Hot Electrons Generated from Doped Quantum Dots via Upconversion of Excitons to Hot Charge Carriers for Enhanced Photocatalysis.

We show that hot electrons exhibiting the enhanced photocatalytic activity in H2 production reaction can be efficiently generated in Mn-doped quantum dots via the "upconversion" of the energy of two excitons into the hot charge carriers. The sequential two-photon-induced process with the long-lived Mn excited state serving as the intermediate state is considered as the pathway generating hot electrons. H2 production rate from doped quantum dots is significantly higher than that from undoped quantum dots and also exhibited the quadratic increase with the light intensity, demonstrating the effectiveness of the hot electrons produced in doped quantum dots in photocatalytic reaction. Due to the very long lifetime of Mn excited state (∼6 ms) in the doped quantum dots, the sequential two-photon excitation requires relatively low excitation rates readily achievable with a moderately concentrated solar radiation, demonstrating their potential as an efficient source of hot electrons operating at low excitation intensities.