Semi-empirical calculations of the electronic and atomic structure of polarons and excitons in ABO3 perovskite crystals

Our qantum chemical calculations performed by means of the intermediate neglect of differential overlap confirm the existence of the self-trapped electrons in KNbO3, KTaO3 and BaTiO3 crystals. The relevant lattice relaxation energies are 0.21, 0.27 and 0.24 eV, whereas the optical absorption energies are 0.78, 0.75 and 0.69 eV, respectively. We suggest theoretical interpretation of the so-called green luminescence (2.2-2.3 eV) in ABO(3) perovskite crystals as a result of the recombination of electrons and holes forming the charge-transfer-vibronic-excitons. The calculated luminescence energies for SrTiO3, BaTiO3, KNbO3 and KTaO3 perovskite crystals are in a good agreement with the experimentally observed energies. (C) 2002 Elsevier Science B.V. All rights resrved.