Photoacoustic and Surface Photovoltaic Characters of Nanocrystalline TiO<SUB>2</SUB>

Abstract

Nanocrystalline TiO_2 was synthesized by sol-gel method. The surface state properties and transport characters of photogenic free charge carriers were probed by the combination of photoacoustic and surface photovoltaic techniques. The results showed that the surface photovoltage (SPV) response appearing at 380 nm of the samples was closely related to the surface electron structure of anatase-type TiO_2 nanoparticles, which belonged to a band-band transition; and that the shoulder peak appearing at 470 nm was related to the surface states of TiO_2 nanoparticles, which was a sub-band-gap charge transfer (CT) transition, and had an obvious donor character. By the energy complementarity between photoacoustic and surface photovoltaic effects of the samples, it was experimentally proved that the nonradiative transitions were responsible for the increasing intensity of photoacoustic signals with decreasing average particle size of the sample; but the number of the nonradiative transitions could be dramatically decreased by a little increase of anatase content in the sample, resulting in increasing quantum-optical efficiency.