Synthesis, optical properties, and band structures of a series of layered mixed-anion compounds

Abstract

We report the synthesis and luminescence properties as well as band structure of a series of layered mixed-anion compounds, including a new layered mixed anion compound, Sr₃Sc₂Ag₂Se₂O₅. The crystal structure, band structure, and optical properties of this new compound and of related compounds Sr₃Sc₂Cu₂Ch₂O₅ (Ch:chalcogen = S, Se) are presented. The compounds have a common perovskite-like layer of (Sr₃Sc₂O₅)²⁺ and different semiconductor layers of (Cu₂S₂)²⁻, (Cu₂Se₂)²⁻ or (Ag₂Se₂)²⁻. Similar band structures are found for the valence band maximum (VBM), while the structure of the conduction band minimum (CBM) is different depending on the chalcogen species, resulting in the different band gap energies of the compounds. The band gap energies are estimated to be 3.3, 2.9, and 2.4 eV for Sr₃Sc₂Cu₂S₂O₅, Sr₃Sc₂Cu₂Se₂O₅, and Sr₃Sc₂Ag₂Se₂O₅, respectively. Excitonic luminescence is observed near the band edge for all three compounds, with different wavelengths according to their band gap. These optical observations are consistent with the DFT calculations. The luminescence properties of the system can be controlled by changing the composition of the semiconductor-layers, thereby offering large flexibility in material design advantageous for various applications.