Interband and Intraband Optical Studies of PbSe Colloidal Quantum Dots

Abstract

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 μm with a small Stokes shift, sub-μs lifetime, and near-unity quantum yield. Upon pumping at 1.064 μm, 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 1Se,h−1Pe,h and 1Pe,h−1De,h intraband excitations. Intraband pump−probe measurements of the 1Se,h−1Pe,h transition reveal a short lifetime and the absence of the phonon bottleneck.