Use of a modified Drude's equation to investigate the optical rotation property of sugars

Sugar compounds (glucose, xylose, arabinose, and galactose) and their mixed solutions were examined using the optical rotatory dispersion (ORD) measurement technique with a modified Drude's equation. Commonly, spectroscopic methods utilize the observation of absorption bands which are, in the case of sugars, located in the UV-spectral range. However, the polarization method used in this study allows us to investigate sugar samples in a convenient visible spectral range where sugar solutions are relatively transparent. The ORD set-up can be simple and robust as we will demonstrate: the self-constructed apparatus consists of only two linear polarizers, placed one after the other, with the angle between their transmission axes adjusted to 45°. The sugar solution sample in a cuvette was put between the polarizers. The set-up was connected to a sample compartment of a commercial UV–vis spectrophotometer. The method provided us the specific optical rotation and concentration of sugar solutions with a reasonable accuracy. In addition, the optical rotation value for mixed sugars has been found to be the average optical rotation value of individual sugar content. Beside use in the laboratory environment, the method could also have industrial on-site monitoring applications, for example in bio fuel production.     

New spectroscopic method for the determination of optical rotatory dispersion

A new spectroscopic methodology is proposed to measure optical rotatory dispersion(ORD)of optically active media.ORD is obtained from a three-step phase shifting algorithm using transmission spectra taken at three independent probing angles.Optical rotation angles of four sugar solutions are investigated.The results obtained by using the new method show excellent agreement with the reference data,indicating the new method can be used as a reliable way for studying ORD of optically active media.     

Optical properties of Li1−xNb1−xEu2xO3 solid solutions

Abstract

The effects of europium substitution on crystalline solubility, structural changes and optical properties of LiNbO₃ is reported. Li_1?xNb_1?xEu_2xO₃ solid solutions exist over a very limited range of europium concentrations (x ≤ 0.01). The solid solutions were characterized by X-ray powder diffraction and density measurements. Within the range of compositions of the solid solutions, the optical properties (emission and excitation spectra) of the Eu³⁺ ions have been characterized. The obtained optical data indicate that two equally abundant europium luminescent species exist in the stoichiometric speciments; these correspond to the Eu³⁺ ions occupying the Li⁺ and Nb⁵⁺ sites, in agreement with the replacement mechanism which is inferred from density measurements. Other Eu³⁺ luminescent species which appear to be closely related with lithium deficiency were found to exist in nonstoichiometric samples, in addition to those which are present in the stoichiometric materials.     

Flow birefringence and stress optical law of viscoelastic solutions of cationic surfactants and sodium salicylate

The optical and rheological properties of different viscoelastic solutions of surfactant are studied in order to gather experimental data used to calculate the value of the stress optical coefficient C. Three surfactants of the same family (CTAB) have been chosen; they differ by the length of the hydrocarbon chain; it concerns the dodecyltrimethylammonium bromide (C₁₅H₃₄BrN or DoTAB), the myristyltrimethylammonium bromide (C₁₇H₃₈BrN or MyTAB), and the hexadecyltrimethylammonium bromide (C₁₉H₄₂BrN or CTAB). Different parameters like the temperature of the solution and the salinity of the solvent have been made to vary. Flow birefringence experiments and rheological measurements are performed on these solutions in order to study the dependence of the extinction angle , of the birefringence intensity and of the shear stress with the shear rate . These data are used to check the stress optical law which turns out to be valid in a wide range of shear rates. The stress optical coefficient C is then computed: it is found to vary with the salinity of the solvent and the temperature of the solution for a given surfactant. Then, for all solutions of this work the variations of C are related to the variations of the polarizability anisotropy and the persistence length. Received: 18 February 1998 / Revised: 23 June 1998 / Accepted: 22 July 1998     

Composition dependent structural and optical properties of Sm-doped sodium borate and sodium fluoroborate glasses

Sodium borate and fluoroborate glasses doped with trivalent samarium (Sm³⁺) were prepared and their detailed spectroscopic analysis was carried out. The FTIR spectra reveal that, the glasses contain BO₃, BO₄, non-bridging oxygen and strong OH⁻ bonds. From the optical absorption spectra, Judd-Ofelt intensity parameters (Ω_λ, λ=2, 4 and 6) have been evaluated and are in turn used to predict radiative properties such as radiative transition probability (A), stimulated emission cross section () and branching ratios (β_R) for the excited levels of Sm³⁺ ions in sodium borate and sodium fluoroborate glasses. The dependence of the spectral characteristics of Sm³⁺ ions due to compositional changes have been examined and reported. The value is found to decrease with the decrease in the sodium content in the glass. The decay from the ⁴G_5/2 level is found to be non-exponential indicating a cross-relaxation among the Sm³⁺ ions.     

Experimental constraints of using slow-light in sodium vapor for light-drag enhanced relative rotation sensing

We report on experimental observation of electromagnetically induced transparency and slow-light (v_g ≈ c/607) in atomic sodium vapor, as a potential medium for a recently proposed experiment on slow-light enhanced relative rotation sensing [Shahriar et al. Phys. Rev. Lett. (submitted for publication), http://arxiv.org/abs/quant-ph/0505192.]. We have performed an interferometric measurement of the index variation associated with a two-photon resonance to estimate the dispersion characteristics of the medium that are relevant to the slow-light based rotation sensing scheme. We also show that the presence of counter-propagating pump beams in an optical Sagnac loop produces a backward optical phase conjugation beam that can generate spurious signals, which may complicate the measurement of small rotations in the slow-light enhanced gyroscope. We identify techniques for overcoming this constraint. Conclusions reached from the results presented here will pave the way for designing and carrying out an experiment that will demonstrate the slow-light induced enhancement of rotation sensing.     

Electronic band structure and optical absorption of nanotubular zinc oxide doped with Iron, Cobalt, or Copper

The absorption spectra of the precursor-derived solid solutions Zn_{1 ? x} M _x O (M = Fe, Co, Cu) with a tubular morphology of aggregates have been investigated in the ultraviolet and visible regions. The maximum metal concentration x in the Zn_{1 ? x} M _x O solid solutions is 0.075 for iron, 0.2 for cobalt, and 0.1 for copper. It has been found that the optical absorption and the band gap of the Zn_{1 ? x} M _x O compounds depend on the type of dopant. The obtained experimental data have been interpreted using the results of the performed ab initio calculations of the electronic band structure and optical absorption.     

Effect of conditions of preparation on the thermoelectric properties of solid solutions of Bi<Subscript>0.5</Subscript>Sb<Subscript>1.5</Subscript>Te<Subscript>3</Subscript>

The effect the conditions of preparing thermoelectric solid solutions of Bi_0.5Sb_1.5Te₃ + 0.06 wt % Pb by hardening from the liquid state with subsequent hot pressing have on their thermoelectric properties is studied. It is found that the optimum thermoelectric quality factors are achieved at a 2200–2800 rpm rate of copper disc rotation.     

EPR and optical absorption studies of Fe ions in sodium borophosphate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectral investigations have been carried out on Fe³⁺ ions doped sodium borophosphate glasses (NaH₂PO₄-B₂O₃-Fe₂O₃). The EPR spectra exhibit resonance signals with effective g values at g=2.02, g=4.2 and g=6.4. The resonance signal at g=4.2 is due to isolated Fe³⁺ ions in site with rhombic symmetry whereas the g=2.02 resonance is due to Fe³⁺ ions coupled by exchange interaction in a distorted octahedral environment. The EPR spectra at different temperatures (123-295 K) have also been studied. The intensity of the resonance signals decreases with increase in temperature whereas linewidth is found to be independent of temperature. The paramagnetic susceptibility (χ) was calculated from the EPR data at various temperatures and the Curie constant (C) and paramagnetic Curie temperature (θ_p) have been evaluated from the 1/χ versus T graph. The optical absorption spectrum exhibits bands characteristic of Fe³⁺ ions in octahedral symmetry. The crystal field parameter (Dq) and the Racah interelectronic repulsion parameters (B and C) have also been evaluated and discussed.     

Electronic properties of Pb(ZrTi)O3 solid solutions

The theoretical backgrounds and some experimental data on the electronic properties of polycrystalline Pb(Zr, Ti)O₃ solid solutions are summarized. These substances occur in the perovskite structure, and so their electronic band structure is presumed to be analogous to other perovskite compounds. Their forbidden gap energy has been determined to be about 3.30–3.56 eV on the basis of optical, photoacoustical, and photoelectrical measurements. Many local levels and traps exist in the forbidden gap because of the polycrystalline character and heterovalent doping. Their actual configurations and states strongly influence the optical, photoelectrical, piezoelectrical, and other physical properties of Pb(Zr, Ti)O₃ solid solutions.     

Far-infrared spectrum of sodium hydride

Rotational spectra in the v = 0, 1, 2, and 3 levels of the ground (¹Σ) state of sodium hydride have been observed using tunable far-infrared radiation generated from the difference frequency between two CO₂ lasers. The Dunham coefficients, which have been determined without the use of optical data or isotopic scaling relations, are Y₀₁ = 146 999.138(38) MHz, Y₀₂ = −10.29481(54) MHz, Y₀₃ = 6.243(49) × 10⁻⁴ MHz, Y₁₁ = −4109.912(68) MHz, Y₁₂ = 0.14695(68) MHz, Y₂₁ = 33.341(34) MHz, Y₂₂ = −2.69(20) × 10⁻³ MHz, and Y₃₁ = −1.0517(55) MHz. The constants are typically an order of magnitude more accurate than the best values previously available, and where comparison is possible, agreement is found to be excellent.     

Band gap and type of optical transitions at the interband absorption edge in solid solutions based on bismuth telluride

The spectra of optical absorption in multicomponent n- and p-type solid solutions based on bismuth and antimony chalcogenides with substitutions in both sublattices of Bi₂Te₃ have been investigated. It has been found that, in all the solid solutions studied, just as in the parent compound Bi₂Te₃, direct allowed transitions occur at the interband absorption edge at T = 300 K. The band gap E _g in the n-Bi_{2 ? x} Sb _x Te_{3 ? y ? z} Se _y S _z solid solutions weakly increases with increasing number of substituted atoms in the Bi and Te sublattices. These atomic substitutions do not leads to an increase in E _g as compared to that of the n-Bi₂Te_2.7Se_0.3 composition. An analysis of the optical absorption spectra suggests that the solid solutions under consideration are weakly degenerate, a conclusion supported by the earlier studies of the thermoelectric and galvanomagnetic properties. It has been established that, in the conduction band of the Bi_1.8Sb_0.2Te_2.7Se_0.15S_0.15 solid solution, there is an additional extremum lying above the main extremum at a distance no more than 0.1 eV.     

K Auger transitions of the free sodium atom

TheK Auger spectrum of the free sodium atom, following electron impact ionization, was measured with 0.16% resolution using a sodium atomic beam as target. The absolute energies and relative intensities ofKLL, KLM and numerous satellite transitions have been determined. The absolute energies of theKLL transitions of the free sodium atom were found to be smaller by 13.1 eV than the corresponding energies found for sodium in Na₂O (relative to the Fermi level) by Fahlmanet al. Also the relativeKLL intensities differed in two cases indicating solid state and/or chemical effects. The present relative intensities agree better with theoretical values calculated by McGuire, Walters and Bhalla, and Chen and Crasemann than those of Na₂O. In an Appendix the natural line widths of theKLL andKM-LLM transitions of sodium have been calculated.     

Formation of copper/gold solid solutions by ion beam mixing

The formation of copper/gold solid solutions due to ion beam mixing was studied by Rutherford backscattering, high-voltage electron microscopy and transmission high-energy electron diffraction. Irradiation of multilayered Cu/Au thin films were performed with Xe⁺ ions or Ar⁺ ions at room temperature to doses ranging from 5×10¹⁵ to 2.5×10¹⁶ ions/cm² and energies from 100 to 300 keV. The ion beam mixing leads to uniformly mixed metal layers. The grain size of mixed layers is pronounced increase. It was found that Cu/Au solid solutions are formed with different composition in dependence on itinial composition and implantation dose. Cu-rich and Au-rich solid solutions are induced by ion beam mixing at an initial composition Cu _x Au_100–x withx70. In addition to these solid solutions, a solid solution of middle composition Cu₆₀...₄₀Au₄₀...₆₀ is formed for an initial composition withx<70. The kinetics of formation of solid solution is discussed as a function of the initial composition and implantation dose. Post-annealing experiments of mixed Cu₅₀Au₅₀ multilayers lead to lattice transformations and provide a superlattice structure CuAuI of the L1₀-type. With this process of ordering is associated the formation of dislocation loops.     

Magnetic, optical, and electrical properties of solid solutions VxFe1−x BO3

Complex studies of magnetic, electrical, and optical properties of V_x Fe_1?x BO₃ solid solutions are carried out in the entire range of concentrations between the extreme compounds VBO₃ and FeBO₃. A concentration semiconductor-insulator transition accompanied by a change in the magnetic structure is observed. It is found that the physical properties of the solid solution under investigation differ from those predicted in the model of a virtual crystal in the form of an aggregate of V and Fe centers taken with the weight of x and 1?x, respectively. The systems of electron energy levels of the VB₆O₆ and FeB₆O₆ clusters are calculated from first principles using the Hartree-Fock method. The calculated electron structure forms the basis for simulating the optical absorption spectra, which are in good agreement with experimental results. A qualitative explanation is given for the entire body of data on electrical conductivity and magnetization.     

Effects of magnesium salt concentrations on B-DNA overstretching transition

In this study, we use optical tweezers to investigate the ionic effects of magnesium salt solutions on the overstretching transition of single B-DNA molecules. The experimental data are compared with those in sodium salt solutions. The overstretching transition force increases when the NaCl or MgCl₂ salt concentration increases. Magnesium cations have much stronger effects on the overstretching transition force than sodium cations. For both NaCl and MgCl₂ salt solutions, the overstretching transition force is linear with the natural logarithm of salt concentration, which confirms the theory proposed in previous paper. The modified ZZO model is applied to study the electrostatic contribution of magnesium salt solutions to the overstretching transition of single B-DNA molecules. The consistency between the experimental data and analytical results shows that the modified ZZO model can simulate the transition behavior of single B-DNA molecules in different NaCl and MgCl₂ salt solutions.     

Synthesis of silver nanoparticles by sonogalvanic replacement on aluminium powder in sodium polyacrylate solutions

The process of the formation of silver nanoparticles (AgNPs) via the method of galvanic replacement (GR) of Ag⁺ with aluminum powder in sodium polyacrylate (NaPA) solutions in the ultrasonic (US) field has been studied. It was observed, that the yellow colloidal solutions of stabilized AgNPs with the absorption maximum at ∼ 410 nm were obtained under the application of US power by 20 W and frequency by 20 kHz in the wide range of AgNO₃ and NaPA concentrations (0.1 – 0.5 mM and 0.5 – 5.0 g/L respectively) at 25 ⁰C. It was shown, that the GR process under US field occurs without of the significant induction period. Using the UV–vis spectroscopy the kinetics of AgNPs formation has been studied and it was observed the first order kinetics with respect to Ag⁺ ions both for the nucleation and growth processes. It was found that observable rate constants of nucleation are close for the all experimental conditions but the observable rate constants of growth decreased with increasing of initial concentration of AgNO₃. Based on the obtained kinetic data it was proposed a mechanism of the formation of AgNPs consisted of the following two main stages: 1) the nucleation with the formation of primary nanoclusters (AgNCs) on aluminum surface followed by their ablation from the surface of the sacrificial metal by ultrasound into bulk of solution; 2) the transformation of AgNCs in AgNPs via growth from the Al surface and / or agglomeration of AgNCs. Using TEM it was found that the size of obtained AgNPs does not exceed of 25 nm and slightly depends on the initial concentrations of precursors. High antimicrobial activity of obtained colloidal solutions against gram-negative and gram-positive bacteria as well as against fungi was observed.     

Electronic band structure, optical absorption, and photocatalytic activity of iron-doped anatase

Quasi-one-dimensional solid solutions of the composition Ti_{1 ? x} Fe _x O_{2 ? x/2} (0.005 ≤ x ≤ 0.050) with the anatase-type structure and extended aggregates have been prepared by the precursor method. The absorption spectra of the solid solutions have been investigated in the ultraviolet and visible regions, and the photocatalytic activity in the oxidation reaction of hydroquinone in water has been estimated. It has been found that the synthesized solid solutions serve as photocatalysts only under ultraviolet irradiation, and their photoactivity increases with an increase in the dopant concentration. The first-principles calculations of the electronic band structure and optical absorption in iron-doped anatase and rutile have been performed using the pseudopotential method LSDA + U (with the VASP software package). The on-site exchange-correlation parameters have been calibrated in the calculations of the electronic band structure of hematite α-Fe₂O₃ and ilmenite FeTiO₃. It has been shown that, despite the appearance of impurity states within the band gap of anatase and rutile, doping with iron does not cause substantial absorption in the visible region, which correlates with the increase in photocatalytic activity only under ultraviolet irradiation. The most probable cause of the experimentally observed absorption in the visible region is the presence of finely dispersed hematite impurities in the obtained samples.     

一种新型的固溶体——Mgx/2Li1-xIO3晶体结构随成分的变化

本文用室温、高温X射线衍射和差热分析等方法,研究了Mg_x/2Li_1-xIO₃晶体结构及其随成份和温度的变化。Mg(IO₃)₂·LiIO₃二元系形成一种新型的连续固溶体。在室温对于富LiIO₃的固溶体,晶体点阵沿x-y,平面产生畸变,其畸变开始随Mg(IO₃)₂含量的增加而加大,晶体的空间群从P6_{3关键词：}     

Formation of nickel magnetic nanoparticles and modification of nickel phthalocyanine matrix by sodium doping

Data for the vapor-phase doping (300°C) of nickel phthalocyanine (NiPc) by sodium taken in different concentrations (x), as well as structural analysis data for Na _{x = 0.2}NiPc, Na _{x = 1}NiPc, and Na _{x = 3}NiPc samples, have been reported. The structure of the samples and their atomic configuration versus the doping level have been studied by transmission electron microscopy, Raman scattering, X-ray diffraction, X-ray absorption spectroscopy, and extended X-ray absorption fine structure (EXAFS) spectroscopy. The structural parameters of Ni–N, Ni–C, and Ni–Ni bonds have been determined, and it has been found that, at a low level of doping by sodium, local structural distortions are observed in some molecules of the NiPc matrix near nickel atoms. The fraction of these molecules grows as the doping level rises from x = 0.2 to x = 1.0. It has been shown that doping changes the oscillation mode of light atoms, which indicates a rise in the electron concentration on five- and six-membered rings. At a high level of sodium doping (x = 3.0), nickel nanoparticles with a mean size of 20 nm and molecule decomposition products have been observed in the NiPc matrix. It has been found that the fraction of nickel atoms in the Na _{x = 3}NiPc nanoparticles as estimated from EXAFS data is sufficient for the room-temperature magnetic properties of the samples to persist for a long time.