Two Nonlinear Optical Thiophosphates Cu5Hg0.5P2S8 and AgHg3PS6 Activated by Their Tetrahedra-Stacking Architecture

Infrared (IR) lasers are very critical in military and civil affairs, but it is also challenging and difficult to develop new infrared nonlinear optical (NLO) crystals. Herein, two new mixed-metal thiophosphates, Cu5Hg0.5P2S8 and AgHg3PS6 were discovered with the noncentrosymmetric (NCS) space group Pmn2(1) (No. 31) and Cc (No. 9). Cu5Hg0.5P2S8 displays a three-dimensional (3D) defective diamond-like structure stacked by (2)(infinity)[Cu2.5Hg0.25PS8](8-) layers. AgHg3PS6 is characterized by a 3D framework consisting of distorted tetrahedrons. Moreover, the optical spectra show the band gaps of Cu5Hg0.5P2S8 and AgHg3PS6 are 2.12 and 1.85 eV, respectively, with a broad transparent range of 0.7-16.0 mu m. In these two compounds, the dipole moments of nonlinear active units are strengthened due to the high-valence element P and the Hg-S bonds with large susceptibility. Therefore, AgHg3PS6 exhibits a moderate second harmonic generation (SHG) response that is half that of AgGaS2 (AGS) at 30-45 mu m, while Cu5Hg0.5P2S8 performs a phase-matching (PM) behavior with a good SHG signal of 0.8 x AGS at 150-200 mu m. The origin of NLO performance and electronic structures were revealed by the calculated dipole moments of distorted tetrahedra and theoretical calculations on the basis of density functional theory.

Automated summary

This study investigates two new mixed-metal thiophosphates with unique features in NLO performance and electronic structures, showing potential applications in infrared lasers.