SrAlB3O6F2: A Fluoroaluminoborate with [Al2B6O14F4] Units and Large Birefringence.

The first strontium fluoroaluminoborate SrAlB3O6F2 was synthesized. Interestingly, it exhibits a two-dimensional warped layer composed of the [Al2B6O14F4] fundamental building units, which are first identified in borates. The experimental results indicate that SrAlB3O6F2 has a short ultraviolet cutoff edge (<200 nm) and large birefringence (0.075@546 nm), which are further verified by theoretical calculation. Thus, SrAlB3O6F2 can be used as the deep-ultraviolet birefringence material.