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 470 nm with time decay in the ns range and the second one peaked at 600 nm, with a lifetime in the order of ms. The bands are assigned to Ti-5(3+) species and to Ti-6(3+)-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. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim