Lead salt (PbX, with X= Se, S) colloidal quantum dots (QDs) have recently attracted much interest both from the point of view of fundamental physics and for their possible application in optoelectronics, photonics, and biophysics. The exciton lifetime in these QDs can reach the µs range, promising for a long coherence time. Differently from conventional II-VI systems, PbX nanocrystals have a direct band gap at the L point of the Brillouin zone. Therefore, the ground state exciton is 64 fold degenerate [1], compared to the 8-fold degeneracy of excitons in spherical quantum dots with direct band gap at the Γ point. Moreover, the exciton Bohr radius is large (46 nm for PbSe and 18 nm for PbS) compared to the typical QD sizes, and PbX nanocrystals can be considered a model system for strong confinement. However, a direct measurement of the intrinsic exciton dephasing time in PbX dots is still missing.

© 2011 IEEE

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