Characterization of Electronic States of TiO_2 Powders by Photoacoustic Spectroscopy

概要

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We have measured the optical absorption of TiO_2 powders by photoacoustic(PA)spectroscopy, which is powerful for detecting small amounts of strongly scattering materials. The band-gap energies E_g of rutile and anatase types of TiO_2 powders with particle radii of 40 nm are 3.06 eV and 3.20 eV, respectively, from PA intensity and PA phase spectra, indicating the usefulness of PA spectroscopy. The PA intensity and phase spectra show that the E_g of anatase-type TiO_2 powders with a particle radius of 11 nm is 3.25 eV(blue shift)within the experimental accuracy, indicating the possible onset of a quantum size effect with decreasing particle size. The PA intensities plotted semilogarithmically vary linearly with photon energy immediately below the band-gap, in accordance with Urbach's rule(exponential tail). The slope of the exponential absorption of rutile-type TiO_2 powders is larger than that of the anatase, indicating that the anatase-type has increasing energy from the displacement of atoms specifically due to oxygen vacancies and/or chlorine impurities in the production processes of the powders.
社団法人応用物理学会の論文
2000-05-30