Superpolyhedron-Built Second Harmonic Generation Materials Exhibit Large Mid-Infrared Conversion Efficiencies and High Laser-Induced Damage Thresholds

Developing excellent infrared nonlinear optical (NLO) materials is challenging because of the incompatibility between a large second harmonic generation (SHG) efficiency and a high laser-induced damage threshold (LIDT). Here, we report three NLO chalcogenides, namely, Na2In4SSe6 (1), NaGaIn2Se5 (2), and NaIn3Se5 (3), whose crystal structures consist of supertetrahedral, superpentahedral, and superoctahedral chalcogenide clusters. Importantly, they exhibit SHG responses 7.0-, 2.1-, and 0.3-fold larger than and LIDTs 5.8-, 6.4-, and 10.7-fold higher than those of AgGaS2, respectively, almost achieving balance between large SHG efficiencies and high LIDTs. Theoretical calculations and structural analysis reveal that the enhanced SHG responses can be attributed to the superpolyhedral chalcogenide clusters. The high LIDTs can be ascribed to their small thermal expansion anisotropy. These findings may provide useful insights into the development of infrared NLO materials with superpolyhedron-built structures.