A nonlinear optical crystal with deep-ultraviolet transparency and appropriate birefringence achieved using π-conjugated confined [B3O3F4(OH)]2−

Based on a π-conjugated confinement strategy, we designed and synthesized a deep-UV NLO crystal, K 2 B 3 O 3 F 4 (OH), exhibiting a moderate birefringence (0.054@550 nm) and deep-UV transparency (<200 nm).