Rare-Earth Substitution Induced Symmetry Breaking for The First Sc-Based Nonlinear Optical Chalcogenide with High-Performance

Chalcogenides are the most important infrared nonlinear optical (NLO) material candidates, and the exploration of high-performance ones is attractive and challengeable. Hitherto, there is no NLO scandium (Sc) chalcogenides experimentally studied. Here, new quaternary Sc thiophosphate CsScP₂S₇ (CSPS) was synthesized by the facile metal oxide-boron-sulfur/reactive flux hybrid solid-state method. It crystallizes in the monoclinic chiral space group C2, and the layered structure is composed by the new ScP₂S₁₁ functional motifs built by ScS₆ octahedra and P₂S₇ dimers, and the structure-performance analysis reveals that the hyperpolarizability of ScP₂S₁₁ is much greater than the assembled units (ScS₆ and PS₄), which makes the first NLO Sc chalcogenide CSPS exhibits strong NLO response (0.8 × AGS) and high laser-induced damage threshold (LIDT) (4.3 × AGS), and a wide bandgap of 3.10 eV. With the coordination number's reduction of rare-earth (RE) ion and the rearrangement of P₂S₇ dimers, the centrosymmetric structure of CsREP₂S₇ family can be broken via substitution with the smallest RE element Sc to form the noncentrosymmetric structure. This work not only discovers a new high-performance infrared NLO material, but also will inspire researchers to explore more potential NLO Sc chalcogenides.