Rare-Earth/d<sup>10</sup> Dual-Metal Oxychalcogenides\nas Infrared Nonlinear-Optical Materials

Oxychalcogenides are receiving increasing\ninterest as\nnonlinear-optical\n(NLO) materials because of the possible combination of advantages\nfrom oxides and chalcogenides. Here, two new pentanary oxythiogermanates\nEu<sub>2</sub>MGe<sub>2</sub>OS<sub>6</sub> [M = Zn (<b>1</b>), Cd (<b>2</b>)] were obtained by the facile metal oxide–boron–sulfur\nsolid-state route. They crystallize with a melilite-type structure\nand feature {[MGe<sub>2</sub>OS<sub>6</sub>]<sup>4–</sup>}<sub>∞</sub> layers built by Ge<sub>2</sub>OS<sub>6</sub> dimers\nand MS<sub>4</sub> tetrahedra. Their optical band gaps are 2.37 and\n2.38 eV. As the first NLO rare-earth (RE)/d<sup>10</sup> dual-metal\noxychalcogenides, they exhibit phase-matchable NLO responses and enhanced\nlaser-induced damage thresholds. Theoretical calculations show that\nthe NLO responses are predominantly contributed by the EuOS<sub>7</sub> motifs. This work provides the potential of RE/d<sup>10</sup> dual-metal-based\nNLO materials.