A Congruent‐Melting Mid‐Infrared Nonlinear Optical Vanadate Exhibiting Strong Second‐Harmonic Generation

Study of mid-infrared (mid-IR) nonlinear optical (NLO) materials is hindered by the competing requirements of optimized second-harmonic generation (SHG) coefficient dij and laser-induced damage threshold (LIDT) as well as the harsh synthetic conditions. Herein, we report facile hydrothermal synthesis of a polar NLO vanadate Cs4V8O22 (CVO) featuring a quasi-rigid honeycomb-layered structure with [VO4] and [VO5] polyhedra aligned parallel. CVO possesses a wide IR-transparent window, high LIDT, and congruent-melting behavior. It has very strong phase-matchable SHG intensities in metal vanadate family (12.0 × KDP @ 1064 nm and 2.2 × AGS @ 2100 nm). First-principles calculations suggest that the exceptional SHG responses of CVO largely originate from virtual electronic transitions within [V4O11]∞ layer; the excellent optical transmittance of CVO arises from the special characteristics of vibrational phonons resulting from the layered structure.This research was financially supported by the National Natural Science Foundation of China (Nos. 51432006 and 52002276), the Ministry of Education of China for the Changjiang Innovation Research Team (No. IRT14R23), the Ministry of Education and the State Administration of Foreign Experts Affairs for the 111 Project (No. B13025), and the Innovation Program of Shanghai Municipal Education Commission. M.G.H. thank the Australian Research Council for support (DP170100411). Author thanks G.Z. and B.X.L. at FJIRSM for the LIDT measurements