Synthesis, Optical, and Magnetic Properties of the Mixed Chalcogenide Semiconductor Series Eu(II)SiSeS, Prepared via the Flux-Assisted Boron Chalcogen Mixture Method.

We report a detailed structural study of a series of five new quaternary Eu(II)-containing mixed chalcogenide phases, EuSiSeS, EuSiSeS, EuSiSeS, EuSiSeS, and EuSiSe, synthesized using the flux-assisted boron chalcogen mixture (BCM) method. High-quality crystals were grown, and their crystal structures were determined by single-crystal X-ray diffraction. All members of the EuSiSeS series crystallize in the monoclinic crystal system with space group 2/, except EuSiSe, which crystallizes in the 2 space group. The crystal structure of EuSiSeS exhibits a complex three-dimensional network and is primarily composed of distorted trigonal prismatic Eu polyhedra that are interconnected by Si tetrahedra. Polycrystalline powders were used for physical property measurements, including the magnetic susceptibility and UV-vis diffuse reflectance. Magnetic measurements indicated paramagnetic behavior with a slightly negative Weiss constant (θ = -13.54). The band gaps of the materials were determined from diffuse reflectance data, with optical band gaps estimated to be 2.04(2) eV, 1.98(2) eV, and 1.90(2) eV for EuSiSeS, EuSiSeS, and EuSiSe, respectively. Band gap tuning was achieved by partially or fully replacing the S sites with Se.