Multiexponential photoluminescence decay in indirect-gap semiconductor nanocrystals

The origin of the multiexponential photoluminescence (PL) decay of Si quantum dots (QDs) has been debated for a long time. We present studies combining time-resolved PL experiments and tight binding calculations of phonon-assisted optical transitions showing that the distribution of lifetimes and its wavelength dependence are quantitatively predictable and can be interpreted as intrinsic properties of the QDs due to the indirect nature of the Si bandgap. This result can be generalized to QD ensembles of any indirect gap semiconductor.