Great enhancement of the second harmonic generation response is achieved in AgHgPS4 by introducing vacancy defects and highly distorted HgS4 tetrahedra using AgGaS2 as the template.

Chalcogenides with diamond-like (DL) structures are a treasury of infrared nonlinear optical (NLO) materials. Here, a ternary Hg-based chalcogenide with a defect DL structure, Hg 3 P 2 S 8 , is synthesized by solid-state reaction. Driven by the highly distorted [HgS 4 ] tetrahedra, this compound displays an interesting structural symmetry degradation from tetragonal to orthorhombic compared with its analogue Zn 3 P 2 S 8 . Meanwhile, the overall performances of Hg 3 P 2 S 8 are quite remarkable, including a very strong phase-matchable secondharmonic generation (SHG) response (4.2 × AgGaS 2 ), large band gap (2.77 eV), wide IR transparent range (0.45−16.7 μm), and high laserinduced damage threshold (4 × AGS). Furthermore, the theoretical analysis and local dipole moment calculations elucidate that the highly distorted [HgS 4 ] tetrahedra contribute a lot to the enhancement of the SHG effect. This discovery will motivate the exploration of other DL Hg-based chalcogenides serving as high-performing mid-IR NLO materials.

Metal chalcogenides play a critical role in the infrared (IR) nonlinear optical (NLO) field. However, Eu-based chalcogenide-type IR NLO materials are still scarce up to now. In this paper, two new quaternary Eu-based chalcogenides, EuHgGeSe4 and EuHgSnS4, containing the “NLO active groups” [HgQ4]6– (Q = S, Se) and [GeSe4]4–/[SnS4]4– were synthesized through traditional high-temperature solid-state reactions. They possess noncentrosymmetric structures, crystallizing in the Ama2 space group, and exhibit strong phase-matchable second-harmonic-generation (SHG) responses (3.1× and 1.77× that of AgGaS2 for EuHgGeSe4 and EuHgSnS4, respectively). Meanwhile, the optical band gaps of EuHgGeSe4 (1.97 eV) and EuHgSnS4 (2.14 eV) were determined from UV–vis–NIR diffuse reflectance spectra. Differential scanning calorimetry (DSC) analyses reveal the congruent-melting behavior of EuHgGeSe4. Furthermore, structural analysis and theoretical calculations verify the critical driving effects of [HgQ4]6– tetrahedra on the strong SHG activity. The overall results demonstrate that EuHgGeSe4 and EuHgSnS4 are potential IR NLO materials.