Analysis of the parameters of a barrier discharge in Kr-I2 and Xe-I2 mixtures

The barrier discharges in Kr-I₂ and Xe-I₂ mixtures are investigated as possible light sources at wavelengths λ=185 and 253 nm. The spectral and current-voltage characteristics of the barrier discharges are obtained. The concentrations of mixture components are calculated, and the kinetic diagrams of the reactions are constructed. The emission efficiencies are estimated to be approximately 20% for both wavelengths. The optimum conditions for emission at these wavelengths in the mixtures Xe-I₂ (400 ± 15 Torr) and Kr-I₂ (200 ± 0.1 Torr) are determined.     

Numerical study of dumbbell-shaped gold nanoparticles using in plasmonic waveguides in near infra-red spectrums

In this paper, we investigated plasmonic waveguides in near infra-red spectrum using dumbbell-shaped gold nanoparticles. It is possible to shift localized surface plasmon resonance (LSPR) to the desired wavelength with proper geometrical properties. 3-D FDTD simulations are used to determine the set of geometrical parameters of nanoparticles to obtain LSPR at 1310 and 1550 nm. Employing different configuration of nanoparticles chains, we not only can design waveguides with better optical characteristics but also achieve the demultiplexing function in V-form arrays. The proposed nanoparticles show sharp resonance peak, 168 FWHM bandwidth for λ?=?1310, and 204 nm for λ?=?1550 nm. Linear chains of particles can transport the electromagnetic energy at λ?=?1310 nm, with transmission losses γ_L?=?3 dB/452 and γ_T?=?3 dB/446 nm and group velocities v_gL?=?0.336C₀ and v_gT?=?0.256C₀ for longitudinal and transverse polarizations, respectively, where C₀ is the speed of light in the vacuum. At λ?=?1550 nm, γ_L?=?3 dB/490, γ_T?=?3 dB/604, v_gL?=?0.382C₀ and v_gT?=?0.260C₀. Moreover, we attained 8.13 as minimum ratio of averaged electric field intensity and 36.8 as minimum ratio of averaged Poynting vector as a function of position between two ports in demultiplexing function.     

Emission from a DC glow discharge in a He/H2O mixture

The electrical and optical characteristics of a longitudinal dc glow discharge in a cylindrical discharge tube in mixtures of helium with saturated water vapor at room temperature are investigated. In the UV range, a broad band with a maximum at λ_max=309.6 nm and Δλ=9 nm prevails. The H_α 656.3-nm, H_β 486.1-nm, and HeI lines in the range 440–670 nm are the main diagnostic spectral lines. The helium partial pressure and the glow discharge current are optimized to achieve the maximum intensities of the 309.6-nm band and HeI and HI spectral lines. The results obtained are of interest for the development of an ecologically safe radiation source based on the products of the decomposition of water molecules and clusters in plasma.     

N-lines in the luminescence spectra of Cr3+-doped spinels: IV. Excitation spectra

Excitation spectra (T = 75–300 K; λ_exc = 450–630 nm) which were measured for the R-lines of Cr³⁺-doped oxides (α-Al₂O₃, β-Ga₂O₃) and for different luminescence lines (R-lines, N-lines) of Cr³⁺-doped spinels (MgAl₂O₄, ZnAl₂O₄, ZnGa₂O₄) are reported. The excitation maxima observed for different luminescence lines of a given compound exhibit considerable differences: 530 nm ? λ^max_exc ? 565 nm for MgAl₂O₄; 530 nm ? λ^max_exc ? 580 nm for ZnAl₂O₄; 545 nm ? λ^max_exc 555 nm for ZnGa₂O₄. According to the interpretation of N-lines to arise from different classes of Cr³⁺ ion swith different short range orderd, the excitation maximum of one distinct line should entirely correspond to the transition Δ : ⁴T₂ ← ⁴A₂ of that Cr³⁺ class from which the line arises. By this method spectroscopic data about the different kinds of Cr³⁺ ions present in a given sample can, therefore, be obtained which are not available from absorption measurements. The experimetal data were found to be in agreement with the results of model calculations. Restrictions which limit the accuracy and relevance of the data are discussed.     

Emission characteristics of a discharge iodine vapor plasma in the spectral region of the main absorption maximum of DNA molecules

Radiation of glow and capacitive discharges in inert gas-iodine vapor mixtures is studied in the spectral range 150–210 nm, which coincides with the main absorption maximum of the DNA molecules. Iodine atomic spectral lines at 150.7, 161.8, 170.2, 183.0, and 206.2 nm are observed in the spectra. The emission intensity of the iodine spectral lines is optimized by varying the glow discharge current, capacitive discharge frequency, as well as pressure and composition of the gas mixtures. The glow and capacitive discharges are ignited in cylindrical quartz tubes with interelectrode gaps of 10 and 6 cm. Helium and neon are found to be the most effective buffer gases. The optimum partial pressures of the light inert gases and iodine vapor in the glow discharge are within 0.4–0.6 kPa and 100–150 Pa, respectively. In the capacitive discharge in He(Ne)-I₂ mixtures, the optimum partial helium, neon, and iodine vapor pressures are within 0.8–2.0 kPa, 0.5–1.0 kPa, and ≤ 60 Pa, respectively. It is demonstrated that pulsed bactericidal radiation sources with light pulse lengths of 400–500 ns and continuous radiation sources emitting within the spectral range 150–207 nm can be designed on the basis of low-density iodine vapor plasma.     

Effect of H-atom concentration on soot formation in premixed ethylene/air flames

Soot formation is a major challenge in the development of clean and efficient combustion systems based on hydrocarbon fuels. Fundamental understanding of the reaction mechanism leading to soot formation can be obtained by investigating the role of key reactive species such as atomic hydrogen taking part in soot formation pathways. In this study, two-dimensional laser induced incandescence (LII) measurements using λ?=?1064?nm laser have been used to measure soot volume fraction (f_V) in a series of rich ethylene (C₂H₄)/air flames, stabilized over a McKenna burner fitted with a flame stabilizing metal disc. Moreover, a comparison of UV (λ?=?283?nm), visible (λ?=?532?nm) and IR (λ?=?1064?nm) laser excited LII measurements of soot is discussed. Recently developed, femtosecond two-photon laser-induced fluorescence (fs-TPLIF) technique has been applied for obtaining spatially resolved H-atom concentration ([H]) profiles under the same flame conditions. The structure of the flames has also been determined using hydroxyl radical (OH) planar laser induced fluorescence (PLIF) imaging. The results indicate an inverse dependence of f_V on [H] for a range of C₂H₄/air rich flames up to an equivalence ratio, Φ?=?3.0. Although an absolute relationship between [H] and f_V cannot be easily derived owing to the multiple steps involving H and other intermediate species in soot formation pathways, the present study demonstrates the feasibility to couple [H] and f_V obtained using advanced optical techniques for soot formation studies.     

Measurement of mean size and evaluation of polydispersity of gold nanoparticles from spectra of optical absorption and scattering

Two methods for determination of the mean size of gold nanoparticles, based on measurement of the wavelengths of the maxima λ_max of side scattering and extinction in the range 400–700 nm, are compared. Four sols with mean particle diameters d of about 15, 20, 25, and 30 nm, measured using the dynamic light-scattering technique, were studied experimentally. The slope of the size dependence λ_max(d) of the spectral position of the scattering peak exceeded that for the extinction peak by a factor of 2.4. This fact ensures a substantially higher accuracy of the scattering method. For simulating polydispersity, mixtures of three colloids with particle diameters of 20, 25, and 30 nm were used: sample S1, with a size distribution close to the normal one of around 25 nm, and sample S2, with equal concentrations of each of the components. The extinction spectra of mixtures S1 and S2 and the initial 25-nm sol (S0) were virtually identical, whereas their scattering spectra showed a pronounced increase in the peak amplitude in the series S0, S1, S2. These results agree with calculations based on the Mie theory. Thus, scattering spectra offer advantages over extinction spectra not only in measuring the mean size of gold particles but also in evaluating their polydispersity.     

Solvatochromic Studies of Fluorescein Dianion in N,N-Dimethylformamide/Water and Dimethylsulphoxide/Water Mixtures

Abstract

The absorption, excitation and fluorescence spectra of the fluorescein dianion (FL^2?) in N, N-Dimethylformamide (DMF)/water (H₂O) and Dimethylsulphoxide (DMSO)/H₂O solvent mixtures have been investigated. It is found that the absorption λ_max and emission maxima EX, _nax are both hypsochromic shifted when the H₂O content in the solvent mixtures increases. However, the shoulder peaks λ_s remain constant at 483. 5nm within the range of H₂O mole fraction, x= 0 to 0. 518 in a DMF/H₂O solvent mixture and at 484. 4nm within the range, x=0 to 0. 304, in a DMSO/H₂O mixture. Further increases in H₂O content, cause a hypsochromic shift in λ_s. The molar energies for the electronic transition from the ground state (S₀) to S₁, the first excited singlet state, (E_T(1)) and to S₂, the 2nd excited singlet state, (E_T(2)) of FL^2?in the solvent mixtures are also plotted against x. Linear straight lines and intersection points are observed at x=0. 73 for E_T(1) and at x=0. 51 for E_T(2) in the DMF/H₂O mixture and at x=0. 71 for E_T(1) and at x=0. 31 &; 0. 69 for E_T(2) in the DMSO/H₂O mixture. Hydrogen-bonding stabilization effects are used to explain the above observations. The variation in relative fluorescence quantum yields of S₁ and S₂ of FL^2? with x in the aprotic solvent-H₂O mixtures to FL^2? in pure aprotic solvent are determined and discussed.     

New method for determining refractive index and thickness of fluorescent thin films

The optical parameters of homogeneous, isotropic, and fluorescent thin films are determined by comparing measured with calculated angular intensity distributions of the s- and p-polarized light emitted into the substrate. The method also yields information about the multipole nature of the emitted radiation. The theory is presented for electric and magnetic dipole transitions. For extremely thin layers of optical thickness n₀d₀ ? λ/8 (where λ is the emission wavelength) analytic expressions for the angular intensity distributions are given. For between 25–30 nm thick evaporated layers of an europium-benzoyltrifluoro-acetone- chelate the refractive index was determined to be n₀ = 1.57 at λ = 612 nm. The fluorescent light emitted by these layers in an about 6 nm wide band centered at λ = 612 nm is emitted by randomly oriented electric dipoles.     

Development and validation spectroscopic methods for the determination of lomefloxacin in bulk and pharmaceutical formulations

Four simple, sensitive spectrophotometric and spectrofluorimetric methods (A-D) for the determination of antibacterial drug lomefloxacin (LMFX) in pharmaceutical formulations have been developed. Method A is based on formation of ternary complex between Pd(II), eosin and LMFX in the presence of methyl cellulose as surfactant and acetate-HCl buffer pH 4.0. Spectrophotometrically, under the optimum conditions, the ternary complex showed absorption maximum at 530 nm. Methods B and C are based on redox reaction between LMFX and KMnO₄ in acid and alkaline media. In indirect spectrophotometry method B the drug solution is treated with a known excess of KMnO₄ in H₂SO₄ medium and subsequent determination of unreacted oxidant by reacting it with safronine O in the same medium at λ_max = 520 nm. Direct spectrophotometry method C involves treating the alkaline solution of LMFX with KMnO4 and measuring the bluish green product at 604 nm. Method D is based on the chelation of LMFX with Zr(IV) to produce fluorescent chelate. At the optimum reaction conditions, the drug-metal chelate showed excitation maxima at 280 nm and emission maxima at 443 nm. The optimum experimental parameters for the reactions have been studied. The validity of the described procedures was assessed. Statistical analysis of the results has been carried out revealing high accuracy and good precision. The proposed methods were successfully applied for the determination of the selected drug in pharmaceutical preparations with good recoveries.     

Renner-teller effect at the initial acetylene thermal transformation stages

It is shown that the vibrational excitation of the acetylene molecule is accompanied by the transformation of its linear structure into a transoid structure because of the Renner-Teller effect. The electron density distribution in transoid acetylene was calculated by nonempirical quantum-chemical methods. It was shown that this structure corresponded to a 1,2-biradicaloid. The intense light absorption in the acetylene spectrum at λ _max = 240 nm and temperature above 800 K was found to be related to the S₂ ? S₀ electron transition. Transoid acetylene 1,2-biradicaloids were shown to participate in the dimerization reaction with the formation of trans-1,4 biradicals. The enthalpies and energy barriers were determined for some elementary stages of the primary thermal transformations of acetylene.     

The isothermal section of the Tb–Co–Cr ternary system at 873 K

The isothermal section of the phase diagram of the Tb–Co–Cr ternary system at 873?K was investigated by means of X-ray diffraction, metallography, and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. Ternary phases and their lattice parameters as a function of composition of solid solution were systematically studied. The existence of one ternary phase reported previously was confirmed. The ternary compound Tb(Co,?Cr)₁₂ crystallizes with ThMn₁₂-type structure, space group I4/mmm. The linear homogeneity range along the line of 7.69 at.% Tb in TbCo_{12? x} Cr _x was found to be about x?=?3.6–5.7, i.e., 27.7–43.8 at.% Cr. The lattice parameters are a?=?0.8326–0.8352?nm and c?=?0.4709–0.4740?nm. The maximum solid solubilities of Cr in Tb₂Co₁₇, TbCo₃, and TbCo₂ are about 20.0, 8.2, and 7.9 at.%, respectively.     

Nano-sized local magnetic field induced by circular motion of ions and molecules in a nanotorus under gigahertz rotating electric fields

Recently, we reported molecular dynamics simulations of stable cyclotron motions of ions and water molecules in a carbon nanotorus, induced by different rotating electric fields (EFs). This study is devoted to the calculation and characterisation of the magnetic field (MF) induced by these cyclotron motions. Results show that carbon nanotorus containing ions or water molecules acts as an EF-to-MF transducer. Components of the instantaneous induced MF show large-scale oscillations superimposed by strong fluctuations arising respectively from overall circular motion and random collisions of moving species. Analysis of the space-dependencies of the induced MF components shows that the induced MF is maximum at the centre of the nanotorus. The MF induced by cyclotron motion of ions follows the orders B(Ca²⁺)?>?B(Na⁺)?≈?B(K⁺) at E?=?1.0?V/nm and B(E?=?1.0?V/nm)?>?B(E?=?0.5?V/nm)?>?B(E?=?0.1?V/nm). The time-averaged induced MF of the cyclotron motion of 81 water molecules is almost 10² times stronger than that of ions. The induced MF strength is decreased with increasing distance from nanotorus and decays effectively at about 17.3–18.1 and 15.9–18.2?nm along the z-axis of the nanotorus for ions and water molecules, respectively. The magnitude of the MF induced by cyclotron motions of water molecules and ions, respectively, decreases and increases in the nanotorus with freed carbon atoms.     

Light conversion in thin films of a mixture of mesotetraphenylporphyrin and erbium-doped yttrium vanadate crystallites: 2. Optical properties

The optical properties of two-component films composed of mesotetraphenylporphyrin (TPP) and erbium-doped yttrium vanadate Yt_0.95Er_0.05VO₄ prepared by spincoating have been studied for the first time. A decrease in the TPP content in the films leads to a hypsochromic shift of the Soret band peak by 1–9 nm; this finding suggests that the degree of aggregation of TPP decreases with decreasing TPP content in the film. The fluorescence peak of TPP is located at an emission wavelength of λ_em = 634 nm and an excitation wavelength of λ_ex = 420 nm. The fluorescence peaks of Y_0.95Er_0.05VO₄ at λ_em = 526, 546, and 555 nm (λ_ex = 300 nm) correspond to the following transitions of the Er3+ ion: the band at 526 nm, to the ² H _11/2 → ⁴ I _15/2 transition; the bands at 546 and 555 nm, to the ⁴ S _3/2 λ ⁴ I _15/2 transition. The fluorescence band peaks preserve their positions with a change in the ratio of components in the film; that is, the fluorescent characteristics of TPP and Y_0.95Er_0.05VO₄ clusters do not depend on their interaction. For both TPP and Y_0.95Er_0.05VO₄, the maximum fluorescence intensity is observed at a TPP content in the film of 40%; the gain with respect to single-component TPP and Y_0.95Er_0.05VO₄ films is 70 and 4–15%, respectively. In this case, a significant effect is exerted not so much by the nature and structure of the components and their interaction as by the topographic features of organization of the photoactive elements in the film, their ratio, and mutual orientation, which determine the energy capture probability.     

Widely tunable fourth harmonic generation of a Ti:sapphire laser based on RBBF crystal

Fourth harmonic generation of a tunable Ti:sapphire laser with a repetition rate of 80?MHz and pulse duration ??150 fs has been realized in a single pass with an RbBe₂BO₃F₂ crystal for the first time. A high average power was obtained which was tunable throughout a wide range from 180 to 232.5?nm. The output power over the whole range exceeded 2?mW, the highest being 43.3?mW at 202.5?nm. Moreover, deep-ultraviolet output with powers above 75?mW was obtained at 193.5 and 200?nm under a stronger focusing condition. This is the first attempt at the generation of tunable deep-ultraviolet light without using a KBBF crystal, which is very difficult to grow due to its strong layering tendency, and our attempt may provide new opportunities for the development of all-solid-state deep-ultraviolet coherent light sources.     

Measurement of the Soret,diffusion, and thermal diffusion coefficients of three binary organic benchmark mixtures and of ethanol–water mixtures using a beam deflection technique

We have measured the Soret (S _T ), diffusion (D), and thermal diffusion (D _T ) coefficients of three binary mixtures of dodecane (DD), isobutylbenzene (IB) and 1,2,3,4-tetrahydronaphthalene (TH) for a concentration of 50 wt% at a temperature of 25°C by means of an optical beam deflection cell. This relevant experimental technique was still missing from a recent benchmark campaign for the measurement of the Soret effect. The measured coefficients agree to within a few percent (10% for S _T , D of TH/IB) with the proposed benchmark values. A detailed analysis of the measurement process of the beam deflection cell, which allows for an elegant extension to include temperature gradients within the windows, is given, and improved benchmark values are suggested. In addition, ethanol–water mixtures have been investigated very carefully over a broad concentration and temperature range. Comparison with data of Kolodner and Wiegand gives a generally good agreement with some systematic deviations. Contrary to theoretical predictions, we have not been able to identify a second sign change of S _T at high ethanol concentrations.     

Fast writing of soliton waveguides in lithium niobate using low-intensity blue light

We experimentally demonstrate the writing of soliton waveguides in lithium niobate with blue violet light, at λ?=?405?nm. This wavelength, obtained from a low-cost laser diode, allows very fast writing of soliton waveguides when comparing with the writing process using green light (532?nm). For the same writing time, there is a decrease of?~4 orders of magnitude of the light intensity necessary for writing soliton waveguides in blue. The writing process is investigated and characterized by tuning parameters, such as beam intensity, external field and beam polarization. The IR guiding capability of these soliton waveguides is tested by guiding femtosecond laser pulses at λ?=?1,550?nm.     

Unusual thermal diffusion in polymer solutions

Thermal diffusion forced Rayleigh scattering results on thermal diffusion of poly(ethylene oxide) (PEO) in ethanol/water mixtures are presented. In water-rich solvent mixtures, PEO is found to migrate towards regions of lower temperature. This is typical for polymer solutions and corresponds to a positive Soret coefficient of PEO. In solvent mixtures with low water content, however, the polymer is found to migrate towards higher temperatures, corresponding to a negative Soret coefficient of PEO in ethanol-rich solutions. To our knowledge, this is the first observed sign change of the Soret coefficient of a polymer in solution. We also present a simple lattice model for the polymer solvent system and calculate Soret coefficients with statistical mechanics methods. The calculated values agree qualitatively with the experimental results.     

A Novel Method for the Assessment of Cortisol Hormone in Different Body Fluids Using A New Photo Probe Thiazole Derivative

A low cost and accurate method for the detection and analytical determination of the cortisol in pharmaceutical preparation, blood serum and urine was developed. The method was based upon the enhancement of fluorescence intensity of the band at 424 nm of the photo probe by different cortisol concentrations in acetonitrile at (pH 5.7, λ_ex?=?320 nm). The influence of the different parameters, e.g. pH, solvent, cortisol concentration and foreign ions concentrations that control the enhancement process of fluorescence intensity of the band of photo probe was critically investigated. The remarkable enhancement of the fluorescence intensity at 424 nm in acetonitrile by various concentrations of cortisol was successfully used as a photo- probe for the assessment of cortisol concentration. The calibration plot was achieved over the concentration range 8.0?×?10^?6–5.5?×?10^?9 mol L^?1 cortisol with a correlation coefficient of 0.998 and a detection limit of 4.7?×?10^?9 mol L^?1. The developed method is simple and proceeds without practical artifacts compared to the other determination methods.