Synthesis and characterization of single-crystal strontium hexaboride nanowires

Catalyst-assisted growth of single-crystal strontium hexaboride (SrB6) nanowires was achieved by pyrolysis of diborane (B2H6) over SrO powders at 760-800 degrees C and 400 mTorr in a quartz tube furnace. Raman spectra demonstrate that the nanowires are SrB6, and transmission electron microscopy along with selected area diffraction indicate that the nanowires consist of single crystals with a preferred [001] growth direction. Electron energy loss data combined with the TEM images indicate that the nanowires consist of crystalline SrB 6 cores with a thin (1 to 2 nm) amorphous oxide shell. The nanowires have diameters of 10-50 nm and lengths of 1-10 microm.     

新型稀土荧光材料的合成及表征

合成了3种新型荧光材料Eu(o-OHC6 H4COO)2(phen)2(NO3)、Eu(p-OHC6 H4CH2COO)3(phen)和Eu(C6H5CHOHCOO)3(phen)(H2O),并通过元素分析、红外光谱、紫外光谱和荧光光谱对其进行了表征.通过对配合物荧光性能的研究,表明这3种配合物是较好的荧光材料.     

Fabrication and characterization of patterned single-crystal silicon nanolines

This letter demonstrates a method for fabricating single-crystal Si nanolines, with rectangular cross sections and nearly atomically flat sidewalls. The high quality of these nanolines leads to superb mechanical properties, with the strain to fracture measured by nanoindentation tests exceeding 8.5% for lines of 74 nm width. A large displacement burst before fracture was observed, which is attributed to a buckling mechanism. Numerical simulations show that the critical load for buckling depends on the friction at the contact surface.     

Cathodoluminescence characterization of rare earth doped composite materials based on porous GaP

Porous GaP layers doped with erbium or europium elements have been obtained by electrochemical etching and further impregnation processes. The thermal treatments for optical activation of rare earth (RE) ions lead to partial oxidation of porous GaP skeleton and a composite material is obtained. The presence of ErPO₄ and EuPO₄ oxide nanophases is detected by X-ray diffraction (XRD) analysis. Visible luminescence from RE ions in the composite material has been investigated by means of the cathodoluminescence (CL) technique in the scanning electron microscope. Intense red and green emission lines characteristic from Er³⁺ and Eu³⁺ ions dominate the CL spectra in the case of parallel and regular nanotubes in the samples. The role of the oxygen content and the detected phases in the luminescence results are discussed.     

Photon avalanche upconversion in rare earth laser materials

We present an overview of the upconversion mechanisms with special attention to the Photon Avalanche (PA) process and to give the state of the art concerning the upconversion pumped solid state lasers.     

稀土配合物杂化材料的制备与性能研究

综述了近年来稀土配合物杂化材料的制备和性能．按基质的不同，稀土配合物杂化材料可分为稀土配合物，无机杂化材料，稀土配合物，有机杂化材料以及稀土配合物，混合基质杂化材料。本文对以上3种杂化材料的优缺点进行了较为详细的分析，并提出一步法制备稀土配合物杂化材料，以简化合戍步骤，提高稀土配合物在基质分布的均匀性，因而该方法有望戍为制备稀土配合物杂化材料的一个重要发展方向。     

稀土有机配合物荧光材料的研究进展

概述稀土有机配合物的荧光发光机理,即有机配体通过对稀土离子的敏化作用,并将其跃迁的能量传递给稀土离子供其发光;列举芳香胺类、β-二酮类和多胺多羧酸类等新型的有机配体结构。提出稀土有机配合物材料的研究与应用应致力于研发高性能有机配体,并着手解决极易被水猝灭和量子产率不高等问题。认为合成平面刚性强并对稀土离子进行有效保护的新型有机配体,可以有效增强稀土有机配合物的荧光强度以改善其应用范围。     

纳米晶稀土贮氢合金的研究

用双辊快淬工艺制备了纳米晶AB5型富镧稀土贮氢合金。对热处理后的合金进行X射线衍射和扫描电镜SEM分析，并测试合金的吸放氢等温平衡曲线PCT。结果表明，处理的合金晶粒尺寸〈50nm，该合金具有良好的吸放氢动力学性能。     

Fabrication of ordered magnetite-doped rare earth fluoride nanotube arrays by nanocrystal self-assembly

We describe a nanocrystal self-assembly method for the preparation of rare earth fluoride nanotube (ReF-NT) arrays and magnetite-doped rare earth fluoride nanotubes (Fe₃O₄-ReF-NTs) by using porous anodic aluminum oxide (AAO) as a hard template. The ReF-NTs can be simply prepared by the impregnation of α-NaYF₄ nanocrystals doped with Yb and Er into the channels of the porous AAO and show a highly ordered nanotube array and excellent upconversion (UC) fluorescence properties. Similarly, the Fe₃O₄-ReF-NTs are obtained by the self-assembly of a mixture of Fe₃O₄ and Yb/Er doped α-NaYF₄ nanocrystals in the AAO pore channels and have a uniform dispersion of magnetite nanocrystals on the rare earth fluoride tube matrix and possess multifunctional magnetic/UC properties. The diameter of these nanotubes can be varied from 60 nm to several micrometers depending on the pore size of the AAO template. The wall thickness can be increased from 10 to 35 nm by increasing the concentration of nanocrystals from 0.02 to 0.4 mmol/L, while the morphology of the nanotubes can be varied from small isolated domain structures to percolating domains and eventually to compact domains. A template-directed formation mechanism is proposed and the quantitative predictions of the model for such self-assembled nanocrystal spreading processes are demonstrated. Strong UC fluorescent emissions are realized for the nanotube arrays and multifunctional nanotubes with UC excitation in the near-infrared (NIR) region. A strong magnetic response of the multifunctional nanotubes is observed, which facilitates their easy separation from solution by magnetic decantation using a permanent magnet.     

Flux growth and characterization by X-ray topography of rare earth arsenates

Optically clear crystals of rare earth arsenates, RAsO₄, have been grown from Pb₂As₂O₇ flux by slow cooling and recovered by a hot-pouring technique. X-ray anomalous transmission topography has shown that the crystals are of good quality, and their perfection is compared with that of RVO₄ crystals grown by a similar method. The surfaces of crystals recovered by hot-pouring were found to contain higher densities of precipitates than those recovered by dissolution of the flux.     

多元稀土氧化物掺杂二氧化锆基陶瓷材料的热物理性能

稀土氧化物(RE)掺杂氧化钇稳定二氧化锆(YSZ)是提高传统YSZ热障涂层隔热性能和高温稳定性的有效途径之一。在1500 ℃高温固相反应烧结24 h制得Gd₂O₃和Yb₂O₃多元稀土氧化物掺杂的YSZ(含3.5%Y₂O₃(摩尔分数))(GY-YSZ)陶瓷材料。采用XRD研究了GY-YSZ 陶瓷材料的晶体结构和物相组成; 采用激光脉冲法研究了Gd₂O₃和Yb₂O₃掺杂对GY-YSZ 陶瓷材料的热物理性能的影响规律。研究发现, 掺杂2.0%~3.0%Gd₂O₃和Yb₂O₃(摩尔分数)后GY-YSZ的热导率为0.90~1.15 W·(m·K)-1, 比YSZ降低30%以上, 显示了良好的隔热性能。稀土氧化物掺杂对YSZ陶瓷材料热物理性能的影响机制为: 掺杂Gd₂O₃和Yb₂O₃导致YSZ中单斜相(M)、 四方相(T)和立方相(C)含量发生变化, 同时YSZ晶格发生畸变。      

The recent development of permanent magnet materials containing rare earth metals

The prospect that permanent magnets with previously unattainable coercivities and energy products might be made from cobalt-rare earth alloys has caused intense research efforts in the last three years. Alternative ways of preparing magnets from powders and by casting were demonstrated in several laboratories.(BH)_{max} approx 20MG.Oe andMH_{c} > 25 000Oe have been achieved with SmCo5, and the development of manufacturing processes for magnets made from this alloy has begun. This paper reviews the basic concepts, properties of the alloys of interest, and the physical factors influencing the coercive force. Approaches to alloy, powder, and magnet fabrication are discussed, with their merits and drawbacks; also problems incurred in the materials development and their possible solutions. Application areas are reviewed and some economic factors considered. It is concluded that theRCo5magnets are indeed beginning to live up to their promise, but that more materials research, process development, and circuit redesign are needed if their potential is to be fully utilized.     

The optical absorption edge of rare earth sesquisulfides and alkaline earth - rare earth sulfides

Optical band gaps were measured by diffuse reflectance spectroscopy on a series of Ln₂S₃ compounds of α, δ, ε and τ structure types and on a series of ternary sulfides MLn₂S₄ (M = Sr, Cd, Mg) of Th₃P₄, CaFe₂O₄ and spinel structure types. Sharp absorption edges are observed with band gaps ranging from 2.2 to 3.5 eV. Systematic changes occur with rare earth radii. Analysis of some of the absorption edges suggests direct forbidden transitions.     

Fabrication and characterization of some novel reaction-bonded silicon carbide materials

Attempts have been made to produce modified reaction-bonded silicon carbide (RBSC) ceramics by incorporating a dispersion of other phases into the initial powder mix. ZrC, TiC, TaC and B₄C were chosen as additives together with TiB₂ as a phase likely to produce microcrack toughening in the final compact. During fabrication an important factor appears to be the possible reactions of the added phase with liquid silicon during the infiltration stage of the process. Thus, while all the carbides react with liquid silicon to form refractory silicides and new silicon carbide, this only significantly affected the reaction-bonding process if the dissolution/reaction kinetics were so fast as to disrupt the formation of the new silicon carbide framework which grows epitaxially to bond the existing silicon carbide particles together. As with conventional RBSC, the initial SiC grits play no part in any reaction except to act as nucleation sites for the new SiC. The microstructures of the various new materials have been characterized by reflected light microscopy, scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction. This has led to an appraisal of the high-temperature reactions observed to have occurred and the unreliability of the high-temperature thermochemical data used to predict their occurrence. The mechanical properties of the new materials have been investigated by indentation testing (hardness and fracture toughness), including temperature-variant tests. Results are presented and the possibility for improving the properties of RBSC are discussed.     

Modelling the concentration dependence of rare earth doping in inorganic materials for optical applications: Application to rare earth doped barium aluminate

This paper reports a method for modelling the concentration dependence of rare earth doping in inorganic materials. The method is applied to barium aluminate, which when doped with rare earth ions has important optical applications as a phosphor material. Interatomic potentials are derived by fitting to the structures of barium aluminates, and used to calculate defect formation energies and thus to predict intrinsic defect disorder in the material. Solution energies for rare earth doping are then calculated, which enable the location of the dopant ions and their solubility limits to be predicted.     

稀土钨酸盐负热膨胀材料研究进展

负热膨胀材料在电子、航空以及光学领域有着广泛的应用前景,使其成为材料科学中近年来新兴的研究热点之一。重点介绍了稀土钨酸盐材料A2W3O12(包括Sc2W3O12、Lu2W3O12、Y2W3O12等)的负热膨胀研究进展,简述了此类材料的"准刚性单元模式"负热膨胀机理,并展望了未来此类负热膨胀材料的研究方向。     

UV–VUV spectroscopy of rare earth doped persistent luminescence materials

The electronic and defect energy level structure of polycrystalline SrAl₂O₄:Eu²⁺,R³⁺ persistent luminescence materials were studied with thermoluminescence and UV–VUV synchrotron radiation emission and excitation spectroscopy. Theoretical calculations using the density functional theory (DFT) were carried out simultaneously with the experimental work. The experimental band gap energy (E_g) value of 6.6 eV agrees very well with the DFT value of 6.4 eV. The 4f⁷ → 4f⁶5d¹ excitation bands of Eu²⁺ were found rather similar irrespective of the R³⁺ co-dopant. The trap level energy distribution depended strongly on the R³⁺ co-dopant except for the shallowest trap energy above the room temperature remaining the same, however. The different processes in the mechanism of persistent luminescence from SrAl₂O₄:Eu²⁺,R³⁺ was constructed and discussed.     

The detection of rare earth impurities in ionic materials by X-ray-stimulated luminescence

The application of X-ray-stimulated luminescence to the detection of trivalent rare earth impurities in ionic materials is discussed. Characteristic luminescent wavelengths allow the identification of individual rare earths. The lower limit of impurity detectable in the particular case of the fluorides is found to be about 0.01 ppm if no positive identification of the rare earth ion is required. This is increased to 1 ppm when positive identification of the specific impurity is required. The application of the technique to the assessment of single crystals and the appropriate starting material is discussed.     

Fabrication and mechanical characterization of 3D woven Cu lattice materials

3D metallic lattices designed to have two distinctly different material architectures have been woven with metallic Cu wires. A vacuum soldering technique was employed to metallurgically bond the wire nodes and form stiff 3D lattice materials. The structures and mechanical properties of the as-woven and soldered lattices were characterized by optical microscopy and micro-scale mechanical property experiments. The measured in-plane shear stiffness shows good agreement with predictions from finite element (FE) models that account for variations in the manufacturing and solder bonding. The study indicates that stiffness is influenced by the percentage of bonded nodes and the location of bonding. The 3D woven lattice materials manufactured in this study exhibited a very high percentage (80%) of bonded nodes and a unique combination of stiffness and density as compared to that typically reported for ultra lightweight lattice materials.