锂组分对纯铌酸锂晶体光折变性能的影响研究

本文研究了低光强下锂组分对纯铌酸锂晶体的可见光折变、紫外光致吸收及紫外光折变性能的影响,发现了光折变中心种类和数量随晶体组分的渐变行为.在组分较低的同成分晶体中,大量本征缺陷形成Q极化子,因而在可见光波段表现出较弱的光生伏打效应;在组分较高的近化学计量比铌酸锂晶体中,双极化子是主要光折变中心,从而引起较高的光生伏打电场.而纯铌酸锂晶体的紫外光致吸收以及紫外光折变性能则具有相似的组分依赖关系.它们随组分的增加过程可分为两个不同的阶段:当组分小于49.70 mol;时,随组分增加缓慢升高,而当组分高于49.70 mol;时,随组分突然猛增并迅速升高.上述实验结果也可采用本征缺陷由Q极化子主导向双极化子主导的渐变过程进行解释.

Influence of Li Composition on the Photorefractive Properties of Pure Lithium Niobate Crystals

The influence of Li composition on VIS-light photorefraction, UV-light-induced absorption and UV-light photorefraction in pure LiNbO_3 crystals at low light intensity was investigated. The experimental results indicate that different defects dominate the photorefractive centers of pure LiNbO_3 with varied compositions. For VIS-light photorefraction, Q polarons are introduced to explain the weak photovoltaic effect in LiNbO_3 with low composition, and bipolarons are considered to be responsible for the enhanced photovoltaic field in LiNbO_3 with high composition. It is also found that the UV-light-induced absorption and UV-light photorefraction have similar composition dependence. They increase slowly with the composition below 49.70 mol% but boosts up very rapidly above this critical composition. These findings are explained by the two different stages in the evolution of photorefractive centers during the increase of the crystal composition, which also proves our suggestion that different defects dominate the photorefractive centers of pure LiNbO_3 with varied compositions.