Giant Second-Harmonic Generation Response and Large Band Gap in the Partially Fluorinated Mid-Infrared Oxide RbTeMo2O8F

Strong second-harmonic generation (SHG) and a wide band gap are two crucial but often conflicting parameters that must be optimized for practical nonlinear optical (NLO) materials. We report herein the first d0-transition-metal (TM) tellurite with half of the d0-TM-octahedra partially fluorinated, namely, quinary RbTeMo2O8F, which exhibits giant SHG responses (27 times that of KH2PO4 (KDP) and 2.2 times that of KTiOPO4 (KTP) with 1064 and 2100 nm laser radiation, respectively), the largest SHG values among all reported metal tellurites. RbTeMo2O8F also possesses a large band gap (3.63 eV), a wide optical transparency window (0.34-5.40 μm), and a significant birefringence (Δn = 0.263 at 546 nm). Theoretical calculations and crystal structure analysis demonstrate that the outstanding SHG responses can be definitively attributed to the uniform alignment of the polarized [MoO5F]/[MoO6] octahedra and the seesaw-like [TeO4], and the consequent favorable summative polarization of the three distinct SHG-active polyhedra, both induced by partial fluorine substitution on the [MoO6] octahedra.This research was financially supported by National Natural Science Foundation of China (no. 51432006), Ministry of Education of China for Changjiang Innovation Research Team (no. IRT14R23), Ministry of Education and State Administration of Foreign Experts Affairs for 111 Project (no. B13025), and the Innovation Program of Shanghai Municipal Education Commission. M.G.H. thanks the Australian Research Council for support (DP170100411)