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

Mid-infrared (mid-IR) nonlinear optical (NLO) materials are vital for the development of photonics research and state-of-the-art laser technology, but the study of these important optoelectronic 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 that are usually needed. Herein, we report the 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. In particular, it displays very strong phase-matchable SHG intensities in the metal vanadate family (12.0 × KH2PO4 @ 1064 nm and 2.2 × AgGaS2 @ 2100 nm). First-principles calculations suggest that the exceptional SHG responses of CVO largely originate from virtual electronic transitions within the [V4O11]∞ layer, and that the excellent optical transmittance of CVO arises from the special characteristics of vibrational phonons resulting from the layered structure. These attributes suggest that CVO is an outstanding mid-IR NLO candidate material.