Alkali Metal/Mercury Dual-Metal Sulfides as Infrared Nonlinear Optical Materials with High Laser-induced Damage Thresholds

Abstract

Two new mercury-based sulfides, Rb2HgGe3S8 and Cs2HgGe3S8, were successfully synthesized by the high-temperature solid-state reaction, and they are isostructural to crystallize in the non-centrosymmetric orthorhombic space group P212121. The results of the experiments indicate that Rb2HgGe3S8 has a large band gap of 3.26 eV, a second harmonic generation (SHG) response of 0.17 × AgGaS2 (AGS) at the particle size of 90−125 μm, and non-phase-matchable (NPM) properties. Additionally, Cs2HgGe3S8 exhibits a SHG response of 0.13 × AGS (particle size of 90−125 μm) as well as type-I phase-matchable (PM) performance at 2090 nm. Moreover, Rb2HgGe3S8 and Cs2HgGe3S8 exhibit high laser-induced damage thresholds of 3.1 and 2.7 × AGS, respectively. Theoretical calculations reveal that Rb2HgGe3S8 and Cs2HgGe3S8 are two direct semiconductors with the calculated band gap of 2.32 and 2.15 eV and the synergistic action of [HgS4] and [GeS4] units realizes their SHG response.