Use of tunable second‐harmonic signal from KNbO3 nanoneedles to find optimal wavelength for deep‐tissue imaging

Nonlinear optical (NLO) responses of perovskite‐type nanostructures have a variety of potential applications owing to the highly efficient frequency conversion guaranteed by both the material itself and the nanometer‐scale configuration. KNbO₃ (KN) nanoneedles have been identified as a promising NLO material because of the superior broadband frequency conversion efficiency, and if incident light is propagating in a direction perpendicular to the axis of a nanoneedle, then the phase‐matching constraint can be relaxed. Here, the second‐harmonic generation (SHG) and third‐harmonic generation (THG) responses of both individual and clustered KN nanoneedles are reported. Based on these results, a novel method is proposed for determining the optimal excitation wavelength for NLO imaging of several biological samples, with KN nanoneedles acting as NLO agents. The method is shown to provide the optical features in the focal plane and a more reliable estimation of the optimal excitation wavelength for deep‐tissue imaging.     

Bandgap engineering of rare earth element doped nanostructured cadmium oxide thin films

Rare earth element (gadolinium) doped cadmium oxide (CdO:Gd) thin films were deposited using the pulsed laser deposition technique. X-ray diffraction analysis reveals that growth temperature has large impact on the preferred orientation of the films. The films grown at low temperature show (1 1 1) preferred orientation, while films grown at high temperature have (2 0 0) orientation. The effect of substrate temperature on optical and electrical properties shows widening in optical bandgap and improvement in electron mobility with increase in growth temperature. These wide bandgap transparent conducting films could be used in optoelectronic applications.     

Valence of “divalent” rare earth metals

It is generally recognized that light rare earths change their valence from 2 to 3 when forming a bulk metal while remaining divalent at the surface. However, performed DFT calculations ultimately indicate that the higher-binding-energy peaks in photoemission spectra (like the −5.3 eV peak for Sm), characteristic of the trivalent 4fⁿ⁻¹5d¹ configuration, correspond not to the ground state, but to excited states induced by radiation. This means that the trivalent state is not inherent for the bulk of divalent rare earths, and therefore they do not become trivalent.     

Influence of the rare earth element substitution on oxygen adsorption-desorption properties of YBCO

The oxygen adsorption-desorption properties of RBa₂Cu₃O_7−δ (R = Gd, Er, Eu, Dy, Sm, Ho and Nd) and Y_1−x La_xBa₂Cu₃O_7−δ (x=0.1, 0.5 and 1.0) were investigated from room temperature to 950 °C by thermogravimetry (TG). The results show that all samples will release oxygen with the increasing of temperature and the released oxygen can be absorbed back into the sample when temperature decreases. However, dependent on the rare earth element, the amount of the released oxygen is different for these samples. Moreover, in the temperature increasing and decreasing circle the repetition of oxygen adsorption-desorption is also different.     

Raman spectroscopic investigation of pure and ytterbium‐doped rare earth silicate crystals

Raman spectroscopy was used to study the molecular structure of a series of selected rare earth (RE) silicate crystals including Y₂SiO₅ (YSO), Lu₂SiO₅ (LSO), (Lu_0.5Y_0.5)₂SiO₅ (LYSO) and their ytterbium‐doped samples. Raman spectra show resolved bands below 500 cm⁻¹ region assigned to the modes of SiO₄ and oxygen vibrations. Multiple bands indicate the nonequivalence of the RE O bonds and the lifting of the degeneracy of the RE ion vibration. Low intensity bands below 500 cm⁻¹ are an indication of impurities. The (SiO₄)⁴⁻ tetrahedra are characterized by bands near 200 cm⁻¹ which show a separation of the components of ν₄ and ν₂, in the 500–700 cm⁻¹ region which are attributed to the distorting bending vibration and in the 880–1000 cm⁻¹ region which are attributed to the symmetric and antisymmetric stretching vibrational modes. The majority of the bands in the 300–610 cm⁻¹ region of Re₂SiO₅ were found to arise from vibrations involving both Si and RE ions, indicating that there is considerable mixing of Si displacements with Si O bending modes and RE O stretching modes. The Raman spectra of RE silicate crystals were analyzed in terms of the molecular structure of the crystals, which enabled separation of the bands attributed to distinct vibrational units. Copyright © 2007 John Wiley & Sons, Ltd.     

The optoelectrical properties of rare earth element Eu doped CuxO based heterojunction photodiode

In this study, the Cu_xO and Eu: Cu_xO thin films were prepared by sol gel spin coating method, which is a cheap and simple method, and coated on glass and n-Si substrates to characterize optical properties and to fabricate heterojunction photodiodes, respectively. The optical properties of Cu_xO films were examined by UV-VIS spectroscopy and the optical band gap of Cu_xO thin film increased from 2.02 eV to 2.04 eV with Eu doping. Raman measurements confirmed a single crystal phase of CuO. The I-V characteristics of the fabricated photodiodes were carried out under dark and various light intensities. The photosensitivity (I_photo/I_dark), ideality factor (n), barrier height (Φ_B) and series resistance (R_S) of diodes were calculated and compared. It was observed that the Eu doping improved the optoelectrical properties of Cu_xO/n-Si photodiode. In addition, the capacitance behavior of diodes was studied by performing C-V measurement and some diode parameters such as Φ_B and depletion width (W_D) were obtained by using capacitance data.     

Magnetic susceptibility of the rare earth element impurities in the IV-VI semiconductors and Curie-Weiss law

Peculiarities of applying the Curie-Weiss law to the analysis of the magnetic susceptibility of the impurities of the rare earth elements in the IV-VI crystals are examined. It is shown that the traditional approach to the determination of the paramagnetic Curie temperature of ferromagnets and antiferromagnets applied to the impurities of ferromagnetic and antiferromagnetic elements in the doped crystal may lead to fundamental mistakes. The results of this examination are used to analyze the high temperature magnetic susceptibility of Eu and Gd impurities in the PbTe doped crystals grown from the melt using the Bridgman method. It is established that the doping of PbTe with Eu leads to the formation of ferromagnetic inclusions and the same doping with Gd leads to the formation of antiferromagnetic inclusions in the crystal. It is shown that these inclusions are most likely the complexes based on the europium or gadolinium oxides EuO and Gd₂O₃, respectively.     

Multi‐element analysis of sea water from Sepetiba Bay,Brazil, by total reflection x‐ray fluorescence spectrometry using synchrotron radiation

Trace elements in the surface waters of Sepetiba Bay were studied by total reflection x‐ray fluorescence spectrometry using synchrotron radiation (SRTXRF). The bay is located in the south of Rio de Janeiro State, Brazil. The water samples were collected at 21 sampling stations, prepared in order to preconcentrate the metallic elements with ammonium pyrrolidinedithiocarbamate and to remove the salt matrix. Samples were spiked with an internal standard (Se) and the precipitated dithiocarbamates of trace elements were separated by filtration through a Millipore filter, then transferred to a Perspex reflector and digested with HNO₃ for SRTXRF measurement. Elemental concentrations of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo and Pb were determined and a comparison was made between the results obtained and the values given in the literature for sea water. Copyright © 2005 John Wiley & Sons, Ltd.     

铸造锌铝合金稀土变质机理的电子理论研究

根据分子动力学理论建立了液态锌铝合金ZA27的模型，结合计算机编程构造出了ZA27合金α 相与液相共存时的原子结构模型，利用递归方法计算了稀土固溶于晶粒内和富集于结晶前沿 时的电子结构.由此得出：稀土处于相界区比在晶内更稳定，从而解释了稀土在α相内溶解 度很小，结晶时富集于结晶前沿液体中的事实；稀土处于液态和晶态的结构能差相对于铝较 大解释了稀土在相界前的富集使α晶枝产生熔断、游离、增殖的观点.原子间的键级积分计 算也表明，稀土处于结晶前沿液体中与铝相比不容易结晶到晶体表面，起到阻碍晶粒长大， 细化晶粒的作用，这就从电子层次解释了稀土的变质机理. 关键词： 电子结构 液固相界原子结构模型 稀土变质机理     

稀土元素替代Y对YBa2Cu3O7-δ氧吸附性能的影响

用热重法研究了RBa2Cu3O7-δ(R=Gd、Er、Eu、Dy、Sm、Ho和Nd)及Y1-xLaxBa2Cu3O7-δ(x=0.1,0.5和1.0)共10种材料在高温下的氧吸附—脱附性能。结果表明,随着温度的升降循环,仅NdBa2Cu3O7-δ(R=Gd)和Y1-xLaxBa2Cu3O7-δ的氧吸附—脱附性能有较好的重复性,其余的6个样品的重复性都很差;并且这10种样品的质量变化率都没有YBCO的大。     

稀土元素(Y,La)掺杂ZnO的电子结构和光学性质

采用基于密度泛函理论的第一性原理平面波超软赝势方法,计算了未掺杂ZnO和稀土(Y,La)掺杂ZnO体系的空间结构、能带、电子态密度与光学性质.结果表明,掺杂后体系的形成能减小,稳定性变强,带隙展宽,费米能级进入导带中,体系呈金属性,载流子发生简并,形成简并半导体.定性分析了掺杂后光学性质的变化. 关键词： 氧化锌 掺杂 第一性原理     

Semiempirical analysis of spin-lattice relaxation in rare earth Kramers' doublets

The spin-lattice coupling constants of Kramers' doublet measured in uniaxial stress experiments, are used to calculate the spin-lattice relaxation times in the direct process range. A comparison with experimental data shows that a true spin lattice relaxation time was obtained only when T₁ was measured as a function of magnetic field at high fields. We suggest that the effect of the phonon bottleneck is important at lower fields.     

[5‐(p‐alkoxy)phenyl‐10, 15, 20‐tri‐phenyl] porphyrin and their rare earth complex liquid crystalline

Three series of porphyrin liquid crystalline compounds, [5‐(p‐alkoxy)phenyl‐10, 15, 20‐tri‐phenyl] porphyrin and their rare earth complexes (Tb (III), Dy (III), Er (III), Yb (III)), with a hexagonal columnar discotic columnar(Col_h) phase have been synthesized. These compounds were characterized by elemental analysis, molar conductances, UV‐visible spectra, infrared spectra, luminescence spectra, and cyclic voltammetry. These compounds exhibit more than one mesophases, which transition points of temperature change from ?33.6 to 16.0 °C, and transition points of temperature for isotropic liquid also increase from 4.9 to 38.2 °C, with increasing chain length. Their surface photovoltage (SPV) response have also been investigated by the means of surface photovoltage spectroscopy (SPS) and field‐induced surface photovoltage spectroscopy (EFISPS). It was found that their SPV bands are analogous with the UV‐visible absorption spectra and derived from the same transition. Copyright © 2007 John Wiley & Sons, Ltd.     

不同价态稀土元素Yb掺杂ZnO的电子结构和光学性质

基于密度泛函理论, 采用第一性原理平面波超软赝势法, 对六方纤锌矿结构的ZnO晶体和Yb²⁺, Yb³⁺分别掺杂ZnO晶体进行几何优化, 并在此基础上计算得到了未掺杂ZnO晶体及不同价态Yb元素掺杂ZnO体系的空间结构、 能带、电子态密度及光学性质.结果表明: 掺杂后体系形成能减少, 稳定性增加, 并引入了Yb-4f杂质能级. 掺杂不同价态的Yb元素对能带结构产生了不同的影响, 并且都使体系的光学性质发生了明显变化.与纯ZnO相比, Yb²⁺, Yb³⁺ 分别掺杂ZnO体系的介电函数虚部在0.46 eV处均出现新峰, 静态介电函数明显增大, 吸收带边均红移, 并在0.91 eV处出现较强吸收峰, 对产生这一现象的原因给出了定性的讨论. 关键词： 掺杂 ZnO 不同价态 第一性原理     

Vibrational modes of rare‐earth formates

In this work we investigate the room‐temperature Raman spectra of several rare‐earth [RE(HCOO)₃; RE = La, Pr, Nd, Gd, Tb and Y] formates. Polarized measurements were carried out for La(HCOO)₃ yielding the observation of most of the Raman‐active phonons predicted by group theory analysis. The respective assignment is given based on the formate vibrations and correlations with previous results in other RE(HCOO)₃ systems. The wavenumber ‘softening’ observed when RE goes from Y to La is accounted for the lattice expansion. Copyright © 2009 John Wiley & Sons, Ltd.     

Photo‐capacitance spectroscopy investigation of deep‐level defects in AlGaN/GaN hetero‐structures with different current collapses

We have investigated electronic deep levels in two AlGaN/GaN hetero‐structures with different current collapses grown at 1150 and 1100 °C by a photo‐capacitance spectroscopy technique, using Schottky barrier diodes. Three specific deep levels located at ～2.07, ～2.80, and ～3.23 eV below the conduction band were found to be significantly enhanced for severe current collapse, being in reasonable agreement with photoluminescence and capacitance–voltage characteristics. These levels probably originate in Ga vacancies and residual C impurities and are probably responsible for the current collapse phenomena of the AlGaN/GaN hetero‐structures. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Obtaining local reciprocal lattice vectors from finite‐element analysis

Finite‐element analysis is frequently used by engineers at synchrotron beamlines to calculate the elastic deformation of a single crystal undergoing mechanical bending or thermal load. ANSYS^® Workbench? software is widely used for such simulations. However, although ANSYS^® Workbench? software provides useful information on the displacements, strains and stresses within the crystal, it does not yield the local reciprocal lattice vectors that would be required for X‐ray diffraction calculations. To bridge this gap, a method based on the shape functions and interpolation procedures of the software itself has been developed. An application to the double‐crystal bent Laue monochromator being designed for the I12 (JEEP) wiggler beamline at the Diamond Light Source is presented.     

Growth of silicon from a layer of moving solvent enriched with rare earth metals

The results of investigations of the applicability of rare earth metals as solvents for growing silicon epitaxial layers using the moving solvent method are described. The temperature ranges, in which zones with the Si-REM composition can move, are determined. The coefficients of diffusion of silicon in Si-REM melts at 1473°K are computed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 13–17, January, 1982.     

A first-principles study of B2 NiAl alloyed with rare earth element Pr, Pm, Sm, and Eu

The structural, elastic, and electronic properties of NiAl alloyed with rare earth elements Pr, Pm, Sm, and Eu are investigated by using density functional theory (DFT). The study suggests that Pr, Pm, Sm, and Eu are all tend to be substituted for Al site. Ni₈Al₇Pm possesses the largest ductility. Only the hardness and ductility of Ni₈Al₇Eu are enhanced simultaneously. The covalency strength of Ni-Al bond in Ni₈Al₇Pm is higher than that in Ni₈Al₇Eu. The covalency strength of Al-Al bond and that of Ni-Ni bond in Ni₈Al₇Eu are higher than that in Ni₈Al₇Pm. Ni-Pm bond and Ni-Eu bond are covalent, and the covalency strength of Ni-Pm bond is greater. Al-Pm bond and Al-Eu bond show great covalency strength and ionicity, respectively.     

Nondestructive evaluation of high‐temperature elastic modulus of 3C‐SiC using Raman scattering

A nondestructive method is reported to measure the high‐temperature modulus of 3C‐SiC coating and bulk samples using Raman scattering. Within the temperature range from 20 °C to 900 °C, both the longitudinal optical and transverse optical phonon frequencies decrease linearly as the temperature increases. The elastic moduli derived from the longitudinal optical phonon agree with previous results measured using other techniques. It is further shown that the grain size and impurity only have a negligible effect on the elastic modulus of 3C‐SiC. Copyright © 2011 John Wiley & Sons, Ltd.