Optical Absorption (optical + absorption)

Distribution by Scientific Domains

Terms modified by Optical Absorption

  • optical absorption measurement
  • optical absorption spectroscopy
  • optical absorption spectrum

  • Selected Abstracts


    Optical absorption, paramagnetic resonance and depolarisation currents in MgAl2O4 spinel

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007
    Roberto Paiva
    Abstract Optical Absorption (OA), Electron Paramagnetic Resonance (EPR) and Thermally Stimulated Depolarisation Currents (TSDC) techniques were applied to study the effects of irradiation and thermal treatments in the formation, aggregation and destruction processes of dipole defects in MgAl2O4 spinel. Irradiated MgAl2O4 crystals present two OA bands centred at 3.4 eV and 5.1 eV. The 3.4 eV band increases with the irradiation-dose, stabilizes its maximum height for doses near 10 kGy and is completely destroyed for thermal treatments above 500 K. This same band decays when the sample is maintained at room temperature reaching a constant value after a few weeks. The EPR spectrum is composed by two superimposed bands at g = 2.011. The gamma dose dependence, the thermal treatments between 370 K and 500 K and the thermal decay of the two bands at room temperature, show that each band behaves in a different way thus indicating that they are associated with two different defects. Gamma dose of 10 kGy produces a TSDC band at 245 K. When the sample is maintained at room temperature, after the gamma irradiation, for several weeks, a displacement in the peak position to 290 K, is observed. Thermal treatments above 500 K destroy the 290 K band. This band is associated to at least two V-type centres. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Silver Nanoparticles with Broad Multiband Linear Optical Absorption,

    ANGEWANDTE CHEMIE, Issue 32 2009
    Osman
    Eine simple Eintopfmethode liefert mit Arylthiolen beschichtete Silber-Nanopartikel mit intensiven, breiten nicht-plasmonischen optischen Eigenschaften. Die Synthese gelingt mit mehreren Arylthiolliganden, einschließlich wasserlöslicher 4-Mercaptobenzoesäure. Die Nanopartikel zeigen eine lineare Absorption, die breiter, stärker und strukturierter ist als bei den meisten konventionellen organischen und anorganischen Farbstoffen. [source]


    Investigation of optical band gap in potassium acid phthalate single crystal

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2008
    S. Krishnan
    Abstract Optical absorption in photonic crystals of potassium acid phthalate has been measured at room temperature, from which the band gap has been determined and the optical band gap was calculated by using absorption spectrum. The analysis of absorption coefficient in the absorption region reveals a direct band gap of 3.70 eV. Further this study includes the theoretical calculations to determine the optical constant of the material and a technique for photonic band gap tuning which is minimally required to develop the optoelectronic device. It was confirmed that potassium acid phthalate crystal has maximum transparency in the entire visible region and hence it exhibits industrial application oriented properties. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Optical absorption and EPR spectral studies of vauquelinite

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2006
    K. Nagamuni Reddy
    Abstract Vauquelinite - a mineral - was investigated by EPR, NIR and optical spectroscopic techniques. EPR studies on powder sample confirm the presence of Cu(II) and Fe(III) impurity in the mineral. Optical absorption spectrum also indicates that Cu(II) impurity is present in rhombically distorted octahedral structure and Fe(III) in octahedral structure. NIR results are due to water fundamentals and phosphate combination tone. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Cr3+ -doped LiNbO3 crystals grown by the Bridgman method

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2005
    Haiping Xia
    Abstract The growth of LiNbO3 crystals doped with Cr3+ ions in 0.1, 0.2, and 0.5 mol % concentrations by Bridgman method were reported. The Cr3+ ion concentrations in crystals were measured by inductively coupled plasma spectrometry. Electron paramagnetic resonance had been used to investigate the sites occupied by the Cr3+ ions. Two Cr3+ ion centers located at Li+ and Nb5+ sites (CrLi3+ and CrNb3+ centers, respectively) were observed. Optical absorption and temperature-dependence emission spectra of the Cr3+ ions were reported. The crystal-field parameters and Racah parameters of the Cr3+ ion defect sites were reported and compared with those grown by Czochralski technique. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Investigations on 1,5-diaminoanthraquinone by laser excitation

    JOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2003
    M. Umadevi
    Abstract Optical absorption and fluorescence emission spectra of 1,5-diaminoanthraquinone (1,5-DAAQ) in different solvents and the surface-enhanced Raman scattering (SERS) spectrum of 1,5-DAAQ in silver sol were investigated. Optical absorption and fluorescence emission studies revealed that the internal and external hydrogen bonds and reorientation of the solvent molecule around the excited state fluorophore are responsible for the observed bathochromic shift and the non-radiative decay process in polar solvents. SERS studies showed that 1,5-DAAQ molecules are chemisorbed through carbonyl groups and the lone pair of electrons on the nitrogen. The orientation of the molecule on the silver surface is found to be stand-on. Copyright © 2002 John Wiley & Sons, Ltd. [source]


    Introductory studies on the growth and characterization of carotenoid solids: an approach to carotenoid solid engineering

    JOURNAL OF RAMAN SPECTROSCOPY, Issue 6-7 2001
    Yuzo Mori
    Solids of seven all- trans isomeric carotenoids, ,-carotene, ,-apo-8,-carotenal, astaxanthin, canthaxanthin, spheroidene, lycopene and zeaxanthin, were studied in the forms of KBr disks, aggregates, thin films and single crystals in an effort to understand and control the molecular arrangement of the solids. Optical absorption and resonance Raman scattering were adopted to characterize the arrangements. Card-packed arrangements and head-to-tail arrangements were realized by changing either the end groups or the growth process. These studies, which reveal the elementary engineering of solid growth and its characterization, may open up carotenoid solid engineering to develop useful applications of the materials in the fields of electronics, photonics and mechanical engineering. Copyright © 2001 John Wiley & Sons, Ltd. [source]


    Thermoluminescence and other optical studies on RbBr:Tb3+ crystals

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2007
    P. K. Manimozhi
    Abstract Optical absorption, photoluminescence, photostimulated luminescence (PSL) and thermoluminescence (TL) studies on RbBr:Tb3+ crystals irradiated with X-rays is reported. The optical absorption in the UV region confirms the presence of terbium in the host matrix in the trivalent state. Photoluminescence of these crystals exhibits characteristic Tb3+ emissions due to transitions from the 5D3 and 5D4 levels to various levels of the 7F septet. On F-bleaching X-irradiated crystals Z3 centers are observed. The TL glow curve indicates a two-step thermal annihilation process for the radiatively created defects. The presence of the characteristic emissions due to terbium ions in the photostimulation at the F band confirms the participation of Tb ions in the defect-production process. Trap parameters for the TL process are calculated and presented. Emissions under the TL glow peaks contain the characteristic emissions of Tb3+ in addition to the emission due to the recombination of the F electron with V-type centers. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Optical properties and structural phase transitions of lead-halide based inorganic,organic 3D and 2D perovskite semiconductors under high pressure

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 14 2004
    K. Matsuishi
    Abstract Optical absorption, photoluminescence and Raman scattering of lead-halide based inorganic,organic perovskite semiconductors were measured under quasi-hydrostatic pressure at room temperature. For the 3D perovskite semiconductor, (CH3NH3)PbBr3, the free exciton photoluminescence band exhibits red-shifts with pressure, and jumps to a higher energy by 0.07 eV at 0.8 GPa, which is associated with a phase transition from a cubic to an orthorhombic structure confirmed by Raman scattering. Above the phase transition pressure, the exciton band shows blue-shifts with further increasing pressure, and eventually disappears above 4.7 GPa. The results are compared with those for the 2D perovskite semiconductor, (C4H9NH3)2PbI4. First principles pseudopotential calculations were performed to investigate changes in octahedral distortion and electronic band structures with pressure. The calculations have explained the origins of the intriguing changes in the electronic states with pressure in view of bonding characters between atomic orbitals in octahedra. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Permanent bleaching of F2 color centers in lithium fluoride under UV light illumination

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007
    M. A. Vincenti
    Abstract Permanent bleaching of F and F2 color centers in gamma irradiated lithium fluoride crystals has been obtained under low power, CW laser illumination at 244 nm. Optical absorption and photoluminescence measurements reveal a selective change in the concentrations of these kinds of electronic defects. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Optical absorption, paramagnetic resonance and depolarisation currents in MgAl2O4 spinel

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007
    Roberto Paiva
    Abstract Optical Absorption (OA), Electron Paramagnetic Resonance (EPR) and Thermally Stimulated Depolarisation Currents (TSDC) techniques were applied to study the effects of irradiation and thermal treatments in the formation, aggregation and destruction processes of dipole defects in MgAl2O4 spinel. Irradiated MgAl2O4 crystals present two OA bands centred at 3.4 eV and 5.1 eV. The 3.4 eV band increases with the irradiation-dose, stabilizes its maximum height for doses near 10 kGy and is completely destroyed for thermal treatments above 500 K. This same band decays when the sample is maintained at room temperature reaching a constant value after a few weeks. The EPR spectrum is composed by two superimposed bands at g = 2.011. The gamma dose dependence, the thermal treatments between 370 K and 500 K and the thermal decay of the two bands at room temperature, show that each band behaves in a different way thus indicating that they are associated with two different defects. Gamma dose of 10 kGy produces a TSDC band at 245 K. When the sample is maintained at room temperature, after the gamma irradiation, for several weeks, a displacement in the peak position to 290 K, is observed. Thermal treatments above 500 K destroy the 290 K band. This band is associated to at least two V-type centres. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Optical absorption and photoluminescence of CuAlTe2

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006
    B. V. Korzun
    Abstract The bulk crystals of the CuAlTe2 semiconductor ternary compound with the chalcopyrite structure were prepared, and their optical properties were investigated. It was determined that the value of band gap energy equals 1.69 and 1.65 eV at 105 and 293 K, respectively. The photoluminescence spectra were measured for the first time and contain broad bands with peaks at 1.09 eV (78 K) and 1.03 eV (293 K). The full width at half maximum (FWHM) for both temperatures is 0.28 eV. The origin of this band is associated with band to deep acceptor optical transition. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Optical properties and transformation mechanism of oxygen centres and their aggregates in CaF2 crystals

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005
    A.S. Mysovsky
    Abstract Oxygen-vacancy dipoles and dimers in CaF2 crystals have been studied ab initio at DFT level and with the shell model using pair potentials. The calculated dipole reorientation barrier is 0.64 eV and the activation energy for diffusion of the dipoles is 1.61 eV. Optical absorption of O2, -VA dipole have been calculated with TD DFT and identified with experimental absorption bands, which appeared to have complex structure. The photodissociation mechanism of the dipole is discussed. Several configurations of the dimer (O2, -VA)2 were calculated. The association energy for the most favourable one is 0.48 eV. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    The role of aluminium and titanium in the point defects of gamma irradiated natural quartz

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005
    G. O. Sawakuchi
    Abstract In this work, the origin of the smoky colour acquired by quartz when exposed to extremely high doses (20 kGy) of ionising radiation is studied. Five paramagnetic centres were detected in the electron paramagnetic resonance (EPR) spectrum of irradiated quartz: [AlO4]0, [TiO4,/Li+]0A, [GeO4,/Na+]0A, [GeO4,/Li+]0C, and E,1. Optical absorption revealed a complex spectrum with superposition of bands. With the technique of thermoluminescence, at least three peaks at around 180, 260 and 320 °C were detected. The peak at around 180 ºC has maximum emission at 470 nm and the peaks at around 260 and 320 °C have maximum emissions at 450 nm. Through correlations between the obtained results with these techniques, it was possible to confirm previous results from the literature, i.e., that the smoky colour of quartz is strongly related to the centre [AlO4]0. Besides, it was verified an excellent correlation between the thermal decay of [AlO4]0 and [TiO4,/Li+]0A, suggesting that at a temperature around 200 ºC the Li leaves the Ti centre and recombines with the aluminium centre destroying the smoky colour of irradiated quartz. On the other hand and differently from the literature this process does not correlate to any of the thermoluminescence peaks. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Low-loss planar optical waveguides fabricated from polycarbonate

    POLYMER ENGINEERING & SCIENCE, Issue 10 2009
    Jian-guo Chen
    Low-loss slab waveguides with air as overcladding based on a high glass transition temperature (Tg) polycarbonate were fabricated through spin-coating. Optical absorption and thermo-optic coefficient were investigated by spectrum analysis and prism coupler, respectively. Prism-coupling and charge-coupled device (CCD) camera imaging method were exploited together to evaluate the overall propagation loss of slab waveguides. The measured results of prism coupler were 0.282 dB/cm at 1310 nm and 0.197 dB/cm at 632.8 nm, whereas 0.07 dB/cm at 632.8 nm using CCD camera imaging method. Based on the same material, straight ridge waveguides and multimode interference couplers were fabricated through photolithograph and reactive ion etching, revealing smooth sides and excellent definition. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers. [source]


    Surfactant-Assisted Hollowing of Cu Nanoparticles Involving Halide-Induced Corrosion,Oxidation Processes

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2006
    Chih-Chia Huang
    Abstract We have demonstrated a simple fabrication of hollow nanoparticles by halide-induced corrosion oxidation with the aid of surfactants. Cuprous oxide Cu2O nanoshells can be generated by simply mixing Cu nanoparticles with alkyltrimethylammonium halides at 55,°C for 16 min. The hollowing mechanism proposed is that absorption of surfactants onto the Cu surface facilitates the formation of the void interior through an oxidative etching process. Upon extending the reaction up to 4 h, fragmentation, oxidation, and self-assembly were observed and the CuO ellipsoidal structures were formed. The headgroup lengths of the surfactants influenced the degree of CuO ellipsoidal formation, whereby longer surfactants favored the generation of ellipsoids. Optical absorption measured by UV-visible spectroscopy was used to monitor both oxidation courses of Cu,Cu2O and Cu2O,CuO and to determine the band-gap energies as 2.4 eV for Cu2O nanoshells and 1.89 eV for CuO ellipsoids. For the contact-angle measurements, the wettability changed from hydrophilicity (18°) to hydrophobicity (140°) as the Cu2O nanoshells shifted to CuO ellipsoids. [source]


    Crystal growth, morphology, spectrographic characterization and thermal properties of 4,5-bis(benzoylthio)-1,3-dithiole-2-thione

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2008
    Xinqiang Wang
    Abstract Single crystals of 4,5-bis(benzoylthio)-1,3-dithiole-2-thione (BBDT), were grown from methylene chloride and the growth morphology was deduced by the Bravais,Friedel Donnay,Harker (BFDH) model. The grown crystals were characterized by optical absorption, infrared, Raman and X-ray powder diffraction spectroscopy. The thermal behavior of BBDT has been investigated by means of thermogravimetric analysis and differential thermal analysis measurements in air. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Heat treatment induced structural and optical properties of rf magnetron sputtered tantalum oxide films

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2007
    S. V. Jagadeesh Chandra
    Abstract Rf magnetron sputtering technique was employed for preparation of tantalum oxide films on quartz and crystalline silicon (111) substrates held at room temperature by sputtering of tantalum in an oxygen partial pressure of 1x10 -4 mbar. The films were annealed in air for an hour in the temperature range 573 , 993 K. The effect of annealing on the chemical binding configuration, structure and optical absorption of tantalum oxide films was systematically studied. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Growth and characterization of semiorganic NLO crystals of LAHClBr

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2006
    P. C. Thomas
    Abstract Single crystals of non-linear optical (NLO) LAHClBr were grown by slow evaporation technique from its aqueous solution. Good optical quality crystals having dimensions up to 12 × 9 × 7 mm3 were obtained. The lattice parameters and morphology for the grown crystals were determined using single crystal XRD. The crystals were characterized by FT-Raman, optical absorption, thermal (DTA and TGA) and dielectric studies. LAHClBr was found to be thermally stable up to 124.3°C. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Growth of ZnO crystals by vapour transport: Some ways to act on physical properties

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2006
    R. Tena-Zaera
    Abstract Nowadays, the growth of ZnO by vapor transport in silica ampoules is generally made in presence of graphite. As it has been already shown, this means that the growth process is carried out in presence of a Zn excess. In order to control that and act, as a consequence, on the physical properties of crystals we have performed a systematic study of the growth process in a wide range of Zn excess compositions using well defined experimental conditions. As a preliminary characterization, optical absorption and electrical properties have been analyzed at room temperature. The results show how some physical properties of as-grown ZnO crystals can be changed in a controlled way by an adequate combination of different growth conditions such as graphite covering of inner ampoule walls, thermal difference between source material and crystallization zone and additional gas (composition and pressure). In this frame some post-growth annealing processes can be avoided reducing the time and cost of processes. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Growth and characterization of FexMn1-xIn2Se4 (0 , x , 1) single crystals

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005
    G. Attolini
    Abstract Single crystals of Mn1-xFexIn2Se4 with 0 , x , 1.0 were grown by chemical vapor transport technique using I2 as transporting agent. The resulting crystals appeared as brilliant black plates. X-ray powder diffraction data could be indexed following the hexagonal structure with space group Rm for the low Fe concentration samples, while the high concentration sample is associated to the space group P63mc. Both polytypes have similar parameters, however the c parameter reduces as the Fe concentration increases, therefore the number of anion slabs decreases. The characterization of the crystals was based on morphological observations and optical absorption as a function of temperature. The obtained energy gap for the samples at different Fe concentrations suggested that they behave as direct energy gap semiconductors. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Growth and optical characterization of cerium and lead-doped Bi12TiO20 sillenite single crystals

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2005
    J. F. Carvalho
    Abstract Bi12TiO20 (BTO) single crystals doped with PbO and CeO2 were grown by the Top Seeded Solution Growth (TSSG) technique from the liquid phase with nominal compositions of 10Bi2O3 : (1,x)TiO2 : x PbO and 10Bi2O3 : (1,x)TiO2 : xCeO2 with x = 0.25 and 0.10. No growth-related difficulties were encountered other than those typical of sillenite crystals. Samples with good optical quality were obtained and were characterized by optical absorption, dark current, spectral photocurrent dependence, optical activity and electro-optic coefficient measurements. A comparison is made of the results of the optical measurements of doped and undoped BTO crystals. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Studies on the growth and optical characterization of dysprosium gadolinium oxalate single crystals

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2004
    A. Elizebeth
    Abstract Preparation and optical characterization of dysprosium gadolinium oxalate (DGO) single crystal is reported. The crystals were grown using silica gel technique, by the controlled reaction of rare earth nitrates with oxalic acid. Crystals were characterized using X-ray powder diffraction, optical absorption and fluorescence studies. Radiative transition probability, fluorescence branching ratio and radiative lifetime of Dy3+ in the crystal are evaluated by the parameterization of the absorption spectrum by the Judd-Ofelt theory. The recorded fluorescence spectrum showed two well resolved peaks at 480 nm and 571 nm and are assigned to the transitions from 4F9/2 , 6H15/2 and 6H13/2 of Dy3+. Stimulated emission crossection and optical gain of these transitions are also evaluated. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Graphene,Polymer Nanofiber Membrane for Ultrafast Photonics

    ADVANCED FUNCTIONAL MATERIALS, Issue 5 2010
    Qiaoliang Bao
    Abstract A freestanding membrane composed of a nanofiber network of a graphene,polymer nanocomposite is fabricated by electrospinning and applied as an optical element in fiber lasers. The functionalization of graphene with conjugated organic molecules provides a handle for improving mechanical and thermal properties as well as tuning the optical properties. A small loading (0.07,wt%) of functionalized graphene enhances the total optical absorption of poly(vinyl acetate) (PVAc) by 10 times. The electrospun graphene,polymer nanocomposites exhibit wideband saturable absorbance for laser pulse shaping, and attain a larger modulation depth and smaller nonsaturable loss than single-walled carbon nanotubes. The results show that electrospun graphene nanocomposites are promising candidates as practical and efficient photonic materials for the generation of ultrashort pulses in fiber lasers. [source]


    Metastable Copper-Phthalocyanine Single-Crystal Nanowires and Their Use in Fabricating High-Performance Field-Effect Transistors

    ADVANCED FUNCTIONAL MATERIALS, Issue 23 2009
    Kai Xiao
    Abstract This paper describes a simple, vapor-phase route for the synthesis of metastable , -phase copper-phthalocyanine (CuPc) single-crystal nanowires through control of the growth temperature. The influence of the growth temperature on the crystal structures, morphology, and size of the CuPc nanostructures is explored using X-ray diffraction (XRD), optical absorption, and transmission electron microscopy (TEM). , -CuPc nanowires are successfully incorporated as active semiconductors in field-effect transistors (FETs). Single nanowire devices exhibit carrier mobilities and current on/off ratios as high as 0.4,cm2 V,1 s,1 and >104, respectively. [source]


    Atomic-Layer Graphene as a Saturable Absorber for Ultrafast Pulsed Lasers

    ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
    Qiaoliang Bao
    Abstract The optical conductance of monolayer graphene is defined solely by the fine structure constant, ,,=, (where e is the electron charge, is Dirac's constant and c is the speed of light). The absorbance has been predicted to be independent of frequency. In principle, the interband optical absorption in zero-gap graphene could be saturated readily under strong excitation due to Pauli blocking. Here, use of atomic layer graphene as saturable absorber in a mode-locked fiber laser for the generation of ultrashort soliton pulses (756 fs) at the telecommunication band is demonstrated. The modulation depth can be tuned in a wide range from 66.5% to 6.2% by varying the graphene thickness. These results suggest that ultrathin graphene films are potentially useful as optical elements in fiber lasers. Graphene as a laser mode locker can have many merits such as lower saturation intensity, ultrafast recovery time, tunable modulation depth, and wideband tunability. [source]


    Epitaxial Growth of Highly Oriented Fibers of Semiconducting Polymers with a Shish-Kebab-Like Superstructure

    ADVANCED FUNCTIONAL MATERIALS, Issue 17 2009
    Martin Brinkmann
    Abstract Highly oriented fibers of regioregular poly(3-alkylthiophene)s (P3ATs) showing a "shish-kebab" morphology are prepared by oriented epitaxial crystallization in a mixture of 1,3,5-trichlorobenzene (TCB) and pyridine. The superstructure of the P3AT fibers consists of an oriented thread-like core several hundreds of micrometers long, the "shish", onto which lateral crystalline fibrils made of folded polymer chains, the "kebabs", are connected in a periodic way with a periodicity in the range 18,30,nm. The P3AT-chain axis is oriented parallel to the fiber axis whereas the ,-stacking direction is oriented perpendicular to it. The oriented character of the shish-kebab fibers results in polarized optical absorption and photoluminescence. The formation of oriented precursors by epitaxial orientation of polymer chains onto long needles of a molecular crystal,TCB in the present case,appears to be an original alternative to the crystallization usually performed under external flow conditions. [source]


    Doping of Conjugated Polythiophenes with Alkyl Silanes

    ADVANCED FUNCTIONAL MATERIALS, Issue 12 2009
    Chi Yueh Kao
    Abstract A strong modification of the electronic properties of solution-processable conjugated polythiophenes by self-assembled silane molecules is reported. Upon bulk doping with hydrolized fluoroalkyl trichlorosilane, the electrical conductivity of ultrathin polythiophene films increases by up to six orders of magnitude, reaching record values for polythiophenes: (1.1,±,0.1),×,103,S cm,1 for poly(2,5-bis(3-tetradecylthiophen -2-yl)thieno[3,2- b]thiophene) (PBTTT) and 50,±,20,S cm,1 for poly(3-hexyl)thiophene (P3HT). Interband optical absorption of the polymers in the doped state is drastically reduced, making these highly conductive films transparent in the visible range. The dopants within the porous polymer matrix are partially crosslinked via a silane self-polymerization mechanism that makes the samples very stable in vacuum and nonpolar environments. The mechanism of SAM-induced conductivity is believed to be based on protonic doping by the free silanol groups available within the partially crosslinked SAM network incorporated in the polythiophene structure. The SAM-doped polythiophenes exhibit an intrinsic sensing effect: a drastic and reversible change in conductivity in response to ambient polar molecules, which is believed to be due to the interaction of the silanol groups with polar analytes. The reported electronic effects point to a new attractive route for doping conjugated polymers with potential applications in transparent conductors and molecular sensors. [source]


    The Influence of UV Irradiation on Ketonic Defect Emission in Fluorene-Based Copolymers,

    ADVANCED FUNCTIONAL MATERIALS, Issue 17 2008
    Horst Scheiber
    Abstract The influence of UV irradiation in inert atmosphere on the emission spectrum of fluorenone containing poly[9,9-bis(2-ethyl)hexylfluorene] (PF2/6) has been investigated by means of optical absorption, photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy. It is shown that a substantial reduction of green emission arising from ketonic defect sites can be achieved by irradiation of thin films with UV light. This is found to be accompanied by partial cross-linking of the films. FTIR measurements show no reduction of the C=O stretching mode upon irradiation, and, moreover, the degree of cross-linking does not scale with the relative fluorenone content (0.1, 0.5, and 5%). Therefore, the reduced emission intensity in the green spectral region is rather associated with the occurrence of interruptions in the polymer backbone, which reduce the effective conjugation length and subsequently inhibit the energy transfer onto the ketonic defect sites. The found results enabled us to build organic light emitting devices (OLEDs) that can be structured by selective illumination of the emitting layer with an intense UV light source. This method allows for the fabrication of rather efficient (2000,cd,m,2 at 7,V) two-color OLEDs. [source]


    Solution-Processed Organic Tandem Solar Cells,

    ADVANCED FUNCTIONAL MATERIALS, Issue 14 2006
    A. Hadipour
    Abstract A solution-processed polymer tandem cell fabricated by stacking two single cells in series is demonstrated. The two bulk-heterojunction subcells have complementary absorption maxima at ,max,,,850,nm and ,max,,,550,nm, respectively. A composite middle electrode is applied that serves both as a charge-recombination center and as a protecting layer for the first cell during spin-coating of the second cell. The subcells are electronically coupled in series, which leads to a high open-circuit voltage of 1.4,V, equal to the sum of each subcell. The layer thickness of the first (bottom) cell is tuned to maximize the optical absorption of the second (top) cell. The performance of the tandem cell is presently limited by the relatively low photocurrent generation in the small-bandgap polymer of the top cell. The combination of our tandem architecture with more efficient small-bandgap materials will enable the realization of highly efficient organic solar cells in the near future. [source]