發(fā)布時間：2018-04-25 03:36

  本文選題：化學計量比鈮酸鋰晶體 + 模擬計算��； 參考：《西南大學》2017年碩士論文

【摘要】：酸鋰晶體(LiNbO_3簡寫為LN)是一種在諸多領(lǐng)域都得到重視的光折變材料,特別是在光學體全息存儲領(lǐng)域有著卓越表現(xiàn),因而很多人認為其可以作為光存儲介質(zhì)材料的首選。優(yōu)良的光電性質(zhì)是該晶體被廣泛運用的基礎(chǔ)。近年來,該晶體光學體全息存儲優(yōu)良特性的發(fā)掘恰好迎合了人們對存儲在海量存儲、高速讀取、高分辨率等方面的要求,該晶體及其各種摻雜系列已成為全息存儲技術(shù)的重要材料,所以需要我們對該晶體及其各種摻雜系列的結(jié)構(gòu)和性質(zhì)做更加細致的研究。光折變摻雜離子作為LN晶體中功能離子在于全息存儲中起著核心作用,抗光折變離子起著抗光損傷的作用,實現(xiàn)光全息存常采用兩者共摻。LN晶體內(nèi)部通常存在本征缺陷結(jié)構(gòu),這些結(jié)構(gòu)既有利于原子的摻雜,也可以單獨或與摻雜離子共同影響晶體的存儲性能。本文采用第一性原理模擬計算并分析所建立的各摻雜體系的電子結(jié)構(gòu)和光學性質(zhì),得出結(jié)論如下:本文第三章研究了In:Mn:LN晶體及其對比組的電子結(jié)構(gòu)和光學性質(zhì)。結(jié)果顯示,Mn:LN晶體中的雜質(zhì)能級主要由Mn的3d態(tài)軌道提供并處于禁帶區(qū)域較淺的位置,價帶的頂端也有Mn的3d態(tài)軌道的貢獻,摻錳后晶體的帶隙相比純LN晶體大幅變窄;除上述外,在吸收譜中還發(fā)現(xiàn)該晶體對1.66eV、2.85eV處出現(xiàn)明顯的光吸收,且1.66eV處是一個強吸收峰;在引入In使得1.66eV附近的吸收強度減弱且范圍變寬了,當摻In濃度達到其閾值(約3mol%)時在該峰繼續(xù)減弱,且又分別在1.68eV,2.13eV兩處產(chǎn)生了新吸收峰。文章認為1.66eV處的吸收峰與Mn2+相關(guān),而其后摻銦出現(xiàn)的2.13eV吸收是因為摻Mn3+,隨著摻銦量增加在兩峰間出現(xiàn)的強弱變化是由電子在錳、銦間的轉(zhuǎn)移所致;提出了在In:Mn:LN晶體若光存儲選擇以1.66eV附近低能段光的記錄光,為達到較高記錄靈敏度需較小的摻銦量等觀點。本文第四章是關(guān)于含本征缺陷的Fe:LN晶體電子結(jié)構(gòu)和光學性質(zhì)的研究,結(jié)果顯示近化學計量比摻鐵鈮酸鋰晶體(Fe:n LN)的帶寬僅為2.29eV,摻鐵后的帶隙較純LN明顯變窄;含小極化子樣品能帶間隙變化很小,且在禁帶區(qū)域形成了缺陷能級;Fe占位的改變,使晶體帶寬明顯改變;含雙極化子的樣品的禁帶區(qū)域出現(xiàn)了一些新的能級;在各體系的吸收譜中出現(xiàn)了個數(shù)不一的吸收峰,但其位置的變化也間接地證明極化子與Fe的共存。研究證實,Fe占位的改變以及其與本征缺陷間的相互作用直接影響了能帶、態(tài)密度的分布以及吸收峰的出現(xiàn)與位置。除此外,還分析得出了在低濃度摻鐵的Fe:n LN晶體,可能存在Fe同時占鋰、鈮位的的情況。
[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.
【學位授予單位】：西南大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：O469

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