Temperature dependence of polarized absorption near the band gap was measured for as-grown anatase single crystals and annealed ones which were heat-treated in oxygen atmosphere. The steepness index obtained indicates that an exciton is self-trapped. An absorption band appears at 2.9 eV after heat treatment. A broad luminescence was observed at 2.3 eV. The large Stokes shift is consistent with the fact that the exciton relaxes to a self-trapped state.
- Self-trapped exciton
- Steepness index