KHg4Ga3S9: A Hg-Based Sulfide with Nonlinear-Optical Activity in the A–MII–MIII–Q (A = Alkali Metal; MII = d10 Metal; MIII = Ga, In; Q = S, Se) System

The search for new high-performance infrared (IR) nonlinear-optical (NLO) materials is a hot topic in the fields of laser chemistry and inorganic solid-state chemistry. Here, a new Hg-based sulfide KHg 4 Ga 3 S 9 in the family of A–M II –M III –Q (A = alkali metal; M II = d 10 metal; M III = Ga, In; Q = S, Se) was synthesized. It crystallizes in the orthogonal system of the C 222 1 structure, which is rare for IR NLO chalcogenides. Its anionic framework {[Hg 4 Ga 3 S 9 ] − } ∞ is constructed by two types of interconnected helical chains, viz., the inner layer ({[Hg 6 Ga 2 S 29/3 ] 4/3– } ∞ ) and the outer layer ({[Hg 2 Ga 4 S 25/3 ] 2/3– } ∞ ). It exhibits a moderate NLO response and a high laser-induced damage threshold. Theoretical calculations indicate that the HgS 4 unit accounts for its much larger NLO response compared to RbCd 4 Ga 3 S 9 . The influence of alkali metals and d 10 metals on the initial phase-matching wavelength is also discussed. This work provides inspiration for improving the properties of NLO materials’ properties.