Anatase-to-Rutile Phase Transition in TiO₂Nanoparticles Irradiated by Visible Light

Abstract

The light-induced phase transition of TiO 2 nanoparticles from anatase to rutile structure is reported depending on the surrounding environment, the transition being accomplished under oxygen-poor conditions. The transition mechanism is interpreted in the framework of oxygen adsorption and desorption phenomena with the involvement of surface oxygen vacancies and F centers. It is shown that the observed phase transition is not thermally driven because the local temperature of the nanoparticles during irradiation is about 370 K (estimated through the Stokes to anti-Stokes Raman peaks ratio). On the contrary, the phase transition is initiated by intragap irradiation (with the exception of the red light one) that acts as TiO 2 surface sensitizer, promoting the activation of the surface and the nucleation of rutile crystallites starting from two activated anatase neighboring nanoparticles.