Effect of tin doping and tin-bromine co-doping on electronic and optical properties of BiOCl crystal: density functional theory

Abstract Bismuth oxychloride (BiOCl) is a layered compound known for its exceptional physical, chemical, and optical characteristics, along with notable photocatalytic performance under visible light irradiation. This investigation employed density functional theory (DFT) to analyze the electronic band structure, projected density of states (PDOS), joint density of states (JDOS), and dielectric functions of both pristine BiOCl and various doped crystalline structures utilizing a projected augmented wave basis set. The crystallographic symmetry of doped and co-doped configurations exhibited congruency with the pristine crystals. Electronic band structures were evaluated for pristine, doped, and co-doped crystalline forms. In the case of the co-doped Sn x Bi 1−x OBr x Cl 1−x crystal (x = 0.0625, 0.125, and 0.25), energy band gaps of 1.40 eV, 1.42 eV, and 1.5 eV were determined, respectively, signifying a reduction in the energy band gap compared to the single doped and undoped BiOCl crystal. Analysis of the PDOS revealed that the valence band (VB) of the Sn x Bi 1−x OBr x Cl 1−x crystal was characterized by Cl (p), Br (p), O (p), and Sn (s, p) states, while the conduction band (CB) primarily consisted of Bi (p) states. JDOS calculations indicated a shift in peak energy towards lower values, indicating that dopants promoted electron transitions from Cl, Sn, O, and Br p states to the Bi p state. Moreover, investigation of the dielectric function for both pure and doped BiOCl demonstrated that tin-bromine co-doping induced modifications in the static dielectric constant and dielectric permittivity of the unmodified BiOCl crystal. Ultimately, the incorporation of tin and bromine through co-doping exerted a substantial influence on the electronic and optical properties of the doped crystalline materials. Based on our computational assessments, the Sn x Bi 1−x OBr x Cl 1−x configuration with x = 0.25 showcased superior visible light absorption efficiency compared to other doped variations and pristine BiOCl.