Defect process in bismuth germanante: A precursor to band-edge engineering and design of stable scintillators

Materials used as Scintillators suffer degradation while in operation due to defects induced in the process. Overcoming this menace require an extensive understanding of the defect process. Knowledge of the defect formation process is also important in the design of resilient scintillators. Bismuth germanate Bi₄ Ge₃ O₁₂ (BGO) has been extensively studied as a luminescent material that emits light in the visible region upon exposure to ionizing radiation. In this work, we studied using density functional theory, the formation energies of vacancies/intersitials, cation antisites in pristine BGO. Furthermore, to provide insights into factors affecting the stability of doped systems and unravel the origin of the activity of doped BGO, we investigate the structural properties, energetics of pristine and REE (Nd, Pr, Ce and Tm)- doped BGO using first- principles methods. The electronic structure and optical properties of pristine and dopant systems were also studied. We obtained stable site for the dopant and established relationship between size of the dopant and oxygen vacancy formation energy. The doping has minimal effect on structural properties of BGO. However, we found it to impact on O vacancy formation. Our studies of the effect of REE doping shows introduction of states close to the conduction band and provides theoretical insight into how band engineering can be applied to modify properties of scintillators even at very small concentration. Our analysis of the optical properties reveals variations in different regions of photon energy spectra.