Two Ultraviolet Optical Crystals K₆B₁₂O₁₉F₄ and K₁₂B₂₈O₄₈: The Effects of Metal Cations Size and the F Ions on the Structure

Borates and fluorooxoborates are advanced optical materials with great potential applications in the ultraviolet (UV) and deep ultraviolet (DUV) regions. Herein, two new UV optical crystals K6B12O19F4 and K12B28O48 were synthesized. Among them, K6B12O19F4 has a rare disorder of BO3 and BO4 units, which is the first time this disordered type has been found in fluorooxoborates. In this paper, the properties of K6B12O19F4 and K12B28O48 were tested and calculated, and their crystal structures and structural evolution were carefully analyzed. In addition, the effects of metal cations size and F ions on the crystal structure were analyzed. This research enriches the structural chemistry of borates and fluorooxoborates, and provides experience for the design of new UV optical crystals.