Light induced TiO2 phase transformation: Correlation with luminescent surface defects

The light induced structural phase transition of TiO2 nanoparticles from anatase to rutile structure is reported with different distribution of defect related surface states. Pristine, defective, and surface passivated samples were irradiated in vacuum condition by intragap visible wavelength to achieve the phase transformation. The surface states were studied by means of intragap excited steady state and time-resolved photoluminescence spectroscopy. Two bands were clearly observed, the first component centered at about 470nm with time decay in the ns range and the second one peaked at 600nm, with a lifetime in the order of μs. The bands are assigned to 5Ti3+ species and to 6Ti3+-OH species located at the surface of the anatase TiO2 nanoparticles. The transition mechanism to the rutile phase is interpreted in the framework of oxygen adsorption and desorption phenomena with the involvement of the surface defects.