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.     

Thermoelectric efficiency of rare earth sesquisulfides

Thermo-electric efficiency of several rare earth sesquisulfides is presented and compared with those of commonly known thermo-electric materials. The available data show that at high temperatures dysprosium sesquisulfide has the best thermo-electric efficiency when compared with other well-known materials.     

Optical absorption near the fundamental absorption edge in some vanadate glasses

The fundamental absorption edges of some samples of V₂O₅-P₂O₅ and V₂O₅-P₂O₅-TeO₂ glasses were measured in the short wavelength part of the visible region, and it was found that the fundamental absorption of these glasses is dependent on composition and arises from direct forbidden transitions and occurs at a photon energy in the range 1.9 to 2.6 eV, depending on composition.     

Position of the optical absorption edge of alkaline earth borates

Based on the results of luminescent measurements on MB₂O₄ (M = Ca, Sr), Ca₂B₅O₉Cl, SrB₆O₁₀, SrAl₂B₂O₇ and the literature data, the influence of the crystal structure of alkaline earth borates on the position of their optical absorption edge is discussed. It is found that the optical absorption edge tends to shift to higher energy from β-BaB₂O₄ (6.4 eV) to M₃(BO₃)₂, MB₂O₄ (6.9–7.2 eV) to SrB₆O₁₀ (7.7 eV), SrB₄O₇ (>7.8 eV). It is shown that this tendency can be interpreted as a result of (a) the removal of M²⁺ states from the top of the valence band; (b) a more efficient stabilization of the O 2p states by B–O covalent bonding with increasing condensation degree of the borate anions.     

Optical downconversion in rare earth (Tb and Yb) doped CdS nanocrystals

CdS host nanocrystals (4.2-5.5 nm in diameter) have been prepared by a low-cost synthetic chemical route using air stable precursors and doped with rare earth (RE) ions, terbium (Tb³⁺) and ytterbium (Yb³⁺). The resulting RE³⁺-doped nanocrystals show a complete broadband absorption below their band edge (400-460 nm) to the deep UV region. CdS host nanocrystals act as an energy receptor and sensitizer for the RE³⁺-ions. A broadband emission in the visible region is observed for the RE³⁺-doped CdS nanocrystals by room temperature photoluminescence (PL) measurements. Our results show that these novel RE³⁺-doped nanocrystals can be used as an optical down-conversion material for solar spectral matching in solar cells or as a wavelength shifting down-converter for nanoscale optoelectronic applications.     

Optical properties of zirconia doped with yttria and some rare earth oxides

Nanometric powders of cubic zirconia stabilized with yttria and rare element oxides (Sm, Nd, Gd) were prepared by crystallization under hydrothermal conditions. The powders were uniaxially compacted, repressed isostatically, pressure-less sintered in oxygen atmosphere and hot isostatically pressed under 300 MPa Ar atmosphere. Fully dense samples were polished from both sides. The optical properties were analyzed based on the spectral dependence of the transmittance (T) and reflectance (R). Spectroscopic measurements have shown that all materials fabricated in the present work are highly transparent, with total transmission above 90% towards the long-wavelength end of the near-IR range of the spectrum. Discussion of these results will be given.     

Excited state absorption in glasses activated with rare earth ions: Experiment and modeling

We present semiempirical approach based on the Judd–Ofelt theory and apply it for modeling the spectral properties of fluoride glasses activated with the rare earth (RE) ions. This method provide a powerful tool for simulating both ground state absorption (GSA) and excited state absorption (ESA) spectra of RE ions, e.g. Nd³⁺, Ho³⁺, Er³⁺ and Tm³⁺ in the ZBLAN glass matrix. The results of theoretical calculations correspond to the experimentally measured data. We also demonstrate that the spectra obtained using the presented approach are applicable in the analysis of up-conversion excitation schemes in these optoelectronically relevant materials.     

Optical properties of TlInS2 layered single crystals near the absorption edge

The sample thickness effect on the optical properties of TlInS₂ layered crystals has been investigated at room temperature. The absorption coefficient of the samples calculated from the experimental transmittance and reflectance in the photon energy range of 1.10–3.10 eV has two absorption regions. The first is a long-wavelength region of 1.16–1.28 eV. The second region lies above 2.21 eV with a thickness-dependent indirect band gap. The energy gap decreases from 2.333 to 2.255 eV as the sample thickness increases from 27 to 66 μm. The differential spectra of absorption coefficient demonstrates the existence of a thickness-dependent impurity level being lowered from 2.360 to 2.307 eV as sample thickness increases from 27 to 66 μm.     

Investigation of infrared absorption spectra of copper phosphate glasses containing some rare earth oxides

The spectra of copper-lutetium-phosphate and copper-erbium-phosphate glasses have been studied within the spectral range 4000 to 400 cm^– by Fourier transform infrared spectroscopy. Incorporation of a small amount of lutetium or erbium influences some band positions compared with binary copper phosphate glasses. The additional bands in the range 491 to 576 cm^–1 are attributed to the presence of Lu-O and Er-O groups. It has been observed that annealing of the samples at 500 ° C leads to a slight shift in the peak positions.     

Magnetic relaxation in rare earth garnets

An attempt has been made to review the ferromagnetic resonance and relaxation data on rare earth iron garnets and in the light of it, to analyze the data on Sm and Eu thin films and Gd and Dy bulk polycrystalline samples obtained in our laboratory. A phenomenological approach adopted to explain the temperature and composition dependence of the line width andg _eff appears to explain the complex spectra in most cases.     

Magnetism of rare earth alloys

The main properties of the rare earth elements are discussed, emphasizing their magnetic properties. However, it is difficult to use these elements in practice, because their Curie points are located below room temperature. In order to take advantage of the properties of these substances, they can be alloyed with iron, cobalt, or nickel. The properties of the rare earth-cobalt alloys are discussed, the phase diagram and the crystal structures are described, and the ferrimagnetic behavior is explained. Alloys of interest for magnet applications are selected.     

稀土纳米材料的研究进展

稀土纳米材料的研究与应用将有助于发现新性质,开拓新材料,已成为当前的研究热点.本文简述了稀土纳米粉体、稀土纳米薄膜、稀土纳米陶瓷和纳米复合与组装的研究进展,介绍了在磁性材料、发光材料、催化剂、光学材料等领域稀土纳米材料的应用和进展.     

Thermodynamics of rare earth sesquioxides

Experimental thermochemical and related data for rare earth sesquioxides, R₂O₃ (R = Sc, Y, La-Lu) are critically reviewed to provide a consistent set of thermodynamic functions covering the temperature range from at least 298 K up to above the melting point taking the polymorphism into account. Discrepancies in the available data are discussed and further studies to resolve them and to fill the gaps in the current knowledge are suggested. The best values for the temperatures of the reversible polymorphic transformations are recommended. Using high-pressure and molar volume data as well as ionic radius of a trivalent rare earth cation as an independent parameter the relative stabilities of different structures (the cubic C-form, the monoclinic B-form, the hexagonal A-form, the hexagonal H-form, and the cubic X-form) are estimated quantitatively for all rare earth sesquioxides. Based on the empirical relationship between the entropy of fusion and the corresponding fractional volume change, the entropies and enthalpies of fusion of the lanthanide sesquioxides are estimated. The reliability of the assessed functions and transition data is tested through the sample calculations of phase diagrams, where R′ and R″ represent different rare earth cations.     

稀土产品中钍的测定

为解决高含量稀土和钍的分离问题对稀土产品中钍进行测定。该方法对比酒石酸、三乙醇胺的用量,设计分离富集工艺,采用743型大孔树脂分离稀土和钍,使用偶氮胂Ⅲ比色法测定。试样经过碱熔,水浸取加入三乙醇胺,过滤。沉淀用盐酸(4mol/L)溶解,在酒石酸存在下,用盐酸(4mol/L)淋洗杂质,用氯化铵溶液(20%)将树脂转化为铵型后,再用草酸铵溶液(4%)洗脱钍。在盐酸(4mol/L)介质中,用偶氮胂Ⅲ显色于波长660nm处测定。实验表明该方法操作简便,设备简单,结果稳定,精密度和准确度高。     

稀土产品中钍的测定

为解决高含量稀土和钍的分离问题对稀土产品中钍进行测定。该方法对比酒石酸、三乙醇胺的用量,设计分离富集工艺,采用743型大孔树脂分离稀土和钍,使用偶氮胂Ⅲ比色法测定。试样经过碱熔,水浸取加入三乙醇胺,过滤。沉淀用盐酸（4mol／L）溶解,在酒石酸存在下,用盐酸（4mol／L）淋洗杂质,用氯化铵溶液（20％）将树脂转化为铵型后,再用草酸铵溶液（4％）洗脱钍。在盐酸（4mol／L）介质中,用偶氮胂III显色于波长660nm处测定。实验表明该方法操作简便,设备简单,结果稳定,精密度和准确度高。     

Resonance modes in rare earth doped microcrystals

Alkaline earth sulfide phosphors doped with Eu²⁺ or Ce³⁺ are good candidates for wavelength conversion in LEDs for general lighting applications. A very broad emission spectrum can be obtained by preparing SrS:Eu-SrS:Ce core-shell particles. These microcrystals are rectangular cuboids and can also be efficiently excited with electrons in a scanning electron microscope. The broad emission spectrum, ranging from 450 nm to 650 nm, consists of the combined emission of Ce³⁺ and Eu²⁺ centers. Using cathodoluminescence (CL) in a scanning electron microscope, evaluation of the emission characteristics of individual cuboids was possible. Sharp peaks in the CL-spectra of individual particles could be observed and described as being resonance modes. The spectral positions and the line widths of resonance modes in these core-shell microcrystals are predicted by an extension of the plane wave model, taking into account the dispersion of the refractive index and the existence of open orbits.     

Volume-collapse transitions in the rare earth metals

We describe current experimental and theoretical understanding of the pressure-induced volume collapse transitions occurring in the early trivalent rare earth metals. General features of orbitally realistic mean-field based theories used to calculate these transitions are discussed. Potential deficiencies of these methods are assessed by comparing mean field and exact Quantum Monte Carlo solutions for the one-band Hubbard and two-band periodic Anderson lattice models. Relevant parameter regimes for these models are determined from local density constrained occupation calculations. This revised version was published online in July 2006 with corrections to the Cover Date.     

稀土掺杂碳纳米管/聚氯乙烯复合材料的吸波性能研究

利用La(NO3)3和Ce(NO3)3掺杂的碳纳米管(MWCNTs-La(NO3)3和MWCNTs-Ce(NO3)3)作为吸收剂、聚氯乙烯(PVC)作为基体,制备出MWCNT-La(NO3)3(或Ce(NO3)3)/PVC复合材料。运用透射电子显微镜和X射线衍射仪对MWCNTs、MWCNTs-La(NO3)3、MWCNTs-Ce(NO3)3的微观结构进行表征分析,使用同步热分析仪和矢量网络分析仪对MWCNT/PVC、MWCNT-La(NO3)3/PVC、MWCNT-Ce(NO3)3/PVC复合材料的热解行为和吸波性能进行测试分析。结果表明,在2～18GHz频率范围内,适量掺杂La(NO3)3或Ce(NO3)3可以使MWCNT/PVC复合材料的吸波性能大幅度提高,而热解行为变化不明显。在反射率R<-10dB的范围内,MWCNT-Ce(NO3)3/PVC复合材料的吸收频宽(约为5.4GHz)虽然不及MWCNT-La(NO3)3/PVC的吸收频宽(约为5.6GHz)宽,但是吸收频段和吸收峰峰值均向高频区域移动,有利于提高复合材料的高频吸波性能。