Showing papers in "Indian Journal of Physics in 2015"

Structural and photoluminescence properties of red-light emitting YVO 4 :Eu 3+ phosphor synthesized by combustion and solid-state reaction techniques: a comparative study

Abstract: In this work, Eu3+-doped YVO4 phosphors were prepared via the solid-state reaction and the combustion method and the role of the synthesis process on the structural and emission properties of YVO4:Eu3+ was investigated. Combustion synthesis yielded tetragonal phase with the space group I41/amd at a relatively low temperature and within short duration. The infrared spectra confirmed the characteristic bands of Y–O and V–O at around 450 and 830 cm−1, while the samples prepared by combustion route exhibited C–O band and O–H–O bending vibrations at 1376 and 1637 cm−1, respectively. The band gap energy of YVO4, prepared by different methods, was found in the range of 3.6–3.73 eV. Upon UV excitation, the Eu3+-activated samples exhibited characteristic red–orange emission lines generated from 5D0 → 7F1,2 transitions of Eu3+ ions, respectively. The red-to-orange emission intensity ratio was found to be around 4.6 for all samples and proved to be competitive with the commercially available red phosphors. However, Y1−x Eu x VO4 phosphors, synthesized by solid-state reaction technique, exhibited elevated Eu3+ solubility and higher emission intensity than the samples prepared by combustion route owing to the larger crystallite size and minor C–O and O–H bonds. The critical concentration of Eu3+ ions for the maximum emission was estimated to be 2.0 and 0.5 mol% for the samples obtained by solid-state reaction and combustion method, respectively. The present phosphors were observed to be effectively excitable via the broad range of UV lights and were proved to be compatible with the UV LEDs.

Effect of laser irradiation on optical properties of Ge 12 Sb 25 Se 63 amorphous chalcogenide thin films

Abstract: The change in photo-induced optical properties in thermally evaporated Ge12Sb25Se63 chalcogenide thin film under 532-nm laser illumination has been reported in this paper. The structure and composition of the film have been examined by X-ray diffraction and energy dispersive X-ray analysis, respectively. The optical properties such as refractive index, extinction coefficient and thickness of the films have been determined from the transmission spectra based on inverse synthesis method and the optical band gap has been derived from optical absorption spectra using the Tauc plot. It has been found that the mechanism of the optical absorption is due to allowed indirect transition. The optical band gap increases by 0.05 eV causing photo-bleaching mechanism, while refractive index decreases because of reduction in structural disordering. Deconvolution of Raman and X-ray photoelectron spectra into several peaks provides different structural units, which supports the optical photo-bleaching.

Chemical synthesis, structural characterization and optical properties of nanophase α-Ag 2 WO 4

Abstract: Silver tungstate (α-Ag2WO4) nanoparticles were synthesized by chemical precipitation method. Thermodynamic stability of the α-Ag2WO4 nanoparticles was studied by thermogravimetric and differential thermal analysis. These nanoparticles were structurally characterized by X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. The structure and morphology of these nanoparticles were studied by scanning electron microscopy and high-resolution transmission electron microscopy. The composition of nanoparticles near and at the surface was estimated by using energy-dispersive X-ray analysis. The optical properties of these nanoparticles were investigated by UV–Visible as well as photoluminescence spectroscopy. The effects of calcination temperature on the geometric parameters and optical properties of α-Ag2WO4 nanoparticle samples was also investigated.

Modifications in device characteristics of La 0.6 Pr 0.2 Sr 0.2 MnO 3 /SrNb 0.002 Ti 0.998 O 3 manganites by swift heavy ion irradiation

Abstract: Present study reports the device characteristics of epitaxially grown La0.6Pr0.2Sr0.2MnO3/SrNb0.002Ti0.998O3 manganite before and after swift heavy ion irradiation at various ion fluences. The modification in the structural, morphological and electrical transport properties of La0.6Pr0.2Sr0.2MnO3/SrNb0.002Ti0.998O3 have been explained based on defect formation and interface annealing effect. Various charge transport models are used to fit the I–V characteristics and the present study suggests that thermionic emission mechanism governs the transport in the pristine and irradiated devices. Irradiation induced variation in structural strain, crystallinity and surface roughness are responsible for the change in transport behavior in the devices.

A theoretical model for investigating the effect of vacuum fluctuations on the electromechanical stability of nanotweezers

Abstract: In this paper, the impact of the Casimir attraction on the electromechanical stability of nanowire-fabricated nanotweezers is investigated using a theoretical continuum mechanics model. The Dirichlet mode is considered and an asymptotic solution, based on path integral approach, is applied to consider the effect of vacuum fluctuations in the model. The Euler-Bernoulli beam theory is employed to derive the nonlinear governing equation of the nanotweezers. The governing equations are solved by three different approaches, i.e. the modified variation iteration method, generalized differential quadrature method and using a lumped parameter model. Various perspectives of the problem, including the comparison with the van der Waals force regime, the variation of instability parameters and effects of geometry are addressed in present paper. The proposed approach is beneficial for the precise determination of the electrostatic response of the nanotweezers in the presence of Casimir force.

Half-metallic ferromagnetism in Be 1−x V x Te alloys: an Ab-initio study

Abstract: First-principles calculations of the structural, elastic, electronic, magnetic and thermodynamic properties of zinc blende Be1−x V x Te alloys (x = 0, 0.25, 0.50, 0.75 and 1) based on spin-polarized density functional theory are performed using full-potential augmented plane wave method, within the spin generalized gradient approximation for the exchange–correlation potential. The equilibrium structural parameters such as lattice constant (a 0 ), bulk modulus (B 0 ) and first pressure derivative of bulk modulus ( $$ B^{\prime } $$ ) are optimized for all alloys. The elastic constants C 11, C 12, C 44 and anisotropy coefficients are also estimated. The calculations of the band structure and the density of states demonstrate that all Be1−x V x Te (x = 0.25, 0.50, 0.75 and 1) alloys are complete half-metals. The investigation of the band structure and the density of states demonstrate that Be0.75V0.25Te alloy is entirely half-metal, whereas Be0.50V0.50Te and Be0.25V0.75Te alloys are nearly half-metal. The estimation of the s(p)–d exchange splitting constants N 0α (conduction band) and N 0β (valence band), as obtained through the density of states, have been used to indicate the magnetic behavior of the compounds. From the total magnetic moment, it is observed that the p–d hybridization reduces the local magnetic moment of V atom from its free space charge of 3µ B and generates small local magnetic moments on the nonmagnetic Be and Te sites. Lastly, based on the quasi-harmonic Debye model, the obtained macroscopic thermodynamic properties, such as thermal expansion coefficient, heat capacities and Debye temperate, are presented in detail.

Facile one step synthesis of novel TiO 2 nanocoral by sol–gel method using Aloe vera plant extract

Abstract: Titanium oxide (TiO2) nanoparticles (NPs) were synthesized by sol gel method using Aloe vera plant extract as a biological capping agent and a cauliflower-nanocoral morphology was observed in this technique. The assynthesized TiO2 nanopowder was calcined at a range of temperatures (300–600 °C) for 1 h. The influence of A. vera plant extract on the thermal, structural and morphological properties of TiO2 nanopowder was evaluated. Thermogravimetric analysis/differential thermal analysis was employed to study the thermal properties of the assynthesized TiO2 nanopowder. The crystallinity, phase transformation and the crystallite size of the calcined samples were studied by X-ray diffraction technique. XRD result confirmed the presence of TiO2 with anatase phase. FT Raman spectra showed the Raman active modes pertaining to the TiO2 anatase phase and Raman band shift was also observed with respect to particle size variation. The different functional group vibrations of as dried pure A. vera plant extract were compared with the mixture of TiO2 and A. vera plant extract by FT-IR analysis. The scanning electron microscopy images apparently showed the formation of spherical shaped NPs and also it demonstrated the effect of A. vera plant extract on the reduction of particles size. The surface area of the TiO2 NPs was measured through Brunauer–Emmett–Teller analysis. Transmission electron microscopy images ascertained that the spherical shaped TiO2 NPs were formed with cauliflower-nanocoral morphology decorated with nanopolyps with the size range between 15 and 30 nm.

Cobalt oxide magnetic nanoparticles–chitosan nanocomposite based electrochemical urea biosensor

Abstract: In this study, a potentiometric urea biosensor has been fabricated on glass filter paper through the immobilization of urease enzyme onto chitosan/cobalt oxide (CS/Co3O4) nanocomposite A copper wire with diameter of 500 µm is attached with nanoparticles to extract the voltage output signal The shape and dimensions of Co3O4 magnetic nanoparticles are investigated by scanning electron microscopy and the average diameter is approximately 80–100 nm Structural quality of Co3O4 nanoparticles is confirmed from X-ray powder diffraction measurements, while the Raman spectroscopy has been used to understand the chemical bonding between different atoms The magnetic measurement has confirmed that Co3O4 nanoparticles show ferromagnetic behavior, which could be attributed to the uncompensated surface spins and/or finite size effects The ferromagnetic order of Co3O4 nanoparticles is raised with increasing the decomposition temperature A physical adsorption method is adopted to immobilize the surface of CS/Co3O4 nanocomposite Potentiometric sensitivity curve has been measured over the concentration range between 1 × 10−4 and 8 × 10−2 M of urea electrolyte solution revealing that the fabricated biosensor holds good sensing ability with a linear slope curve of ~45 mV/decade In addition, the presented biosensor shows good reusability, selectivity, reproducibility and resistance against interferers along with the stable output response of ~12 s

Nano-composite polymer gel electrolytes containing ortho-nitro benzoic acid: role of dielectric constant of solvent and fumed silica

Abstract: In this paper, nano-composite polymer gel electrolytes containing polymethylmethacrylate, dimethylacetamide, diethyl carbonate, fumed silica and ortho-nitro benzoic acid have been synthesized. Electrical conductivity, viscosity, pH and thermal behavior of these electrolytes have been studied. The effect of acid, polymer, fumed silica concentration on conductivity, pH and viscosity has been discussed. The effect of dielectric constant of solvent on conductivity behavior of composite polymer gel electrolytes has also been studied. Two maxima in conductivity behavior have been observed with fumed silica concentration for composite polymer gel electrolytes, which have been explained on the basis of double percolation threshold model. Maximum conductivity of 3.20 × 10–4 and 2.46 × 10−6 S/cm at room temperature has been observed for nano-composite polymer gel electrolytes containing 10 wt% polymethylmethacrylate in 1 M solution of o-nitro benzoic acid in dimethylacetamide and diethyl carbonate respectively. The intensity of first maximum observed in conductivity at low concentration of fumed silica has been found to decrease with the decrease in acid concentration for composite polymer gel electrolytes, while the intensity of second maximum at higher fumed silica concentration remains unaffected. The conductivity of composite gels does not show much change in the temperature range of 20-100 °C and also remains constant with time, making them suitable for use as electrolytes in various devices like fuel cells, proton batteries, electrochromic window applications etc.

Spectroscopic and dielectric study of iodine chloride doped PVA/PVP blend

Abstract: Optical and dielectric properties of Poly (vinyl alcohol)/ Poly (vinyl pyrrolidone) blend and blend loaded with different concentrations of ICl2 were studied. UV–Vis spectral analysis before and after γ-irradiation suggested that the addition of iodine led to complete complexation between ICl2 and polymer blend were observed. The values of optical parameters λ o , S o and n ∞ were determined from by reflection and transmission spectra in the range of 200–800 nm. The refractive index was found to change non-monotonically with the increase of iodine. Infrared analysis revealed the formation of new species between blend and iodine content. There were some changes in IR absorption bands, position and their intensities. The AC conductivity (σ ac ) behavior of all prepared films was investigated in the frequency range 42 Hz–5 MHz and under different isothermal stabilization in the temperature range 300–400 K. The dependence of the imaginary modulus (M″) on frequency at lower frequencies was estimated. The increasing values of M″ may be attributed to the bulk effect with the increase in temperature.

Effect of zinc induced compressive stresses on different properties of copper oxide thin films

Abstract: Thin films of pure and zinc doped copper oxide have been grown on Si (1 0 0) substrate using pulsed laser deposition at varying concentrations of zinc. The effects of the doping concentration on structural, surface and optical properties of all thin films have been investigated. X-ray diffraction shows the presence of monoclinic CuO phase and compressive stresses in all thin films. The Raman spectra show an up-shift in the Raman peak position for doped thin films. Micrographs show smooth surface morphology, free from micron sized laser generated particulates. Spectroscopic el- lipsometry has been used to study the optical constants (w, D ,n , k,e1, e2). Optical bandgap energies have been calculated and found to be dependent on stresses in the films. Consequently, Zn doping induced stresses have strong effects on microstructure and optical properties of thin films.

Rogue-wave solutions of a higher-order nonlinear Schrödinger equation for inhomogeneous Heisenberg ferromagnetic system

Abstract: In this paper, a higher-order nonlinear Schrodinger equation for the inhomogeneous Heisenberg ferromagnetic spin system is studied. By virtue of the generalized Darboux transformation, higher-order rogue-wave solutions are derived. Rogue-wave propagation and interaction are analyzed. We have observed that perturbation parameter and inhomogeneities in the medium affect the propagation speed and direction of first-order rogue waves and interaction of second-order rogue waves.

Electrical and interfacial properties of Au/n-InP Schottky contacts with nickel phthalocyanine (NiPc) interlayer

Abstract: The electrical and interfacial properties of the Au/n-InP and Au/NiPc Schottky contact on n-type InP have been analyzed by I–V, C–V, C–f and G–f measurements. The NiPc-based device shows an excellent rectifying behaviour. The Schottky barrier heights of the Au/n-InP and Au/NiPc Schottky contacts are obtained as 0.59 eV (I–V)/0.71 eV (C–V) and 0.82 eV (I–V)/1.14 eV (C–V) with ideality factors of 1.22 and 1.83, respectively. Investigation results reveal that the NiPc organic interlayer increases the effective barrier height by influencing the space charge region of the n-type InP. Further, the difference between barrier heights obtained from I–V and C–V measurements is discussed. From the forward bias C–f and G–f characteristics, the interface state density and their relaxation times are estimated. Furthermore, it is observed that both the interface state density and the relaxation time of interface states decrease with bias voltage for the Au/n-InP and Au/NiPc Schottky contacts.

Effect of mechanical milling induced strain and particle size reduction on some physical properties of polycrystalline yttrium iron garnet

Abstract: The effect of mechanical milling induced strain and particle size reduction on structural, micro-structural and magnetic properties of un-milled and milled polycrystalline samples of yttrium iron garnet, Y3Fe5O12 (YIG), for different duration, 3, 6, 9 and 12 h, have been studied using X-ray powder diffractometry, scanning electron microscopy, infrared spectroscopy, Mossbauer spectroscopy, high field magnetization and low field (0.5 Oe) ac susceptibility measurements. YIG on milling is found to decompose into Y3Fe5O12 and yttrium ortho-ferrite, YFeO3, phases, as reflected from various characterizations. The infrared and Mossbauer spectroscopic studies give an indication for the loss of oxygen on milling. The shift in Neel temperature with particle size reduction has been described by finite size scaling. The observed changes in M–H loop are mainly due to strain induced increase in surface anisotropy on milling. The two transitions have been observed in the thermal variation of ac susceptibility curves, corresponding to ferrimagnetic YIG-phase and another due to weak ferromagnetic YFeO3-phase.

Optical properties of YVO 4 :Eu 3+ nano-phosphors at different europium concentrations

Abstract: In the present work, YVO4:Eu3+ nano-phosphors are synthesized for various concentrations of europium. X-ray diffraction, Fourier transform infrared spectroscopy, UV–visible spectroscopy and photoluminescence spectroscopy are used for the characterization of the YVO4:Eu3+ nano-phosphors. It is observed that the crystallite size decreases with the increase of the europium concentration. The Fourier transform infrared spectra show crystal structure with tetragonal phase. The phosphors synthesized at 5 mol% exhibit sharp peaks with higher intensities, which reflect better luminescent properties as compared to the samples at other concentration through excitation at 325 nm. The peaks between 250 and 350 nm are due to the charge transfer transitions from ligand to europium ion in the UV–visible spectroscopy. This study concludes that with the increase in the concentration of europium up to 5 mol%, the luminescence intensity increases and then decreases for further increase in the europium concentrations. The results are likely to be useful for the understanding the role of the optimum europium concentration in the nano-phosphors.

Spectroscopic studies of chromium doped alkali earth lead zinc phosphate glasses

Abstract: X-Ray diffraction, energy dispersive X-ray, Fourier transform infrared, Raman spectroscopy, differential scanning calorimetry, UV–Visible spectroscopy and electron paramagnetic resonance spectroscopic studies have been carried out on alkali earth lead zinc phosphate glasses doped with 0.1 % chromium ions. The energy dispersive X-ray spectra reveal fundamental compositional information of the glasses. Infrared spectra indicate that phosphate network is depolymerized with progressive substitution of alkali earth content and inform the characteristic vibrations of PO4 3− units. Raman spectra suggest that these glasses are consisting of metaphosphate [Q2] units along with some bands related to pyrophosphate [Q1] and orthophosphate [Q0] units. The crystal-field parameter and inter-electronic repulsion parameters have been evaluated from optical absorption spectral data. Electron spin resonance spectra of Cr3+ systems indicate that g ∥ > g ⊥ and Cr3+ ions are located at sites with lower symmetry. It is obtained that the glass transition temperatures fall in region of 377–360 °C. Increase in density of the glass system brings changes in structure of the glasses on replacement of alkali earth content.

Dependence of structural phase transition and lattice strain of Fe 3 O 4 nanoparticles on calcination temperature

Abstract: Fe3O4 nanoparticles were synthesized, using a simple co-precipitation method and then calcined at various temperatures in the range of 50–850 °C for 1 h in air. After calcination, the nanoparticles were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and vibrating sample magnetometer. The X-ray diffraction results indicated that Fe3O4 nanoparticles were converted to γ-Fe2O3 by calcining at 250 °C for 1 h and then to α-Fe2O3 on calcining in the range of 550–650 °C. The average crystallite size of the nanoparticles was calculated by using the Scherrer and Williamson-Hall methods. The average crystallite size of the iron oxides NPs increased from 7.2 to 35.8 nm by increasing calcination temperature from 50 to 850 °C. A small strain existed, which were affected on the physical and structural properties of Fe3O4. The vibrating sample magnetometer results indicated that, the as-synthesized nanoparticles converted from superparamagnetic to ferromagnetic phase with calcinations up to 650 °C, due to increasing size of nanoparticles from a single domain to multidomain as indicated in the X-ray diffraction results.

Combustion synthesis and photoluminescence properties of Eu 3+ activated Y 2 Zr 2 O 7 nano phosphor

Abstract: Series of Y(2−x)Zr2O7:xEu3+ red-emitting phosphors have been synthesized by a combustion route and their structures and photo-luminescent properties have been investigated at room temperature. Powder X-ray diffraction analysis shows structural purity of as-synthesized phosphor. Topographical study of prepared sample is done through scanning electron microscopy. Emission spectra show an intense red emission at 609 nm due to 5D0 → 7F2 transition of Eu3+. Intensity of 5D0 → 7F2 emission (activated at wavelength of 264 nm) is found to increase with the doping concentration of Eu3+. Under UV excitation, Y2Zr2O7:Eu3+ shows emission in red region corresponding to 5D1 → 7F2 transition of Eu3+ ion. The emission spectra exhibit red performance (CIE chromaticity coordinates: x = 0.662, y = 0.337), which is due to 5D0 → 7FJ transitions of Eu3+ ions.

Analytical solutions of position-dependent mass Klein-Gordon equation for unequal scalar and vector Yukawa potentials

Abstract: Analytical solutions of the position-dependent mass Klein–Gordon equation in the presence of unequal scalar and vector Yukawa potentials for arbitrary l-state are obtained by using the generalized parametric Nikiforov–Uvarov method. With an approximation scheme to deal with the centrifugal term, we get the bound state energy eigenvalues and the corresponding wave functions, expressed in terms of the Jacobi polynomials. Subsequently, we consider a special case for α = 0 and explicitly obtain the energy eigenvalues as well as the corresponding eigenfunctions in terms of the Laguerre polynomials. Some results are also compared with the previous studies.

Study on highly filtration efficiency of electrospun polyvinyl alcohol micro-porous webs

Abstract: Nanofibers have enormous applications in various areas such as environment, new energy, National security, filtration and so on. In this paper, polyvinyl alcohol micro-porous webs with excellent properties and highly filtration efficiency are fabricated using electrospinning. The solvent chosen is anhydrous formic acid and formic acid with concentration of 88 wt%. Filtration efficiency of fabrics strongly depends upon fiber size and pore size. A mathematical relationship between filtration efficiency and pore size is suggested.

Structural, electronic and optical properties of Zn 1−x Zr x O nanotubes: first principles study

Abstract: First-principles calculations are performed to determine the effects of zirconium doping on structural, electronic and optical properties of zinc oxide nanotubes. Dielectric tensor is derived within the random phase approximation and optical properties are calculated for both parallel and perpendicular electric field polarizations with respect to nanotube axis. Results show that for all impurity concentrations, the formation energy is negative; hence all doped systems are stable. Energy gap of zirconium-doped single walled zinc oxide nanotube is smaller than their pristine zinc oxide nanotube. Our results show that pristine zinc oxide nanotube is a direct gap semiconductor, while it is an indirect gap when zirconium is doped into zinc oxide nanotube. In Zn1−xZrxOs, the absorption edge has red shift to that of pure zinc oxide nanotube and is located at the visible region. Our results show optical anisotropy of pristine and zirconium-doped zinc oxide nanotube.

Stochastic resonance in FizHugh-Nagumo model driven by multiplicative signal and non-Gaussian noise

Abstract: The stochastic resonance phenomenon in FizHugh-Nagumo neural system induced by a multiplicative periodic signal and non-Gaussian noise is studied. Based on path integral approach and two-state theory, the Fokker–Planck equation and signal-to-noise ratio are derived. By analyzing the influence of different parameters in the optimization of signal-to-noise ratio, we observe that the conventional stochastic resonance and double stochastic resonance occur in FizHugh-Nagumo neural model under different values of system parameters. Furthermore, there is a critical value of non-Gaussian noise intensity D, above which the increase of D weakens the resonant effect and below which it enhances the resonant effect.

Elastic, electronic and optical properties of the cubic fluoro-perovskite KCaF 3 under pressure

Abstract: The elastic, electronic and optical properties of the cubic fluoro-perovskite KCaF 3 have been calculated using the full potential linearized augmented plane wave based on density functional theory. Exchange and correlation effects are taken into account by a generalized gradient approximation and an orbital independent modified Becke–Johnson potential coupled with generalized gradient approximation. The equilibrium lattice parameter, bulk modulus and its pressure derivative have been obtained using optimization method. The results are in good agreement with the available theoretical and experimental data. The elastic properties such as elastic constants, shear modulus, Young modulus, Poisson’s ratio, $$B/G$$ ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature and specific heat have been calculated. The pressure dependence of the elastic moduli has been also evaluated. Furthermore, elastic anisotropic properties for KCaF 3 have been analyzed in the pressure range of 0–40 GPa by calculating directional dependence of the Young’s moduli in the crystal. From calculations of the electronic properties, it is found that the band gap is 10.4 (6.1) eV at the $$R$$ – $$\Gamma $$ direction in the Brillouin zone using modified Becke–Johnson potential coupled with generalized gradient approximation (generalized gradient approximation). The variation of the band gap versus pressure is well fitted to a quadratic function. The calculations show that indirect $$R$$ – $$\Gamma $$ to direct $$\Gamma $$ – $$\Gamma $$ band gap transition occurs at 20 GPa. Moreover, optical properties, such as the dielectric function, refractive index and extinction index, have been calculated for radiation up to 35 eV.

Fabrication of multilayer SnO 2 –ZnO–PPy sensor for ammonia gas detection

Abstract: The sensitivity of SnO2–ZnO composites in multilayer with PPy and Al2O3 has been studied. Composites of SnO2–ZnO have been prepared and multilayer sensor has been fabricated using screen printing technique with Al2O3 as substrate on glass plate and PPy in multilayer with SnO2–ZnO. The morphologies of composites of SnO2–ZnO and PPy have been studied by scanning electron microscopy and crystallite size by X-ray diffraction. Sensitivity has been found to be more for 70SnO2:30ZnO/PPy/Al2O3 multilayer sensor, which is supported by scanning electron microscopy and X-ray diffraction studies. It has been found that with the increase in concentration of NH3 gas, the response of multilayer sensor increases.

Characterization of metal-free D-(π-A)2 organic dye and its application as cosensitizer along with N719 dye for efficient dye-sensitized solar cells

Abstract: The optical, electrochemical and density functional theory molecular simulation of a metal-free D-(π-A)2, i.e., 3,3′-(5,5′-(9-hexyl-9H-carbazole-3,6-diyl)bis(thiophene-5,2-diyl))bis(2-cyanoacrylic acid) denoted as D has been investigated. A stepwise cosensitization of D with N719 dye is adopted to enhance the power conversion efficiency of dye-sensitized solar cells. The metal-free dye possesses strong absorption in the 370–450 nm wavelength range and effectively overcomes the competitive light absorption by I 3 − /I −. The N719/D cosensitized dye-sensitized solar cell shows a power conversion efficiency of about 7.24 %, which is higher than the dye-sensitized solar cells based on either N719 (5.78 %) or D (3.95 %) sensitizers. The improved power conversion efficiency of the cosensitized dye-sensitized solar cell is attributed to the combined enhancement of both short-circuit photocurrent and open-circuit voltage. The short-circuit photocurrent improvement is attributed to the increase in the both light-harvesting efficiency of the cosensitized photoanode and charge collection efficiency of the dye-sensitized solar cell. However, the open-circuit voltage is improved due to better adsorption and surface coverage of TiO2 on cosensitization and an associated reduction in the back electron recombination with increased electron lifetime. These effects are analyzed using electrochemical impedance spectroscopy and dark current–voltage measurements of the dye-sensitized solar cells.

Effect of co-substitution of La/Li on structure, microstructure, dielectric and piezoelectric behavior of Bi 0.50 Na 0.50 TiO 3 ceramics

Abstract: Polycrystalline specimens with compositions x = 0.04 and y ≤ 0.10 in (Bi1−xLax)0.5(Na1−yLiy)0.5TiO3 system are synthesized by semi-wet technique. Structure, microstructure, dielectric and piezoelectric properties are investigated in order to observe the effect of co-substitution of La/Li ions on A-sites of BNT ceramic system. Rietveld analysis of X-ray diffraction data for all the specimens reveals single phase formation with rhombohedral structure. Microstructures of these specimens indicate a decrease in grain size with homogeneous grain growth up to y ≤ 0.075 followed by anomalous grain growth for y = 0.100. The temperature dependence of dielectric plots exhibits a broad maximum whose position (T m ) is frequency dependent up to y ≤ 0.075. A switching from frequency dependent to frequency independent dielectric behaviour is observed with increasing Li concentration. All the samples show nearly saturated P–E loop at room temperature. The composition x/y = 0.04/0.025 exhibits improved ferroelectric with P r = 29.26 µC/cm2 and piezoelectric constant of d 33 = 70 pC/N.

Scattering states of Cusp potential in minimal length Dirac equation

Abstract: In this article, we investigate the scattering state of spin-half particle within the framework of minimal length quantum mechanics for Cusp potential in terms of Whittaker functions. We calculate the reflection and transmission coefficients for spin and pseudospin symmetry limits using the conditions of equation of continuity of the wave functions.

Investigation on nonautonomous soliton management in generalized external potentials via dispersion and nonlinearity

Abstract: We investigate the controllable behavior of nonautonomous soliton in external potentials with variable dispersion and nonlinearity management functions, which describes the propagation of optical pulses in an inhomogeneous fiber system. We derive the Lax pair with a variable spectral parameter and the exact multi-soliton solution is generated via Darboux transformation. Based on these solutions, several novel optical solitons are constructed by selecting appropriate functions and the main evolution features of these waves are shown by some interesting figures with computer simulation. As few examples, breathers in periodic potential, soliton compression in an exponentially dispersion decreasing fiber and interaction of boomerang solitons are discussed. The presented results have applications in the study of nonautonomous soliton birefringence-managed switching architecture. These results are potentially useful in the management of nonautonomous soliton with external potentials in the optical soliton communications and long-haul telecommunication networks.

Photoionization of confined hydrogen atom by short laser pulses

Abstract: The photoionization of hydrogen atom confined by a spherical barrier in ultrashort laser pulses is studied. The spectrum of confined hydrogen atom is worked out by employing finite basis set method based on B-spline as well as B-polynomial representation of wavefunction. Effect of confinement on spectra is studied and the effect of pulse parameters and confinement on photoexcitation and ionization is particularly stressed on.

Enhanced electro-magnetic properties in La 0.7 Sr 0.3 MnO 3 /ZrO 2 composites

Abstract: (La07Sr03MnO3)1−x /(ZrO2) x (x = 00–0150, step 0025) composites have been prepared via solid state reaction process The X-ray diffraction and scanning electron microscopic observations indicate that there are ZrO2 grains separated from La07Sr03MnO3 matrix It has been found that the inclusion of ZrO2 content decreases the conductivity, magnetization and metal–semiconductor transition, whereas it increases the low field magnetoresistance Possible effects of grain boundaries on the low field magnetoresistance have been discussed The small ZrO2 grains are trapped between La07Sr03MnO3 grains may be acting as a barrier for spin-polarized tunneling and enhance the low-field magnetoresistance