Interband and intraband optical studies of PbSe colloidal quantum dots

PbSe nanocrystal colloids exhibit a well-defined excitonic structure with the lowest energy exciton tuning from 0.5 to 1 eV, as a function of size. Band-edge fluorescence is observed from 1.2 to 2 mum with a small Stokes shift, sub-mus lifetime, and near-unity quantum yield. Upon pumping at 1.064 mum, the first exciton decay is consistent with radiative relaxation at low pump intensity and with Auger recombination at higher pump intensities. Optically induced absorption is observed at approximately midgap. These transitions exhibit strengths similar to the interband exciton and are size-tunable. They are assigned to the 1S(e,h)-1P(e,h) and 1P(e,h)-1D(e,h) intraband excitations. Intraband pump-probe measurements of the 1S(e,h)-1P(e,h) transition reveal a short lifetime and the absence of the phonon bottleneck.