Rare-Earth/d10 Dual-Metal Oxychalcogenides as Infrared Nonlinear-Optical Materials

Oxychalcogenides are receiving increasing interest as nonlinear-optical (NLO) materials because of the possible combination of advantages from oxides and chalcogenides. Here, two new pentanary oxythiogermanates Eu₂MGe₂OS₆ [M = Zn (1), Cd (2)] were obtained by the facile metal oxide-boron-sulfur solid-state route. They crystallize with a melilite-type structure and feature {[MGe₂OS₆]^4-}_∞ layers built by Ge₂OS₆ dimers and MS₄ tetrahedra. Their optical band gaps are 2.37 and 2.38 eV. As the first NLO rare-earth (RE)/d¹⁰ dual-metal oxychalcogenides, they exhibit phase-matchable NLO responses and enhanced laser-induced damage thresholds. Theoretical calculations show that the NLO responses are predominantly contributed by the EuOS₇ motifs. This work provides the potential of RE/d¹⁰ dual-metal-based NLO materials.