Photoexcited silicon nanocrystals: mediators for the excitation of organic molecules

We report on spin-flip activation of organic molecules from the ground state to one of the excited states having different electronic spin configurations. Based on photoexcitations in silicon (Si) nanocrystals, stored electronic energy can be transferred to other substances. The huge hydrogen passivated surface being accessible for acceptor molecules, the tunable confinement energy of excitons and their very long radiative lifetime allow Si nanocrystals to act efficiently as photosensitizers. We demonstrate that the energy transfer is governed by electron exchange mechanism. Therefore a good overlap of the electron wave functions, of donor and acceptor, is crucial for the efficiency of this type of interaction.