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 SO 4 groups. Herein, two superior-performing sulfate optical materials, namely, noncentrosymmetric Hg 3 O 2 SO 4 and centrosymmetric CsHgClSO 4  ⋅ H 2 O, have been successfully synthesized through the introduction of a highly polarizable d 10 metal cation, Hg 2+ . The unique component layers in the reported compounds, [Hg 3 O 2 SO 4 ] ∞ layers in Hg 3 O 2 SO 4 and [HgClSO 4 (H 2 O)] ∞ - layers in CsHgClSO 4  ⋅ H 2 O, induce enlarged birefringence in each sulfate. Remarkably, Hg 3 O 2 SO 4 exhibits a very large SHG response (14 times that of KH 2 PO 4 ), which is the strongest efficiency among all the reported nonlinear optical sulfates. Detailed theoretical calculations confirm that the employment of highly polarizable Hg 2+ is an effective strategy to design superior optical materials with large birefringence and strong SHG response.