Designing a Deep-UV Nonlinear Optical Fluorooxosilicophosphate

摘要

Structures composed of SiO_xF_(6-x) (x = 1, 2, 3, 4, 5) or SiO_xF_(4-x) (x = 1, 2, 3) species have thus far been observed in only a few compounds, and their functional properties are completely unknown in silicate chemistry. By introducing the least electronegative element, cesium, and the most electronegative element, fluorine, into the silicophosphate system, we successfully designed the first noncentrosymmetric fluorooxosilicophosphate with Si-F bonds, CsSiP_2O_7F, whose structure consists of an unprecedented SiP_2O_(10)F moiety containing hexacoordinate SiO_5F species. The experimental results highlight CsSiP_2O_7F as the first fluorooxosilicophosphate deep-UV nonlinear optical (NLO) material. The first-principles calculations reveal that the SiP_2O_(10)F moiety is a new type of NLO-active unit and that both cesium and fluorine increase the deep-UV transparency of CsSiP_2O_7F. This work provides a new source of deep-UV NLO materials and insights into obtaining noncentrosymmetric structures that are indispensable to functional materials in nonlinear optics, piezoelectricity, ferroelectric, pyroelectricity, etc.