Regensburg 2007 – scientific programme

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DS: Fachverband Dünne Schichten

DS 16: Organic Light Emitting Diodes (SYOE 9)

DS 16.1: Talk

Wednesday, March 28, 2007, 14:30–14:45, H32

Dynamics of the triplet state in Alq₃ — •Nils A. Reinke, Johannes Höchtl, Valentin Kamm, and Wolfgang Brütting — University of Augsburg, Institute of Augsburg, Experimental Physics IV, Augsburg, Germany

As demonstrated by recent work, the organic electroluminescent material Alq₃ has a long–lived triplet state with a lifetime in the 10ms range [1]. Depending on the excitation density and the sample preparation delayed fluorescence and phosphorescence with varying relative intensities can be detected at low temperature. In order to get deeper insight into the underlying mechanism, we have combined different experimental techniques to study the triplet dynamics in Alq₃. Using time–resolved photoluminescence measurements on neat films, matrix-isolated molecules as well as films doped with phosphorescent emitters the direct observation of the excited states dynamics is possible in a broad time-window from the nanosecond to the millisecond range. Relatively intense phosphorescence can be observed in Alq₃ doped with phosphorescent molecules containing heavy metal atoms, such as Ir(ppy)₃[2]. A significantly reduced lifetime in such systems indicates that the transition rate of the triplet state to the ground state is strongly affected by the phosphorescent dopant. We will further demonstrate an indirect determination of the triplet lifetime in Alq₃ from singlet emission using a novel pump–probe technique. [1] M. Cölle et al., JAP 96 (2004) 6133-6141, [2] I. Tanaka et al., PRB 71 (2005) 205207