Browsing by Subject "Absorption and fluorescence spectra"

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    Optical and electrochemical properties of polyether derivatives of perylenediimides adsorbed on nanocrystalline metal oxide films
    (Elsevier, 2008) Kus M.; Hakli O.; Zafer C.; Varlikli C.; Demic S.; Özçelik S.; Icli S.
    We report optical and electrochemical properties of polyether derivatives of perylenediimides (PDIs) thin films formed in various materials (semiconductor, insulator, amorphous and self-assembly). Perylenediimides adsorbed on nanocrystalline TiO2 (NT) nanocrystalline alumina (NA), amorphous silicon (PS) and neat self-assemblied (SA) films were prepared and characterized based on spectroscopic, electrochemical, spectro-electrochemical techniques. The absorption and fluorescence spectra of PDIs in chloroform exhibit vibronic features. The fluorescence quantum yields (Φf) of PDIs with end amino substituents in chloroform solutions are over 0.95, while the quantum yield of triethoxyphenyl substituted PDI Φf value is 0.024 in solution. Optical spectroscopy proves that PDIs in metal oxide thin films form aggregated type complexes. An electrochromism, a color change from red to blue/violet, is observed on metal oxide films, that indicates existence of mono and dianion forms of PDIs. Reversibility of electrochemical reductions in NT film depends on the scanning rate. However, electrochromism in NA films is stable and reversibility is independent from scanning rate. Stable mono and diaionic species are formed on NA films. SA films show broad absorption peaks during the voltammetric scan. On the other hand, the first reduction onset potentials of PDIs are almost equal to the onset potential of capacitive current of TiO2 which lead to low efficiency in dye-sensitized solar cells. © 2008 Elsevier B.V. All rights reserved.
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    The radioluminescence and optical behaviour of nanocomposites with CdSeS quantum dot
    (Elsevier B.V., 2017) Keskin İ.Ç.; Türemiş M.; Katı M.İ.; Kibar R.; Şirin K.; Çipiloğlu M.A.; Kuş M.; Büyükçelebi S.; Çetin A.
    In this work, highly luminescent alloyed CdSeS QDs are successfully synthesized by two phase route method by using oleic acid (OA) as a surfactant. OA capped CdSeS QDs prepared in two different synthesis duration were compared in terms of luminescence and optical properties. The nanocomposites blended with CdSeS QDs which have highly luminescent efficiency in different ratios by Low Density Polyethylene (LDPE) and these nanocomposites were mainly investigated radioluminescence (RL) and optical properties (UV/VIS absorption). Structural, morphological, thermal properties of the nanocrystal and nanocomposites were examined using; XRD, FT-IR, TEM, SEM, TG-DTA techniques. OA capped CdSeS and also nanocomposites were showed two RL spectrum peaks in green and red region at around 528 nm and 710 nm respectively. Also, it is seen that the radioluminescence intensity changes linearly with the particle size of the QDs and about 12% size change of quantum dot led to a threefold increase in RL intensity. The luminescence glow curves are in compliance with absorption and fluorescence spectra. The absorption bands showed a significant blue shift for the nanocomposites as compare to powder CdSeS. The optical band gap of the OA capped CdSeS calculated as 1.77 eV. It was observed that the optical band gap of LDPE was decreased by the adding ratio of CdSeS from 3.71 eV to 2.25 eV. © 2017 Elsevier B.V.