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 x 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, 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 (approximate to 3.04-3.07 eV), large PM d(eff) (approximate to 2.2-3.0 x AgGaS2), ultra-high laser-induced damage threshold (approximate to 14.8-15 x AgGaS2), and suitable Delta n (approximate to 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 x benchmark AgGaS2) and puts forward a new design avenue for the construction of more efficient IR-NLO candidates.