Optical properties of porous titanium doixide

Abstract

This paper presents optical absorption spectra and refractive index dispersion curves of porous anatase thin layers on glass substrate. The results have been measured in the photon energy range 1,5-3,5 eV at room temperature. Estimated samples porosity is about 58 percent in framework of Bruggeman effective medium approximation. Indicatrix of diffusion was measured at 632.8 nm. Defects absorption gives the major contribution into transmitted light losses below the gap in comparison with scattering phenomena. We obtained optical band gaps for both direct -Eg = 3.69 eV and indirect transitions Eg = 3.42 eV. The Urbach tail width 180 meV obtained from the optical absorption measurements agrees with the magnitude of trap depth 185 meV from the conductivity temperature dependencies for the similar anatase nanocrystallines.