Deep-ultraviolet (UV) nonlinear optical materials play a vital role in a variety of high-tech scientific instruments. Traditionally, the sources of these materials were usually limited to π-conjugated systems such as borates and carbonates, while the non-π-conjugated system such as phosphates and silicates is relatively unexplored.
In a study published in J. Am. Chem. Soc., a research group led by Prof. LUO Junhua and Prof. ZHAO Sangen from Fujian Institute of Research on the Structure of Matter (FJIRSM) of Chinese Academy of Sciences, reported a new non-π-conjugated nonlinear optical fluorooxosilicophosphate CsSiP2O7F, which is the first non-centrosymmetric fluorooxosilicophosphate with Si-F bonds.
The researchers found that the introduction of the element cesium with the least electronegative property and the element fluorine with the largest electronegative helps to form the non-centrosymmetric structure of CsSiP2O7F. In this structure, the element cesium forms locally asymmetric CsO5F2 polyhedra and element fluorine forms SiO5F species to lower the local symmetry of SiP2O10F moiety.
The second harmonic generation (SHG) intensity of powder CsSiP2O7F sample is approximately 0.7 times that of KH2PO4 and shows phase-matching behavior. According to the first-principles calculations, the SHG response mainly results from the unprecedented SiP2O10F moiety. As a result, the SiP2O10F moiety in this structure is a new type of nonlinear optical active gene.
In addition, relevant experimental and calculated results indicated that CsSiP2O7F is deep-UV transparent, and both cesium and fluorine favor the deep-UV transparency of CsSiP2O7F.
This study provides a new source for deep-UV nonlinear optical materials, and insight into how to obtain non-centrosymmetric structures that are indispensible to functional materials on nonlinear optics, piezoelectricity, ferroelectric, pyroelectricity, etc.
Schematic illustration of the research (Image by Prof. LUO’s group)
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