Achieving a strong second harmonic generation response and a wide band gap in a Hg-based material

Abstract

A new Hg-based infrared nonlinear optical (IR NLO) crystal, [Ba₄Cl₂][HgGa₄S₁₀], was synthesized based on a property-oriented structural design strategy. It crystallizes in the noncentrosymmetric tetragonal space group (I) and consists of a 3D [HgGa₄S₁₀]⁶⁻ anionic moiety formed by corner-sharing tetrahedral HgS₄ and supertetrahedral Ga₄S₁₀ clusters, as well as a 3D [Ba₄Cl₂]⁶⁺ cation network. The physical property measurements show that it can exhibit well-balanced NLO performances, including a large second-harmonic generation (SHG) response (1.5 × AgGaS₂), wide band gap (2.95 eV), and high laser damage threshold (∼15 × AgGaS₂). First-principles calculations indicate that the large SHG response of [Ba₄Cl₂][HgGa₄S₁₀] mainly originates from the strong covalent HgS₄ and GaS₄ tetrahedra and the ionic bonding [Ba₄Cl₂]⁶⁺ guest network contributes to the wide band gap of [Ba₄Cl₂][HgGa₄S₁₀].