Absorption spectra of anatase TiO2 single crystals heat-treated under oxygen atmosphere

Anatase TiO2 single crystals large enough to measure the optical properties have been grown by chemical vapor transport reaction. As-grown crystals having blue color were heat-treated under oxygen atmosphere. The change in crystal color from blue through yellow to colorless depending on oxygen annealing was detected by optical absorption spectra. The blue color is due to free carrier absorption. The yellow color is originated from an oxygen vacancy which is a color center. Models are discussed for these change during the oxygen annealing. (C) 2000 Elsevier Science Ltd. All rights reserved.