High‐Performance Sulfate Optical Materials Exhibiting Giant Second Harmonic Generation and Large Birefringence

Discovering novel sulfate optical materials with strong second-harmonic generation (SHG) and large birefringence is confronted by a great challenge attributed to the intrinsically weak polarizability and optical anisotropy of tetrahedral SO4 groups. Herein, two superior-performing sulfate optical materials, namely, noncentrosymmetric Hg3 O2 SO4 and centrosymmetric CsHgClSO4 ⋅ H2 O, have been successfully synthesized through the introduction of a highly polarizable d10 metal cation, Hg2+ . The unique component layers in the reported compounds, [Hg3 O2 SO4 ]∞ layers in Hg3 O2 SO4 and [HgClSO4 (H2 O)] ∞- layers in CsHgClSO4 ⋅ H2 O, induce enlarged birefringence in each sulfate. Remarkably, Hg3 O2 SO4 exhibits a very large SHG response (14 times that of KH2 PO4 ), which is the strongest efficiency among all the reported nonlinear optical sulfates. Detailed theoretical calculations confirm that the employment of highly polarizable Hg2+ is an effective strategy to design superior optical materials with large birefringence and strong SHG response.