Expanding the Spectral Range in T2-Supertetrahedral Nonlinear Optical Chalcogenides via Incorporating Inorganic...

Metal-chalcogenide supertetrahedral clusters that exhibit significant hyperpolarizability are highly sought after as promising nonlinear optical (NLO) function modules. However, these "naked" anionic clusters are commonly coordinated with organic ligands to maintain electrical neutrality, which unfortunately limits their utility in the mid- and far-infrared (MFIR) region due to strong absorption. In this study, we successfully substituted the organic ligand with the unprecedented (X₄K₈Ba₂)⁸⁺ supertetrahedral cations, which are suitable size and high charge, and integrated them with (In₄Se₁₀)^8- supertetrahedral clusters to form 3D salt-inclusion chalcogenides (SICs), [K₄BaX₂][In₆Se₁₁] (X = Cl 1, Br 2). As anticipated, the parallel arrangement of the (In₄Se₁₀)^8- clusters yielded splendid second-harmonic generation intensities (2.2-2.4 × benchmark AgGaS₂ @1910 nm for 1 and 2, respectively), ranking among the top within the SICs category. Most importantly, the introduction of inorganic polycations with a broad cut-off IR edge is a key factor in enabling 1 to achieve an ultrawide transparency range (0.7 to 18.1 µm) that covers the crucial atmospheric windows (3-5 and 8-14 µm). Indeed, replacing the organic ligand with an inorganic polycation allows supertetrahedra-based chalcogenides to fulfill the broad-spectrum criteria of NLO materials.