抗光折变离子和本征缺陷下的光折变掺杂铌酸锂晶体的第一性原理研究

发布时间：2018-04-25 03:36

本文选题：化学计量比铌酸锂晶体 + 模拟计算　；参考：《西南大学》2017年硕士论文

【摘要】：酸锂晶体(LiNbO_3简写为LN)是一种在诸多领域都得到重视的光折变材料,特别是在光学体全息存储领域有着卓越表现,因而很多人认为其可以作为光存储介质材料的首选。优良的光电性质是该晶体被广泛运用的基础。近年来,该晶体光学体全息存储优良特性的发掘恰好迎合了人们对存储在海量存储、高速读取、高分辨率等方面的要求,该晶体及其各种掺杂系列已成为全息存储技术的重要材料,所以需要我们对该晶体及其各种掺杂系列的结构和性质做更加细致的研究。光折变掺杂离子作为LN晶体中功能离子在于全息存储中起着核心作用,抗光折变离子起着抗光损伤的作用,实现光全息存常采用两者共掺。LN晶体内部通常存在本征缺陷结构,这些结构既有利于原子的掺杂,也可以单独或与掺杂离子共同影响晶体的存储性能。本文采用第一性原理模拟计算并分析所建立的各掺杂体系的电子结构和光学性质,得出结论如下:本文第三章研究了In:Mn:LN晶体及其对比组的电子结构和光学性质。结果显示,Mn:LN晶体中的杂质能级主要由Mn的3d态轨道提供并处于禁带区域较浅的位置,价带的顶端也有Mn的3d态轨道的贡献,掺锰后晶体的带隙相比纯LN晶体大幅变窄;除上述外,在吸收谱中还发现该晶体对1.66eV、2.85eV处出现明显的光吸收,且1.66eV处是一个强吸收峰;在引入In使得1.66eV附近的吸收强度减弱且范围变宽了,当掺In浓度达到其阈值(约3mol%)时在该峰继续减弱,且又分别在1.68eV,2.13eV两处产生了新吸收峰。文章认为1.66eV处的吸收峰与Mn2+相关,而其后掺铟出现的2.13eV吸收是因为掺Mn3+,随着掺铟量增加在两峰间出现的强弱变化是由电子在锰、铟间的转移所致;提出了在In:Mn:LN晶体若光存储选择以1.66eV附近低能段光的记录光,为达到较高记录灵敏度需较小的掺铟量等观点。本文第四章是关于含本征缺陷的Fe:LN晶体电子结构和光学性质的研究,结果显示近化学计量比掺铁铌酸锂晶体(Fe:n LN)的带宽仅为2.29eV,掺铁后的带隙较纯LN明显变窄;含小极化子样品能带间隙变化很小,且在禁带区域形成了缺陷能级;Fe占位的改变,使晶体带宽明显改变;含双极化子的样品的禁带区域出现了一些新的能级;在各体系的吸收谱中出现了个数不一的吸收峰,但其位置的变化也间接地证明极化子与Fe的共存。研究证实,Fe占位的改变以及其与本征缺陷间的相互作用直接影响了能带、态密度的分布以及吸收峰的出现与位置。除此外,还分析得出了在低浓度掺铁的Fe:n LN晶体,可能存在Fe同时占锂、铌位的的情况。
[Abstract]:Lithium acid crystal LiNbO3 is a kind of photorefractive material which has been paid attention to in many fields, especially in the field of optical volume holographic storage, so many people think that it can be used as the first choice of optical storage dielectric material. Excellent optoelectronic properties are the basis for the wide application of the crystal. In recent years, the discovery of the excellent properties of the optical volume holographic storage of the crystal meets the requirements of mass storage, high-speed reading, high resolution, and so on. The crystal and its doped series have become important materials for holographic storage, so we need to do more detailed research on the structure and properties of the crystal and its doped series. Photorefractive doped ions, as functional ions in LN crystals, play a central role in holographic storage, and anti-photorefractive ions play a role in anti-photodamage. These structures not only facilitate the doping of atoms, but also affect the storage performance of crystals either alone or in conjunction with doped ions. In this paper, the electronic structure and optical properties of each doped system are calculated and analyzed by first-principle simulation. The conclusions are as follows: in chapter 3, the electronic structure and optical properties of In:Mn:LN crystal and its contrast group are studied. The results show that the impurity energy levels in mn: LN crystals are mainly provided by the 3D state orbitals of mn and are in the shallow position of the forbidden band region. The band gap of mn doped crystals is much narrower than that of pure LN crystals, and the contribution of mn 3D state orbitals is also found at the top of the valence bands. In addition to the above, it is also found in the absorption spectrum that the crystal exhibits obvious light absorption at 1.66 EV ~ (2. 85) EV and a strong absorption peak at 1.66eV, and that the absorption intensity near 1.66eV decreases and the range widens when in is introduced. When the concentration of in reached its threshold value (about 3 mol), it continued to weaken at this peak and produced a new absorption peak at 1.68 EV and 2.13 EV, respectively. It is considered that the absorption peak at 1.66eV is related to Mn2, while the 2.13eV absorption in indium is due to the Mn3 doping. The change of the intensity between the two peaks with the increase of indium content is caused by the transfer of electrons between mn and indium. In order to achieve the higher recording sensitivity, it is proposed that the recording light of low energy segment light near 1.66eV should be selected for storage in In:Mn:LN crystal, and the amount of indium doped should be smaller in order to achieve higher recording sensitivity. In the fourth chapter, the electronic structure and optical properties of Fe:LN crystal with intrinsic defects are studied. The results show that the bandwidth of Fe: n LN doped lithium iron niobate crystal is only 2.29 EV, and the band gap of Fe doped lithium niobate crystal is obviously narrower than that of pure LN. The energy band gap of the sample with small polaron changes very little, and the defect energy level Fe occupation changes in the forbidden band region, which makes the crystal bandwidth change obviously, and some new energy levels appear in the forbidden band region of the sample with double polaron. There are different number of absorption peaks in the absorption spectra of each system, but the change of their positions also indirectly proves the coexistence of polaron and Fe. It is proved that the change of the occupation of Fe and its interaction with intrinsic defects directly affect the energy band, the distribution of density of states, and the appearance and location of absorption peaks. In addition, it is also found that Fe may share lithium and niobium sites in Fe:n LN crystals with low Fe concentration.
【学位授予单位】：西南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O469

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