Optical absorption edge and some shallow donor levels in LiNbO3 systems

In LiNbO 3 the position of the conduction band edge formed by Nb 4d states strongly depends on the presence of antisite niobiums (Nb on Li Site) lowering the band edge. Based on this property the measurement of the UV absorption edge can be used for detemining the Li/Nb ratio in the crystal with high precision, especially in the near-stoichiometric region where the relative 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 processes between Nb 5+/4+ polaron and Ti 4+/3+ shallow donor levels and Jahn-Teller effects of the involved d 1 paramagnetic states have been observed in reduced LiNbO 3 : Mg : Ti and are compared with literature results in LiNbO 3 : Ti.