Large Second-Harmonic Response and Giant Birefringence of CeF₂(SO₄) Induced by Highly Polarizable Polyhedra

Second-harmonic generation (SHG) response and birefringence are two critically important properties of nonlinear optical (NLO) materials. However, the simultaneous optimization these key remains a major challenge because their contrasting microstructure requirements. Herein, we report first tetravalent rare-earth metal fluorinated sulfate, CeF2(SO4). Its structure features novel net-like layers constructed by highly distorted [CeO4F4] polyhedra, which further interconnected [SO4] tetrahedra to form three-dimensional structure. CeF2(SO4) exhibits strongest SHG effect (8 times that KH2PO4) largest for sulfate-based NLO materials, latter exceeding birefringent limit oxides. Theoretical calculations crystal analysis reveal unusually large giant can be attributed introduction polarizable polyhedra as well favorable alignment tetrahedra. This research affords new paradigm designed synthesis high-performance