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  • 1
    Electronic Resource
    Electronic Resource
    Thermally stimulated photoluminescence in poly(2,5-dioctoxy p-phenylene vinylene) (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 5016-5023 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results of thermally stimulated photoluminescence (TSL) measurements in poly(2,5-dioctoxy p-phenylene vinylene) (DOO–PPV) are reported. The obtained results are analyzed in terms of the hopping model of TSL in disordered organic materials. It is shown that the experimentally obtained TSL curve can be fitted on the basis of a double-peak Gaussian density-of-states distribution. The upper peak is associated with intrinsic localized states while the lower one can be ascribed to aggregates. The latter assignment is also supported by measurements of steady-state and time-resolved photoluminescence in DOO–PPV films and solutions. Possible mechanisms of charge carrier photogeneration in DOO–PPV are discussed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1464235
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  • 2
    Electronic Resource
    Electronic Resource
    Special features of spectral and luminescent properties of squarilic dyes in polymer matrices (2000)
    Springer
    Optics and spectroscopy 88 (2000), S. 352-358 
    Details
    ISSN: 1562-6911
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study was made of spectral and luminescent properties of a squarilic dye on the basis of 1,3,3-trimethyl-3H-indoline in comparison with the cationic polymethine dye representing a derivative of the same heterocycle. The squarilic dye was introduced into polymer films of poly-N-epoxypropylcarbazole, which is capable of bearing photoproduced charges, and polystyrene, which lacks this ability. Luminescence spectra of films with different dye concentrations at temperatures of 4.2 and 300 K were studied. Spectral and luminescent properties of squarain in both types of polymers were found to be determined by the dye tendency to aggregation. For poly-N-epoxypropylcarbazole, this tendency is less pronounced than for polystyrene, which is associated with the enhancement of specific solvation of a bipolar squarain molecule by polar groups of poly-N-epoxypropylcarbazole. The structure with an angle between chromophore directions of 180° is shown to be the most likely spatial structure of associates. The advantage of this structure is that it is stabilized at both ends of bipolar molecules by electrostatic attractive forces between opposite charges.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.626801
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  • 3
    Electronic Resource
    Electronic Resource
    Structural defects in carbazolyl-containing polymers with polymethine dye impurities (2000)
    Springer
    Physics of the solid state 42 (2000), S. 1548-1553 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Photoluminescence spectra and thermoluminescence curves of pure and doped carbazolyl-containing polymers polyvinyl carbazole (PVC) and poly-N-epoxypropyl carbazole (PEPC) are investigated in the temperature range 5–300 K. The impurities are cationic indocarbocyanines with various lengths (n) of the polymethine chain: HIC (n=1), HID (n=2), HIT (n=3) and squaryl dye HISq with the same polymethine chain length and the same structure of heterocyclic end groups as for the HID dye. It is found that solvation of dye molecules by polar groups of a polymer is accompanied by conformation changes in the polymer, which are considerably enhanced with increasing n, as well as upon a transition from a rigid-chain PVC macromolecule to a more flexible PEPC molecule. As a result, the concentration of structural defects, viz., excimer-forming sites playing the role of traps for singlet excitons and charge carriers, increases considerably in doped PEPC films. This leads to the emergence of a band with a peak at 460 nm in the luminescence spectra of PEPC films with HID and HIT and at 480 nm for films with the HISq impurity, while the thermoluminescence curve for PEPC with HISq acquires an additional band with a peak at 275 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1307069
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  • 4
    Electronic Resource
    Electronic Resource
    Geminate recombination of long-lived electron-hole pairs in doped carbazole-containing amorphous molecular semiconductors (1997)
    Springer
    Physics of the solid state 39 (1997), S. 1047-1051 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper reports an investigation into the features of geminate recombination of long-lived electron-hole pairs in films of poly(N-epoxypropylcarbazole) (PEPC) containing intramolecular charge transfer compounds as centers of photogeneration of charge carriers carried out by measuring the attenuation kinetics of isothermal recombination luminescence over a wide range of temperatures (4.2–300 K) for times t〉1 s, along with the kinetics of photoinduced EPR signals. A study is made of how the presence of a potential barrier to the reverse transition of carriers to the recombination center and the initial triplet state of the charged pairs affects the geminate recombination. It is established that the kinetics of isothermal recombintation luminescence attenuation follow the law I(t)∝t −m for the times under study, where m takes values from 0.65 to 1.05. The first observations of a nonmonotonic change in m with temperature are reported (m passes through a minimum at a certain temperature), and a mechanism is proposed for recombination of charged pairs in PEPC containing intramolecular charge-transfer compounds as an explanation for this phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130012
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  • 5
    Electronic Resource
    Electronic Resource
    Unusual temperature dependences of the photoconductivity and recombination luminescence of amorphous molecular semiconductors doped with ionic dyes (1999)
    Springer
    Physics of the solid state 41 (1999), S. 179-184 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A nonexponential increase in photoconductivity with increasing temperature is discovered for poly(N-epoxypropylcarbazole) (PEPK) films doped with polymethine dyes. It is postulated that traps for nonequilibrium charge carriers form in these films during irradiation and are destroyed as the temperature is raised. Such traps are manifested by broadening of the high-temperature shoulder on the thermally stimulated luminescence (TSL) curves following the preliminary irradiation of PEPK films doped with polymethine and xanthene ionic dyes in the visible or UV range at 250–320 K and by the appearance of a new narrow TSL maximum near the preliminary irradiation temperature. These TSL features disappear after prolonged storage of the films in the dark or heating to higher temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130751
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  • 6
    Electronic Resource
    Electronic Resource
    Features of the temperature-dependent behavior of the pyroelectric luminescence of organic crystals (1989)
    Springer
    Journal of applied spectroscopy 50 (1989), S. 33-36 
    Details
    ISSN: 1573-8647
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00665455
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  • 7
    Electronic Resource
    Electronic Resource
    On the application of thermoluminescence for probing the energetic disorder in amorphous molecular solids (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 7 (1997), S. 99-103 
    Details
    ISSN: 1057-9257
    Keywords: amorphous molecular solids ; poly(N-epoxypropylcarbazole) ; thermoluminescence ; charge trapping ; charge transport ; energetic disorder ; dipole moments ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The low-temperature thermoluminescence (TL) technique has been applied for probing the energetic disorder in doped poly(N-epoxypropylcarbazole)(PEPC) polymer films. Strong polar dopants were used for varying the degree of dipolar disorder. It was found that (1) the TL of the studied systems can be well interpreted in terms of the disorder model and (2) TL spectroscopy can provide the shape of the deepest part of the localised state distribution and the degree of energetic disorder as well. The charge trap distribution on the high-temperature side of the TL peak appears to be a Gaussian function and its halfwidth correlates well with the disorder parameter obtained from charge transport measurements. An unusual electric field effect on the TL of PEPC doped with strong polar dopants was found and is explained in terms of the contribution of the charge-dipole interaction to the energy of localised states. This effect indicates that the TL phenomenon for the studied systems cannot be explained purely by molecular γ-relaxation in the polymer. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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