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

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 AgGaS₂ ) 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, AEHgGeS₄ (AE = Sr and Ba), based on the centrosymmetric (CS) AEIn₂ S₄ . The derived AEHgGeS₄ displays excellent NLO properties such as a wide E_g (≈3.04-3.07 eV), large PM d_eff (≈2.2-3.0 × AgGaS₂ ), ultra-high laser-induced damage threshold (≈14.8-15 × AgGaS₂ ), 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 [HgS₄ ] and [GeS₄ ] 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 AgGaS₂ ) and puts forward a new design avenue for the construction of more efficient IR-NLO candidates.