Mechanistic Insights into Li⁺, Bi³⁺ Co-doped BaCeO₃: Eu³⁺ phosphors - defect passivation and enhanced charge-transfer...

BaCeO₃ perovskites doped with Eu³⁺ ions exhibit strong charge-transfer (CT)-excited orange-red emission but suffer from oxygen-vacancy-induced non-radiative losses. In this study, Li⁺ and Bi³⁺ were introduced as aliovalent co-dopants to modulate defect chemistry and local symmetry in BaCeO₃: Eu³⁺ (BCE). A compositional series BaCe_0.96-xEu_0.04Li_xBi_xO₃ (x = 0-0.04) was synthesized via gel combustion method. Structural refinements confirmed single-phase orthorhombic (Pnma) perovskite with systematic lattice expansion upon co-doping. Co-doping suppressed oxygen-vacancy-related defect states, as evidenced by decreased Urbach energy (0.664 → 0.621 eV) and narrowed O 1s defect bands in XPS. Under 321 nm excitation, corresponding to the O²⁻ → Ce⁴⁺ CT transition, photoluminescence (PL) intensity increased nearly two-fold (at x = 0.02) relative to BCE. Lifetime analysis revealed longer average decay (1.02 → 1.37 ms) and improved radiative fraction. The external quantum efficiency (EQE) rose from 38% to 51%. The enhancement originates from charge-compensated defect passivation and Bi³⁺-mediated CT coupling. These findings provide mechanistic insight into defect-structure-emission correlations and establish co-doped BaCeO₃ as a robust 321 nm-excitable phosphor platform.