Stark spectroscopy of CdSe nanocrystallites: The significance of transition linewidths

We use Stark spectroscopy to examine the nature of the excited states of CdSe nanocrystallites. The Stark spectra we obtain are in the small coupling limit in which the changes induced by the electric field to the absorption spectrum are small compared to the transition linewidths. Within this limit, we theoretically examine the dependence of the line shape of Stark difference spectra on the linewidth of the transitions involved. For systems such as CdSe nanocrystallites, which have overlapping transitions coupled by the electric field, we find that the usual association of derivatives of absorption features with dipole moments and polarizabilities is problematic. We show that the Stark absorption spectrum of the CdSe nanocrystallites can be explained by polarizable and delocalized nonpolar excited states.