Breaking Through the Trade-Off Between Wide Band Gap and Large SHG Coefficient in Mercury-Based Chalcogenides for IR Nonlinear Optical Application.

It is substantially challenging for non-centrosymmetric (NCS) Hg-based chalcogenides for infrared nonlinear optical (IR-NLO) applications to realize wide band gap (E g > 3.0 eV) and sufficient phase-matching (PM) second-harmonic-generation intensity (d eff > 1.0 × benchmark AgGaS 2 ) simultaneously due to the inherent incompatibility. To address this issue, this work presents a diagonal synergetic substitution strategy for creating two new NCS quaternary Hg-based chalcogenides, AEHgGeS 4 (AE = Sr and Ba), based on the centrosymmetric (CS) AEIn 2 S 4 . The derived AEHgGeS 4 displays excellent NLO properties such as a wide E g (≈3.04-3.07 eV), large PM d eff (≈2.2-3.0 × AgGaS 2 ), ultra-high laser-induced damage threshold (≈14.8-15 × AgGaS 2 ), and suitable Δn (≈0.19-0.24@2050 nm), making them highly promising candidates for IR-NLO applications. Importantly, such excellent second-order NLO properties are primarily attributed to the synergistic combination of tetrahedral [HgS 4 ] and [GeS 4 ] functional primitives, as supported by detailed theoretical calculations. This study reports the first two NCS Hg-based materials with well-balanced comprehensive properties (i.e., E g > 3.0 eV and d eff > 1.0 × benchmark AgGaS 2 ) and puts forward a new design avenue for the construction of more efficient IR-NLO candidates.