Partial congener substitution induced wide band gap witnessed in diamond-like chalcogenide ZnHg2P2S8 and its second-order nonlinear optical properties

Abstract

Infrared nonlinear optical (IR NLO) materials play a pivotal role in laser technology, yet achieving a balance between a wide band gap and a strong second-harmonic generation (SHG) response remains challenging. Here, we report the rational design and synthesis of ZnHg₂P₂S₈, a novel diamond-like (DL) chalcogenide developed through a partial congener substitution strategy. The precise partial substitution of Zn²⁺ for Hg²⁺ in the normal [Hg1S₄] tetrahedra, while preserving the structurally distorted [Hg2S₄] units critical for NLO effects, simultaneously enhances the band gap to 2.91 eV (compared to 2.77 eV in the parent compound Hg₃P₂S₈) and maintains a strong SHG response of 1.5 × AgGaS₂. First-principles calculations elucidate the structure–property relationship, showing that the preserved [Hg2S₄] motifs dominate the SHG effect, while the introduction of Zn enlarges the band gap. This work not only presents an exceptional IR NLO candidate overcoming the band gap–NLO efficiency paradox, but also establishes a general design strategy for developing high-performance IR NLO materials through targeted structural engineering.