Rb_%283%29Hg_%282%29%28SO_%284%29%29_%283%29Cl新型紫外非线性光学晶体材料.pdf

第 38 卷 第 7 期 无 机 材 料 学 报 Vol.38 No.7 2023 年 7 月 Journal of Inorganic Materials Jul.,2023 收稿日期:2022-11-09;收到修改稿日期:2022-12-27;网络出版日期:2023-03-15 基金项目:国家自然科学基金(22222510,21975255);福建省自然科学基金(2021J011080,2021J01514);福建工程学院科研启动基金(GY-Z20042);中国科学院青年创新促进会(2019303)National Natural Science Foundation of China(22222510,21975255);Natural Science Foundation of Fujian Province(2021J011080,2021J01514);Startup Foundation of Fujian University of Technology(GY-Z20042);Youth Innovation Prmotion Association CAS(2019303)作者简介:宋云霞(1992),女,讲师.E-mail: SONG Yunxia(1992),female,lecturer.E-mail: 通信作者:颜 涛,副研究员.E-mail:;罗 敏,研究员.E-mail: YAN Tao,associate professor.E-mail:;LUO Min,professor.E-mail: 文章编号:1000-324X(2023)07-0778-07 DOI:10.15541/jim20220667 Rb3Hg2(SO4)3Cl 新型紫外非线性光学晶体材料 宋云霞1,韩颖磊2,颜 涛2,罗 敏2(1.福建工程学院 电子电气与物理学院,福州 350108;2.中国科学院 福建物质结构研究所,光电材料化学与物理重点实验室,福州 350002)摘 要:作为实现全固态激光器频率转换功能的关键材料,紫外非线性光学晶体发挥着不可替代的作用。设计兼具大的非线性光学系数、合适的双折射和宽带隙的紫外非线性光学晶体仍然是该领域亟待攻克的一个难题。由于具有宽的带隙,硫酸盐已成为紫外非线性光学晶体领域的一个重要研究方向。SO4四面体基团具有接近非极性的 Td对称性,使其极化率各向异性和二阶极化率较小,因而对晶体的非线性系数和双折射贡献很小。通常引入畸变程度高的阳离子多面体可以增加晶体的非线性效应和双折射。本工作将易于形成畸变多面体的 Hg2+离子引入到硫酸盐体系中,采用高温熔体法合成出新型非线性光学晶体材料 Rb3Hg2(SO4)3Cl。该晶体属于单斜晶系,空间群为 P21,晶胞参数为 a=0.78653(2)nm,b=0.97901(2)nm,c=1.00104(3)nm,=110.95(3),Z=2。其晶体结构由SO4四面体、HgO5和HgO4Cl多面体以角共享的方式连接形成空间网状结构,而 Rb+填充在孔洞中。Rb3Hg2(SO4)3Cl 晶体的粉末倍频效应为 1.5 倍 KDP,且能够在可见光区实现相位匹配。紫外漫反射光谱测试表明,紫外截止边为 251 nm,对应光学带隙为 4.94 eV。利用偏光显微镜确定该晶体在 546.1 nm 处的双折射为 0.04。此外,第一性原理计算表明,晶体的非线性系数主要来源于扭曲的HgO5、HgO4Cl和SO4多面体。上述结果表明,Rb3Hg2(SO4)3Cl 是具有潜在应用前景的紫外非线性光学晶体材料。关 键 词:紫外;汞基硫酸盐;非线性光学晶体;晶体结构；非线性光学 中图分类号:TQ174 文献标志码:A New Ultraviolet Nonlinear Optical Crystal Rb3Hg2(SO4)3Cl SONG Yunxia1,HAN Yinglei2,YAN Tao2,LUO Min2(1.School of Electronic,Electrical Engineering and Physics,Fujian University of Technology,Fuzhou 350108,China;2.Key Laboratory of Optoelectronic Materials Chemistry and Physics,Fujian Institute of Research on the Structure of Matter,Chinese Academy of Sciences,Fuzhou 350002,China)Abstract:Ultraviolet(UV)nonlinear optical(NLO)crystals play an irreplaceable role as the key materials to realize the frequency conversion for all solid state lasers.To date,it is still difficult to design UV NLO crystals with large second harmonic generation(SHG)coefficients,moderate birefringences and wide band gaps.Benefiting from the large band gap,sulfate has become an important research direction of UV NLO crystals.However,since SO4 is isotropic tetrahedral building units with nearly nonpolar Td symmetry,it exhibits small microscopic second order 第 7 期 宋云霞,等:Rb3Hg2(SO4)3Cl 紫外非线性光学晶体材料 779 polarizability and polarizability anisotropy,which tends to result in a weak SHG effect and small birefringence.In this work,we introduced Hg2+ions that are easy to form distorted polyhedrons into the sulfates,resulting in a new NLO material,Rb3Hg2(SO4)3Cl.It crystallizes in a monoclinic space group(P21)with the lattice parameters a=0.78653(2)nm,b=0.97901(2)nm,c=1.00104(3)nm,and=110.95(3)(Z=2).Structure of Rb3Hg2(SO4)3Cl consists of SO4 tetrahedra,HgO5 and HgO4Cl polyhedral,which connected by a common corner to form a spatial 3D network.All the Rb atoms reside in the cavity of 3D network.The powder SHG measurement proposed by Kurtz and Perry indicates that Rb3Hg2(SO4)3Cl is a phase-matchable material in the visible region and exhibits a moderate SHG response about 1.5 times that of KH2PO4(KDP).In addition,the UV-Vis-NIR diffuse reflectance spectral measurement indicates that Rb3Hg2(SO4)3Cl has a short UV cut-off edge of 251 nm,corresponding to the band gap of 4.94 eV.Its polarizing microscope measurement reveals that Rb3Hg2(SO4)3Cl has a moderate birefringence(The birefringence of Rb3Hg2(SO4)3Cl crystal at 546.1 nm is 0.04).Moreover,first-principles calculations uncover that the distorted HgO5,HgO4Cl and SO4 polyhedral are responsible for its SHG effect.Our study shows that Rb3Hg2(SO4)3Cl may have potential applications as a UV NLO crystal.Key words:ultraviolet;Hg-based sulfate;nonlinear optical crystal;crystal structure;nonlinear optical 全固态紫外激光器在材料微加工、激光医疗、光刻等方面具有重要的应用1。在全固态紫外激光器中,紫外非线性光学晶体以其独特的变频能力成为核心元件。因此,迫切需要开发高性能的紫外(2(I)0.0304/0.0703 R/wR(all data)0.0317/0.0712 GOF on F2 1.023 Largest diff.peak and hole(e/nm3)1.22103 and 1.76103 三 类SO4 多面体 的 SO 键 长 范 围 为 0.1437 0.1516 nm,OSO 键角范围为 105.34111.60;分别形成不规则的四面体。HgO5多面体的 HgO 键长范围为 0.21270.2502 nm,OHgO 键角范围为77.06138.77;HgO4Cl多面体的HgO键长范围为0.21080.2838 nm,OHgO 键角范围为 77.53 173.46,分别形成不规则的多面体。三种多面体以角共享的方式连接,如图 4(b)所示。Rb+填充在孔洞中,最终形成空间网状结构,如图 4(c)所示。2.5 紫外可见漫反射光谱 Rb3Hg2(SO4)3Cl 的紫外漫反射光谱如图 5 所示。分析可知其紫外截止边为 251 nm,对应光学带隙为4.94 eV。相较于 HgSO4晶体(300 nm),在含 Hg 硫酸盐内引入卤素和碱金属,紫外截止边显著降低,带隙明显拓宽,说明引入卤素可以使含 Hg 硫酸盐晶体的光谱发生有效蓝移。2.6 双折射 由于晶体尺寸太小,采用配备 546.1 nm 可见光光源的偏光显微镜进行双折射测量,计算公式为:eo|RnnDnD ,其中:R 为光程差,ne为 e光折射率,no为 o 光折射率,n 为双折射率,D 为被测晶体沿入射光方向的长度。测试结果如图 6 所示,测量的光程差为1541 nm,晶体厚度为36.8 m,利用公式计算可得,Rb3Hg2(SO4)3Cl 的双折射为0.04546.1nm。2.7 粉末倍频效应 按照 Kurtz 和 Perry 提出的方法31,将待测样品Rb3Hg2(SO4)3Cl 和标准样品 KDP 研磨成粉末后过筛,筛选出颗粒度分别为 2044、4474、74105、105149、149210 m 的粉末,装入载样盒内。以Nd3+:YAG 调 Q 激光器输出的 1064 nm 激光作为基频光,依次通过载样盒内不同粒径的粉末。测试采集的数据由 DS1052E 50-MHz 示波器(美国 RIGOL公司)显示电压值,其大小与倍频光强度成正比。粉末倍频强度的变化可以通过示波器的电压信号来反映,其强度的变化趋势可判断晶体是否能实现相位匹配。图 4 Rb3Hg2(SO4)3Cl 的晶体结构 Fig.4 Crystal structure of Rb3Hg2(SO4)3Cl(a)Coordination environment of S and Hg ions;(b)Stacking of SO4,HgO5 and HgO4Cl polyhedra within a single cell;(c)Spatial network structure 782 无 机 材 料 学 报 第 38 卷 图 5 Rb3Hg2(SO4)3Cl 的紫外可见近红外漫反射光谱图 Fig.5 UV-Vis-NIR diffuse reflectance spectrum of Rb3Hg2(SO4)3Cl 图 6 Rb3Hg2(SO4)3Cl 的双折射测试结果 Fig.6 Images of Rb3Hg2(SO4)3Cl birefringence (a)Crystals in polarized light;(b)Completed extinction of the crystal with forward compensation;(c)Completed extinction of the crystal with reverse compensation;(d)Thickness of measured crystal Rb3Hg2(SO4)3Cl 的粉末倍频测试结果如图 7 所示,在 1064 nm 激光下的倍频系数为 1.5 倍 KDP,同时发现倍频强度随粉末粒径而逐渐增加,表明该晶体可实现相位匹配。考虑到 Rb3Hg2(SO4)3Cl 是极性材料,为了更好地理解其倍频响应的起源,基于键价法进行了偶极矩分析。计算结果如表 2 所示。每 图 7 Rb3Hg2(SO4)3Cl 的粉末倍频效应与颗粒度的关系 Fig.7 SHG measurements of Rb3Hg2(SO4)3Cl ground crystals(red)with KDP(black)as a reference 表 2 Rb3Hg2(SO4)3Cl 的偶极矩 Table 2 Calculated dipole moments of Rb3Hg2(SO4)3Cl Dipole moment/D Species x y z Total HgO5(type)1.2770.673 0.563 1.549 HgO5(type)1.2770.673 0.5631.549 HgO 0 1.346 0 1.346 HgO4Cl(type)0.2703.231 1.5913.611 HgO4Cl(type)0.2623.224 1.5913.605 HgO&HgCl 0.0086.455 0 6.455 SO4(type)0.9280.103 2.0472.250 SO4(type)1.1771.609 0.6072.084 SO4(type)1.7670.702 1.5052.425 SO4(type)0.9280.102 2.0392.243 SO4(type)1.7650.702 1.5122.428 SO4(type)1.1761.611 0.6082.085 SO 0.0011.611 0.0141.611 个晶胞中HgO5、HgO4Cl和SO4单元沿 y 轴的净偶极矩分别为 1.346 D、6.455 D 和 1.611 D,而沿 x和 z 方向的净偶极矩由于对称性几乎相互抵消而为零。因此,HgO5、HgO4Cl和SO4多面体沿 y 方向的微观极化,是Rb3Hg2(SO4)3Cl宏观极化的来源,亦即倍频系数的主要来源。2.8 理论计算分析 理论计算方法采用的是 CASTEP 模块下基于密度泛函理论的平面波赝势法32-35。采用的软件为Material studio,计算光学性质及电子密度的泛函为GGA36-37泛函,计算能带结构的泛函为 PBE0 杂化泛函38。参与计算的原子轨道分别为:O:2s22p4,S:3s23p44s2,Cl:3s23p5,Rb:4p65s1,Hg:5p65d106s2。所采用的 X 射线单晶结构数据未做进一步优化,其余参数设置参考 CASTEP 程序的默认值。图 8(a)为计算的 Rb3Hg2(SO4)3Cl 能带图,利用PBE0 泛函计算的带隙为 5.01 eV,略高于实验值,但仍在误差允许范围内。后续光学计算采用 GGA计算得到的带隙为 2.83 eV,因此需设置剪刀值2.11 eV。图 8(b)显示了总的和部分的态密度图,其中价带2510 eV 范围内的能态主要由 Rb5s、Cl3s、S3s、S3p 和 O2s 组成;价带顶100 eV 范围内的能态主要由 Hg5d、Rb5p、Cl3p、S3s、S3p 和O2p 组成;导带底 57 eV 主要由 Hg6s 组成;导带720 eV 主要由 Hg6p、S3s、S3p 和 O2p 组成。25 10 eV 范围内 S 与 O 的轨道发生强烈的杂化,这是由SO4多面体内原子的强共价相互作用引起的;而100 eV 范围内 Hg、Cl 与 O 的轨道发生强烈的杂化,这是由HgO5和HgO4Cl多面体内原子第 7 期 宋云霞,等:Rb3Hg2(SO4)3Cl 紫外非线性光学晶体材料 783 的强共价相互作用引起的。此外,价带(VB)的最大值和导带(CB)的最小值主要由 O2p、S3p、Cl3p、Hg6s 和 Hg5d 组成。由于非线性光学性质主要与禁带附近的电子跃迁有关,带隙附近的态密度图表明Rb3Hg2(SO4)3Cl 的倍频效应是由扭曲的HgO5、HgO4Cl和SO4多面体贡献的。同样,计算得到的电子密度图显示,电子主要分布在 Hg、S、O、Cl原子周围,说明倍频的贡献是在 HgO、HgCl 和SO 键上(图 9)。图 8 Rb3Hg2(SO4)3Cl 的能带结构及态密度分布 Fig.8 Energy band structures and electronic density distribu-tion of Rb3Hg2(SO4)3Cl(a)Diagram of calculated electronic band structures;(b)Diagrams of calculated PDOS 图 9 Rb3Hg2(SO4)3Cl 计算的电子密度图 Fig.9 Calculated electron density diagram of Rb3Hg2(SO4)3Cl 图 10 为计算的 Rb3Hg2(SO4)3Cl 晶体的二阶非线性光学系数。由于空间群 P21对应的点群为 2,根据 Kleinman对称约束,二阶非线性系数存在四个独立的张量:d21,d22,d23,d25。从图中可以看出,在1.16 eV(1064 nm)处,d25的非线性光学系数最大,数值为0.704 pm/V,与实验测量的倍频响应相当。图 10 Rb3Hg2(SO4)3Cl 计算的非线性光学系数随能量的变化曲线 Fig.10 Calculated SHG coefficients of Rb3Hg2(SO4)3Cl 图 11 为计算的折射率色散曲线。Rb3Hg2(SO4)3Cl属于双轴晶体,折射率关系为 nxnynz。三个方向在546.1 nm 处的折射率分别为 1.665、1.660、1.625。计算得到的双折射值为 0.04546.1 nm,与实验值相近。图 11 计算得到的 Rb3Hg2(SO4)3Cl 的折射率色散曲线 Fig.11 Calculated refractive index dispersion curves of Rb3Hg2(SO4)3Cl 3 结论 本工作采用高温熔体法制备了新型非线性光学晶体 Rb3Hg2(SO4)3Cl。粉末倍频测试表明,该晶体具有合适的倍频系数(1.5 倍 KDP),并且能够实现可见光波段的相位匹配。紫外可见近红外漫反射光谱表明,晶体具有较宽的紫外透过波段,截止784 无 机 材 料 学 报 第 38 卷 边为 251 nm。利用偏光显微镜测得晶体具有合适的双折射:0.04546.1 nm。理论计算分析可知,晶体的倍频响应以及双折射来源于畸变的HgO5、HgO4Cl 和 SO4 多 面 体。上 述 研 究 表 明Rb3Hg2(SO4)3Cl 是一种潜在的紫外非线性光学晶体材料。参考文献:1 SAVAGE N.Ultraviolet lasers.Nature Photonics 2007,1:83.2 LUO M,LIANG F,SONG Y,et al.M2B10O14F6(M=Ca,Sr):two noncentrosymmetric alkaline earth fluorooxoborates as promising next-generation deep-ultraviolet nonlinear optical materials.Jour-nal of the American Chemical Society,2018,140:3884.3 SONG Y,LUO M,YE N,Ultraviolet nonlinear optical crystals in-conjugated system.Chinese Journal of Structural Chemistry,2020,39:105.4 XIA F,WANG F,HU H,et al.Application of second harmonic generation in characterization of 2D materials.Journal of Inor-ganic Materials,2021,36(10):1022.5 SONG Y,LIANG F,TIAN H,et al.Molecular engineering design of the first Sr2Be2B2O7-type fluoride carbonates AMgLi2(CO3)2F(A=K,Rb)as deep-ultraviolet birefringent crystal.Acta Chimica Sinica,2022,80(2):105.6 LIU Y,LIN Z,LI Y,et al.Nonpolar Na10Cd(NO3)4(SO3S)4 exhibits a large second-harmonic generation.CCS Chemistry,2021,4:526.7 TIAN H,LIN C,ZHAO X,et al.Design of a new ultraviolet nonlinear optical material KNO3SO3NH3 exhibiting an unexpected strong second harmonic generation response.Materials Today Physics,2022,28:100849.8 MUTALIPU M,ZHANG M,WU H,et al.Ba3Mg3(BO3)3F3 poly-morphs with reversible phase transition and high performances as ultraviolet nonlinear optical materials.Nature Communications,2018,9:3089.9 ZHAO S,GONG P,BAI L,et al.Beryllium-free Li4Sr(BO3)2 for deep-ultraviolet nonlinear optical applications.Nature Communi-cations,2014,5:4019.10 ZOU G,LIN C,JO H,et al.Pb2BO3Cl:a tailor-made polar lead borate chloride with very strong second harmonic generation.Angewandte Chemie International Edition,2016,55:12078.11 YU H,KOOCHER N Z,RONDINELLI J,et al.Pb2BO3I:a borate iodide with the largest second-harmonic generation(SHG)response in the KBe2BO3F2(KBBF)family of nonlinear optical(NLO)ma-terials.Angewandte Chemie International Edition,2018,57:6100.12 LUO M,SONG Y,LIANG F,et al.Pb2BO3Br:a novel nonlinear optical lead borate bromine with a KBBF-type structure exhibiting strong nonlinear optical response.Inorganic Chemistry Frontiers,2018,5:916.13 Zou G H,Ye N,Huang L,et al.Alkaline-alkaline earth fluoride carbonate crystals ABCO3F(A=K,Rb,Cs;B=Ca,Sr,Ba)as nonlinear optical materials.Journal of the American Chemical Society,2011,133(49):20001.14 TRAN T,HE J,RONDINELLI J M,et al.RbMgCO3F:a new beryllium-free deep-ultraviolet nonlinear optical material.Journal of the American Chemical Society,2015,137:10504.15 DONG X,HUANG L,LIU Q,et al.Perfect balance harmony in Ba2NO3(OH)3:a beryllium-free nitrate as a UV nonlinear optical material.Chemical Communications,2018,54(45):5792.16 SHAN P,SUN T,CHEN H,et al.Crystal growth and optical characteristics of beryllium-free polyphosphate,KLa(PO3)4,a pos-sible deep-ultraviolet nonlinear optical crystal.Scientific Reports.2016,6:25201.17 YU P,WU L,ZHOU L,et al.Deep-ultraviolet nonlinear optical crystals:Ba3P3O10X(X=Cl,Br).Journal of the American Chemical Society,2014,136(1):480.18 YU H,YOUNG J,WU H,et al.M4Mg4(P2O7)3(M=K,Rb):Structural engineering of pyrophosphates for nonlinear optical applications.Chemistry of Materials,2017,29:1845.19 CHEN J,XIONG L,CHEN L,et al.Ba2NaClP2O7:unprecedented phase matchability induced by symmetry breaking and its unique fresnoite-type structure.Journal of the American Chemical Society,2018,140:14082.20 LU X,CHEN Z,SHI X,et al.Two pyrophosphates with large bire-fringences and second-harmonic responses as ultraviolet nonlinear optical materials.Angewandte Chemie International Edition,2020,59(40):17648.21 DONG X,HUANG L,HU C,et al.CsSbF2SO4:an excellent ultra-violet nonlinear optical sulfate with a KTiOPO4(KTP)-type struc-ture.Angewandte Chemie International Edition,2019,58:6528.22 HE F,DENG Y,ZHAO X,et al.RbSbSO4Cl2:an excellent sulfate nonlinear optical material generated due to the synergistic effect of three asymmetric chromophores.Journal of Materials Chemistry C,2019,7:5748.23 HE F,WANG Q,HU C,et al.Centrosymmetric(NH4)2SbCl(SO4)2 and non-centrosymmetric(NH4)SbCl2(SO4):synergistic effect of hydrogen-bonding interactions and lone-pair cations on the frame-work structures and macroscopic centricities.Crystal Growth&Design,2018,18:6239.24 SANKAR R,RAGHAVAN C M,BALAJI M,et al.Synthesis and growth of triaquaglycinesulfatozinc(II),Zn(SO4)(C2H5NO2)(H2O)3,a new semiorganic nonlinear optical crystal.Crystal Growth&Design,2007,7(2):348.25 SONG Y,HAO X,LIN C,et al.Two tellurium(IV)-based sulfates exhibiting strong second harmonic generation and moderate bire-fringence as promising ultraviolet nonlinear optical materials.Inor-ganic Chemistry,2021,60(15):11412.26 LI Y,YIN C,YANG X,et al.A nonlinear optical switchable sulfate of ultrawide bandgap.CCS Chemistry.2020,3:2298.27 LI Y,LUO J,JI X,et al.A short-wave UV nonlinear optical sulfate of high thermal stability.Chinese Journal of Structural Chemistry,2020,39(3):485.28 SUN Y,LIN C,TIAN H,et al.A2BeS2O8(A=NH4,K,Rb,Cs)deep ultraviolet nonlinear optical crystals.Chemistry of Materials,2022,34(8):3781.29 HAN Y,ZHAO X,XU F,et al.HgSO4:an excellent mid-infrared sulfate nonlinear optical crystal with wide band gap and strong second harmonic generation response.Journal of Alloys and Com-pounds,2022,902:163727.30 BENGT B.The crystal structures of Tl3(Hg(SO4)2)(HgSO4Cl)and Rb3(Hg(SO4)2)(HgSO4Cl).Acta Chemica Scandinavica,Series A:Physical and Inorganic Chemistry,1976,30:241.31 KURTZ S,PERRY T.A powder technique for evaluation of nonli-near optical materials.Journal of Applied Physics,1968,39(8):3798.32 KOHN W.Nobel Lecture:electronic structure of matter-wave fun-ctions and density functionals.Reviews of Modern Physics,1999,71(5):1253.33 MILMAN V,WINKLER B,WHITE J A,et al.Electronic structure,properties and phase stability of inorganic crystals:a pseudopoten-tial plane-wave study.International Journal of Quantum Chemistry,2000,77(5):895.34 YUAN G,MA X,HE H,et al.Plane strain on band structures and photoelectric properties of 2D monolayer MoSi2N4.Journal of Inorganic Materials,2022,37(5):527.35 SEGALL M D,LINDAN P J D,PROBERT M J,et al.First-principles simulation:Ideas,illustrations and the CASTEP code.Journal of Physics-Condensed Matter,2002,14(11):2717.36 PERDEW J P,BURKE K,ERNZERHOF M.Generalized gradient approximation made simple.Physical Review Letters,1997,78(7):1396.37 WEN Z,HUANG B,LU T,et al.Pressure on the structure and thermal properties of PbTiO3:first-principle study