Hg₃(SeO₃)₂(SO₄): A UV Nonlinear Optical Mercury Selenite Sulfate Constructed by Neat [Hg₆O₈(SeO₃)₄]_∞ Layers and SO₄ Tetrahedra

Abstract

A novel mercury selenite sulfate named Hg₃(SeO₃)₂(SO₄) has been successfully synthesized under a mild hydrothermal method. Hg₃(SeO₃)₂(SO₄) crystallizes in a monoclinic space group P2₁ and features a unique three-dimensional (3D) frame structure formed by [Hg₆O₈(SeO₃)₄]_∞ layers and SO₄ tetrahedra, which enables it to exhibit a comprehensive performance of a moderate second-harmonic generation (SHG) response of approximately 1.3 times that of baseline KH₂PO₄ (KDP), a moderate birefringence (0.118@546 nm), and a wide band gap (4.70 eV), which indicates that it has potential for application as an ultraviolet (UV) nonlinear optical material. Detailed theoretical calculations show that the Hg²⁺-based polyhedra with large polarizability and deformability and the SeO₃ groups with stereochemically active lone pair (SCALP) electrons are the main contributors to moderate optical properties.