Hot Electrons from Consecutive Exciton-Mn Energy Transfer in Mn-Doped Semiconductor Nanocrystals

We investigated the generation of hot electrons occurring via two consecutive exciton-Mn energy transfer processes in Mn-doped semiconductor nanocrystals. Due to the fast exciton-Mn energy transfer rate combined with the long lifetime of the intermediate state of Mn(2+) ions, consecutive energy transfer from two excitons to one Mn(2+) ion can efficiently generate hot electrons even under weak cw excitation. The evidence for the occurrence of two consecutive energy transfers was obtained from the measurement of the intensity of luminescence from the excited state of Mn(2+) ions serving as the intermediate acceptor state. Under the excitation condition, hot electrons can be generated via consecutive energy transfer, and Mn-doped nanocrystals also exhibit the stronger photoreducing capability of methylene blue than undoped nanocrystals, demonstrating a potential benefit in photocatalysis.