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MO: Fachverband Molekülphysik

MO 20: Transport and Spectroscopy in Molecular Nanostructures II (related to SYMN, jointly with CPP)

MO 20.1: Talk

Thursday, March 17, 2011, 10:30–10:45, TOE 317

Ultrafast electronic dynamics in a polyfluorene based guest-host system — •Henning Marciniak, Maik Teicher, and Stefan Lochbrunner — Institut für Physik, Universität Rostock

Guest-host systems are frequently used for organic solid state lasers to achieve tunability of the emission wavelength and low lasing thresholds. Efficient excitation energy transfer from the host to the guest material and the behavior at high exciton densities are thereby important. We investigate a polyfluorene based guest-host system that shows optically pumped lasing in a distributed feedback structure [1]. Combined analysis of steady state and time resolved spectroscopic studies gives rise to a complex picture of the photoinduced dynamics. Steady state and time resolved fluorescence measurements on the nanosecond timescale show emission signatures from the guest material pointing to efficient excitation transfer from the hostto the guest. However, femtosecond pump probe absorption measurements find no signatures of stimulated emission from the guest material but pronounced nonlinear dynamics on the picoseconds timescale. As one quenching mechanism amplified spontaneous emission from the host system is identified, which arises under high excitation densities. However, since the excitation parameters are similar to the nanosecond fluorescence measurements, additional mechanisms have to be taken into account.

[1] T. Riedl, T. Rabe, H.-H. Johannes, W. Kowalsky, J. Wang, T. Weimann, P. Hinze, B. Nehls, T. Farrell, and U. Scherf, Appl. Phys. Lett. 88 (2006), 241116.