Simple yet extraordinary: Super-polyhedra-built 3D chalcogenide framework of Cs5Ga9S16 with excellent infrared nonlinear optical performance

Non-centrosymmetric chalcogenides are attracting considerable attention as highly promising infrared nonlinear optical (IR-NLO) candidates, but it is challenging to simultaneously achieve sufficient second-harmonic-generation coefficient (deff > 0.5 × AgGaS2) and large energy gap (Eg > 3.5 eV). In this work, a novel ternary chalcogenide, Cs5Ga9S16 with an ultra-wide Eg of 4.05 eV, has been successfully obtained. This sulfide belongs to the monoclinic space group Pn (No. 7) with a novel 3D anionic [Ga9S16]5– framework that is formed by super-polyhedral [Ga9S23] units through corner-sharing S atoms. Such a unique crystal structure displays desirable characteristics which indicate a promising IR-NLO candidate: favourable phase-matching feature, sufficient deff (0.7 × AgGaS2), ultrahigh laser-induced damage threshold (31.6 × AgGaS2) and broad transparent region (0.27−14.96 µm). In addition, systematic theoretical studies and structural analysis suggest that the desirable IR-NLO performances can be attributed to the super-polyhedral building blocks. This finding may provide useful insight into the understanding and designing other high-performance IR-NLO candidates with super-polyhedral-built structures.