Investigations of the OH⁻ absorption bands in congruent and near-stoichiometric LiNbO₃:Hf crystals

¹ School of Material Science and Engineering, Hebei University of Technology - Tianjin 300130, China
² Department of Physics, Tianjin Urban Construction Institute - Tianjin 300384, China
³ The MOE Key Laboratory of Weak-Light Nonlinear Photonics, Nankai University - Tianjin 300457, China

^a yanwenbo@hebut.edu.cn

Received: 21 April 2010
Accepted: 2 August 2010

Abstract

OH⁻ absorption bands of both congruent and near-stoichiometric LiNbO₃:Hf crystals were investigated. The abrupt blueshift of OH⁻ absorption bands was found between the doping levels of 2 and 2.5 mol% 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_Li³⁺ 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.