Helical {[HgS]} Chain-Induced Balanced Nonlinear-Optical Performance for Trigonal Mercury Sulfide

Large second-harmonic-generation (SHG) response and enhanced laser-induced damage threshold (LIDT) compared with benchmark AgGaS₂ (AGS), together with a simple chemical composition and exclusion of the light-sensitive Ag element, are vital for exploration of superior IR nonlinear-optical (NLO) materials beyond AGS. Herein, we report trigonal HgS as a highly promising IR NLO material. It was obtained by a facile one-pot hydrothermal reaction, and its noncentrosymmetric P3₂21 structure features a unique dumbbell-shaped HgS₂ group and a neutral helical {[HgS]} chain, which first served as a SHG functional motif. Its polycrystalline powder sample exhibits a phase-matchable SHG response comparable to that of AGS and a LIDT value of 1.2 × AGS. Structural analysis and theoretical calculation suggest that the {[HgS]} chain plays an important role for excellent NLO performance. This work not only provides a strong candidate for IR NLO application but also introduces a new SHG functional motif for the design of future NLO materials.