Synthesis, Crystal Structure, and Optical Properties of the First Alkali Metal Rare-Earth Iodate Fluoride: Li2Ce(IO3)4F2

The first alkali metal rare-earth iodate fluoride, Li2Ce(IO3)4F2, was synthesized using a hydrothermal method. This compound features a novel [CeI4O12F2]∞ infinite layer with each [CeO6F2] dodecahedron connected to six parallel umbrella-like [IO3] groups. Each layer is connected by [Li2I2O8F2] rings to form a condensed 3D structure. The first-principles calculations indicate that Li2Ce(IO3)4F2 possesses moderate birefringence (Δn = 0.054, λ = 589 nm), which is mainly originated from the umbrella-like [IO3] group and the [CeO6F2] polyhedrons. Li2Ce(IO3)4F2 is possibly a birefringence crystal for visible light.