11 research outputs found
Theory of Exciton Migration and Field-Induced Dissociation in Conjugated Polymers
The interplay of migration, recombination, and dissociation of excitons in
disordered media is studied theoretically in the low temperature regime. An
exact expression for the photoluminescence spectrum is obtained. The theory is
applied to describe the electric field-induced photoluminescence-quenching
experiments by Kersting et al. [Phys. Rev. Lett. 73, 1440 (1994)] and Deussen
et al. [Synth. Met. 73, 123 (1995)] on conjugated polymer systems. Good
agreement with experiment is obtained using an on-chain dissociation mechanism,
which implies a separation of the electron-hole pair along the polymer chain.Comment: 4 pages, RevTeX, 2 Postscript figure
Excitons in quasi-one dimensional organics: Strong correlation approximation
An exciton theory for quasi-one dimensional organic materials is developed in
the framework of the Su-Schrieffer-Heeger Hamiltonian augmented by short range
extended Hubbard interactions. Within a strong electron-electron correlation
approximation, the exciton properties are extensively studied. Using scattering
theory, we analytically obtain the exciton energy and wavefunction and derive a
criterion for the existence of a exciton. We also systematically
investigate the effect of impurities on the coherent motion of an exciton. The
coherence is measured by a suitably defined electron-hole correlation function.
It is shown that, for impurities with an on-site potential, a crossover
behavior will occur if the impurity strength is comparable to the bandwidth of
the exciton, corresponding to exciton localization. For a charged impurity with
a spatially extended potential, in addition to localization the exciton will
dissociate into an uncorrelated electron-hole pair when the impurity is
sufficiently strong to overcome the Coulomb interaction which binds the
electron-hole pair. Interchain coupling effects are also discussed by
considering two polymer chains coupled through nearest-neighbor interchain
hopping and interchain Coulomb interaction . Within the
matrix scattering formalism, for every center-of-mass momentum, we find two
poles determined only by , which correspond to the interchain
excitons. Finally, the exciton state is used to study the charge transfer from
a polymer chain to an adjacent dopant molecule.Comment: 24 pages, 23 eps figures, pdf file of the paper availabl
Master 2000 Konkretisierungsphase im Ideenwettbewerb fuer Leitprojekte 'Innovative Produkte' Abschlussbericht
The report presents the results of the above mentioned project. Intention was to define a project for the development of radiation curable materials and the application and curing technology for the application in the automobile industry. (orig.)SIGLEAvailable from TIB Hannover: DtF QN1(73,57) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman
Empirische Forschung in der Deutschdidaktik. Band 1: Grundlagen
Wie wird aus einer ersten Idee ein konkretes Forschungsprojekt? Der vorliegende Band widmet sich im ersten Teil den theoretischen Grundlagen empirischen Forschens: Was unterscheidet qualitative und quantitative Forschung? Welcher Forschungsansatz ist fĂŒr meine Fragestellung der richtige und was sind die Vor- und Nachteile verschiedener Untersuchungsdesigns? Im zweiten Teil werden praxisrelevante Hilfestellungen fĂŒr die Organisation, DurchfĂŒhrung und Auswertung der Erhebung gegeben, wobei der gesamte Prozess von der Auswahl der Probanden ĂŒber Datenschutzfragen, Softwareeinsatz bis hin zu statistischen Grundlagenkenntnissen berĂŒcksichtigt wird
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