Ba(MoO2F)2(QO3)2 (Q = Se, Te): Partial Fluorination of MoO6 Octahedra Enabling Two Polar Solids with Strong and Phase Matchable SHG Response

The first polar molybdenum oxyfluoride in selenite and tellurite systems, namely, Ba(MoO2F)2(SeO3)2 and Ba(MoO2F)2(TeO3)2, was achieved successfully by partial fluorination of MoO6 octahedra under hydrothermal reactions. Their structures feature a unique staggered grid layer with trans O–Mo–O bonds participating in the six-member polyhedral rings. Compared with the pure oxides in Ba2+–Mo6+–Se4+/Te4+–O2– systems, the title compounds exhibit enhanced second-harmonic generation (SHG) responses, especially for the tellurite. As the first noncentrosymmetric fluorinated d0 transition metal (TM) tellurite, Ba(MoO2F)2(TeO3)2 presents high thermal stability, broad transparent range, and large and phase matchable SHG effect. As expected, the molybdenum oxyfluoride octahedra have played the main role in their SHG processes based on the theoretical calculations. This study has demonstrated that partial fluorination of d0 TM oxygen octaherdra in tellurites is an effective approach for creating new nonlinear optical materials with excellent SHG properties.