K, Rb-hydroxyborates series with deep-ultraviolet KRbB5O8(OH) possessing moderate second harmonic generation response

Three new hydroxyborate crystals, KRbB 5 O 8 (OH) (I), KRbB 6 O 9 (OH) 2 (II), and K 3.3 Rb 0.7 B 10 O 15 (OH) 4 (III) were synthesized. I features a short DUV cut-off edge (190 nm), an SHG (0.9 × KDP), and an experimental birefringence of 0.025@546.1 nm.