“…First, the alkali or alkaline-earth metals were selected as cations because they have no d–d or f–f electron transitions, which are beneficial to having a high transparency in the UV or deep-UV spectral region. Second, we all know that the introduction of halogen atoms to borate could expand the transmission region of the materials and affect the symmetry of borate frameworks. , In recent years, a number of borates containing additional halogen atoms have been obtained, such as Ba 4 B 11 O 20 F, Pb 2 BO 3 Cl, Pb 2 B 5 O 9 I, AZn 2 BO 3 X 2 (A = NH 4 + , Rb, K; X = Cl, Br), and AB 4 O 6 F (A = NH 4 + , K, Rb, Cs), − which exhibit large second-harmonic-generation (SHG) responses and short UV absorption edges. Therefore, we expect to obtain a good NLO material with a wide transmission range by leading the halogen atoms into the boron–carbonate system.…”