Abstract:A new family of quaternary diamond-like semiconductors (DLSs), Li 2 HgMS 4 (M = Si, Ge, Sn), were successfully discovered for the first time. All of them are isostructural and crystallize in the polar space group (Pmn2 1 ). Seen from their structures, they exhibit a three-dimensional (3D) framework structure that is composed of countless 2D honeycomb layers stacked along the c axis. An interesting feature, specifically, that the LiS 4 tetrahedra connect with each other to build a 2D layer in the ac plane, is also observed. Experimental investigations show that their nonlinear optical responses are about 0.8 for Li 2 HgSiS 4 , 3.0 for Li 2 HgGeS 4 , and 4.0 for Li 2 HgSnS 4 times that of benchmark AgGaS 2 at the 55-88 µm particle size, respectively. In addition, Li 2 HgSiS 4 and Li 2 HgGeS 4 also have great laser-damage thresholds that are about 3.0 and 2.3 times that of powdered AgGaS 2 , respectively. The above results indicate that title compounds can be expected as promising IR NLO candidates.