Synthesis, structure, and optical properties of the quaternary diamond-like compounds I2–II–IV–VI4 (I=Cu; II=Mg; IV=Si, Ge; VI=S, Se).

Three new diamond-like compounds with the formula of I2−II−IV−VI4 (I=Cu; II=Mg; IV=Si, Ge; VI=S, Se) have been synthesized via traditional high-temperature solid-state reactions and structurally characterized by single crystal X-ray diffraction analysis. All the three compounds crystallize in the space group Pmn21 in the wurtzite-type superstructure with a=7.563(4), b=6.448(3), c=6.179(3)Å, Z=2 for Cu2MgSiS4 (1); a=7.953(5), b=6.797(4), c=6.507(4)Å, Z=2 for Cu2MgGeS4 (2); a=7.638(4), b=6.515(4), c=6.225(3)Å, Z=2 for Cu2MgSiSe4 (3). All atoms in these compounds are tetrahedrally coordinated. Optical diffuse reflectance UV/Vis/NIR spectra indicate that compounds 1 and 2 have the band gaps of 3.20 and 2.36eV, respectively. Electronic structure calculations using the CASTEP code indicate that they are all direct band gap compounds. [ABSTRACT FROM AUTHOR]