Exciton Channel of Photoactivation for Redox Reactions on the Surface of 2D ZnO Nanostructures

Abstract

The resonance excitation of excitons was used for the first time to activate photocatalytic redox reactions on ZnO. The sample activity was tested using the photoactivated oxygen isotope exchange (POIE), which can be used to predict both oxidation and reduction reactions. When the excitation energy is transferred to the surface by an electrically neutral exciton, then the main losses in transferring the photogenerated e–/h+ pairs due to recombination and to overcoming the surface potential barrier are strongly reduced. The radiative decay of an exciton on the ZnO surface is excluded by a 2D structure ZnO/ZnO1–x/O–, in which the exciton decays nonradiatively into a pair of long-lived (up to 8 × 103 s) electron and hole local states, on which in its turn a chemical reaction can take place. These centers decay at 450 K, emitting green luminescence. The exciton resonance excitation allows one to obtain the order-of-magnitude higher values of the efficiency of redox reaction compared to the case of interband excitation.