Multifrequency spectroscopy of laser active centers Nd3+ and Yb3+ in nearly stoichiometric LiNbO3

Lithium niobate crystals doped with neodymium and ytterbium were studied with the help of the electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and optical absorption. Tremendous narrowing of magnetic resonance lines in nearly stoichiometric samples in comparison with congruent ones allowed us to distinguish four non-equivalent centers (NEC) of Nd3+ and five NEC of Yb3+, as well as line splitting caused by hyperfine interaction of neodymium electrons with nuclear spins of magnetic isotopes 143Nd, 145Nd,171Yb and 173Yb. It was shown that some of the centers has axial C3 symmetry, whereas all others have lowest C1 symmetry due to presence of intrinsic defects or/and charge compensation defects in the near neighborhood of Nd3+ and Yb3+. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)