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Proceedings Paper

Influence of the molecular geometry on the photoexcitations of highly emissive organic semiconductors
Author(s): Shu-Chun Yang; Wilhelm Graupner; Suchismita Guha; Peter Puschnig; Chris Martin; Holakere R. Chandrasekhar; Meera Chandrasekhar; Guenther Leising; Claudia Ambrosch-Draxl
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Paper Abstract

Para-phenylene type molecules are efficient photoluminescence emitters in the ultraviolet-blue-green spectral range. They are used in light emitting diodes (LEDs) and photopumped lasers. Photoexcited para-phenylene type molecules give rise to strong emission from singlet excitons, bleaching of the singlet exciton absorption, induced absorption from triplet excitons and induced absorption from polarons. Since the latter two processes represent absorption of the emitted light of singlet excitons, the presence of polarons and triplet excitons might be a fundamental problem for laser diodes made from para-phenylene type molecules. In our experiments we modify the molecular geometry by the application of hydrostatic pressures up to 80 kbar in a temperature range of 10 to 300 K. In particular we show how triplet and polaron states, which are present in LEDs under operation, react to the induced geometric changes. The spectra of ground state absorption, excited state emission, bleaching of the singlet exciton absorption, induced absorption from triplet excitons and induced absorption from polarons are significantly broadened and shifted in energy. In order to explain the observed behavior we have performed three-dimensional bandstructure calculations within density functional theory for the planar poly(para-phenylene). By varying the intermolecular distances and the length of the polymer repeat unit pressure effects can be simulated.

Paper Details

Date Published: 17 December 1999
PDF: 12 pages
Proc. SPIE 3797, Organic Light-Emitting Materials and Devices III, (17 December 1999); doi: 10.1117/12.372714
Show Author Affiliations
Shu-Chun Yang, Univ. of Missouri/Coumbia (Taiwan)
Wilhelm Graupner, Virginia Polytechnic Institute and State Univ. (United States)
Suchismita Guha, Marquette Univ. (United States)
Peter Puschnig, Technische Univ. Graz (Austria)
Chris Martin, Univ. of Missouri/Columbia (United States)
Holakere R. Chandrasekhar, Univ. of Missouri/Columbia (United States)
Meera Chandrasekhar, Univ. of Missouri/Columbia (United States)
Guenther Leising, Technische Univ. Graz (Austria)
Claudia Ambrosch-Draxl, Technische Univ. Graz (Austria)


Published in SPIE Proceedings Vol. 3797:
Organic Light-Emitting Materials and Devices III
Zakya H. Kafafi, Editor(s)

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