Observation of domain-wall dynamic lattice distortion in rare-earth orthoferrites while overcoming the sound barrier

In rare-earth orthoferrites TmFeO₃ and DyFeO₃ light diffraction on dynamic lattice distortions, produced during the domain wall (DW) motion at the moment of passing through the sound barrier, has been observed. The lifetime and the width of excitations have been determined to be 20 ns and 2×10⁻⁶ m, respectively. A polarization change that can be compared with the Faraday rotation value for orthoferrites of this type has been detected. At that moment the DW is shown to become curved along the whole width of the specimen plate.     

Magnetorefractive effect in manganites with a colossal magnetoresistance in the visible spectral region

The magnetotransmission, magnetoreflection, and magnetoresistance of the La_0.7Ca_0.3MnO₃ and La_0.9Ag_0.1MnO₃ epitaxial films have been investigated. It has been found that the films exhibit a significant magnetorefractive effect in the case of reflection and transmission of light in the fundamental absorption region both in the vicinity of the Curie temperature and at low temperatures. It has been shown that the magnetorefractive effect in the infrared spectral region of the manganites is determined by a high-frequency response to magnetoresistance, whereas the magnetorefractive effect in the visible spectral region of these materials is associated with a change in the electronic structure in response to a magnetic field, which, in turn, leads to a change in the electron density of states, the probability of interband optical transitions, and the shift of light absorption bands. The obtained values of the magnetotransmittance and magnetoreflectance in the visible spectral region are less than those observed in the infrared region of the spectrum, but they are several times greater than the linear magneto-optical effects. As a result, the magnetorefractive effect, which is a nongyrotropic phenomenon, makes it possible to avoid the use of light analyzers and polarizers in optical circuits.     

Photolysis of MAg4I5 superionic films

Photolysis studies on MAg₄I₅ films are reported. The electrical conductivities of MAg₄I₅ films have been found to change when exposed to mercury light. This is explained on the basis of a model similar to Mott-Gurney theory of photolysis for silver halides. The formation of silver specks has been confirmed by photomicrographic studies.     

Opto-galvanic spectroscopy of some molecules in discharges: NH2, NO2, H2 and N2

The change of the discharge voltage when laser light crossing the discharge is tuned to a molecular transition has been measured. Experiments have been performed in the wavelength region between 570 nm and 620 nm with discharges in NH₃, NO₂, H₂, N₂, O₂ and argon. Transitions from the ground states of NH₂ and NO₂ and transitions from metastable states of N₂ and H₂ have been detected. The spacial dependence of the opto galvanic in a low pressure dc-discharge of H₂ and N₂ has been studied.     

Model of the magnetorefractive effect in manganites within the effective medium theory

The magnetorefractive effect (MRE) in manganites has been studied within the effective medium theory. The MRE has been calculated in manganites La_1–xK_xMnO₃ (x = 0.1 and 0.15) for light transmission and reflection. Good agreement with experimental results demonstrates direct relation of the MRE to the magnetoresistance and optical properties of manganites with various substitution levels. It has been shown that the MRE can exceed 10% in the near- and mid-IR region near the magnetic phase transition and can change sign during light transmission and reflection in the region of phonon modes. The results make it possible to recommend the MRE as a contactless method for studying magnetoresistive materials and for developing sensors and microelectronic elements.     

Raman studies of lattice and local vibrational modes of GaInNAs prepared by molecular beam epitaxy

Polarized Raman spectra have been studied on the lattice-matched Ga_0.94In_0.06N_0.025As_0.975 epitaxial layers grown on (100) GaAs by molecular beam epitaxy. Polarization dependence of TO and LO phonon modes has been examined. The N-related local vibrational mode (LVM) in GaInNAs has been studied with emphasis on the light polarization and the effect of the thermal annealing. The thermal annealing-induced change of the N-related LVM in GaInNAs is discussed in terms of the local atomic arrangement around N atoms.     

Influence of grain size distribution on the lattice thermal conductivity of Bi2Te3-Sb2Te3-based nanostructured materials

The change of the lattice thermal conductivity of bulk nanostructured materials based on Bi₂Te₃-Sb₂Te₃ solid solutions with grain size distribution has been studied. These materials have a polycrystalline structure with grain sizes ranging from a few tens of a nanometer to a few micrometers. Large grains may contain inclusions or consist of several smaller parts which can be identified with coherent scattering regions seen in X-ray diffraction. The change of the lattice thermal conductivity mediated by additional scattering by inclusions and grain boundaries has been calculated. This calculation allows for the effect of nanoparticle size distribution. The calculated estimates are compared with the available experimental data.     

Si3O cluster: excited properties under external electric field and oxygen-deficient defect models

This paper investigates the excited states of Si₃O molecule by using the single-excitation configuration interaction and density functional theory. It finds that the visible light absorption spectrum of Si₃O molecule comprises the yellow and the purple light without external electric field, however all the visible light is included except the green light under the action of external electric field. Oxygen-deficient defects, which also can be found in Si₃O molecule, have been used to explain the luminescence from silicon-based materials but the microstructures of the materials are still uncertain. Our results accord with the experimental values perfectly, this fact suggests that the structure of Si₃O molecule is expected to be one of the main basic structures of the materials, so the oxygen-deficient defect structural model for Si₃O molecule also has been provided to research the structures of materials.     

LiNbO3:Fe晶体中光感应自衍射观察

用He-Ne激光束沿LiNbO₃:Fe晶体的x轴或y轴方向聚焦照射较薄样品时,在晶体后面的屏上观察到十分规则的衍射图样。这与前人在该晶体中观察到的由晶体中光折变形成的位相噪音栅引起的光感应光散射现象迥然不同。我们观察到的这种自衍射图样,可用聚焦激光束入射时在晶体中形成的复杂类透镜效应和自衍射理论来解释。它可以清楚地表明聚焦激光束入射时晶体中光折变过程的特点、还可由衍射条纹的数目直接推算晶体中光折变△n的最大值。文中还实验研究与讨论了光感应自衍射的形成条件及其与光感应光散射的竞争关系。 关键词：     

High pressure studies of the erbium-hydrogen system

High-pressure X-ray diffraction investigations up to 25 GPa using diamond anvil cell techniques (DAC) have been carried out on erbium and a series of erbium hydrides. The equations of state have been evaluated for ErH_1.95, ErH_2.091 (in the β-phase) and for γ-ErH₃. For comparison, the compressibility of pure erbium metal has also been determined in the same pressure range. A rapid drop of lattice volume at a pressure of about 14.5 GPa has been observed for ErH_2.091 accompanied by a color change of reflected light. This phenomenon was not observed in ErH_1.95 where the molar volume varied smoothly up to the highest pressure. A pressure-induced transformation from hexagonal to cubic phase has been detected for erbium trihydride. For pure erbium metal, a transition from hexagonal to samarium structure has been revealed, confirming previously reported behavior.     

Can the incident photo-to-electron conversion efficiency be used to calculate short-circuit current density of dye-sensitized solar cells

The relationship between the integration of the incident photo-to-electron conversion efficiency (IPCE) and the measured short-circuit current density (J_SC) of dye-sensitized solar cell (DSC) has been analyzed. The J_SC of DSC under full sun is usually considered to be determined by the overlap between its spectral IPCE and the spectral photon flux incident on the cell. However, the IPCE spectrum has been found to be influenced by the bias light intensity in many practical cases. Through theoretical deduction, we have proved that J_SC calculated from IPCE spectrum is related to the slope at corresponding incident light intensity on the short-circuit photocurrent density–incident light intensity (J_SC?E_light) curve. The equal relation between J_SC calculated from IPCE and J_SC practically measured can only be obtained when the J_SC?E_light curve is a straight line through the origin of the coordinates. The measured results of four DSC samples with different working condition show a good agreement with the theory. In addition, a simple method to validate the accuracy of IPCE measurement is also demonstrated.     

Solvent Extraction of Eu(III) by Dihexyl-N,N-Diethylcarbamoyl Methyl Phosphonate (DHDECMP) from Perchlorate and Nitrate Media

Eu(III) extraction by DHDECMP has been studied from aqueous solution of perchlorate and nitrate. In case of perchlorate the distribution of Eu was found to be first power dependent on pH and third power dependent on extractant concentration. From nitrate it was found that D for Eu(III) is also first power with respect to pH but second power dependency on DHDECMP. The reaction mechanisms have been suggested and discussed in the light of the data obtained. The effect of adding some electron donor compounds decreases the extractability of DHDECMP for Eu(III) but does not change the nature of extracted species. The equilibrium constants of all the extracted species have been calculated and discussed. The extractant behaves as a chelate in low acidic media and extracted complex species is suggested to be Eu(NO₃)₂DHDECMP·DHDECMP from nitrate solutions.     

Magnetocrystalline symmetry, spin statics and dynamics in high-temperature superconductors

The symmetry analysis of the magnetic structures of La₂CuO₄ and YBa₂Cu₃O_6+δ (δ 0.4) antiferromagnetic oxide has been carried out. The spin configurations and spin-reorientation transition fields have been found. The frequencies of uniform spin oscillations and the external field dependence of their polarization properties have been calculated. It has been shown that the spin excitation branches may include exchange modes among which some dipole-active modes can be present. The spectrum of the inelastic light scattering accompanied with the excitation of spin and libration (tilting) freedom degrees has been discussed.     

Preparation and photoluminescence properties of a new orange–red Ba3P4O13:Eu phosphor

A new orange–red Ba₃P₄O₁₃:Eu³⁺ phosphor has been synthesized by solid-state technique, and its photoluminescence properties were investigated. X-ray powder diffraction (XRD) analysis indicates that doping Eu³⁺ does not change the lattice of Ba₃P₄O₁₃. Field-emission scanning electron microscope (FE-SEM) images illustrate that microstructure of the phosphor consists of oval grains with average diameter of 1 μm and heavy agglomerate phenomenon. The excitation spectra indicate the phosphor can be effectively excited by near ultraviolet (NUV) light, making it attractive as conversion phosphor for LED applications. The phosphor exhibits a bright orange–red emission excited by 394 nm light. The CIE chromaticity can be varied slightly by adjusting the content of Eu³⁺, which is attributed to the different lattice sites occupied by Eu³⁺ in Ba₃P₄O₁₃ host. The photoluminescence studies indicate that Ba₃P₄O₁₃:Eu³⁺ is a potential orange–red phosphor for near-ultraviolet InGaN-based white light-emitting diodes (WLEDs).     

静电场作用下α-碘酸锂单晶的透射光异常现象的进一步观察

本文利用投影法、光学傅里叶频谱分析法和纹影法,对静电场作用下α-碘酸锂单晶的透射光场异常分布作了进一步观察。考察了z-切样品的透射光场的空间频谱随电压升高而改变的情况。利用高通滤波器进行滤波,观察到晶体的透射光的衍射效率与外加电压成线性关系,并与电场方向和晶体电正极面之相对取向有关,但是不依赖于入射光的偏振状态。消光比的测量表明,静电场的作用不改变光的偏振态。定量地记录了衍射效率随时间变化的弛豫过程。     

Variation of band gap in Se-based chalcogenide glasses

The random network model for amorphous alloys proposed by White has been developed for the system irradiated with light. The model suggests that the photobleaching in GeSe₂ film and the photodarkening in AsSe film may be due to change in the number of the bonds.     

Development and implementation of an angle detector using nanoporous silicon-based photovoltaic sensor

The present work deals with the design, development, and implementation of an angle detector using n-ATO/p-PSi photovoltaic sensor. Nanoporous structures have been developed over p-type porous silicon wafers by anodization technique under optimized conditions. Photoluminescence studies of porous silicon show emission between 700 and 702 nm for the constant excitation at 350 nm, which illustrates that the band gap can be tuned according to the HF:H₂O:C₂H₅OH ratio. n-ATO/p-PSi O heterojunction photovoltaic sensor has been developed by cost-effective Spray pyrolysis method. I–V characteristics under dark and different illumination intensities have been investigated, and the results are discussed. The fabricated sensor is employed for sensitive angle detection of a light source. The sensor is attached to a DC motor, which rotates at 30 rpm. When the light is from the source incident on the light sensor, a dc voltage has been produced, which in turn is amplified, and the signal has been used to stop the motor. The motor is coupled to a rotary transducer, which is calibrated to read or display 0–3.60 V for 0–360°. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Features of the electronic spectrum and optical absorption of ultrathin Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> films

The electronic spectra and relative permittivity of ultrathin (1–3 QL) films of Bi₂Se₃ topological insulator have been calculated by the density functional theory. The calculated spectra exhibit a characteristic feature: the range of 0.0–0.9 eV below the Fermi level contains two doubly degenerate valence bands (“U-bands”), which are geometrically congruent to low-lying spectral branches in the conduction band. It has been shown that the saturation of optical absorption can result in a significant rearrangement of the electronic structure and properties in the near infrared spectral range in the considered film. In particular, the semiconductor (in the absence of interaction with light) type of conductivity of the film can be changed to the metallic type of conductivity strongly nonlinear in the intensity of light.     

Melt crystalfization and crystal morphology of two low molecular weight linear polyethylene fractions

Melt-crystallization behavior and single-crystal morphology of two low molecular weight (LMW) linear polyethylene (PE) fractions of 3900 and 5800 have been investigated. Linear growth rates along the b axis (G _b) of these fractions were measured via polarized light microscopy (PLM). The two fractions show a growth rate change at an undercooling of 17°C (at 117°C and 120°C, respectively, for these two fractions), which may be identified as the regime I/II transition. This transition does not correspond to a single-crystal morphological change from a truncated lozenge with curved (200) and (110) planes to a lenticular crystal as proposed previously. However, this morphological change can be observed at a temperature higher than the regime transition (at 122°C and 124°C), at which the cusps of the G _b data can be observed for these two fractions. Based on our morphological study via PLM, transmission electron microscopy, electron diffraction, small-angle x-ray scattering (SAXS), and differential scanning calorimetry (DSC) experiments, it is found that within a 2°C temperature region, the G _b change is accompanied by a sharp long period increase and a drastic change in single-crystal morphology from a truncated lozenge with curved (200) and (110) planes to a lenticular-shape crystal. The morphological change may result from a sudden increase in the G _b coupled with a smaller change in the growth rate along the a axis with undercooling. This implies that, within this temperature region (2°C), the crystals may undergo substantial changes in the geometry of the (110) and (200) crystal growth fronts and chain folding behavior.     

THz spectroscopy of diluted magnetic semiconductors and semiconductor quantum structures in ultrahigh magnetic fields

Magneto-absorption spectra in ferromagnetic semiconductor In_1−xMn_xAs films and self-organized PbSe/PbEuTe quantum dot superlattices have been studied in the terahertz range at very high magnetic fields up to 500 T. Both heavy hole (HH) and light hole (LH) cyclotron resonance (CR) have been observed in bulk In_1−xMn_xAs thin films with different Mn concentrations. The detailed Landau level calculation in terms of the effective mass approximation well explained the CR peak positions, line shapes and the dependence of the circular polarization of the incident light on the CR spectra. In InMnAs/GaSb heterostructures that have higher ferromagnetic transition temperature (T_c) than the bulk samples, the observed HH and LH cyclotron masses are larger than that in the bulk thin films. We found that the CR peak position and its line shape suddenly change in the vicinity of the ferromagnetic transition temperature, suggesting the change in the electronic structure due to the ferromagnetic transition. Electron CR in PbSe/PbEuTe quantum dots has been observed and it was found that the effective mass of the electrons is considerably modified by the quantum confinement potential and the lattice strain around the dots. A large wavelength dependence of the absorption intensity was observed due to the interference effect of the radiation inside the sample.