Hannover 2020 – scientific programme

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MO: Fachverband Molekülphysik

MO 4: Electronic Spectroscopy I

MO 4.8: Talk

Monday, March 9, 2020, 16:00–16:15, f142

Direct measurement of multiexcitonic structure in colloidal CdSeS/ZnS quantum dots by multiple-quantum 2D fluorescence spectroscopy — •Stefan Müller, Julian Lüttig, Luisa Brenneis, and Tobias Brixner — Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

The multiexcitonic states of semiconductor quantum dots are of great relevance for their optoelectronic applications such as lasers and photovoltaics. Especially hot multiexcitons are discussed to be involved in the mechanism of carrier multiplication, a process that can significantly enhance solar cell efficiencies [1]. However, it is difficult to observe hot multiexcitons directly spectroscopically due to their short lifetime. To address this, we demonstrate our recently developed method of multiple-quantum two-dimensional (2D) fluorescence spectroscopy on colloidal CdSeS/ZnS alloyed core/shell quantum dots. We report a systematic measurement protocol that simultaneously probes biexcitonic and triexcitonic quantum coherences by fourth- and sixth-order nonlinear processes. This is achieved by appropriate phase cycling of fully collinear femtosecond multipulse trains in combination with fluorescence detection, as previously demonstrated [2]. Our results directly reveal various hot multiexcitonic states, enabling to measure the binding energies of these many-body species.

[1] R. D. Schaller et al., Nat. Phys. 1, 189-194 (2005).

[2] S. Mueller et al., Nat. Commun. 10, 4735 (2019).