Na2SrB16O26: a new borate with independent interpenetrating B–O networks and deep-ultraviolet cutoff edge

A new borate, Na2SrB16O26, was synthesized by the high-temperature solution method. It exhibits complicated interpenetrating 3D B–O frameworks composed of the functional building block (FBB) [B8O16]. The UV-vis-NIR diffuse reflectance spectroscopy shows that it has a deep-ultraviolet (DUV) cutoff edge (<200 nm). The relationship between the structures and optical properties was uncovered by theoretical calculations. By the first-principles calculation, the birefringence is estimated to be 0.07 at 1064 nm. The response electron distribution anisotropy (REDA) analysis indicates that the [BO3] units contribute mainly to the generation of the moderate birefringence.