【摘要】：非線性光學(xué)晶體是固體激光器進(jìn)行頻率轉(zhuǎn)換的核心器件,受到了科學(xué)家們廣泛關(guān)注。目前為止,亟需探索新的具有優(yōu)良性能的適用于深紫外波段的非線性光學(xué)晶體。有效的設(shè)計(jì)合成新的非線性光學(xué)晶體,需要建立在微觀機(jī)理的研究基礎(chǔ)上。最近通過復(fù)合堿金屬、堿土金屬以及引入鹵素,科學(xué)家們陸續(xù)合成了一大批鹵素硼酸鹽,但是由于晶體合生長(zhǎng)方面等存在困難,依然缺乏應(yīng)用于深紫外波段的非線性光學(xué)材料。本文主要基于密度泛函理論,選擇一定體系對(duì)鹵素硼酸鹽的電子結(jié)構(gòu)-光學(xué)性質(zhì)進(jìn)行研究,討論了離子替換、活性基元替換對(duì)材料光學(xué)性質(zhì)的影響,并尋找出一例具有優(yōu)良性能的鹵素硼酸鹽。主要工作如下:(1)基于密度泛函理論,研究了ANa_2B_6O_(13)X(A=Na,Rb;X=Cl,Br)體系中離子替換對(duì)帶隙和雙折射率的影響。電子結(jié)構(gòu)顯示這個(gè)體系中決定帶隙的是B-O鍵,堿金屬離子(Rb+和Na+)和鹵素離子(Cl-和Br-)之間的替換對(duì)帶隙影響不大;堿金屬離子之間的替換對(duì)雙折射率影響較大。Na_3B_6O_(10)X(X=Cl,Br)含有更加共平面化的B_6O_(13)基團(tuán),這是它們的雙折射率大于RbNa_2B_6O_(13)X(X=Cl,Br)的雙折射率的原因。(2)為了尋找具有優(yōu)良性能非線性光學(xué)材料,基于密度泛函理論,我們研究了含有基元B_7O_(13)的鹵素硼酸鹽MgB_7O_(13)Cl(MBOC)的電子結(jié)構(gòu)和光學(xué)性質(zhì)。計(jì)算結(jié)果顯示化合物MBOC具有大的帶隙8.43 eV和可觀倍頻效應(yīng)0.41 pm/V,其優(yōu)良的性能可以和目前為止性能最優(yōu)異的晶體KBBF(8.64 eV和0.46 pm/V)相媲美。這說明MBOC在短波段有機(jī)會(huì)得到應(yīng)用。我們還分析了MBOC具有大帶隙和可觀倍頻效應(yīng)的原因。采用單軸加壓的模擬方法,發(fā)現(xiàn)隨著外加壓強(qiáng)的增大,B_7O_(13)基團(tuán)的各向異性會(huì)增大,MBOC的雙折射率也隨著增大。本部分工作證實(shí),設(shè)計(jì)合成含有B_7O_(13)基團(tuán)的化合物,其中B_7O_(13)基團(tuán)含有較大畸變的BOx(x=3,4)基團(tuán),會(huì)獲得具有大帶隙和可觀倍頻效應(yīng)的非線性光學(xué)晶體。(3)為了尋找新型非線性光學(xué)活性基元,基于密度泛函理論研究了BMO_4(M=P,As)的電子結(jié)構(gòu)及其光學(xué)性質(zhì)。AsO_4基團(tuán)替換PO_4基團(tuán)后,BAsO_4依然具有較大的帶隙。MO_4(B,P,As)基團(tuán)和BO_3基團(tuán)的帶隙(?Eg)大小有以下順序:?Eg(BO_4)?Eg(PO_4)?Eg(AsO_4)≈?Eg(BO_3)。BMO_4(M=P,As)有較大的倍頻系數(shù),未成鍵的O-2p軌道與B/P或As之間的強(qiáng)烈雜化是它們具有較大倍頻系數(shù)的原因。BAsO_4中四面體基元的各向異性明顯大于BPO_4中四面體的基元的各向異性,因此BAsO_4的雙折射率較大。本工作表明,AsO_4基團(tuán)是一種新的非線性光學(xué)活性基元,它替換PO_4基團(tuán)后,不僅保留了大帶隙和大倍頻之間的平衡,還增大了雙折射率。這為設(shè)計(jì)合成新的應(yīng)用于深紫外波段的非線性光學(xué)材料提供了新思路。
[Abstract]:Nonlinear optical crystal is the core device of solid-state laser frequency conversion, and has been widely concerned by scientists. Up to now, there is an urgent need to explore new nonlinear optical crystals with excellent properties suitable for deep ultraviolet band. The effective design and synthesis of new nonlinear optical crystals need to be based on the study of microscopic mechanism. Recently, a large number of halogen borates have been synthesized by composite alkali metals, alkaline earth metals and the introduction of halogens. However, due to the difficulties in crystal syntheses, there is still a lack of nonlinear optical materials used in deep ultraviolet band. Based on the density functional theory, the electronic structure-optical properties of halogen borates are studied in this paper. The effects of ion substitution and active unit substitution on the optical properties of the materials are discussed. An example of halogen borate with excellent properties was found. The main works are as follows: (1) based on the density functional theory, the effects of ion substitution on the band gap and birefringence in ANa_2B_6O_ (13) X (ANa_2B_6O_) system are studied. The electronic structure shows that the band gap is determined by B-O bond. The substitution of alkali metal ions (Rb and Na) and halogen ions (Cl- and Br-) has little effect on the band gap. The substitution of alkali metal ions has great influence on the birefringence. Na_3B_6O_ (10) X (XnCl _ (13) contains a more coplanar B6O _ (13) group. This is the reason why their birefringence is larger than that of RbNa_2B_6O_ (13) X (XnClCnbr). (2) in order to find nonlinear optical materials with excellent properties, the density functional theory is used. The electronic structure and optical properties of the halogen borate MgB_7O_ (13) Cl (MBOC) containing the basic unit B _ 7O _ (13) have been studied. The results show that the compound MBOC has a large band gap of 8.43 eV and an observable frequency-doubling effect of 0.41 pm/V,. Its excellent performance is comparable to that of the most excellent crystal KBBF (8.64 eV and 0.46 pm/V) so far. This shows that MBOC has an opportunity to be applied in short band. We also analyze the reason why MBOC has large band gap and observable frequency doubling effect. The uniaxial compression simulation method is used. It is found that the anisotropy of B _ S _ 7O _ (13) group increases and the birefringence of MBOC increases with the increase of the applied pressure. In this part, it is proved that the compounds containing B _ S _ 7O _ (13) group have been designed and synthesized, in which the B _ S _ 7O _ (13) group contains a large distorted BOx (XN _ 3O _ (4) group. Nonlinear optical crystals with large band gap and observable frequency doubling effect will be obtained. (3) in order to find new nonlinear optical active elements, the density functional theory (DFT) is used to study BMO_4 (Mupp). The electronic structure and optical properties of As. When the AsO_4 group replaces the PO_4 group, the BAsO_4 still has a large band gap. The band gap (? Eg) of the As) group and the BO_3 group have the following order:? Eg (BO_4)? Eg (PO_4)? Eg (AsO_4) 鈮，

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