Electronic states and exciton fine structure in colloidal CdTe nanocrystals

We prepared colloidal zinc-blend CdTe nanocrystals (NCs) with sizes ranging from 1.85 to 6.6 nm. Temperature-controlled two-dimensional photoluminescence excitation spectroscopy was applied to investigate their size-dependent electronic properties and enabled the examination of up to nine electronic excited states. At low temperatures, the exciton fine structure of the first excited state was significantly enhanced, which allowed an accurate measurement of the exchange splitting energy for the CdTe NCs via estimations of the resonant Stokes shift. It was found that the exchange splitting energy in zinc blend CdTe NCs decreases linearly with R-^3.17, which is consistent with the theoretical prediction of R^-3.