From Ca3Be(SeO3)4 to SrBe(SeO3)2: Two Unprecedented Alkaline Earth Metal Beryllium Selenites with Large Band Gaps and Enhanced Birefringence

Abstract

Beryllium-based selenite has rarely been reported. Herein, the first two alkaline earth metal beryllium-based selenites, Ca3Be(SeO3)4 and SrBe(SeO3)2, have been synthesized by a mild hydrothermal method. Both of them feature unique [Be(SeO3)4]6- composite groups. Due to different connection forms of [Be(SeO3)4]6-, these two crystals exhibit significantly different optical anisotropy. From Ca3Be(SeO3)4 to SrBe(SeO3)2, the birefringence range from 0.005@546 nm to 0.058@546 nm. Theoretical calculations confirmed the dominant role of [SeO3]2- in the optical anisotropy of these two crystals. In addition, both of them exhibited large band gaps (5.40 and 5.28 eV) and high thermal stability (596 and 570 °C). This work demonstrates that the introduction of beryllium can effectively increase the band gap of selenite to over 5eV, and offers new ideas for the development of large bandgap selenite.