Design of Pentanary Mixed-Chalcogenides AgInSiSSe ( = 1, 2) Based on the Bucket Effect: Local Structural Difference and High-Performance Nonlinear-Optical Properties Realized by Partial Congener Substitution.

Noncentrosymmetric chalcogenides are promising candidates for infrared nonlinear-optical (NLO) crystals, and exploring high-performance ones is a hot topic and challengeable. Herein, the combination of AgQ, InQ, and SiQ (Q = S, Se) units with different S/Se ratios resulted in the discovery of the tetrahedral chalcogenides AgInSiSSe () and AgInSiSSe (). They both crystallize in the monoclinic space group with different local structures. Co-occupied S/Se sites only exist in , and the arrangement of [InSiQ] six-membered rings builds different helical chains and 3D [(InSiQ)] polyanionic frameworks in and . They show balanced NLO performances, including phase-matchable moderate NLO responses (0.7 and 0.5 × AGS) and enhanced laser-induced damage thresholds (4.5 and 5.1 × AGS). Theoretical calculations reveal that their NLO responses are predominantly contributed by the AgQ and InQ units.