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.