EPR of Nd3+ in congruent and nearly stoichiometric lithium niobate

Lithium niobate crystals doped with neodymium were studied with the help of electron paramagnetic resonance, EPR in the temperature range of 4.2-20 K. Tremendous narrowing of the EPR lines in nearly stoichiometric samples in comparison with congruent ones allowed us to distinguish four non-equivalent centers, as well as line splitting caused by hyperfine interaction of neodymium electrons with nuclear spins of both magnetic isotopes 143 Nd and 145 Nd. It is shown that one of the centers has axial C 3 symmetry, whereas all others have lowest C 1 symmetry due to presence of intrinsic defects or/and charge compensation defects in the near neighborhood of Nd 3+ .