Optical absorption edge and some shallow donor levels in LiNbO3 systems

In LiNbO3 the position of the conduction band edge formed by Nb 4d states s trongly depends on the presence of antisite niobiums (Nb on Li site) loweri ng the band edge. Based on this property the measurement of the UV absorpti on edge can be used for determining the Li/Nb ratio in the crystal with hig h precision, especially in the near-stoichiometric region where the relativ e precision is 0.01 mol%. The same Nb states can form shallow donor levels due to nearby impurities and/or the polaron effect. Charge transfer process es between Nb5+/4+ polaron and Ti4+/3+ shallow donor levels and Jahn - Tell er effects of the involved d(1) paramagnetic states have been observed in r educed LiNbO3:Mg:Ti and are compared with literature results in LiNbO3:Ti.