Diamond-Like HgIn₂Q₄ (Q = Se, Te) Synthesized by Flux-Assisted Boron-Chalcogen Method Exhibit Noteworthy Nonlinear Optical Properties Contributed by Three Types of Tetrahedral Motifs

Diamond-like (DL) chalcogenides have emerged as promising candidates in the field of infrared (IR) nonlinear optical materials (NLO), owing to their exceptional nonlinear optical performance, which fulfills critical requirements for mid- and far-infrared applications. Herein, two ternary DL Hg-based chalcogenides HgIn₂Q₄ (Q = Se, Te) were synthesized by the facile flux assisted boron-chalcogen solid-state method. Both of them crystallize in the tetragonal space group, exhibiting three-dimensional structures constructed by HgQ₄ and In(1)Q₄, and In(2)Q₄ tetrahedra. As the first studied NLO member in the M-In-Q (M = Zn, Cd, Hg; Q = S, Se, Te) series, HgIn₂Se₄ exhibits a significant second-harmonic generation response ∼1.4× AgGaS₂, and an enhanced laser-induced damage threshold of 2.9× AgGaS₂. Theoretical calculations indicate that the NLO coefficient χ₃₂ of HgIn₂Se₄ reaches 23.93 pm/V at a photon energy of 0.59 eV, which is primarily attributed to the synergetic contribution of [InSe₄] and [HgSe₄] tetrahedra. Therefore, the M-In-Q system demonstrates significant potential for future exploration of mid-infrared NLO crystals.