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Coherent exciton delocalization in strongly coupled quantum dot arrays
Ryan W Crisp1, Joel N Schrauben, Matthew C Beard
1National Renewable Energy Laboratory , 15013 Denver West Pkwy, Golden, Colorado 80401, United States.
Nano Letters
|September 18, 2013
Summary
Quantum dots in disordered arrays show bulk-like transport. Ultrafast spectroscopy reveals excitons delocalize over 200% of the quantum dot diameter, forming larger excited states.
Area of Science:
- Materials Science
- Quantum Physics
- Spectroscopy
Background:
- Quantum dots (QDs) exhibit unique optical properties due to quantum confinement.
- Disordered QD arrays can display bulk-like transport phenomena.
- Understanding exciton delocalization is crucial for QD applications.
Purpose of the Study:
- To investigate exciton delocalization in disordered CdSe quantum dot films.
- To measure electron-hole wave function overlap and its dependence on inter-QD coupling.
- To correlate optical properties with transport characteristics in QD arrays.
Main Methods:
- Ultrafast cross-polarized transient grating (CPTG) spectroscopy was employed.
- Chemically modified CdSe QD surfaces were used to tune electronic coupling.
- CPTG decay dynamics were compared between QD films and isolated QDs.
Main Results:
- Excitons were found to coherently delocalize in the QD arrays.
- The delocalized excited states were measured to be over 200% larger than the individual QD diameter.
- Evidence of bulk-like transport was observed, linked to exciton delocalization.
Conclusions:
- Chemically tuning inter-QD coupling influences exciton delocalization.
- Coherent exciton delocalization is a key mechanism for bulk-like transport in disordered QD systems.
- QD arrays can support excitonic states significantly larger than individual quantum dots.
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