共价键合氟优化氟化硼酸盐的深紫外非线性光学性能

Nonlinear optical (NLO) crystals are pivotal in laser application technology, which can convert the laser frequency to generate coherent light in the deep-ultraviolet (deep-UV, wavelengthλ≤200 nm) to far-infrared spectral range, and widely used in solid-state system detection, tissue imaging, quantum information,and more [1]. To expand the diversity of optical functional units and then discover novel NLO materials.

New opportunities for ferroelectric deep-UV nonlinear optical crystals

Deep-ultraviolet(deep-UV)light with the wavelength below200 nm is one of the most crucial elements of both laser-driven industrial and scientific applications in recent years[1].DeepUV light has been produced using a variety of techniques,such as gas discharge lamps,synchrotron radiation,excimer lasers,free electron lasers,and nonlinear frequency conversion.

非线性光学数据库:理论预测助力材料的快速发现

现代激光技术迫切需要能够通过二次谐波产生相干光的非线性光学材料.然而,只有很少一部分非中心对称晶体材料的非线性光学性质被实验或者理论研究,针对高性能非线性光学晶体材料的探索仍非常有限.本工作建立了迄今为止最大的计算非线性光学晶体材料数据库,其中包含2354个非中心对称晶体结构,以及它们的倍频系数和带隙.本文提供了理论数据的计算细节和其与实验数据的对比验证,以及数据库的详细描述.该数据库的重要特点之一是它包含大量通过进化算法搜索发现的新的热力学稳定和亚稳定结构,这为寻找具有更好性能的新型非线性光学材料提供了可能性.

Clamping effect driven design and fabrication of new infrared birefringent materials with large optical anisotropy

Infrared(IR)birefringent materials with large optical anisotropy and wide transparency range are important for efficient light manipulation in various IR optical devices.Herein,two new IR birefringent materials AMgGeSe_(3)(A=Li,Na)with large optical anisotropy were rationally designed by a rigid octahedron and flexible dimer combined strategy and fabricated in experiment.The introduction of rigid[LiSe_(6)]/[NaSe_(6)]and[MgSe_(6)]octahedra effectively regulates the geometry and arrangement of the flexible[Ge2Se6]dimers,resulting in the birefringence as large as 0.334@1,064 nm in LiMgGeSe_(3) and 0.445@1,064 nm(the largest one in the reported[Ge_(2)Se_(6)]dimer-contained selenides)in NaMgGeSe_(3).Density functional theory(DFT)calculations and statistical analyses highlight the influence of polarizability anisotropy,density,arrangement of units,as well as layer distance on birefringence.The results indicate that AMgGeSe_(3)(A=Li,Na)crystals are the promising IR birefringent materials and it gives an insight into the exploration of new IR birefringent materials with large birefringence based on the clamping effect from rigid groups.

Ba_(2)B_(9)O_(13)F_(4)·BF_(4):first fluorooxoborate with unprecedented infinite [B_(18)O_(26)F_(8)] tubes and deep-ultraviolet cutoff edge

Fluorooxoborate has emerged as a promising system for exploring optical materials due to their rich structural chemistry and physicochemical properties,yet so far not fully studied.Herein,we report a new fluorooxoborate,Ba_(2)B_(9)O_(13)F_(4)·BF_(4),which contains the greatest variety of structural basic units,[BO_(3)],[BO_(2)F_(2)],[BO_(3)F],and[BF_(4)],and exhibits unprecedented 1D infinite[B_(18)O_(26)F_(8)]tubes.The unique structure avoids the dangling bonds caused by terminal oxygens,which is beneficial to the large bandgap and deep-ultraviolet cutoff edge.This article expands the crystal structure of fluorooxoborates and contributes to the exploration of deep-ultraviolet optical materials in fluorooxoborate systems.

A Cation-Driven Approach toward Deep-Ultraviolet Nonlinear Optical Materials

The design of new materials with special performances is still a great challenge,especially for the deep-ultraviolet nonlinear optical materials in which it is difficult to balance large bandgaps and strong second harmonic generation responses due to their inverse relationship.Cation variation not only influences the whole structure frameworks but also directly participates in the formation of electronic structures,both of which could lead to the uncontrollability of the properties of the designed materials.Here,a novel approach,aiming at purposeful and foreseeable material designs,is proposed to characterize the role of cations.By the verification of several series of borates,the influences of cation variation on property changes are explored systematically.Accordingly,a feasible strategy of designing deep-ultraviolet nonlinear optical materials by substituting barium for lead has been concluded,which could obviously blue-shift the ultraviolet cutoff edge and maintain the relatively strong second harmonic generation response(more than 2 times of KH2PO4),achieving the property optimization,and especially works efficiently in fluorooxoborates.The property optimization design strategy and the cation characterization method are not only helpful in exploring nonlinear optical materials but also enlightening in material design and selection.

新的非线性光学材料K7MRE2B15O30（M=Ca andBa,RE=La and Bi）的合成、表征和理论分析（英文）

本文采用高温熔液法合成了三种新型复合硼酸盐化合物K7CaBi2B15O30、K7CaLa2B15O30和K7BaBi2B15O30. K7CaLa2B15O30和K7CaBi2B15O30结晶于三方手性空间群R32中,K7BaBi2B15O30结晶于非中心对称正交极性空间群Pca21.这三个化合物具有相似的三维晶体结构,由孤立的B5O10基团和LaO6或BiO6八面体组成,K^+、Ca^2+、Ba^2+阳离子填充于空隙中以保持电荷平衡.根据我们的调研,在K7MⅡRE2B15O30体系内(MⅡ=Ca,Sr,Ba,Zn,Cd,Pb,K/RE0.5;RE=Sc,Y,La,Gd,Lu,Bi),K7BaBi2B15O30是唯一一个结晶于不同空间群的化合物,其丰富了硼酸盐的结构化学.详细的结构分析表明,碱土金属阳离子的尺寸和配位数的差异是导致结构变化的主要原因.此外,UVVis-NIR光谱分析和倍频效应(SHG)测试表明K7CaBi2B15O30具有较短的截止边(大约282 nm)和适中的倍频效应(约0.6×KDP).我们还进行了热重差热和红外光谱的测试.为了更好地理解上述化合物的结构性能关系,我们还进行了第一性原理计算.

Ba4M（CO3）2（BO3）2（M=Ba,Sr）:在开放体系下通过高温溶液法合成两种硼酸-碳酸盐（英文）

本文中,我们成功合成了两种复合的硼酸-碳酸盐Ba4M(CO3)2(BO3)2 (M=Ba,Sr).这是第一例在开放体系下合成的硼酸-碳酸盐.它们的结构由单晶X射线衍射确定,结晶在相同的Pnma空间群.它们的晶体结构是由BaO8多面体(SrO8多面体)、孤立的BO3和CO3三角形组成的三维网络结构.详细的结构分析表明,共生长的[Ba3(BO3)2]/[Ba2Sr(BO3)2]和[BaCO3]层是有利于这两种硼酸-碳酸盐的合成的.此外,还研究了它们的合成、光谱性质和热行为.

From borophosphate to fluoroborophosphate:a rational design of fluorine-induced birefringence enhancement

The introduction of oxofluoride anion into anionic group assists to tune optical properties owing to the change of coordination,electronegativity,and according anionic framework.Here,we proposed a rational design of new compounds by fluorine-driven structure and optical property evolution.A new borophosphate Ba_(2)BP_(3)O_(11)with the monoclinic space group P2_(1/c) has been synthesized in the sealed system.Ba_(2)BP_(3)O_(11)exhibits a rare P-O-P bridge formation,which is the first example in alkaline-earth metal borophosphates.By further substituting[BO_(4)]^(3-)with[BO_(3)F]^(4-),the first alkaline-earth metal/lead fluoroborophosphates M_(2)BP_(2)O_(8)F(M=Ba and Pb)with the same space group were designed.Since the scissors effect of fluorine,in M_(2)BP_(2)O_(8)F(M=Ba and Pb),a BO_(3)F tetrahedron corner-sharing with three PO_(4)tetrahedra forms 1D chains along the b-axial direction,which are filled by MO_(n)(M=Ba/Pb,n=5,6,8)distorted polyhedra.The first principles calculation shows that the borophosphate Ba_(2)BP_(3)O_(11)has a birefringence about 0.013@1,064 nm,while the fluoroborophosphates M_(2)BP_(2)O_(8)F(M=Ba and Pb)have the values of 0.035 and 0.043@1,064 nm,respectively.Such an apparent enhancement in birefringence is derived from synergies of the oxyfluoride and cation.The introduction of fluorine-containing heteroanionic groups provides a feasible strategy to design novel promising optical materials.

Toward the Enhancement of Critical Performance for Deep-Ultraviolet Frequency-Doubling Crystals Utilizing Covalent Tetrahedra

Deep-ultraviolet(deep-UV,λ<200 nm)coherent light is emerging as an indispensable driving force behind the innovation of optics and materials science.The deep-UV-driven applications range from laser interference photolithography to precise micromachining to futuristic ideas such as space propulsion using remotely controlled positioning lasers.Unlike conventional approaches to obtaining deep-UV light,for instance,synchrotron radiation,direct laser excitation,and gas discharge,nonlinear frequency conversion can be regarded as a more attractive way to endow such resource with high photon energy,high photon flux,and high spectral resolution.Actually,the nonlinear frequency conversion can be efficient only with the use of highperforming frequency-doubling crystals,which should be well-suited to the physics of nonlinear optical process.However,the necessary prerequisites for a practical frequency-doubling crystal are extremely strict,and thus very few crystals can be used to generate the deep-UV light.Faced with this,sustained effort has been expended by chemists and materials scientists toward discovering novel deep-UV frequency-doubling crystals.Studies have so far indicated that the main difficulty in finding a perfect candidate comes from the combination of three critical properties(absorption edge,nonlinear optical coefficients,and birefringence)into one crystal because they share the mutual relation of restriction and influence.In this Account,we present recent progress in discovering emergent deep-UV frequency-doubling crystals with the discussion of our efforts to balance the three critical properties by introducing the covalent tetrahedra[MO4−nXn](n=1−3),in which M refers to central atoms such as B,P,Si,S,Al,Zn,and Be and X can be apical atoms such as F,Cl,Br,and N.By analyzing the influence of the covalent tetrahedra on optical properties,we came to the conclusion of how to use the oxidized tetrahedra to achieve the improvement of the absorption edge,nonlinear optical coefficients,and birefringence for deep-UV frequency-doubling crystals.The followings are the key points in achieving the above goals:(i)elimination of dangling bonds with covalent tetrahedra to push the absorption edge of crystals into the deep-UV spectral region;(ii)orbital hybridization enhancement,charge-transfer energy reduction,and symmetry breaking of original tetrahedra with the introduction of X atoms and thereby the achievement of the enhancement of nonlinear optical coefficients;and(iii)uniform alignment of tetrahedral distorted units and the introduction of polarized X atoms containing[MO_(4−n)X_(n)]tetrahedra with high polarizability anisotropy to cause the large enhancement of birefringence.These findings allow us to understand the microcosmic behaviors of covalent tetrahedra on pushing the current limitations and provide an optional functional group toward the maximum thresholds of three critical parameters for deep-UV frequency-doubling crystals.Finally,we conclude this Account with a better understanding of the positive roles of covalent tetrahedra in enhancing the optical performance and how they can facilitate the construction of high-performing deep-UV crystals.

Rb_(5)Ba_(2)(B_(10)O_(17))_(2)(BO_(2)):The formation of unusual functional [BO_(2)]^(-) in borates with deep-ultraviolet transmission window

The design and synthesis of new deep-ultraviolet(DUV)optical materials are important but challenging.It is well known that the polarizability anisotropy of linear[BO_(2)]^(−)is larger than those of[BO_(3)]^(3−)and[BO_(4)]^(5−),which is the better choice for exploring excellent optical materials.Here,we search for such crystals in borate systems based on the unusual fundamental structural unit[BO_(2)]^(−).By combining the linear[BO_(2)]^(−)with the traditional triangular[BO_(3)]^(3−)and tetrahedral[BO_(4)]^(5−)units,a new mixed metal borate,Rb_(5)Ba_(2)(B_(10)O_(17))_(2)(BO_(2))was obtained via high-temperature solution method.It exhibits excellent optical properties including a DUV transmission window(188 nm)and suitable birefringence(0.06).It also has good thermal stability and its crystal plates can be prepared easily.Furthermore,the strategies of designing borates with[BO_(2)]^(−)units have been proposed from the transformation of crystal framework and the preparation method.

An excellent deep-ultraviolet birefringent material based on[BO2]∞ infinite chains

Birefringent materials play indispensable roles in modulating the polarization of light and are vital in the laser science and technology.Currently,the design of birefringent materials operating in the deep-ultraviolet region(DUV,λ≤200 nm)is still a great challenge.In this work,we developed a new DUV birefringent crystal LiBO_(2) based on[BO2]∞infinite chains in the Li-B-O system,which simultaneously achieves the shortest UV cutoff edge(164 nm)and the largest birefringence(≥0.168 at 266 nm)among all the reported borate-based DUV birefringent materials.Single crystals of LiBO_(2) with dimensions up to Ø55×34 mm^(3) were grown by the Czochralski method,providing access to large-sized single crystal with low cost.Moreover,it has a high laser damage threshold and stable physicochemical properties.These outstanding characters unambiguously support that LiBO_(2) can be an excellent birefringent material for DUV application.