Ce-activated A 2+ B 4+ O3 perovskites represent a class of compounds currently under active exploration for their potential as scintillators. Depending on the chemistry and synthesis conditions, perovskites can crystallize in multiple crystal structures and a Ce substitutional dopant in an ABO3 perovskite can adopt different charge states (i.e., Ce 3+ or Ce 4+) as well as different substitutional sites (namely the 12-fold coordinated A-site or the octahedrally coordinated B-site). Here, we use first-principles density functional theory (DFT) and hybrid functional based computations to study relative trends in structure, energetics and electronic structure of bulk ABO3 perovskites, where A = Ca, Sr and Ba and B = Hf and Zr. Subsequently, we consider the relative energetics of preferential solution sites for Ce as a function of charge states, chemical potential and defect configurations. Our results reveal that while Ce 3+ or Ce 4+ defects can be thermodynamically stable, depending on the choice of the substitutional site and synthesis conditions (i.e., prevailing chemical potential), only Ce 3+ dopant at the A-site leads to an electronic structure that can exhibit scintillation. Our comparative analysis shows that while the positions of 5d 1 and 4f levels of Ce 3+ doped at the A-site are favorably placed in the band structure, these levels are consistently higher for the Ce 4+ charge state and are unlikely to manifest any luminescence. Findings of the present study are also discussed in relation to previously reported results and display an excellent agreement with past experimental observations. In general, it is demonstrated that controlling Ce charge state and local chemical environment can be used-in addition to band gap and band edge engineering-to manipulate the relative position of scintillating states with respect to valence band maximum (VBM) and and conduction band minimum (CBM). While the the present study specifically focused on perovskites, the results (in particular, the relative alignment of the positions of 5d 1 and 4f levels of Ce dopant as a function of the activator's charge state) are expected to be general and thus transferable to other chemistries.