K2(H2O)WO3F2: A new nonlinear optical material with remarkable second-harmonic generation response and enhanced laser damage threshold

Nonlinear optical (NLO) crystal is the key component in all-solid-state lasers. Herein, a new tungsten oxyfluoride with O/F orientationally order, K2(H2O)WO3F2, has been successfully obtained. It is interesting that the distorted [WO4F2] octahedra are induced by the trigonal [K2(H2O)]2+ motifs into an oriented arrangement. Remarkably, K2(H2O)WO3F2 exhibits the strongest phase-matching second-harmonic generation (SHG) response of 6 × KH2PO4 and the highest laser damage threshold of 274.45 MW/cm2 among reported transition-metal oxyfluorides. Theoretical calculations eluciate that its large SHG response mainly derives from the uniform alignment of the distorted [WO4F2] octahedra. This result is beneficial to the modulation of anion order and the exploration of high-performance NLO materials.