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Abstract Birefringent materials are widely used in various advanced optical systems, owing to their vital role in creating and controlling polarized light. Currently, Sn²⁺‐based compounds containing stereochemically active lone‐pair (SCALP) cations are extensively investigated and considered as one class of promising birefringent materials. To solve the problem of relatively narrow bandgap of Sn²⁺‐based compounds, alkali metals and multiple halogens are introduced to widen the bandgap during the research. Based on this strategy, four new Sn²⁺‐based halides, A₂Sn₂F₅Cl and ASnFCl₂(A = Rb and Cs), with large birefringence, short ultraviolet (UV) cutoff edge, and wide transparent range are successfully found. The birefringences of A₂Sn₂F₅Cl (A = Rb and Cs) are 0.31 and 0.28 at 532 nm, respectively, which are among the largest in Sn‐based halide family. Remarkably, A₂Sn₂F₅Cl possess relatively shorter UV cutoff edge (<300 nm) and broad infrared (IR) transparent range (up to 16.6 µm), so they can become promising candidates as birefringent materials applied in both UV and IR regions. In addition, a comprehensive analysis on crystal structures and structure–property relationship of metal Sn²⁺‐based halides is performed to fully understand this family. Therefore, this work provides insights into designing birefringent materials with balanced optical properties. 

Pb₂Ga₃F₆(SeO₃)₂X₃·2H₂O achieve a better balance between the large SHG effect and wide band gap in the current HTO family. 

Nine new rare earth magnesium-containing thiosilicates of the formula RE3Mg0.5SiS7 (Ln = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er) were synthesized in an alkali halide flux using the boron chalcogen mixture (BCM) method. Crystals of high quality were produced, and their structures were determined by single-crystal X-ray diffraction. The compounds crystallize in the hexagonal crystal system in the P63 space group. Phase pure powders of the compounds were used for magnetic susceptibility measurements and for second harmonic generation (SHG) measurements. Magnetic measurements indicate that Ce3Mg0.5SiS7, Sm3Mg0.5SiS7, and Dy3Mg0.5SiS7 exhibit paramagnetic behavior with a negative Weiss temperature over the 2−300 K temperature range. SHG measurements of La3Mg0.5SiS7 demonstrated SHG activity with an efficiency of 0.16 times the standard potassium dihydrogen phosphate (KDP).