Cation-anion synergetic interactions achieving tunable birefringence in quasi-one-dimensional antimony(Ⅲ)fluoride oxalates

Birefringent materials with large optical anisotropy,which can be used to modulate the polarization of light,play a key role in laser techniques and science.However,the exploration studies of new,superior birefringent materials develop extremely slowly due to the lack of effective guidelines for rational design.Herein,three antimony(Ⅲ)fluoride oxalates,namely,Na_(2)Sb_(2)(C_(2)O_(4))F_(6),K_(2)Sb_(2)(C_(2)O_(4))F_(6),and Cs_(2)Sb_(2)-(C_(2)O_(4))_(2)F_(4)·H_(2)O,were successfully synthesized through a rational combination ofπ-conjugated C_(2)O_(4)^(2-)anions and Sb^(3+)cations with stereochemically active lone pairs.These oxalates feature unique quasi-one-dimensional chain structures that induce large optical anisotropy.Remarkably,Cs_(2)Sb_(2)(C_(2)O_(4))_(2)-F_(4)·H_(2)O exhibits the largest birefringence(0.325@546 nm)among all reported antimony(Ⅲ)-based oxysalts.Detailed structural analysis and theoretical calculations confirmed that the optical anisotropy of these oxalates could be tuned through the synergetic interactions of templated cations and anionic functional groups.This work may open the door to efficiently designing excellent birefringent materials and guide the further discovery of other novel structure-driven functional materials.

LiGaF2(IO3)2:A mixed-metal gallium iodate-fluoride with large birefringence and wide band gap

The first mixed alkali-metal gallium iodate-fluoride,namely,LiGaF2(IO3)2,was successfully obtained under hydrothermal conditions.The structure of LiGaF2(IO3)2 features a novel two-dimensional(2D)[GaF2(IO3)2]layer composed of[Ga2F4(IO3)6]4 dimers further bridged by(IO3)groups.LiGaF2(IO3)2 exhibits a wide band gap of 4.33 eV,corresponding to the ultraviolet(UV)absorption edge of 230 nm.Calculations of linear optical property revealed that LiGaF2(IO3)2 has a remarkably large birefringence of 0.181@1064 nm and 0.206@532 nm,indicating that it is a potential birefringent material that could be used from visible to UV region.This study provides a new method for the future discovery of promising optical crystals.