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

Abstract

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)] <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow></mml:mrow> <mml:mi>∞</mml:mi> <mml:mo>-</mml:mo></mml:msubsup> </mml:math> 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.