Multiexciton engineering in seeded core/shell nanorods: transfer from type-I to quasi-type-II regimes.

Multiple excitations in core/shell CdSe/CdS-seeded nanorods of different core diameters are studied by quasi-cw multiexciton spectroscopy and envelope function theoretical calculations. For core diameters below 2.8 nm, a transfer from binding to repulsive behavior is detected for the biexciton, accompanied by significant reduction of the triexciton oscillator strength. These characteristics indicate a transition of the electronic excited states from type-I localization in the core to a quasi-type-II delocalization along the entire rod as the core diameter decreases, in agreement with theoretical calculations.