Spectral Switching of Type-II Quantum Dots by Charging

We report photoluminescence (PL) spectral switching of quantum dots (QDs) by chemically controlling transfers of electrons in and out of the type-II heterostructures. When electron charged, CdTe/CdSe (core/shell) QDs show huge PL blue shifts (up to ∼100 nm) whereas PL of CdSe/CdTe (core/shell) QDs red-shifts. We demonstrate reversible spectral switching of type-II QDs by repeated charging and neutralization processes. The PL spectral shifts are due to the interactions between injected spectrator electrons and type-II character excitons. Electron charged CdTe/CdSe QDs show PL blue shifts because of the strong repulsions between the shell-localized excitonic electrons and injected spectrator electrons. It is opposite for CdSe/CdTe QDs, where injected electrons in surface states attract the holes in the shells. We investigate the interactions of spectrator electrons and excitons as varying the dimensions of type-II QDs. We also compare the type-II QDs with type-I QDs such as CdSe, CdTe, and CdTeSe alloyed QDs. We showcase unique optical properties of charged type-II QDs, which have many potential applications such as electro-optic modulators.