Deep-Ultraviolet Bialkali-Rare Earth Metal Anhydrous Sulfate Birefringent Crystal.

Birefringence is an important linear optical property of anisotropic crystals that plays a significant role in regulating light polarization. A new bialkali-rare earth metal sulfate, NaRbY(SO) compound, consisting of non-π-conjugated alkali metals and rare earth metal-centered dodecahedral YO has been synthesized. The structure analysis suggests that the three-dimensional (3D) structure of the compound is found to be attributable to the combination of dodecahedral YO and tetrahedral SO groups with Na and Rb located in the cavities. The ultraviolet, visible, and near-infrared (UV-vis-NIR) spectra reveal that the compound exhibits transparency at a wavelength of less than 200 nm. The observed birefringence of the compound is 0.045@550 nm, which is comparatively larger than that of most deep-ultraviolet (DUV) birefringent crystals. The birefringence mainly originated from the YO dodecahedron, which is suggested by first-principles calculations. This research work can provide a useful perspective to explore new DUV sulfates with excellent birefringence.