Berlin 2008 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 43: Quantum dots and wires: Optical properties II
HL 43.3: Talk
Thursday, February 28, 2008, 14:30–14:45, EW 201
Ultrafast Spin Dynamics in Colloidal ZnO Quantum Dots — •Nils Janßen1, Tobias Hanke1, Florian Sotier1, Tim Thomay1, Kelly Whitaker2, Daniel Gamelin2, and Rudolf Bratschitsch1 — 1Department of Physics and Center for Applied Photonics, University of Konstanz, D-78457 Konstanz, Germany — 2Department of Chemistry, University of Washington, Seattle, WA 98195, USA
We have performed time-resolved Faraday rotation measurements in the Ultraviolet (UV) to reveal the ultrafast spin dynamics of electrons in colloidal ZnO quantum dots. A biexponential decay in the ensemble spin dephasing time T2* is observed. The fast decay component on the order of 200 ps is dominated by the recombination of UV excitons. In a competing process, optically excited holes are trapped in dot surface states, which results in negatively charged quantum dots and a long decay component on the order of nanoseconds in the Faraday rotation signal. Time-resolved differential transmission measurements show a biexponential decay with comparable timescales, and photoluminescence emission measurements confirm this interpretation. The spin dephasing dynamics measured by time-resolved Faraday rotation will be compared to those estimated from electron paramagnetic resonance lineshape analysis for charged colloidal ZnO quantum dots.