From Ba 3 Nb 2 O 2 F 12 (H 2 O) 2 to Ba 0.5 NbO 2 F 2 (H 2 O): Achieving Balanced Nonlinear Optical Performance by O/F Ratio Regulation.

Metal oxyhalides have attracted extensive attention as fascinating nonlinear optical (NLO) materials. Here, two barium niobium oxyfluorides, Ba 3 Nb 2 O 2 F 12 (H 2 O) 2 ( 1 ) and Ba 0.5 NbO 2 F 2 (H 2 O) ( 2 ), have been obtained by regulating the O/F ratio in Nb-O-F units (NbOF 6 pyramids to NbO 4 F 2 octahedra). The overall NLO effect is improved from 1 to 2 with larger second-harmonic generation (SHG) intensities (0.9 to 1.7 × KH 2 PO 4 (KDP)) and maintainable large band gaps (>3.0 eV) by regulating the O/F ratio in Nb-O-F units (1:6 to 4:2).