We independently determine the subpicosecond cooling rates for holes and electrons in CdSe quantum dots using time-resolved luminescence and time-resolved TeraHertz spectroscopy. The rate of hole cooling, following photoexcitation of the quantum dots, depends critically on the electron excess energy. This constitutes a direct proof of electron-to-hole energy transfer, the hypothesis behind the Auger cooling mechanism proposed in quantum dots, which is found to occur on a 1 ± 0.15 ps time scale. This is only marginally slower than the timescale of intraband relaxation of electrons in single crystal CdSe. In bulk CdSe, sequential multi-phonon emission allows for cooling rates of (0.4 ps)-1 at room temperature.

Bellingham: SPIE
J.-J. Song , Kong-Thon Tsen , M. Betz , A.Y. Elezzabi

Pijpers, J.J.H, Hendry, E, & Bonn, M. (2008). Ultrafast intraband relaxation in colloidal quantum dots. In J.-J Song, Kong-Thon Tsen, M Betz, & A.Y Elezzabi (Eds.), Ultrafast Phenomena in Semiconductors and Nanostructure Materials XII : San Jose, CA, USA 20 January 2008. Bellingham: SPIE. doi:10.1117/12.761665