PHOTOLUMINESCENCE AND ELECTROLUMINESCENCE AT THE TIO2-ELECTROLYTE INTERFACE

The photoluminescence (PL) and electroluminescence (EL) of polycrystalline TiO2 film electrodes with anatase and rutile structure were studied in aqueous electrolyte solutions. The main difference between the PL spectrum of anatase samples and that of rutile samples was the presence of a band peaking at 850 nm in the latter. The dependence of this band intensity on the penetration depth of exciting light is well described within the framework of the dead-layer model. On the basis of this description, the luminescent centers responsible for the appearance of the 850 nm band were concluded to be mainly bulk states whose nature is discussed. The EL behaviour of TiO2 film electrodes under negative polarization was shown to depend, to a considerable extent, on the nature of the alkali metal cation in the solution. The PL and EL bands in the visible spectral region (lambda(max) = 580-650 nm) observed at potentials more negative than E(fb) are assigned to the luminescent centers produced by the penetration of alkali metal cations into the near-surface region of the electrode. Electroluminescence with a wide spectrum observed at potentials at which the hydrogen evolution reaction proceeds is attributed to the radiative recombination of holes injected into the valence band from electrogenerated radicals with electrons located at the states produced by the incorporation of atomic hydrogen into the oxide lattice. The possible mechanisms of the transfer of charges involved in the EL process through the TiO2-electrolyte interface are discussed.