Highly distorted HgS4 tetrahedra induced moderate second-harmonic generation response of EuHgGeS4
A quaternary Eu-based sulfide EuHgGeS4 is synthesized by a high-temperature solid-state reaction. It crystallizes in the noncentrosymmetric orthorhombic space group Ama2, and features highly distorted HgS4 tetrahedra. It shows phase-matchable second-harmonic generation (SHG) behavior and has the intensity around 0.9 times that of AgGaS2. Theoretical calculations on its electronic structure and optical properties are performed and the results are well consistent with the experimental ones. Structural analysis suggests that HgS4 tetrahedron plays an important role in the SHG activity.