“…Subsequently, numerous borate-based NLO materials were discovered by making structural modifications to the favorable layered structures of KBBF or SBBO. [14,15,[20][21][22][23][43][44][45][46][47] Most of these materials are transparent down to the deep-UV region, possess considerable SHG responses, and display favorable growth habits, but still few obtained crystals or predicted structures can achieve PM behavior in the deep-UV region below 200 nm. To the best of our knowledge (see Figure 4), in addition to KBBF, RBBF, and SBBO, few crystals including experimentally obtained BaBe 2 BO 3 F 3 (BBBF), [43a] NH 4 Be 2 BO 3 F 2 (ABBF), [44] Be 2 BO 3 F (C2), [45] Be 2 BO 3 F (R32), [44] Cs 2 Al 2 (B 3 O 6 ) 2 O, [43b] and CsAlB 3 O 6 F [43c] as well as theoretically designed LiBe 2 BO 3 F 2 (R32), [46] NaBe 2 BO 3 F 2 (R32), [46] Be 2 BO 3 F (P6 2c), [47] NaBeBO 3 (P6 c), [48] and NaBeBO 3 (P6 ) [48] can be expected to emit deep-UV laser light by the direct SHG method.…”