF phase not only improved the conductivity but also facilitated in absorption of the incoming microwave radiation due to synergetic effect from MWNT and BaFe. The shielding effectiveness (SE) was measured in X and K-u band, and an enhanced SE of -37 dB was noted at 18 GHz frequency. PMMA, which acted as an interfacial modifier in PC/PVDF blends further, resulting in a significant enhancement in the mechanical properties besides retaining high SE. This study opens a new avenue in designing mechanically strong microwave absorbers with a suitable combination of materials.

Photoluminescence properties of LaF3: Eu3+ nanoparticles prepared by refluxing method

The europium-doped LaF3 nanoparticles were prepared by refluxing method in glycerol/water mixture and characterized with X-ray diffraction(XRD), field emission scanning electron microscopy(FE-SEM), UV-vis diffuse reflectance spectrum, and photoluminescence spectra. The results of XRD indicated that the obtained LaF3: Eu3+ nanoparticles were well crystallized with a hexagonal structure. ne FE-SEM image illustrated that the LaF3: Eu3+ nanoparticles were spherical with an average size around 30 nm. Under irradiation of UV light, the emission spectrum of LaF3: Eu3+ nanoparticles exhibited the characteristic line emissions arising front the D-5(0)-> F-7(J), (J=1, 2, 3, 4) transitions of the Eu3+ ions, with the dominating emission centered at 590 nm. In addition, the emissions from the 51), level could be clearly observed due to the low phonon energies (-350 cm(-1)) of LaF3 matrix. The optimum doping concentration for LaF3: Eu3+ nanoparticles was determined to be 20mol.%.

Different microstructures of ss-NaYF4 fabricated by hydrothermal process: Effects of pH values and fluoride sources

beta-NaYF4 microcrystals with a variety of morphologies, such as microrod, hexagonal microprism, and octadecahedron, have been synthesized via a facile hydrothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra were used to characterize the samples. The intrinsic structural feature of beta-NaYF4 seeds and two important external factors, namely, the pH values in the initial reaction solution and fluoride sources, are responsible for shape determination of beta-NaYF4 microcrystals. It is found that the organic additive trisodium citrate (Cit(3-)) as a shape modifier has the dynamic effect by adjusting the growth rate of different facets under different experimental conditions, resulting in the formation of the anisotropic geometries of various beta-NaYF4 microcrystals. The possible formation mechanisms for products with various architectures have been presented. A systematic study on the photoluminescence of Tb3+-doped beta-NaYF4 samples with rod, prism, and octadecahedral shapes has shown that the optical properties of these phosphors are strongly dependent on their morphologies and sizes.

Synthesis and photoluminescence properties of erbium-doped BaF2 nanoparticles

Erbium-doped BaF2 nanoparticles were prepared from the microemulsion of cetyl trimethyl ammonium bromide (CTAB), n-butanol, n-octane and water. The X-ray diffraction (XRD) patterns were indexed to a pure BaF2 cubic phase. Transmission electron microscopy (TEM) images showed that BaF2 products were monodispersed with 15-20 nm in size at the dopant concentration of 0.06 mol%. At higher dopant concentration, there was no significant increase in particle size, but more polydispersed. Photoluminescence (PL) properties of the final products were examined. We can observe fluorescence of Er3+ around 1540 nm and with the increase of dopant concentration, the fluorescent intensity increases.