含本征缺陷的掺铁铌酸锂晶体的电子结构和吸收光谱的第一性原理研究

First Principles Study of the Electronic Structures and Absorption Spectrum of Fe∶LiNbO_3 Crystals with Intrinsic Defects

该文基于密度泛函理论的第一性原理,研究了含本征缺陷的掺铁铌酸锂晶体的电子结构和光学特性.研究显示,近化学计量比掺铁铌酸锂晶体的能带间隙约为2.29eV;含小极化子样品的能带间隙有微小改变;Fe离子占位变化,能带间隙有较大改变;含双极化子样品在禁带中出现新的能级;各掺杂体系的吸收光谱中出现了个数不一的吸收峰.研究结果表明:能带、态密度分布的变化及吸收峰的出现与位置的变化均源于铁占位的改变及与本征缺陷的相互作用;在低掺铁近化学计量比铌酸锂晶体中,铁离子占锂位和占铌位会同时存在.

Based on the first-principles density functional theory under the generalized gradient approximation(GGA),the electronic structures and optical properties of iron-doped lithium niobate crystals with intrinsic defects are studied in this paper.The results show that the band gap of Fe∶LN(about 2.29eV)is narrower than that of LN;the band gap of Fe(P)∶LN,Fe(HP)∶LN and Fe(HB)∶LN sample is2.26 eV,2.37 eV and 2.24 eV respectively.The Fe∶LN,Fe(P)∶LN and Fe(HP)∶LN sample displays absorption peak at 2.05 eV,2.07 eV and 2.34 eV respectively in the visible region,which contributed by electron transfer of iron ions;Fe(HB)∶LN crystal has two peaks in the visible region at 2.34 eV and1.96 eV,originated from Fe ions and biopolarons.Bipolaron level hasn't any advantage for the double optical storage with the two-center.One consider that the peak at about 2.0eV is relative with the position(Nb or Li)occupied by Fe ions;it can be proposed that the FeNb exists even if the dose of iron is low(<1mol%)in Fe∶nSLN crystal.