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    The effect of laser wavelength on the photorefractive characteristics of PMDA-DR19 based photorefractive polymeric materials
    (1997-09-01)
    Chang, CJ
    ;
    Wang, HC
    ;
    Liao, GY
    ;
    Whang, WT
    ;
    Liu, JM
    The photoconductivity and photorefractive characteristics of PMDA-DR19-based photoconducting nonlinear optical polymeric films with different compositions were studied using red and green lasers. Contributions of dopants and the host to the photoconductive and photorefractive properties are systematically discussed. The virgin nonlinear optical material PMDA-DR19 was neither photoconductive nor photorefractive in nature. However, it became photoconductive and photorefractive once the charge transport material was incorporated into the PMDA-DR19/PVB polymer film. Films containing more nonlinear optical chromophore exhibited higher diffraction efficiency. Response speed was further elevated when an additional charge generation material was doped in. Diffraction grating was observed under zero electric field and was confirmed due to a photorefractive effect by the two-beam coupling effect. In addition to composition modification, the laser light source was also an important factor in changing the PR response speed. The photorefractive response speed was tremendously improved when films were written and read by two different laser beams, either red/green lasers or green/red lasers. (C) 1997 Elsevier Science Ltd.
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    A study of the relationship between the electroluminescence characteristics and compositions of PPV-PVA-based polymers
    (1996-08-01)
    Chang, WP
    ;
    Whang, WT
    ;
    材料科學與工程學系
    ;
    Department of Materials Science and Engineering
    A series of poly(p-phenylene vinylene) (PPV)-poly(vinyl alcohol) (PVA)-based polymers were prepared from the PPV precursor and PVA aqueous solution mixtures. The luminescence characteristics of the PPV-PVA-based polymers were dependent on their composition and the following treating conditions. The emitted light of the PPV-PVA-based light-emitting diodes (LEDs) shifted from yellow-green (550 nm) to blue (485 nm) as the PVA component increased. The infra-red (i.r.) absorption spectra showed that some part of the PPV precursor could react with PVA to form C-O-C linkages and interrupted the conjugation of PPV polymer chains. This resulted in decrease of the conjugated chain length, as evidenced in ultraviolet-visible u.v.-vis. absorption spectra. The relative photoluminescence (PL) intensity increases with decreasing the conjugated chain length. The relative electroluminescence (EL) decreases with the increase of the PVA component in the polymers. However, both PL and EL intensity normalized with PPV molar ratio of PPV-PVA-based polymers were higher than that of pure PPV. The relative low threshold voltage at 4-6 V was found in these PPV-PVA-based polymer LEDs with Al (negative) and indium-tin oxide ITO (positive) as the two electrodes. Copyright (C) 1996 Elsevier Science Ltd.
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    Quinoxalines incorporating triarylamines: Dipolar electroluminescent materials with tunable emission characteristics
    (2006-02-01)
    Huang, TH
    ;
    Whang, WT
    ;
    Zheng, HG
    ;
    Lin, JTS
    ;
    材料科學與工程學系
    Dipolar compounds (abbreviated as QuPy) featuring quinoxaline acceptors and diarylamine or triarylamine donors were prepared via palladium-catalyzed C-N or C-C bond formation in good yields. They possess high thermal stability with a high decomposition temperature (T-d > 400 degrees C) and exhibit no crystalline character. The emission colors of the materials vary from green to orange red and are dependent on the nature of the electron-withdrawing segments and solvents. Two types of double-layer organic light-emitting diodes (OLEDs) were constructed using these dipolar compounds as hole-transporting/emitting layers and TPBI or Alq(3) as an electron-transporting layer: (I) ITO/QuPy/Alq(3)/Mg:Ag and (II) ITO/QuPy/TPBI/Mg:Ag (TPBI = 1,3,5-tris(N-phenylbenzimidazol-2-yl)-benzen; Alq(3) = 1,3,5-tris(N-phenyl-benzimidazol-2-yl)-benzene). The recombination zone in most of those devices were confined in the quinoxaline layers, The green to orange colors in these devices correspond well with the film PL of the material used. The relation between the energy levels of the compounds and the performance of the light-emitting diode are discussed.
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    Single-layer organic electroluminescent devices by vapor deposition polymerization
    (1997-09-08)
    Wen, WK
    ;
    Jou, JH
    ;
    Chiou, JF
    ;
    Chang, WP
    ;
    Whang, WT
    A novel method is presented herein regarding the preparation of a single-layer organic electroluminescent (EL) polymer thin film device. The device was made by simultaneously co-depositing two polymer thin film forming monomers, a hole-transporting molecule triphenyldiamine derivative (TPD) and an EL active molecule 1,1 4, 4-tetraphenyl-1,3-butadiene (TPB) on an indium-tin-oxide (ITO) glass substrate. The device structure was composed of the ITO glass, the TPD, and TPB co-doped polymer thin film, and a thermally evaporated aluminum electrode. Carrier injection from the two electrodes was significantly observed and the blue light in EL spectra, with an emission maximum at 435 nm, was triggered at a driving voltage of 17 V. (C) 1997 American Institute of Physics.