AHgSnQ (A = Sr, Ba; Q = S, Se): A Series of Hg-Based Infrared Nonlinear-Optical Materials with Strong Second-Harmonic-Generation Response and Good Phase Matchability.

Four Hg-based IR nonlinear-optical materials, AHgSnQ (A = Sr, Ba; Q = S, Se), were discovered and investigated systematically. Their structures are built of two-dimensional [HgSnQ] layers, which are assembled alternately by distorted (HgQ and SnQ) tetrahedra and separated by eight-coordinated A cations. The two sulfides AHgSnS (A = Ba, Sr) exhibit large second-harmonic-generation (SHG) responses (2.8 and 1.9 × AgGaS at 2.09 μm), as well as large band gaps (2.77 and 2.72 eV). The two selenides AHgSnSe (A = Ba, Sr) show even stronger SHG responses, about 5 times that of AgGaS. Furthermore, all four compounds show phase-matching behavior, and the results of first-principles calculation elucidate the key role of the HgQ group in the enhanced SHG effect in β-BaHgSnS and BaHgSnSe.