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

BaCeO 3 perovskites doped with Eu 3+ ions exhibit strong charge-transfer (CT)-excited orange–red emission but suffer from oxygen-vacancy-induced non-radiative losses. In this study, Li + and Bi 3+ were introduced as aliovalent co-dopants to modulate defect chemistry and local symmetry in BaCeO 3 : Eu 3+ (BCE). A compositional series BaCe 0.96−x Eu 0.04 Li x Bi x O 3 (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 Bi 3+ -mediated CT coupling. These findings provide mechanistic insight into defect–structure–emission correlations and establish co-doped BaCeO 3 as a robust 321 nm-excitable phosphor platform.