摘要：Solid-state ultraviolet(UV)lasers are widely used for their various applications in commercial and scientific *** nonlinear optical(NLO)crystals with high NLO coefficients and good quality are key factors for the harmonic generation of UV light sources[1-3].The fourth harmonic generation(FHG)using NLO crystals is an effective method to achieve a high-power UV laser at 266 nm[4,5].

摘要：Exploration of new infrared(IR) nonlinear optical(NLO) materials is still in urgency owing to the indispensable roles in optoelectronic devices, resource exploration, and long-distance laser communication. The formidable challenge is to balance the contradiction between wide band gaps and large second harmonic generation(SHG) effects in IR NLO materials. In the present work, we proposed new kinds of NLO active units, d^0 transition metal fluorooxofunctional groups for designing mid-IR NLO materials. By studying a series of d^0 transition metal oxyfluorides(TMOFs),the influences of fluorooxo-functional groups with different d^0 configuration cations on the band gap and SHG responses were explored. The results reveal that the fluorooxo-functional groups with different d^0 configuration cations can enlarge band gaps in mid-IR NLO materials. The first-principles calculations demonstrate that the nine alkali/alkaline earth metals d^0 TMOFs exhibit wide band gaps(all the band gaps >3.0 e V), large birefringence Δn(> 0.07), and two W/Mo TMOFs also exhibit large SHG responses. Moreover, by comparing with other fluorooxo-functional groups, it is found that introducing fluorine into building units is an effective way to enhance optical performance. These d^0 TMOFs with superior fluorooxo-functional groups represent a new exploration family of the mid-IR region, which sheds light on the design of mid-IR NLO materials possessing large band gap.

摘要：深紫外全固态激光(波长短于200 nm)因波长短、光子能量高等特点,在工业、科研等领域有着重要的应用价值.当前,利用可见/近红外全固态激光器为基频光源,通过深紫外非线性光学晶体的非线性谐波技术多级变频,是发展深紫外全固态激光器的有效途径.本文概述了近年来深紫外非线性光学晶体设计与制备方面的重要进展;分析了潜在深紫外非线性光学晶体材料的体系分布情况;重点探讨了新型深紫外非线性光学晶体材料氟化驱动设计策略;介绍了氟化硼酸盐等典型非线性光学材料实例,研究表明,氟与非金属键合的“氟化”对氟化硼酸盐的结构和性质均起到调控作用.最后,展望了深紫外非线性光学晶体面临的挑战,并对新材料设计、晶体生长、性质极限、“无人区”新应用等方面的发展方向进行了讨论.

摘要：As a promising candidate,the fluorooxoborate has enkindled new explorations of nonlinear optical materials to meet the deep-ultraviolet ***,big challenges and open questions still remain facing this exciting new field,especially the birefringence and dispersion of refractive index which are fundamental parameters for determining the phasematching second harmonic generation *** we designed possible anionic groups in fluorooxoborates,and analyzed the optical anisotropy to check its influence on birefringence,which was proved further by the response electronic distribution anisotropy *** functional modules modulating birefringence in fluorooxoborates were explored *** developed an approach for evaluating the behavior of the refractive index dispersions and found that the fluorooxoborates had small refractive index dispersions owing to the introduction of fluorooxoborate *** results demonstrate that fluorooxoborates can be utilized to realize short phase-matching wavelength markedly and offer a path toward novel performance-driven materials design.

摘要：Wide transmittance range is an essential factor for the design of infrared optical ***,the designs of mid-far infrared crystals have focused on oxygenfree systems of chalcogenides and ***,the introduction of elements with large atomic numbers,such as the lone-pair cation Pb^(2+) and halogen anion I^(-),based on the oxyhalides,can broaden the infrared transmittance ***,two new polymorphs of Pb(Ⅱ)-containing oxyhalides,Pb_(14)O_(8)I_(12)(α-POI)and Pb_(7)O_(4)I_(6)(β-POI),are successfully synthesized via the high-temperature solution ***,they crystallize in the same space group,P1,and present unprecedented[O_(8)Pb_(14)]clusters from the perspective of oxocentered[OPb_(4)]basic ***,POI exhibits a quite wide transparent range(0.47-16.0μm),which enlightens the oxyhalides with prominent infrared optical ***,the first principles calculations show that they have large birefringence(0.139 and 0.108 for α-and β-POI at 1064 nm,respectively),which makes POI promising infrared optical materials.

摘要：探索具有深紫外相位匹配能力的新型非线性光学材料是当前研究热点.本文从硼氧阴离子框架出发,发现由π共轭BO_(3)基团组成一维(BO_(2))∞链的电子离域导致了极化特性增强,可实现非线性光学性能的优化.据此,本文预测了以(BO_(2))∞链为阴离子框架的CaBO_(2)F体系.重点研究了三种能量最低的结构CaBO_(2)F-Ⅰ,CaBO_(2)F-Ⅱ和CaBO_(2)F-Ⅲ,设计了热力学上可进行的反应路径.第一原理计算表明,CaBO_(2)F-Ⅰ,CaBO_(2)-F-Ⅱ和CaBO_(2)F-Ⅲ具有较宽的带隙,合适的双折射(0.076–0.108@1064 nm)和较大的倍频系数(2.1–2.7×KDP).其中,计算得到CaBO_(2)F-Ⅰ的最短相位匹配波长在约为195 nm(基于HSE06带隙修正剪刀算符),证明了含有定向电子离域的(BO_(2))∞链是深紫外非线性光学材料的潜在阴离子框架.本文通过将机理研究与验证性的结构预测相结合实现了自上而下设计深紫外非线性光学结构模板,该研究为探索新型非线性光学材料提供了新的策略.

摘要：以著名的LiB_(3)O_(5)为模板,通过增强其结构中B_(2)O_(5)的夹角使双折射更小,在封闭体系中通过高温溶液法获得了两种新的用于制造零级波片的双折射晶体Li_(2)MLaB_(18)O_(30)(M=Rb,Cs).有趣的是,相邻的B_(2)O_(5)接近垂直排列,使得它们表现出比商用石英晶体(Δn~0.0092在可见光区域)小得多的双折射率(分别为0.0032@532 nm和0.0027@532 nm).此外,Li_(2)MLaB_(18)O_(30)(M=Rb,Cs)晶体的紫外截止边均低于200 nm,表明它们可用作深紫外区域的零级波片材料.

摘要：A new deep-ultraviolet(DUV)birefringent crystal,LiB_(5)O_(5)F_(2)(OH)_(4)(LBOFH),was designed and synthesized by a high-temperature solution *** structure features a[B_(5)O_(5)F_(2)(OH)_(4)]anionic group that is constructed by four π-conjugated units,i.e.,two[BO_(3)]units and two[BO(OH)_(2)]units connected by the[BO_(2)F_(2)]unit,which forms a near-coplanar *** group exhibits large anisotropic polarizability and highest unoccupied molecular orbital-lowest unoccupied molecular orbital(HUMO-LUMO)gap,thus providing a good balance between the large birefringence(0.124 at 546 nm)and band gap(7.99 eV)in *** work suggests new possibilities for the design and fabrication of advanced DUV birefringent crystals using the novel anionic group and the expansion of their alternative system with new hydroxyfluorooxoborates.

摘要：The thermal expansion coefficient(TEC)and thermal conductivity(k)of thermal fillers are key factors for designing thermal management and thermal protection composite *** to its unique advantages,hexagonal boron nitride(h-BN)is one of the most commonly used thermal ***,its TEC and k values are still unclear due to the inconsistency of characterization techniques and sample *** this work,these disputes were addressed using the quasi-harmonic approximation(QHA)method and phonon Boltzmann transport equation(BTE)theory based on the density functional theory(DFT),*** accuracy of our calculated TEC and k values was confirmed by previously reported experimental results,and the underlying physical principles were analyzed from the phonon *** TEC results show that the h-BN has small in-plane negative value and large cross-plane positive value,which are-2.4×10^(-6) and 36.4×10^(-6) K^(-1) at 300 K,*** the anisotropic TEC is mainly determined by the anisotropic isothermal bulk modulus and the low-frequency out-of-plane longitudinal phonon *** found that the convergence of cutoff radius and q-grid size have significant effect on the accuracy of k of *** results show that the in-plane k is much higher than the cross-plane k,and the values at 300 K are 286.6 and 2.7 W m^(-1) K^(-1),*** anisotropic phonon group velocity arising from the vibration behaviors of acoustic phonon modes should be primarily responsible for the anisotropic *** calculated TEC and k values will provide important references for the design of h-BN composite materials.

摘要：Finding crystals with high birefringence(Δn),especially in deep-ultraviolet(DUV)regions,is important for developing polarization devices such as optical fiber *** materials are usually discovered using experimental techniques,which are costly and inefficient for a large-scale ***,we collected a database of crystal structures and their optical properties and trained atomistic line graph neural network to predict theirΔ*** estimate the level of confidence of the trained model on new data,D-optimality criterion was *** trained graph neural network,we searched for novel materials with highΔn in the Materials Project database and discovered two new DUV birefringent candidates:NaYCO_(3)F_(2) and SClO_(2)F,with highΔn values of 0.202 and 0.101 at 1064 nm,*** analysis reveals that strongly anisotropic units with various anions andπ-conjugated planar groups are beneficial for highΔn.