Polar CdSe nanocrystals: Implications for electronic structure

We report direct spectroscopic evidence for parity-forbidden electronic transitions in CdSe nanocrystals and relate it through perturbation theory to an internal electric field. This field is consistent with an estimated spontaneous polarization of $P_s\text{=−0.6}$ $\mu {\mathrm{C/cm}}^2$ for CdSe. The observed mixing of odd and even band edge hole states by this symmetry breaking internal electric field indicates that current theories of nanocrystal electronic structure, which assume inversion symmetry, require substantial revision.