本文研究了铪铁双掺铌酸锂(LN∶Fe, Hf)晶体的衍射效率随光栅写入角度的变化曲线, 并对该关系曲线进行了拟合分析, 发现超阈值的铪铁双掺铌酸锂晶体的体光生伏打系数κ值相比于单掺铁铌酸锂晶体大幅增加。造成κ值变化的原因可能是由于铪离子的掺入消除了晶体中存在的本征缺陷, 而晶格环境的完美化使得留在锂位的铁离子的光生伏打系数大幅上升。此外, 实验结果还表明超阈值的铪铁双掺铌酸锂晶体中参与光折变的缺陷中心浓度约为14.5 ppm (1 ppm=10-6), 即约有4.8%的铁离子仍然“残存”在锂位中, 而这些铁离子可以引起足够强的光折变效应, 成为主导铌酸锂晶体光折变性能的缺陷中心。此外, 还从杂质缺陷-氢氧根基团角度讨论了铁离子晶格占位的可能性。

In this paper, the diffraction efficiency as a function of grating writing angle in LN∶Fe, Hf crystals was studied, and the relationship curve was fitted and analyzed. It is found that the bulk photovoltaic coefficient κ increases significantly when the Hf-doping concentration exceeds the threshold. The dramatic increase of the coefficient κ to the fact that the Hf-doping eliminates the intrinsic defects in the crystal and the perfection of the lattice environment enhances the photovoltaic coefficient k of the Fe ions remaining at Li sites. The experimental results also show that the concentration of photorefractive centers is about 14.5 ppm (1 ppm=10-6) in LN∶Fe, Hf crystals, that is, 4.8% of the Fe ions still “remain” in the Li site even though the Hf-doping concentration already exceeds the threshold, and that these Fe ions can cause sufficiently strong photorefractive effect and become the dominant photorefractive centers in the LN crystal. In addition, the possibility of Fe ion occupation in LN lattice from the perspective of impurity-hydroxyl defect complex was discussed.