Photoluminescence of TiO₂: Effect of UV Light and Adsorbed Molecules on Surface Band Structure

Abstract

The photoluminescence (PL) of TiO(2) at 529.5 nm (2.34 eV) has been found to be a sensitive indicator of UV-induced band structure modification. As UV irradiation occurs, the positive surface potential changes and shifts the depth of the depletion layer. In addition, reversible band bending due to the adsorption of the electron-donor NH(3) and CO molecules has been observed in measurements combining PL with FTIR surface spectroscopy. It has been found that the O(2) molecule acts in two ways: as a reversibly adsorbed electron-acceptor molecule and as an irreversibly adsorbed molecule that heals natural oxygen vacancy defects in the near-surface region.

Towards Long‐Term Photostability of Solid‐State Dye Sensitized Solar Cells

“…The continual emptying of a large number of deep trap sites through recombination with holes in spiro‐OMeOTAD will result in a steady‐state population of vacant deep trap sites and in the subsequent consumption of a large number of injected electrons in the TiO 2 . Additionally, the O 2 desorption will lead to the disappearance of the depletion layer, a flattening of the CB‐edge and a lowering of the Fermi level . This would enhance interfacial recombination with excess holes in the spiro‐OMeTAD by increasing the average electron density near the interface, and also be consistent with positive shift in the surface potential and lowering of the open‐circuit voltage seen in Figure .…”

“…These adsorbed negative oxygen molecules (superoxide radical O 2 − ) induce a positive potential at the TiO 2 surface, and hence establish a depletion layer (increase in the work function), which results in an upward bend in the CB . Oxygen adsorption in the form of superoxide radical (O 2 − ) at the TiO 2 surface therefore not only reduces the density of deep traps but also subsequently generate a Schottky potential barrier, inhibiting interfacial charge recombination, which could also aid in the rapid separation of charge following photo‐induced electron transfer.…”

Electron Transfer in Dye‐Sensitised Semiconductors Modified with Molecular Cobalt Catalysts: Photoreduction of Aqueous Protons

“…Kinetic studies: Direct band-gap excitation of TiO 2 generates electron/hole pairs, which typically exhibit recombination lifetimes on the microsecond timescale. [25] In order to increase the lifetime of the charge separated state to the timescale needed for proton reduction, we have employed two different strategies. First, the incorporation of a molecular photosensitiser, such as RuP, allows for charge separation to occur through interfacial electron injection into the TiO 2 CB, a process that can proceed almost quantitatively on ultrafast timescales.…”

Synergistic Effects of Sm and C Co-Doped Mixed Phase Crystalline TiO2 for Visible Light Photocatalytic Activity

“…Such a recombination process was less pronounced in the codoped TiO 2 , indicating that the recombination was suppressed for C and Sm co-doped into TiO 2 . Besides, multiple PL signals in the visible region (430–550 nm) are apparent for all samples, which corresponded to the shallow traps on the surface or bulk defect sites [50,51]. The carbon and samarium weakly reduced the PL intensity which originates from the increase of octahedral dipole moments in TiO 2 due to the changes of the lattice parameters.…”