Regensburg 2010 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 6: Electronic and Optical Properties of Organic Systems I

CPP 6.2: Vortrag

Montag, 22. März 2010, 12:00–12:15, H39

Selective excitation of exciton transitions in PTCDA crystals and films — •Reinhard Scholz¹, Linus Gisslen¹, Venkat R. Gangilenka², Lyubov V. Titova², Leigh M. Smith², L. A. Ajith De Silva³, and Hans-Peter Wagner² — ¹Walter Schottky Institut, Technische Universität München — ²Department of Physics, University of Cincinnati — ³Department of Physics and Geology, Northern Kentucky University

Photoluminescence excitation studies on 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) single crystals and polycrystalline PTCDA films are compared to the calculated excitonic dispersion deduced from an exciton model including the coupling between Frenkel excitons and charge transfer (CT) along the stacking direction. For excitation energies below the 0-0 Frenkel exciton absorption band at 5 K, these measurements enable the selective excitation of several CT states. The CT2 state involving stacked PTCDA molecules gives an excitation resonance for photoluminescence from the self-trapped CT2 exciton and from the non-relaxed CT2-nr state. Moreover, the fundamental transition of the CT1 involving both basis molecules in the crystal unit cell can be determined from the respective excitation resonance. The excitation energy dependence of the different emission bands allows the assignment of the fundamental transition energies of the CT2 and CT1 excitons to 1.95 eV and 1.98 eV, respectively. When the excitation energy exceeds 2.10 eV, we observe a dominating emission channel related to the indirect minimum of the lowest dispersion branch dominated by Frenkel excitons.