Light induced TiO₂ phase transformation: Correlation with luminescent surface defects

Abstract

The light induced structural phase transition of TiO 2 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 5 Ti 3þ species and to 6 Ti 3þ -OH species located at the surface of the anatase TiO 2 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.

Photo-Catalytic Properties of TiO2 Supported on MWCNTs, SBA-15 and Silica-Coated MWCNTs Nanocomposites

“…The unsupported TiO 2 and TiO 2 /SBA-15 samples showed peaks at 425, 433, 460, 485, 488, 492 and 530 and a peak at 562 nm which was absent on the unsupported titania. The origin of these peaks are still an intense area of debate and study within the literature, since the PL spectra can originate from defects on the surface of titania [ 59 , 63 – 65 ], oxygen vacancies or under-coordinated Ti 3+ [ 59 , 63 , 65 ], or from self-trapped excitons [ 59 , 63 ]. In addition, the surface chemistry can affect the PL spectra [ 65 , 66 ].…”

Laser-flash-photolysis-spectroscopy: a nondestructive method?

“…In fact, the photoinduced desorption/adsorption of oxygen molecules on the surface of nanometer sized TiO 2 particles is reported to play a fundamental role for the non-thermal phase transition induced upon laser illumination. 37,38,40,41 Hereby, the phase transition was attributed to surface modications resulting from a proper depletion of adsorbed oxygen on the crystal surface. The desorption of oxygen molecules as well as atoms from the TiO 2 lattice yielding oxygen vacancies leads to an enhancement of the surface chemical reactivity.…”

A one-step laser process for rapid manufacture of mesoscopic perovskite solar cells prepared under high relative humidity

“…Both the furnace-and laser-treated compact TiO2 films exhibit the peaks at 144 cm -1 (Eg)*, 399 cm -1 (B1g)*, 519 cm -1 (B1g)*, and 639 cm -1 (Eg)*, corresponding to anatase TiO2 with tetragonal symmetry. [30] This indicates that the laser processing successfully achieved the crystallization of the amorphous compact TiO2 film with no phase transformation to rutile. X-ray diffraction (XRD) patterns of the laser-treated amorphous TiO2 compact film in Figure 2b show the peak at 25.3° corresponding to 101anatase phase, as further evidence for crystallization induced by the laser irradiation.…”