Cu2EuMQ4 (M = Si, Ge; Q = S, Se): Syntheses, structure study and physical properties determination

Three europium chalcogenides , Cu 2 EuSiS 4 ( 1 ), Cu 2 EuGeS 4 ( 2 ), and Cu 2 EuGeSe 4 ( 3 ) were obtained by a high-temperature solid-state method. They crystallize in the noncentrosymmetric space groups P 3 1 21 ( 1 ), P 3 2 21 ( 2 ), and Ama 2 ( 3 ), respectively. Their structures can be described as EuQ 8 bicapped trigonal prisms ( btp s) constructed 3 D frameworks, and Cu and Si/Ge atoms occupying the tetrahedral cavities. The 3 D network built by CuQ 4 and Si/GeQ. 4 tetrahedra in 3 is different from that in 1 and 2 . Their energy band gaps are determined to 2.36, 2.32, and 1.74 eV for 1 – 3 , respectively. Compound 1 shows typical photoluminescence of Eu 2+ ion. All of them show antiferromagnetic-like behaviors, and are not second-harmonic generation-active. Theoretical calculations indicate that 1 and 2 show direct band gaps, while 3 indirect.