坩埚下降法生长的LiNbO_3,Fe∶LiNbO_3,Zn∶Fe∶LiNbO_3单晶的吸收光谱特性

Absorption Spectra of LiNbO_3, Fe∶LiNbO_3, and Zn∶Fe∶LiNbO_3 Crystals Grown by Bridgman Method

用紫外可见光谱 (UV/VisibleSpectra)测试并研究了坩埚下降法生长的LiNbO3 、Fe∶LiNbO3 ,以及Zn∶Fe∶LiN bO3 晶体的吸收特性。分析了产生这些吸收特性的原因以及与工艺生长方法的内在联系。研究结果表明 :LiNbO3 单晶沿晶体生长方向 ,其紫外吸收边向长波方向移动 ,且在 35 0～ 4 5 0nm波段的吸收也逐渐增大 ,这是由于Li的分凝与挥发 ,逐渐产生缺锂所造成的 ;在Fe∶LiNbO3 单晶中观察到Fe2 + 离子在 4 80nm附近的特征吸收峰 ,并发现沿生长方向 ,Fe2 + 离子的浓度逐渐增加 ,这与提拉法生长得到的晶体不同 ;在Fe∶LiNbO3 单晶中掺入质量分数为 1.7%ZnO后 ,吸收边位置发生蓝移 ,而掺杂质量分数达到 3.4 %时 ,观察到有红移现象。Fe2 + 离子在Zn∶Fe∶LiNbO3 单晶中的浓度与ZnO掺杂量有密切关系。在掺杂质量分数 1.7%ZnO的Fe∶LiNbO3 单晶中 ,Fe2 + 离子从底部到顶部的浓度变化比在掺杂质量分数 3.4 %ZnO晶体中大 ,这是由于Zn2 + 抑制Fe2 + 离子进入Li位的能力随掺杂量的增加而逐渐减弱造成的。就该下降法工艺技术对Fe2 +

The UV/visible absorption spectra of LiNbO_3, Fe∶ LiNbO_3, and Zn∶ Fe∶ LiNbO_3 crystals grown by Bridgman method were measured and investigated. The characteristics of the absorption were explained, and the effects of growth processing on the absorption spectra were also discussed. The results indicate that the absorption edge of lithium niobate shifts to longer wavelength, and the absorption intensity in the range of 350~450 nm band increases along the direction of crystal growth. The reason of above causes is lacking of lithium composition in crystal, which resulted from the volatilization and segregation of lithium in growth period. A band at 480 nm which attributed to Fe^(2+) ion absorption was observed in Fe∶LiNbO_3 crystal, and it was found that the intensity of the band increases along the growth direction, which means the increase of Fe^(2+) ion along the direction, and the incorporation of Fe in LiNbO_3 resulted in a red shift of absorption edge. However, the concentration of Fe^(2+) ion in the obtained crystal increases obviously compared with that of Fe∶LiNbO_3 in same quantity of Fe dopant, which was quite different from that of crystal grown by the Czochralski method. When ZnO in w(ZnO)=1.7% was doped, a blue shift of absorption edge was observed, but a slightly red shift for w(ZnO)=3.4% ZnO. Among Fe-doped and Zn/Fe co-doped LiNbO_3 crystals, 1.7% ZnO doped Fe∶LiNbO_3 has biggest change of Fe^(2+) ion mass fraction from bottom to top part of crystal. A stronger suppressing effect on Fe^(2+) concentration in Zn∶Fe∶LiNbO_3 single crystals resulted from doping w(ZnO)=1.7% than w(ZnO)=3.4%. The effect of the special growth technology on the Fe^(2+) concentration was analyzed and discussed.