Influence of the molecular geometry on the photoexcitations of highly emissive organic semiconductors

Shu-Chun Yang; Wilhelm Graupner; Suchismita Guha; Peter Puschnig; Chris Martin; Holakere R. Chandrasekhar; Meera Chandrasekhar; Guenther Leising; Claudia Ambrosch-Draxl

doi:10.1117/12.372714

17 December 1999 Influence of the molecular geometry on the photoexcitations of highly emissive organic semiconductors

Shu-Chun Yang, Wilhelm Graupner, Suchismita Guha, Peter Puschnig, Chris Martin, Holakere R. Chandrasekhar, Meera Chandrasekhar, Guenther Leising, Claudia Ambrosch-Draxl

Author Affiliations +

Proceedings Volume 3797, Organic Light-Emitting Materials and Devices III; (1999) https://doi.org/10.1117/12.372714
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1999, Denver, CO, United States

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.

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Shu-Chun Yang, Wilhelm Graupner, Suchismita Guha, Peter Puschnig, Chris Martin, Holakere R. Chandrasekhar, Meera Chandrasekhar, Guenther Leising, and Claudia Ambrosch-Draxl "Influence of the molecular geometry on the photoexcitations of highly emissive organic semiconductors", Proc. SPIE 3797, Organic Light-Emitting Materials and Devices III, (17 December 1999); https://doi.org/10.1117/12.372714

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