Single-crystalline and monodisperse LaF3 triangular nanoplates from a single-source precursor

Single-crystalline and monodisperse LaF3 triangular nanoplates (2.0 x 16.0 nm) in trigonal tysonite structure were synthesized by the thermolysis of a single-source precursor (SSP), La(CF3COO)3, in a hot oleic acid/octadecene solution. The combined use of SSP and coordinating and noncoordinating solvents was demonstrated to have played key roles in the formation of such high-quality nanoplates, which could spontaneously organize into two types of superlattices (edge-to-edge and face-to-face) on a large area. This SSP approach has advantages of one-step, mass production, and easy operation, and may represent a rather general route toward metal fluoride nanocrystals.     

High-quality sodium rare-earth fluoride nanocrystals: controlled synthesis and optical properties

We report a general synthesis of high-quality cubic (alpha-phase) and hexagonal (beta-phase) NaREF4 (RE: Pr to Lu, Y) nanocrystals (nanopolyhedra, nanorods, nanoplates, and nanospheres) and NaYF(4):Yb,Er/Tm nanocrystals (nanopolyhedra and nanoplates) via the co-thermolysis of Na(CF3COO) and RE(CF3COO)3 in oleic acid/oleylamine/1-octadecene. By tuning the ratio of Na/RE, solvent composition, reaction temperature and time, we can manipulate phase, shape, and size of the nanocrystals. On the basis of its alpha --> beta phase transition behavior, along the rare-earth series, NaREF4 can be divided into three groups (I: Pr and Nd; II: Sm to Tb; III: Dy to Lu, Y). The whole controlled-synthesis mechanism can be explained from the point of view of free energy. Photoluminescent measurements indicate that the value of I610/I590 and the overall emission intensity of the NaEuF4 nanocrystals are highly correlative with the symmetries of the Eu3+ ions in both the lattice and the surface.     

棒状LaF3∶Eu3+纳米晶的制备与发光性能

采用一种简单的液相反应法在室温下合成了棒状的LaF3∶Eu3+纳米晶, 对其结构和发光性能进行了表征. XRD分析结果表明, 室温下即可得到结晶良好的六方晶相的LaF3, 灼烧之后样品的衍射峰增强, 没有杂相产生. TEM照片表明, 棒状LaF3∶Eu3+纳米材料的直径为8 nm左右, 长度达到50 nm. 荧光光谱表明, 室温下合成的棒状LaF3∶Eu3+纳米晶的最强发射峰位于589 nm, 对应于Eu3+的5D0-7F1跃迁发射, 说明Eu3+占据LaF3基质中La3+晶格点的C2对称格位上. 同时Eu3+的猝灭摩尔分数为5%, 荧光寿命随着灼烧温度的升高而延长.     

Monodisperse lanthanide oxysulfide nanocrystals

Monodisperse lanthanide oxysulfide nanoplates and short nanorods were synthesized by the thermal decomposition of molecular precursors in the presence of oxygen. The nanoplates have uniform thicknesses and further self-organize to nanowires up to micron scale. The Eu2O2S and Eu3+-doped Gd2O2S nanocrystals both show unusual fluorescence properties obviously differing from the bulk powder phosphors, which are related to the surface-modification effects.     

LaF3纳米片和棒束的选择性合成及表征

室温条件下,以简单的液相法,通过改变氟源NaBF4和K2SiF6,制得不同形貌的LaF3纳米晶(片及棒束).X射线衍射(XRD)结果显示所得的2种不同形貌的产物均为结晶良好的六方相LaF3.场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)结果表明由NaBF4制得大量均匀、厚度约为20 am的六边形纳米片....     

Phase- and size-controllable synthesis of hexagonal upconversion rare-earth fluoride nanocrystals through an oleic acid/ionic liquid two-phase system

Herein, we introduce a facile, user- and environmentally friendly (n-octanol-induced) oleic acid (OA)/ionic liquid (IL) two-phase system for the phase- and size-controllable synthesis of water-soluble hexagonal rare earth (RE = La, Gd, and Y) fluoride nanocrystals with uniform morphologies (mainly spheres and elongated particles) and small sizes (<50?nm). The unique role of the IL 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)) and n-octanol in modulating the phase structure and particle size are discussed in detail. More importantly, the mechanism of the (n-octanol-induced) OA/IL two-phase system, the formation of the RE fluoride nanocrystals, and the distinctive size- and morphology-controlling capacity of the system are presented. BmimPF(6) is versatile in term of crystal-phase manipulation, size and shape maintenance, and providing water solubility in a one-step reaction. The luminescent properties of Er(3+)-, Ho(3+)-, and Tm(3+)-doped LaF(3), NaGdF(4), and NaYF(4) nanocrystals were also studied. It is worth noting that the as-prepared products can be directly dispersed in water due to the hydrophilic property of Bmim(+) (cationic part of the IL) as a capping agent. This advantageous feature has made the IL-capped products favorable in facile surface modifications, such as the classic Stober method. Finally, the cytotoxicity evaluation of NaYF(4):Yb,Er nanocrystals before and after silica coating was conducted for further biological applications.     

Adsorption of dye from wastewater using chitosan-CTAB modified bentonites

Multifunctional magnetic-fluorescent nanohybrids were successfully fabricated by a facile layer-by-layer (LBL) self-assembly of in situ generated Eu, Gd co-doped LaF(3) nanocrystals (LaF(3):Eu:Gd) on the surface of multi-walled carbon nanotubes (MWNTs). Photoluminescence (PL) quenching occurred when LaF(3):Eu:Gd nanoparticles were directly coated on the surface of MWNTs. By growth of a SiO(2) shell spacer between MWNTs and LaF(3):Eu:Gd nanocrystals, we circumvented the PL quenching and achieved the magnetic-fluorescent MWNTs. Moreover, the nanohybrids showed powerful T(1) and T(2)-weighted magnetic resonance imaging (MRI) signal in water and could be used as MRI contrast agents. As a result, the nanohybrids can be expected to act as a promising multimodal MRI/optical imaging probe.     

沉淀转化法制备多孔片状纳米LaF3

采用实验中所合成的LaPO4纳米棒为前驱体,通过沉淀的转化作用,大面积地制备了单分散的片状纳米LaF3。采用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)、BET(Brunauer-Emmett-Teller)测试对片状纳米LaF3的形貌、结构、相组成及表面性质进行了分析。片状纳米LaF3底边长约为40 nm,片的厚度约为35 nm,大小均一,具有多孔结构。通过改变反应溶剂,可以控制LaF3粒子的成核、生长和团聚,从而有效地调控多孔片状纳米LaF3的颗粒尺寸和分散性。对多孔片状纳米LaF3的生长机制进行了研究,结果表明LaPO4和LaF3的溶度积常数差导致了片状纳米LaF3的生成;体系中自身存在的Ostwald ripening作用使片状纳米LaF3出现了多孔结构。     

Luminescence behavior of Eu3+ doped LaF3 nanoparticles

Europium-doped LaF3 nanoparticles have been prepared by the ionic reaction in the ethanol at 60 degrees C. From the XRD pattern of nanoparticles and the emission spectra of Eu3+ ions, it has been concluded that the Eu3+ ions could easily substitute the La3+ sites and the solid solution La(1-x)Eu(x)F3 can be synthesized. Due to very low phonon energies of LaF3 matrix, the 5D1 emission of Eu3+ ions in La(1-x)Eu(x)F3 nanoparticles can be observed at room temperature when doping concentration of Eu3+ ions is lower than 30 mol%. The quenching process of 5D1 emission can be attributed to cross-relaxation. Since clusters of Eu3+ ions and resonance energy transfer only occurs within one particle due to the hindrance by the particle boundary, the concentration quenching resulted from resonance energy transfer between neighboring Eu3+ ions occurs at higher Eu3+ concentrations in the Eu3+ doped LaF3 nanoparticles.     

Mesoporous rare earth fluoride nanocrystals and their photoluminescence properties

YF(3) and YF(3):Eu(3+) mesoporous hexagonal nanocrystals were successfully synthesized via a simple hydrothermal process based on the in situ assembly of the as-synthesized YF(3) and YF(3):Eu(3+) nanoparticles. The well defined mesoporous nanostructures are formed by phenanthroline assisted assembly of ～20 nm nanoparticles, and 2-4 nm pores are contained as indicated by N(2) adsorption-desorption studies. The obtained YF(3):Eu(3+) mesoporous hexagonal nanoplates show a significant photoluminescence intensity enhancement compared with other shaped YF(3):Eu(3+) nanocrystals.     

Improvement in the luminescence properties and processability of LaF3/Ln and LaPO4/Ln nanoparticles by surface modification

The surface of lanthanide(III)-doped LaPO4 nanoparticles was modified by reaction with an alcohol, leading to a covalent bond between the ligand and the particle surface. The surface of lanthanide(III)-doped LaF3 nanoparticles was modified to alter the solubility of the nanoparticles and study the influence of surface effects on the luminescence of lanthanide ions doped in the nanoparticles. The coordinated organic ligands can be modified by a quantitative exchange reaction in solution or by using functionalized ligands during the synthesis. Variation of the ratio of ligand to core reagents had a significant influence on the size of the nanoparticles. Smaller nanoparticles were formed with a higher ligand ratio. The optical properties of these nanoparticles show a strong dependence on nanoparticle size, indicating the influence of quenching probably by CH and OH groups at or near the surface of the nanoparticle cores. The luminescence lifetime of LaF3/Eu nanoparticles varied from 6.5 to 7.4 ms for nanoparticles with an average size of 7.1 to 8.4 nm. A significant reduction of the quenching from the surface of the nanoparticles was obtained by the synthesis of core-shell nanoparticles, in which a shell of LaF3 was grown epitaxially around the doped core nanoparticles. This leads to an increase in the luminescence lifetime of the Eu3+ ion and the observation of emissions from the 5D2 energy level, in addition to emissions from the 5D1 and 5D0 levels. The quantum yield of LaF3/Ce,Tb nanoparticles could be increased from 24 to 54% by the growth of a LaF3 shell around the nanoparticles.     

Single‐Crystalline and Near‐Monodispersed NaMF3 (M=Mn,Co, Ni,Mg) and LiMAlF6 (M=Ca,Sr) Nanocrystals from Cothermolysis of Multiple Trifluoroacetates in Solution

We report the synthesis of single‐crystalline and near‐monodispersed NaMF₃ (M=Mn, Co, Ni, Mg), LiMAlF₆ (M=Ca, Sr), and NaMgF₃:Yb,Er nanocrystals (quasisquare nanoplates, nanorods, and nanopolygons) by the cothermolysis of multiple trifluoroacetates in hot combined organic solvents (oleic acid, oleylamine, and 1‐octadecene). The nanocrystals were characterized by XRD, TEM, superconductive quantum interference device (SQUID), and upconversion luminescence spectroscopy. By regulating the polarity of the dispersant, the NaMF₃ (M=Mn, Co, Ni) nanoplates were partially aligned to form nanoarrays on copper TEM grids. The sizes of the NaMF₃ nanocrystals were easily tuned by the use of proper synthetic conditions such as reaction temperature and time and solvent composition. On the basis of a series of experiments in which the reaction conditions were varied, together with GC–MS and FTIR analysis, the reaction pathways for the formation of these nanocrystals from trifluoroacetate precursors were proposed. The magnetic measurements showed that the differently sized NaMnF₃ square plates displayed interesting weak ferromagnetic behavior on the nanometer scale. The strong red upconversion luminescence emitted from the NaMgF₃:Yb,Er nanorods under 980‐nm near‐IR laser excitation suggests that NaMgF₃ may be a good candidate host material for red upconversion luminescence.     

孔状Co_3O_4纳米片和纳米棒的选择性合成和表征(英文)

利用两步实验选择性合成孔状Co3O4纳米片和纳米棒:首先,以Co(NO3)2·6H2O,NaOH和不同量的NH4F为原料在120℃水热6h的条件下合成了Co(OH)2-Co3O4纳米片(S1)和Co(OH)F-Co3O4纳米棒(S2);然后将所得纳米片和纳米棒在400℃时加热2h即得到多孔的Co3O4纳米片和纳米棒。所得产物用X射线衍射(XRD)、场发射扫描电子显微镜(FE-SEM)和透射电子显微镜(TEM)进行了表征。此外电化学测试表明Co3O4纳米棒的电容量比Co3O4纳米片的更大。     

Hydrothermal preparation and luminescence of LaF3:Eu3+ nanoparticles

LaF3:Eu3+ nanoparticles were prepared by a simple hydrothermal process at low temperature and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and fluorescence spectrum. Well-dispersed nanoparticles with an average size of 30 nm and a hexagonal shape were obtained. The influences of reaction temperature and time on the preparation and luminescence of LaF3:Eu3+ nanoparticles were investigated. Luminescent quenching occurred at a much higher concentration ( approximately 25mol%) and stronger luminescent intensity than in bulk LaF3:Eu3+. Fluorescence intensity of the LaF3:Eu3+ nanoparticles varied remarkably with calcination temperatures. It was found that samples without any further calcinations can emit quite strong fluorescence.     

SiO2/LaF3:Eu3＋核壳结构发光粒子的制备与表征

采用简单的液相法合成了SiO2/LaF3:Eu3＋核壳结构发光粒子, 并对其结构及发光性能进行了表征. XRD分析表明包覆层LaF3:Eu3＋为立方晶相结构, 红外光谱表明SiO2颗粒表面有柠檬酸的修饰, 电镜照片表明合成了球形的核-壳结构的复合粒子, 包覆层厚度为10～20 nm, 光谱测试表明核-壳复合粒子与纯的LaF3:Eu3＋具有相同的发光性能, 均以589 nm附近的5D0—7F1磁偶极跃迁为最强发射峰, 说明Eu3＋在LaF3基质中占据的格位相同.     

Liquid‐Phase Epitaxial Growth of Two‐Dimensional Semiconductor Hetero‐nanostructures

Although many two‐dimensional (2D) hybrid nanostructures are being prepared, the engineering of epitaxial 2D semiconductor hetero‐nanostructures in the liquid phase still remains a challenge. The preparation of 2D semiconductor hetero‐nanostructures by epitaxial growth of metal sulfide nanocrystals, including CuS, ZnS and Ni₃S₂, is achieved on ultrathin TiS₂ nanosheets by a simple electrochemical approach by using the TiS₂ crystal and metal foils. Ultrathin CuS nanoplates that are 50–120 nm in size and have a triangular/hexagonal shape are epitaxially grown on TiS₂ nanosheets with perfect epitaxial alignment. ZnS and Ni₃S₂ nanoplates can be also epitaxially grown on TiS₂ nanosheets. As a proof‐of‐concept application, the obtained 2D CuS–TiS₂ composite is used as the anode in a lithium ion battery, which exhibits a high capacity and excellent cycling stability.     

Lanthanide doping-facilitated growth of ultrasmall monodisperse Ba2LaF7 nanocrystals with excellent photoluminescence

Lanthanide doping not only works as sensitizer and activator, but also plays an important role to facilitate the growth of nanocrystal and to control the size, shape, and property of nanocrystals. Here, reported was the synthesis of monodisperse Ba(2)LaF(7) nanocrystals with the size of sub-10nm through a solvothermal method. We found the dopants of Ho(3+), Er(3+), or Yb(3+) facilitated the growth of Ba(2)LaF(7) nanocrystals obviously to a certain size within a shorter reaction time. Similar phenomenon can also be observed in the synthesis of LaF(3) nanocrystals. We find that Ln(3+) (e.g., Ho(3+), Er(3+), or Yb(3+)) with smaller radius can reduce the nucleation energy and lead to heterogeneous nucleation, which favors the growth of Ba(2)LaF(7) nanocrystals obviously. In addition, intense upconversion emission can be observed from Ln(3+)-doped Ba(2)LaF(7) nanocrystals under the 980 nm laser excitation, providing great potential application in biological imaging. Especially, Ba(2)LaF(7):Yb/Er (20/1 mol%) nanocrystals present more intense upconversion emission than α-NaYF(4):Yb/Er (20/1 mol%) nanocrystals under the same conditions.     

Spontaneous organization of uniform CeO2 nanoflowers by 3D oriented attachment in hot surfactant solutions monitored with an in situ electrical conductance technique

Uniform CeO(2) nanoflowers were synthesized by rapid thermolysis of (NH(4))(2)Ce(NO(3))(6) in oleic acid (OA)/oleylamine (OM), by a unique 3D oriented-attachment mechanism. CeO(2) nanoflowers with controlled shape (cubic, four-petaled, and starlike) and tunable size (10-40 nm) were obtained by adjusting the reaction conditions including solvent composition, precursor concentration, reaction temperature, and reaction time. The nanoflower growth mechanism was investigated by in situ electrical conductance measurements, transmission electron microscopy, and UV/Vis spectroscopy. The CeO(2) nanoflowers are likely formed in two major steps, that is, initial formation of ceria cluster particles capped with various ligands (e.g., OA, OM, and NO(3) (-)) via hydrolysis of (NH(4))(2)Ce(NO(3))(6) at temperatures in the range 140-220 degrees C, and subsequent spontaneous organization of the primary particles into nanoflowers by 3D oriented attachment, due to a rapid decrease in surface ligand coverage caused by sudden decomposition of the precursor at temperatures above 220 degrees C in a strong redox reaction. After calcination at 400 degrees C for 4 h the 33.8 nm CeO(2) nanoflowers have a specific surface area as large as 156 m(2) g(-1) with high porosity, and they are highly active for conversion of CO to CO(2) in the low temperature range of 200-400 degrees C. The present approach has also been extended to the preparation of other transition metal oxide (CoO, NiO, and CuO(x)) nanoflowers.     

Electronic polarizability and Judd-Ofelt parameters of Nd3+ and Er3+ ions in transparent crystallized glasses with nonlinear optical Ba2 TiSi2O8 nanocrystals

Transparent crystallized glasses consisting of nonlinear optical Ba(2)TiSi(2)O(8) nanocrystals are prepared in Eu(2)O(3)-, Nd(2)O(3)-, and Er(2)O(3)-doped 40BaO-20TiO(2)-40SiO(2) glasses by a conventional heat treatment method in order to clarify the optical properties of rare-earth (RE) ions in nanocrystals. The electronic polarizabilities of crystallized glasses are evaluated from the values of density and refractive index, and are found to decrease due to nanocrystallization, which indicates that the chemical bonding state in the crystallized glasses is more covalent compared to the precursor glasses. It is proposed from x-ray diffraction analyses and photoluminescence spectra of Eu(3+) ions that RE ions such as Nd(3+) and Eu(3+) are incorporated into Ba(2)TiSi(2)O(8) nanocrystals. The Judd-Ofelt parameters, Omega(t) (t=2, 4, and 6), of Nd(3+) and Er(3+) ions are evaluated from optical absorption spectra. It is observed that the Omega(2) parameter of Nd(3+) and Er(3+) increases largely due to nanocrystallization, suggesting that the site symmetry of Nd(3+) and Er(3+) ions in nanocrystallized glasses is largely distorted due to their incorporations into the Ba(2+) sites in Ba(2)TiSi(2)O(8) nanocrystals. The change in the Omega(4) and Omega(6) parameters due to nanocrystallization is small. It is proposed that nonlinear optical Ba(2)TiSi(2)O(8) nanocrystals including RE ions would have a high potential as active optical materials.     

Inorganic Sn-X-complex-induced 1D, 2D, and 3D copper sulfide superstructures from anisotropic hexagonal nanoplate building blocks

A facile route was demonstrated for inorganic Sn-X-complex-induced syntheses of self-assembled 1D columnar, 2D raftlike, and 3D stratiform anisotropic Cu(2)S hexagonal nanoplates. The factors (reaction time, temperature, the concentration of Sn-X complex, and so on) that influence the size, phase, monodispersity, and self-assembly ability of the Cu(2)S hexagonal nanoplates were studied in detail. It was found that the Sn-X complex could inhibit the growth of the <001> direction of monoclinic Cu(2)S nanocrystals, which further induced the formation of the hexagonal lamellar structure. Furthermore, it revealed that the formation of the 1D arrangement was preferred as particles stacked in a face-to-face configuration by maximizing ligand-surface interactions. Then, high ligand density along the side of the 1D columnar arrangement induced well-defined 2D raftlike and 3D stratiform self-assembly.