Optical Absorption Analysis Research Articles

Influence of Ba2+ ions on defect concentration in bismuth silicate glasses evidenced by FTIR and UV‐visible spectroscopy

AbstractBismuth silicate glasses containing Ba2+ ions were prepared by a normal melt quench technique in a wide range of composition. The present study includes structural and optical characterization of these glasses by using the techniques of IR and UV‐visible spectroscopy. The variation in density and molar volume with Ba2+ ion concentration was related to structural changes occurring in the glass. The large difference in crystalline temperature (TC) and glass transition temperature (Tg) value shows the thermal stability of these glasses. Analysis of IR spectra shows the occurrence of broad and strong band around 456‐471 cm‐1, attributed to both Bi‐O‐ stretching vibrations in distorted linked [BiO6] units and bending vibrations of the silicate network. The shifting of center of the band around 800 ‐ 1100 cm‐1 with the increase in Ba2+ ions concentration in glass matrix suggests a decrease in Si‐O‐Si bond angle and causes glass network shrinkage which is also supported by observed decrease in molar volume. The analysis of optical absorption spectra of these glasses reveals that the position of absorption edge and cutoff wavelength shift towards blue as Ba2+ ion concentration increases in the glass composition. The variation in optical band gap energy (Eg) with change in glass composition may be attributed to the indirect influence of the Ba2+ ions on the band gap and can be evaluated from the Tauc's plots for indirect allowed and indirect forbidden transitions. The increase in optical band gap (Eg) from optical absorption analysis indicates that the glass network becomes more compact and degree of disorder decreases with increase of concentration of Ba2+ ions. The origin of Urbach's energy is associated with phonon‐assisted indirect transitions and its value varies with the random internal electric field either due to lack of long range order or presence of defects. From Urbach energy values, it was concluded that the defect concentration could be controlled by the presence of Ba2+ ions in the present glass system (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

About some properties of electro-synthesized short Oligo(Para-Fluoro-Anisole) (OPFA): A combined experimental and theoretical study

Short Oligo(Para-Fluoro-Anisole) (OPFA) was electrochemically synthesized. Infrared absorption, Raman scattering, optical absorption and thermal analysis (TGA and DTA) techniques were used to justify the chemical structure and to prove the vibrational and optical properties of the oligomer under study. Furthermore, theoretical calculations based on ab initio Density Functional Theory (DFT) were performed in order to elucidate the structure–property relationship of OPFA oligomer and to argue the experimentally observed results. On the other hand, time-resolved photoluminescence (TR-PL) spectroscopy was used to investigate their decay process both in chloroform solution and film states. The faster PL decays in thin film, is the consequence of both conformational structure and intermolecular π–π stacking interactions.

Absorption and fluorescence studies of Sm 3+ ions in lead containing sodium fluoroborate glasses

Lead containing calcium zinc sodium fluoroborate glasses (LCZSFB) with molar composition of 20PbO+5CaO+5ZnO+10NaF+(60− x) B 2O 3+ x Sm 2O 3, ( x=0.1, 0.25, 0.5, 1.0 and 2.0 mol%) were prepared and investigated by the XRD, FTIR, optical absorption, photoluminescence and decay curve analysis. Judd–Ofelt theory was applied to the experimental oscillator strengths to evaluate the phenomenological J– O intensity parameters Ω λ ( λ=2, 4 and 6). Using the J– O intensity parameters as well as from the emission and decay measurements, various radiative parameters such as transition probabilities ( A R ), radiative lifetimes ( τ R ), measured lifetimes ( τ m ), calculated branching ratios ( β R ), measured branching ratios ( β m ), effective bandwidth (Δ λ eff ) and stimulated emission cross sections σ( λ p ) have been calculated for the excited 4G 5/2 luminescent level. The nature of decay curves of 4G 5/2 level for different Sm 3+ ion concentrations in all LCZSFB glasses has been analyzed and the lifetimes are noticed to decrease with increase of concentration. The concentration quenching has been attributed to the energy transfer through the cross-relaxation between Sm 3+ ions. Based on these results, the utility of Sm 3+ ions doped lead containing fluoroborate glasses as laser active materials in the visible region is discussed.

Effects of Cathode Confinement on the Performance of Polymer/Fullerene Photovoltaic Cells in the Thermal Treatment

Polymeric photovoltaic (PV) cells based on poly(3-hexylthiophene-2,5-diyl):[6, 6]-phenyl C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">61</sub> butyric acid methyl ester (P3HT:PCBM) with the cathode confinement in the thermal treatment show better performance than the PV cells without the cathode confinement in the thermal treatment. The functions of the cathode confinement are investigated in this paper by using X-ray photoelectron spectroscopy, atomic force microscopy, optical absorption analysis, and X-ray diffraction analysis. It is found that the cathode confinement in the thermal treatment strengthens the contact between the active layer and the cathode by forming Al-O-C bonds and P3HT-A1 complexes. The improved contact effectively improves the device charge collection ability. More importantly, it is found that the cathode confinement in the thermal treatment greatly improves the active layer morphology. The capped cathode effectively prevents the overgrowth of the PCBM molecules and, at the same time, increases the crystallization of P3HT during the thermal treatment. Thus, a better bicontinuous interpenetrating network is formed, which greatly reduces the exciton loss and improves the charge transport capability. Meanwhile, the enhanced crystallites of P3HT improve the absorption property of the active layer. All these aforementioned effects together lead to the great performance improvement of polymeric PV cells.

X-ray line broadening and photoelectrochemical studies on CdSe thin films

Cadmium Selenide (CdSe) thin films have been prepared on Indium doped tin oxide coated conducting glass (ITO) substrates at various deposition potential and solution pH values using potentiostatic cathodic electrodeposition technique. The deposited films are characterized using X-ray diffraction, scanning electron microscopy, energy dispersive analysis by X-rays, optical absorption, and photoelectrochemical techniques, respectively. X-ray diffraction pattern revealed that the deposited films are found to exhibit hexagonal structure with preferential orientation along (002) plane. X-ray line profile analysis technique by the method of variance has been used to evaluate the microstructural parameters such as crystallite size, rms microstrain, dislocation density, and stacking fault probability. The variation of microstructural parameters with deposition potential, solution pH values, and annealing temperature are studied. Surface morphology and film composition are investigated by scanning electron microscopy and energy dispersive analysis by X-rays, respectively. Optical absorption analysis has been carried out to evaluate the optical parameters such as refractive index, extinction coefficient, real and imaginary dielectric constants, and packing density, respectively. Photoelectrochemical solar cells are constructed using as-deposited and annealed CdSe thin films as photocathode, and their power output characteristics are studied. The experimental observations are discussed in detail.

Comparison of the defective pyrochlore and ilmenite polymorphs of AgSbO3using GGA and hybrid DFT

Silver antimonate, AgSb${O}_{3}$, in both its defective pyrochlore and ilmenite structural polymorphs, has been suggested as a possible candidate mixed metal oxide for use in the photocatalytic splitting of water in visible light. In this study, we report electronic-structure calculations, using both standard and hybrid density-functional-theory approaches, on both structural forms of AgSb${O}_{3}$ to fully characterize the band structure and composition of the valence and conduction bands. Analysis of conduction properties and optical absorption is also used to compare the predicted properties of the two materials. Results show that the valence band is dominated by O 2$p$ and Ag 4$d$ states, whereas the conduction band is composed mainly of Ag and Sb 5$s$ states. Band-edge effective-mass calculations indicate the materials operate via an $n$-type mechanism, with conduction properties being comparable for the two materials. The fundamental and optical band gaps are also predicted to be compatible with visible light adsorption.

Optical and electrical properties of SnS semiconductor crystals grown by physical vapor deposition technique

Tin sulfide (SnS) is a material of interest for use as an absorber in low cost solar cells. Single crystals of SnS were grown by the physical vapor deposition technique. The grown crystals were characterized to evaluate the composition, structure, morphology, electrical and optical properties using appropriate techniques. The composition analysis indicated that the crystals were nearly stoichiometric with Sn-to-S atomic percent ratio of 1.02. Study of their morphology revealed the layered type growth mechanism with low surface roughness. The grown crystals had orthorhombic structure with (0 4 0) orientation. They exhibited an indirect optical band gap of 1.06 eV and direct band gap of 1.21 eV with high absorption coefficient (up to 10 3 cm −1) above the fundamental absorption edge. The grown crystals were of p-type with an electrical resistivity of 120 Ω cm and carrier concentration 1.52×10 15 cm −3. Analysis of optical absorption and diffuse reflectance spectra showed the presence of a wide absorption band in the wavelength range 300–1200 nm, which closely matches with a significant part of solar radiation spectrum. The obtained results were discussed to assess the suitability of the SnS crystal for the fabrication of optoelectronic devices.

Optical and two‐photon absorption analysis of radiation‐grafted fluoropolymer

AbstractGrafting by gamma irradiation has a significant influence on the dispersion properties of polymeric materials. Accordingly, we study the effect of grafting on the material electronic structure parameters such as the fundamental absorption edge and bandgap structure. The optical absorption of grafted polymeric films of poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA‐g‐PAAc) is determined in a very wide spectral range of 0.2–3 μm. The nonlinear two‐photon absorption coefficient is determined that showed an increase as a result to the grafting process. Moreover, a significant increase in the optical conductivity for the polymeric films is acquired after grafting. Positron annihilation spectroscopy is used to study polymer structure and volume size of nanoholes of Ps. The data revealed an increase of crosslinking with a smaller average volume size with grafting. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2045–2051, 2010

The influence of oxygen-containing functional groups on the dispersion of single-walledcarbon nanotubes in amide solvents

Surface composition plays an important role in carbon nanotube dispersibility in differentenvironments. Indeed, it determines the choice of dispersion medium. In this paper theeffect of oxidation on the dispersion of HiPCO single-walled carbon nanotubes (SWNTs) inN-methyl-pyrrolidinone (NMP),N, N-dimethylformamide (DMF),N, N-dimethylacetamide(DMA), N-dodecyl-pyrrolidinone (N12P) and cyclohexyl-pyrrolidinone (CHP) was systematicallystudied. During the oxidation process, similar amounts of carboxylic acid and phenolicgroups were introduced to mostly already existing defects. For each solvent thedispersion limits and the absorption coefficients were estimated by optical absorptionanalysis over a range of SWNT concentrations. The presence of acid oxygenatedgroups increased SWNT dispersibility in NMP, DMF and DMA, but decreased inN12P and CHP. The absorption coefficients, however, decreased for all solventsafter oxidation, reflecting the weakening of the effective transition dipole of theπ–π transition with even limited extension functionalization and solvent interaction. Theanalysis of the results in terms of Hansen and Flory–Huggins solubility parametersevidenced the influence of dipolar interactions and hydrogen bonding on the dispersibilityof oxidized SWNTs.

Fluorescence characteristics of Dy 3+ ions in calcium fluoroborate glasses

Calcium fluoroborate (CFB) glasses doped with different concentrations of trivalent dysprosium ions were prepared and investigated by the FTIR, optical absorption, photoluminescence and decay analysis. Free-ion Hamiltonian model and Judd–Ofelt theory have been used to analyze the energy level scheme and the spectral intensities of Dy 3+ ions in CFB glasses. From the emission spectra it is observed that the samples emit intense light yellowish color which is nearer to white light. Chromaticity color coordinates have been calculated and the dominant emission wavelength has also been indicated. Decay curves of 4F 9/2 level for the samples with different concentrations have been analyzed using the Inokuti–Hirayama model and the energy transfer and non-radiative decay rates have been determined.

Influence of substrate temperature on growth of a-Si:H films by reactive facing target sputtering deposition

Hydrogenated amorphous silicon (a-Si:H) films were deposited by reactive facing target sputtering (FTS) technique with a mixture of Ar and H2 reaction gas. Fourier transform infrared (FTIR) absorption, Raman scattering and ultraviolet-visible optical absorption are used to investigate the microstructure and optical properties of the deposited films. The decrease of the concentration of bonded hydrogen, especially that of (Si-H2) n with increasing substrate temperature (Ts), was observed in FTIR spectra, suggesting the atomic density increases and the concentration of microvoids decrease in a-Si:H films. The increase of both the short range order and the intermediate range order of amorphous network for a-Si:H films were verified by Raman scattering spectra, in which increasing Ts decreasing the band width of TO and the scattering intensity ratio I TA/I TO were obtained. All above results clarify the effect of increasing Ts on the microstructure amelioration for a-Si:H films. The reduction of disordered domains is correlated with the film growing process, where the increased surface diffusion mobility and etching of weak bonds is induced by increasing Ts. Furthermore, analysis of optical absorption indicates that the films with a lower optical band gap and a narrower band edge can be obtained by this FTS technique.

SYNTHESIS AND CHARACTERIZATION OF DYE (PHENOSAFRANINE) SENSITIZED FLOWER-TYPE ZnO NANORODS

Flower-type ZnO nanorods were synthesized by two-step low temperature solution growth and dye-sensitized with phenosafranine for the first time. The scanning electron microscope result shows that the diameter and the length of a single rod of the flower-type nanostructures depend on the method of synthesis. Optical absorption analysis shows a visible absorption at 517 nm, which was otherwise absent in nano ZnO . The photoluminescence spectra of ZnO and dye-sensitized ZnO nano flowers were also analyzed.

Spectroscopic analysis of dipole interaction of metallic nanoparticles in dielectric multilayer dielectric thin film

Using electron beam gun PVD system, the thin film with multiple alternative layers of SiO 2 + Ag (300 nm)/SiO 2 (10–60 nm) was deposited on silica substrate. Annealing test was undertaken for optical absorption analysis. The annealing agglomerated metallic nanoparticles in each layer has enhancement effect for plasmon resonance absorption, these precipitated nanoparticles also cause absorption peak red shift. When the thickness of alternative dielectric layer becomes small enough, there is a coupling phenomenon between the electric dipoles of nanaoparticles in the alternative metallic particle doped layers.

Mineralogical characteristics of unusual “Anatolian” diaspore (zultanite) crystals from the İlbirdağı diasporite deposit, Turkey

The İlbirdağı diasporic metabauxite (diasporite) deposit of the Milas (Muğla) region of Turkey is a unique deposit including both metamorphic (primary) and hydrothermal-remobilized (secondary) diaspore that formed during different geological periods. Microscopic diaspore crystals with a metamorphic origin are common and are the main constituent of the metabauxite ore, which was metamorphosed during from the Late Cretaceous to Late Paleocene Periods. However, secondary macroscopic diaspore crystals filling fracture zones that crosscut the metabauxite ore formed during the Late Paleocene, Eocene and Oligocene Periods as the result of later hydrothermal solutions that remobilized constituents of the metabauxite. The macroscopic diaspore crystals can be distinguished from the metamorphosed microscopic diaspore crystals, based on size, appearance, occurrence, and origin. Approximately 60% of the macroscopic diaspore crystals have an opaque appearance and pale green coloration and are not considered attractive. By contrast, the other 40% are gem quality and exhibit a marked change in color under different types of illumination. The crystals are mostly olive-green and soil-brown in daylight. A small number of the crystals display color-change, such as green in daylight or equivalent illumination and carmine in low-wattage tungsten lights. X-ray diffraction (XRD) study, using a comparative matching technique, reveals that these Anatolian diaspore (zultanite) crystals [AlO(OH)] are polycrystalline and that their X-ray spectrum includes the overlapped XRD peaks of some mineral inclusions consisting of donbassite [Al 5.33Si 3O 10(OH) 8] (di-di-octahedral sheeted Al-rich chlorite), corundum (Al 2O 3), boehmite [AlO(OH)], quartz (SiO 2), ilmenite (FeTiO 3), goethite [FeO(OH)] and chloritoid [(Fe, Mg, Mn) 2Al 4Si 2O 10(OH) 4]. We label these unusual inclusions as sub-microscopic inclusions, because they cannot be seen with a polarizing microscope. Polarizing microscope (PM), scanning electron microscope (SEM), optical absorption (OA), Fourier transform-infrared (FT-IR) and simultaneous differential-thermogravimetric analysis (DTA/TGA) investigations were performed to reveal the mineralogical characteristics of the Anatolian diaspore crystals.

Structural, optical and magnetic characterization of Cu-doped ZnO nanoparticles synthesized using solid state reaction method

Polycrystalline undoped and Cu-doped Zinc oxide (Zn0.98Cu0.02O) nanocrystals were successfully synthesized by solid-state reaction method. The micro structural, optical and magnetic properties have been characterized using powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive analysis using X-rays (EDAX), UV–Visible spectroscopy, Photoluminescence, Vibrating sample magnetometer and Electron paramagnetic resonance spectroscopy. XRD pattern reveals that the samples possess hexagonal wurtzite structure of ZnO without any secondary phase after copper doping. Optical absorption analysis of the samples showed a red shift in absorption band edge with copper doping in ZnO. Photoluminescence spectra of the samples shows prominent peaks corresponding to near band edge UV emission and defect related green emission in the visible region at room temperature and their possible mechanism have also been discussed. Magnetic measurements using VSM showed that the nanocrystalline copper doped ZnO exhibits ferromagnetic behaviour at 300 K. EPR analysis also confirms the substitution of Zn site by Cu2+.

Dielectric dispersion and certain other physical properties of ZnO-Ga2O3-P2O5 glass system

Dielectric properties viz., dielectric constant ϵ, loss tanδ and a.c conductivity σa.c (over a wide ranges of frequency and temperature) and dielectric breakdown strength of (45-x) ZnO-xGa2O3-55P2O5 (with 5< = x< = 20) glasses are studied. The analysis of these results with the aid of the data on optical absorption, IR spectra and Differential Thermal Analysis indicate the glasses are more stable when Ga2O3 present in small quantities (∼5mol %) in the glass matrix.

Auxin-Responsive Genes AIR12 Code for a New Family of Plasma Membrane b-Type Cytochromes Specific to Flowering Plants

We report here on the identification of the major plasma membrane (PM) ascorbate-reducible b-type cytochrome of bean (Phaseolus vulgaris) and soybean (Glycine max) hypocotyls as orthologs of Arabidopsis (Arabidopsis thaliana) AIR12 (for auxin induced in root cultures). Soybean AIR12, which is glycosylated and glycosylphosphatidylinositol-anchored to the external side of the PM in vivo, was expressed in Pichia pastoris in a recombinant form, lacking the glycosylphosphatidylinositol modification signal and purified from the culture medium. Recombinant AIR12 is a soluble protein predicted to fold into a beta-sandwich domain and belonging to the DOMON (for dopamine beta-monooxygenase N terminus) domain superfamily. It is shown to be a b-type cytochrome with a symmetrical alpha-band at 561 nm, fully reduced by ascorbate, and fully oxidized by monodehydroascorbate radical. AIR12 is a high-potential cytochrome b showing a wide bimodal dependence from the redox potential between +80 mV and +300 mV. Optical absorption and electron paramagnetic resonance analysis indicate that AIR12 binds a single, highly axial low-spin heme, likely coordinated by methionine-91 and histidine-76, which are strongly conserved in AIR12 sequences. Phylogenetic analyses reveal that the auxin-responsive genes AIR12 represent a new family of PM b-type cytochromes specific to flowering plants. Circumstantial evidence suggests that AIR12 may interact with other redox partners within the PM to constitute a redox link between cytoplasm and apoplast.

Phase separation phenomenon in MOCVD-grown GaInP epitaxial layers

In-rich and Ga-rich GaInP films were intentionally grown on (0 0 1) GaAs substrates by low-pressure MOCVD to investigate the effect of lattice strain on composition. High-resolution X-ray diffraction (HRXRD) measurement showed that a GaInP single layer exhibits a double-diffracted peak phenomenon. Such a double peak represents a composition separation in the grown film, resulting in two absorption cutoff energies in optical absorption analysis. Cross-sectional transmission electron microscopic (TEM) observation confirmed the composition separation in an In-rich GaInP film. Furthermore, the composition separation amount of a Ga-rich GaInP film after substrate removal was found to be ∼0.5%, which reflects the actual effect of lattice strain on composition during growth stage.

Room temperature electrosynthesis of ZnSe thin films

In the present study, we report the room temperature electrosynthesis of Zinc selenide (ZnSe) thin films on stainless steel (SS) and fluorine doped tin oxide (FTO) coated glass substrates. In addition, the influence of the substrate on the microstructural properties of ZnSe is plausibly explained. Voltammetric curves were recorded in order to characterize the electrochemical behaviour of Zn 2+ /SeO 2 system. The as-deposited ZnSe thin films have been characterized for structural (X-ray diffraction (XRD)), surface morphological (scanning electron microscopy (SEM)), compositional (energy dispersive analysis by X-rays (EDAX)), surface topographical (atomic force microscopy (AFM)) and optical absorption analysis. Formation of cubic structure with preferential orientation along the (1 1 1) plane was confirmed from structural analysis. A significant observation seen from the SEM micrograph was the formation of porous layer on the FTO coated glass substrate. However, this is not seen in case of stainless steel substrate. Similar observation was predicted in case of AFM analysis for the films deposited on FTO. The optical band gap for ZnSe thin films was found to be 2.7 eV.

Optical absorption red and blue shifts in ZnFe 2O 4 nanoparticles

Nanoparticles of zinc ferrite (ZnFe 2O 4) prepared by both wet- and dry-high-energy ball milling (HEBM), have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), surface area and pore size distribution (BET) and wavelength-dependent diffuse reflectance and scattering turned into absorption coefficient estimation using the Kubelka–Munk theory. It was found that after 72 h of HEBM, the particle size was decreased from 220 nm for the initial material to 16.5 nm and 9.4 nm for the wet- and dry-milled samples, respectively. The optical absorption analysis revealed that the energy gap is increased (blue shift) for wet-milled and decreased (“anomalous” red shift) for dry-milled samples of ZnFe 2O 4 as the particle size decreased. The likely origins for the phenomena, namely the blue and red shifts as large as 0.45 eV and 0.14 eV, respectively, are proposed and discussed, and the effects are quantitatively estimated.