Strategic Integration Between Trigonal Architecture Construction and Molecular Polarization Enhancement for Record...

Although possessing similar structural and electronic configurations with the tetrahedral nonlinear optical (NLO) active units, such as [SO₄], [PO₄] and so on, the development of selenates with [SeO₄] units have been long term hindered due to the lack of effective approaches to enhance polarizability and optical anisotropy. Here, a strategic integration between trigonal architecture construction and molecular polarization enhancement was proposed, which resulted in the discovery of an exceedingly performant selenate optical material, namely Hg₆O₂H(SeO₄)₃I₃ (HSOI). This compound possess unique pseudo-planar [Hg₃OI₃] secondary building units (SBUs), which formed the cloverleaf-shaped layer and further construct the sandwich structure with the polar [SeO₄H] FBUs inserted between the layers. Notably, HSOI exhibits an exceptionally large second harmonic generation (SHG) response (14.6×KDP), achieving a new record that is 170% higher than the previous value of nonlinear metal selenates. Meanwhile, a record high birefringence of selenates (∼ 0.2) was also achieved in HSOI. Theoretical calculations were carried out to reveal its optical origins and provide new insights for further structure-driven functional materials design.