RbB7O10(OH)2 and NaB11O16(OH)2: Alkali Metal Hydroxyborates with Two-dimensional Layered Structures and Large Birefringence

Abstract

Hydroxyborates have attracted much research attention due to their rich structural and outstanding optical properties. Herein, two new alkali metal hydroxyborates, RbB7O10(OH)2 and NaB11O16(OH)2, with two-dimensional (2D) layered structures have been synthesized in a closed system using the high-temperature solution method. UV-VIS-NIR diffuse reflectance spectrum shows that RbB7O10(OH)2 has a UV cutoff edge below 200 nm. Theoretical calculations indicate that both compounds exhibit large band gaps (7.40 and 7.41 eV) and large birefringence (0.074 and 0.105 at 1064 nm), respectively. Additionally, the origin of the birefringence in title compounds has been analyzed using the Response Electron Distribution Anisotropy (REDA) method.