Resonant Two-Photon Oxidation in Vanadium Oxyhydrate Nanowires above a Threshold Laser Intensity

The present work discloses the unusual photooxidation observed for V3O7 center dot H2O nanowires under 514 nm excitation above a threshold intensity of 0.30 kW/cm(2). We explicate this phenomenon by in-situ Raman and photoluminescence spectroscopy at varying laser intensities as well as models for the transformation kinetics and energy band structure associated with H2OVO5 octahedron. The photooxidation is found to be triggered by two-photon cleavage of the H2O V bond through excitation via nonbonding d-states. Subsequently, V3O7 spontaneously oxidizes to V2O5. However, the competing process of H2O's rebonding is also realized. Hence, transformation to V2O5 occurs only if the H2O V bond-cleavage rate exceeds a threshold, pushing the number of concomitantly broken bonds in the smallest structural unit to a critical number.