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Science 7 November 2008:
Vol. 322. no. 5903, pp. 929 - 932
DOI: 10.1126/science.1159832
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Reports

Slow Electron Cooling in Colloidal Quantum Dots

Anshu Pandey and Philippe Guyot-Sionnest*

Hot electrons in semiconductors lose their energy very quickly (within picoseconds) to lattice vibrations. Slowing this energy loss could prove useful for more efficient photovoltaic or infrared devices. With their well-separated electronic states, quantum dots should display slow relaxation, but other mechanisms have made it difficult to observe. We report slow intraband relaxation (>1 nanosecond) in colloidal quantum dots. The small cadmium selenide (CdSe) dots, with an intraband energy separation of ~0.25 electron volts, are capped by an epitaxial zinc selenide (ZnSe) shell. The shell is terminated by a CdSe passivating layer to remove electron traps and is covered by ligands of low infrared absorbance (alkane thiols) at the intraband energy. We found that relaxation is markedly slowed with increasing ZnSe shell thickness.

James Franck Institute, University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA.

* To whom correspondence should be addressed. E-mail: pgs{at}uchicago.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)