The investigation of optoelectronic properties of doped and co-doped Tm3+ and Tb3+ Bi4Ge3O12 scintillation crystal: New insights from the first principle study

Abstract

In this article, the structural, electronic, and optical characteristics of Germanium Bismuthate Ge3Bi4O12 doped and co-doped Tm and Tb have been studied through ab initio calculations based on density functional theory (DFT). The pure Ge3Bi4O12 was studied by plane DFT using the modified Becke-Johnson approximation (mBJ). To gain a better understanding of the electronic structure and optical properties of Tm and Tb doped Germanium Bismuthate, Ge3Bi4O12, compounds, the GGA + U approximation to density functional theory, in which a generalized gradient approximation (GGA) functional is coupled with a localization correction to tackle on-site correlation as inspired by the Hubbard model, is offered as an alternate technique. The optical parameters like real/imaginary dielectric function, absorption, energy loss function, extension coefficient, and the density of states were calculated and discussed. The electronic structure of Germanium Bismuthate, Ge3Bi4O12, reveals an indirect band gap in both its pure and Tm, Tb-doped forms, with the valence and conduction bands positioned at different points in the Brillouin zone. The electronic structure analysis confirms that an intermediate band is present in Germanium Bismuthate, Ge3Bi4O12, doped with Thulium (Tm); however, this feature is absent in the Terbium (Tb)-doped variant. The valence band near the Fermi level is predominantly derived from the electronic states associated with the O-p orbitals and the Ge-p orbitals. The presence of intermediate bands in the electronic structure of the doped compounds plays a critical role in influencing the optical parameters in the visible region. The doped compounds exhibit optical behaviors in the UV region that are consistent with those of the host materials, demonstrating pronounced peak intensities that are largely independent of their density. This study provides a comprehensive analysis of the electronic and optical properties of the doped compounds, which are essential for understanding their potential technological applications. These findings can guide the design of novel materials by highlighting how specific dopants influence these properties.