An unprecedented planar π-conjugated [B₂P₅]⁵⁻ group with ultra-large birefringence and nonlinearity: an ab initio study

Abstract

Ten new ternary fluorooxoborate structures (B2O2F2, Ⅰ-Ⅹ) were obtained from firstprinciples prediction. Coplanar aligned triangle structure units [BO2F] 2and [BOF2]like [BO3] 3in borates were found from the computational simulation. We identified new covalent coordination patterns of the F atom connected with the B atoms which are located in the bridging site, -B--F--B-. Besides, one molecular crystal with [B4O4F4] molecular unit was attached. As a branch of inorganic crystal materials, 1-2 fluorooxoborates exhibit a diverse structural chemistry leading to fascinating properties and are used widely in many fields, such as ionic conductor for solid state batteries, 3 birefringent crystals for fiber optics isolators, 4-8 and nonlinear optical (NLO) frequency conversion material. 9-12 In particular, NH 4 B 4 O 6 F, 10 CsB 4 O 6 F, 11 etc. are promising NLO materials for next generation deep-ultraviolet (DUV) all-solid-state laser devices. 12 The general structure types of fluorooxoborates are as follow: A-site cations with oxyfluoride chromophores [BO x F 4−x ] (x = 1, 2, 3), sometimes with [BO X ] (x=3, 4) existed in the structure, A-site cations can be alkali metals, alkaline-earth metals, posttransition metals, such as NaBOF

The Rise of Infrared Nonlinear Optical Pnictides: Advances and Outlooks

“…But over the past few decades, most of the research in this field is concentrated in the non‐centrosymmetric metal chalcogenides, [6] which results in many IR‐NLO chalcogenides with excellent comprehensive properties, such as BaGa 4 S 7 , [7] BaGa 4 Se 7 , [8] SnGa 4 S 7 , [9] Sn 2 Ga 2 S 5 , [10] Hg 3 P 2 S 8 , [11] γ‐NaAsSe 2 , [12] Li 2 CdGeS 4 , [13] α‐Li 2 ZnGeS 4 , [14] La 4 InSbS 9 , [15] Na 2 ZnGe 2 S 6 , [16] CsGa 2 SnSe 6 , [17] Li 2 ZnSiS 4 , [18] Li 2 BaGeS 4 , [19] CuHgPS 4 , [20] BaHgGeSe 4 , [21] Sr 5 ZnGa 6 S 15 , [22] [Li 2 Cs 2 Cl][Ga 3 S 6 ], [23] [Rb 3 Br][PGa 3 S 8 ], [24] [CsBa 2 Cl][Ga 4 S 8 ], [25] [Ba 4 Cl 2 ][ZnGa 4 S 10 ] [26] and so on and so forth. Compared with a large number of research results in IR‐NLO chalcogenides, only a few IR‐NLO pnictides are discovered in this area [28–61] and the major research works are still focused on classical binary or ternary semiconductors, such as GaAs, [27] ZnGeP 2 , [5] CdSiP 2 [7] and CdGeAs 2 [29] . Generally, pnictides exhibit small band gaps (E g <2.5 eV) and are difficult to synthesize, which limit their development in the IR‐NLO field.…”

“…Generally, pnictides exhibit small band gaps (E g <2.5 eV) and are difficult to synthesize, which limit their development in the IR‐NLO field. The challenges in synthesis for pnictides mainly comes from the following aspects: (1) high vapor pressure of P and reaction temperature, which could make the silica tubes crack or explode during reactions; (2) red phosphorus with insufficient reaction can be easily converted into white phosphorus, which is easy to produce toxic gas in the air; (3) an excellent stable binary pnictide admixtures is often formed in the reaction process, which inhibits the further progress of the reaction [37,43,49] . But it is undeniable that pnictides commonly possess bigger d eff compared with chalcogenide systems.…”

Series of Crystals with Giant Optical Anisotropy: A Targeted Strategic Research

“…Functional modules (FMs), [11,12] which are building blocks of the microstructure and the main source of physicochemical properties,are indispensable condition for functional materials.C urrently,m ost typical birefringence-active FMs are the units with p-conjugated orbitals such as [ 3À ,a nd the groups containing lone-pair electrons or d 10 electrons. [10,[13][14][15][16][17][18][19][20][21] At the same time,i solated parallel distribution, quasi-1D chain, and quasi-2D plane of anionic groups are proper arrangement modes in favor of the superposition of microscopic effects in FMs. [9,22,23] To date,the experimentally birefringent maximum in the alkali/alkaline earth metal carbonates is 0.164 at 1064 nm (calcite), [9] 0.14 at 1064 nm (Ca(BO 2 ) 2 )i nt he alkali/alkaline earth metal borates.…”

“…Meanwhile, many studies were carried out to push forward. For instance, benefited from π‐conjugated [C 3 N 3 O 3 ] 3− units, [7, 8, 22] cyanurate β‐Sr 3 (C 3 N 3 O 3 ) 2 presents a large birefringence of 0.35; [7] BaTiS 3 has a giant birefringence of 0.76, which is derived from the quasi‐one‐dimensional (quasi‐1D) framework and constituent ions with large polarizability difference; [9] Na 2 BP 2 possesses a giant birefringence of 0.68 attributed to the coplanar π‐conjugated [B 2 P 5 ] 5− group [10] . However, owing to the limited applicable wavelength and difficulties in crystal growth, birefringent materials with large optical anisotropy are still to be explored.…”

“…Functional modules (FMs), [11, 12] which are building blocks of the microstructure and the main source of physicochemical properties, are indispensable condition for functional materials. Currently, most typical birefringence‐active FMs are the units with π‐conjugated orbitals such as [CO 3 ] 2− , [BO 3 ] 3− , [B 3 O 6 ] 3− , [C 3 N 3 O 3 ] 3− , and the groups containing lone‐pair electrons or d 10 electrons [10, 13–21] . At the same time, isolated parallel distribution, quasi‐1D chain, and quasi‐2D plane of anionic groups are proper arrangement modes in favor of the superposition of microscopic effects in FMs [9, 22, 23] .…”