The first quaternary rare-earth oxythiogermanate with second-harmonic generation and ferromagnetic behavior.

The discovery of new functional materials is attractive since they have the opportunity to change some important fields. Of these materials, oxychalcogenides constitute an increasing type of nonlinear optical (NLO) material. Herein, a new rare-earth oxythiogermanate EuGeOS crystallizing with a polar orthorhombic 2 structure is studied. Its three-dimensional structure is constructed from unique [EuOS] monocapped trigonal prisms and isolated [GeOS] tetrahedra, featuring a new type of oxysulfides. Its band gap is 2.05 eV, and it exhibits obvious second-harmonic generation (SHG) response and high laser-induced damage threshold. In addition, EuGeOS exhibits Curie-Weiss ferromagnetic behavior in the high-temperature region. The SHG effect is ascribed to the synergistic effect of [EuOS] and [GeOS] units based on theoretical calculation results. This work is the first investigation of quaternary rare-earth oxythiogermanates as NLO materials.