非化学计量比铌酸钾锂晶体的光谱特征

The Spectrum Characterization of Non-Stoichiometry Potassium Lithium Niobate Crystals

用顶部籽晶法生长了一批不同组成的铌酸钾锂晶体。利用近红外cw：Ti-sapphire激光研究了三种组成的经过精细抛光的晶体样品的二次谐波性质，结果表明晶体的二次谐波效应与晶体组成密切相关，Li含量越高的样品倍频效率越高。利用红外Raman光谱技术调查了晶体非线性晶格振动特征，分析了晶体中组分离子浓度对晶体红外Raman光谱特征的影响，探讨了组分离子对晶体二次谐波性质影响的原因。结果表明，晶体中位于C格位的Li离子浓度对晶体Raman光谱产生了强烈的影响，低Li含量晶体中[-NbO6]^6-八面体所对应的3个Raman特征光谱线没有峰发生分裂；当晶体中Li离子浓度增加时，屿所对应的Raman峰有所加宽，垅振动模式出现分裂峰，并在100-400cm^-1范围出现小峰数量增多；当Li离子浓度接近铁电相边界时，[-NbO6]^6-八面体结构接近解体，屿所对应的Raman峰分裂成3个峰，v1和v2振动模式发生部分分裂，在100～400cm^-1范围小峰更为突出。这些影响的本质在于晶体中Li含量的提高导致晶体中[NbO6]^6-八面体畸变程度加大，与晶体非线性光学性质相一致。

A batch of potassium lithium niobate（KLN） crystals with different compositions were grown by using TSSG technique. Samples with three different compositions were well polished. By using near infrared cw： Ti-sapphire laser, their Second Harmonic Generation （SHG） properties were investigated. The results showed that the SHG effect is related to the composition of the samples, and their frequency-doubling efficiency enhanced with the raise of Li ions content in the crystal. By using infrared Rarnan technique, the properties of nonlinear lattice vibration of thee samples were investigated, and the character of Raman spectrum were analyzed, as well the effect of composition on the SHG properties were discussed. The analysis results showed the striking effects of Li content for these Raman peaks. For KLN sample with small Li content, the three character peaks belonged to [NbO6 ]^7- octahedron show simple peak. With the raise of Li content in crystal, the peaks belonged to v2 mode were partly split, and the peak belongs to vs mode was broadened. When the Li content approach to the chemical composition KLN crystal, and the structure of [NbO6 ]^7-octahedron is almost to be disorganized, the peaks belonged to vs mode were split, and the peaks belonged to v1 mode and v2 mode were partly split also, with more distinct weak peaks in the wavelength range of 100- 400 cm^-1. These effects were caused by the raise of Li content, which leads to the severer aberrance of [-NbO6 ]^7-octahedron in KLN crystal, and disturbing the lattice vibration of the octahedron. This phenomenon is agreed with the nonlinear properties of potassium lithium niobate crystal.