From Ba3Nb2O2F12(H2O)2 to Ba0.5NbO2F2(H2O): 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, Ba3Nb2O2F12(H2O)2 (1) and Ba0.5NbO2F2(H2O) (2), have been obtained by regulating the O/F ratio in Nb–O–F units (NbOF6 pyramids to NbO4F2 octahedra). The overall NLO effect is improved from 1 to 2 with larger second-harmonic generation (SHG) intensities (0.9 to 1.7 × KH2PO4 (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).