Investigations of the OH~- absorption bands in congruent and near-stoichiometric LiNbO_3:Hf crystals

摘要

OH~- absorption bands of both congruent and near-stoichiometric LiNbO_3:Hf crystals were investigated. The abrupt blueshift of OH ~- absorption bands was found between the doping levels of 2 and 2.5mol% in the congruent crystals, which confirms the exact optical-damage threshold for Hf doping. The absorption difference of OH ~- bands between the congruent and near-stoichiometric crystals shows that after Li incorporation H~+ ions no longer prefer the sites of 3500 cm ~(-1). Moreover, with the increase of Hf doping in the near-stoichiometric crystals, H~+ ions were found to gradually transfer to the sites of 3489 cm ~(-1). These results are explained by the breakdown of the association of Hf _(Nb)~- and H ~+ ions and the subsequent redistribution of H~+ ions around Hf _(Li)~(3+) ions in V _(Li)~- -deficient lattice. Additionally, the link between the intrinsic defects and how they influence the optical-damage threshold upon adding Hf was discussed in detail.