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

The present work discloses the unusual photooxidation observed for V₃O₇·H₂O nanowires under 514 nm excitation above a threshold intensity of 0.30 kW/cm². 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.