Structure and optical properties of a noncentrosymmetric borate RbSr4(BO3)3

A new noncentrosymmetric borate, RbSr4(BO3)3 (abbreviated as RSBO), has been grown from Rb2OB2O3RbF flux and its crystal structure was determined by single crystal x-ray diffraction. It crystallizes in space group Ama2 with cell parameters of a=11.128(10) Å, b=12.155(15) Å, c=6.952(7) Å, Z=4. The basic structural units are isolated planar BO3 groups. Second harmonic generation (SHG) test of the title compound by the Kurtz–Perry method shows that RSBO can be phase matchable with an effective SHG coefficient about two-thirds as large as that of KH2PO4 (KDP). Finally, based on the anionic group approximation, the optical properties of the title compound are compared with those of the structure-related apatite-like compounds with the formula “A5(TOn)3X”.

Graphical abstractRbSr4(BO3)3 and some other borate NLO compounds, namely Ca5(BO3)3F RCa4(BO3)3O (R=Y or Gd) and Na3La2(BO3)3 can be viewed as the derivatives of apatite. They have similar formula composed of five cations and three anion groups (we call them 5/3 structures). The detailed SHG coefficients and optical properties of the apatite-like NLO crystals were compared and summarized.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A new noncentrosymmetric borate RbSr4(BO3)3 was grown from flux. ► The RbSr4(BO3)3 can be viewed as a derivative of the apatite-like structure. ► The structure and its relationship to the optical properties of RbSr4(BO3)3 are compared with other NLO crystals with apatite-like structures. ► The basic structural units are the planar BO3 groups in the structure. ► Second harmonic generation (SHG) test shows that RbSr4(BO3)3 can be phase matchable with an effective SHG coefficient about two-thirds as large as that of KH2PO4.