Berlin 2005 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 34: Novel materials II

CPP 34.1: Talk

Wednesday, March 9, 2005, 11:15–11:30, TU C230

Exciton recycling in graded gap nanocrystal structures — •Thomas Franzl, Thomas A. Klar, Stefan Schietinger, Andrey L. Rogach, and Jochen Feldmann — Photonics and Optoelectronics Group, Physics Department and CeNS, Ludwig-Maximilians-Universität München

We present a cascaded energy transfer (CET) structure made of CdTe nanocrystals motivated by natural antenna complexes and by semiconductor heterostructure lasers. Funnel like band gap profiles are realized by applying layer-by-layer assembly to CdTe nanocrystals of distinct sizes. For high-energetic excitation, the CET structure comprising only one layer of red-emitting nanocrystals emits 4 times more red light than a reference sample of equal absorbance consisting of only red emitting nanocrystals. Hence the final excitation density in the single emitting layer of large nanocrystals is increased by a factor of 28. Time resolved measurements show that the photoluminescence from the central layer is fed from long lived states. The super-efficient exciton funneling can be explained by a fast direct energy transfer along the structure and a recycling of surface trapped excitons that are usually lost for photoluminescence [1].
T. Franzl, T.A.Klar, S. Schietinger, A.L. Rogach, J. Feldmann, "Exciton recycling in graded gap nanocrystal structures" Nano Letters, 4, 1599 (2004)