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

Abstract

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 identified. It is attributed to Ti3+ (3d1) by comparison with the already known EPR data of Ti3+ in LiNbO3. We are able to explain the g values of this center in LiNbO3 as well as in LiTaO3, by a model calculation involving a dynamic pseudo Jahn-Teller effect. Spin-orbit coupling, lattice vibration, pseudo Jahn-Teller interaction, and the Zeeman term 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 investigating the temperature dependence of the thermally activated intervalence transfer, we have determined the ionization energy of Ti3+ with respect to Nb(Li)4+ to be 0.11 eV /- 0.02 eV.