Pb₂(SeO₃)(SiF₆): the first selenite fluorosilicate with a wide bandgap and large birefringence achieved through...

Birefringent crystals serve as the core elements of polarizing optical devices. However, the inherent challenge of balancing bandgap and birefringence poses a significant hurdle in designing crystals with excellent overall performance. In this study, we propose a novel approach, namely modification with perfluorinated groups, to achieve dual enhancement of the bandgap and birefringence of selenite materials. We have successfully synthesized the first selenite fluorosilicate, namely, Pb₂(SeO₃)(SiF₆). This compound exhibits a three-dimensional structure composed of two-dimensional lead selenite layers bridged by SiF₆ octahedrons. Notably, by introducing a perfluorinated SiF₆ group, the bandgap of the lead selenite compound has been expanded to 4.4 eV. Furthermore, Pb₂(SeO₃)(SiF₆) demonstrates a large birefringence (0.161 @ 546 nm), surpassing most of the selenite compounds with a bandgap larger than 4.2 eV. Theoretical calculations suggest that the large birefringence of Pb₂(SeO₃)(SiF₆) can be attributed to the synergistic effects of SeO₃, PbO₄ and PbO₃F₄ polyhedrons. Our research not only pioneers a new system for selenite materials, enriching the diversity of selenite structures, but also provides a design methodology for obtaining wide bandgap birefringent selenite.