Stereochemically active lone-pair (SCALP) cations are one attractive type of nonlinear optical (NLO)-active units because of their large microcosmic polarizability and anisotropy. Currently, the single and/or dual lone-pair cation-based noncentrosymmetric (NCS) oxides have been extensively investigated and verified to be one class of outstanding NLO materials. From the perspective of function optimization, the integration of three kinds of SCALP cations into one crystal may synergistically improve the NLO properties, which is greatly expected but unexplored to date. Herein, by introducing flexible metal halide bonds to guarantee the stereochemical activity and overcome the energetically favorable antiparallel arrangements of lone-pair cations, the first type of three lone-pair-cation (Pb 2+ , Bi 3+ , and Se 4+ )-coexisting NCS oxides PbBi(SeO 3 ) 2 F (I) and Pb 2 Bi(SeO 3 ) 2 Cl 3 (II) was obtained. As expected, both compounds show outstanding NLO properties, such as the strong second-harmonic-generation signal (10.5× and 13.5 × KDP), large birefringence (0.103 and 0.186), relatively wide energy band gaps (3.75 and 3.45 eV), and good physicochemical stability. Theoretical calculations demonstrated the effect of three lone-pair-cation-based polyhedra and the halide anion on NLO properties.

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Two bismuth iodates via tuning of alkali–metal ions reveal a structural transition from the centrosymmetric chain to a non-centrosymmetric double layer.

Excellent nonlinear optical materials simultaneously meet the requirements of large SHG response, phase‐matching capability, wide transparency windows, considerable energy band‐gap, good thermal stability and structure stability. Herein, two new promising nonlinear optical (NLO) crystals LiMII(IO3)3 (MII=Zn and Cd) are rationally designed by the aliovalent substitution strategy from the commercialized α‐LiIO3 with the perfect parallel alignment of IO3 groups. Compared with parent α‐LiIO3 and related AI2MIV(IO3)6, the title compounds exhibit more stable covalent 3D structure, and overcome the racemic twinning problem of AI2MIV(IO3)6. More importantly, both compounds inherit NLO‐favorable structure merits of α‐LiIO3 and show larger SHG response (≈14× and ≈12×KDP), shorter absorption edge (294 and 297 nm) with wider energy band‐gap (4.21 and 4.18 eV), good thermal stability (460 and 430 °C), phase‐matching behaviors, wider optical transparency window and good structure stability, achieving an excellent balance of NLO properties.

Metal iodates with large polarizability have long been overlooked as potential birefringent materials. By introducing highly coordinated Ba- and La-based MO n Cl m polyhedra into an iodate system, we present herein five birefringent materials of metal iodate chlorides, namely, Ba­(IO3)Cl (1), Ba­(IO3)­Cl­(H2O) (2), Ba7(IO3)5Cl9 (3), La­(IO3)2Cl (4), and La2(IO3)5Cl (5), which exhibit diversified structures with diverse M x Cl y and M x (IO3) y structural motifs and tunable birefringence. In 1, high coordinate Ba ions are respectively linked by iodates and chlorides to form two-dimensional (2D) cationic [Ba­(IO3)] n and three-dimensional (3D) open [BaCl] n structural motifs that are fused together to finish a 3D dense structure. Compared with 1, Ba ions in 2 are bridged by water molecules into dimers that are linked by chlorides into 2D [BaCl­(H2O)] n double layers, which are further linked by iodates into a 3D framework. In 3, eight Ba ions and four chlorides form a [Ba8Cl6 1] cube, and adjacent cubes are diagonally corner-shared to form a [Ba7Cl6] n chain that is attached by additional chlorides to achieve anionic [Ba7Cl9] n chains. Adjacent [Ba7Cl9] n chains are bridged by iodates into a 3D framework. 4 exhibits a 3D framework alternately composed of [La3(IO3)6] n sandwich-type triple layers and [LaCl2] zigzag chains. High coordinate La ions in 5, with LaO9 and LaO8Cl coordination geometries, are linked by iodates into a complicated 3D framework containing La–O chains of edge-shared LaO9 polyhedra. Theoretical calculations indicate that 1 and 2 possess larger birefringences of 0.118 and 0.106, while 4 and 5 have smaller values of 0.038 and 0.045 at 1064 nm, which is contrary to unit volume density of IO3 groups but can be rationalized by spatial orientation of IO3 groups. Band structure calculations indicate that IO3 groups and Cl– determine the optical properties of these compounds.