VIBRONIC STRUCTURE, ENERGY-LEVEL, AND INCORPORATION MECHANISM OF TI3+IN LINBO3 AND LITAO3

In reduced LiTaO3, an axially symmetric EPR signal with g(parallel-to) = 1.948 +/- 0.003 and g(perpendicular-to) = 1.827 +/-0.003 has been i dentified. It is attributed to Ti3+ (3d1) by comparison with the alrea dy known EPR data of Ti3+ in LiNbO3. We are able to explain the g valu es of this center in LiNbO3 as well as in LiTaO3, by a model calculati on involving a dynamic pseudo Jahn-Teller effect. Spin-orbit coupling, lattice vibration, pseudo Jahn-Teller interaction, and the Zeeman ter m are treated on equal footing. Intervalence transfer from Ti3+ to Nb5 +, forming a Nb(Li)4+ polaron, has been identified. This transfer can be stimulated either by visible light or by thermal activation. By inv estigating the temperature dependence of the thermally activated inter valence transfer, we have determined the ionization energy of Ti3+ wit h respect to Nb(Li)4+ to be 0.11 eV +/- 0.02 eV.