• • Cl doping below x = 0.2 enhances intrinsic STE formation through lattice softening, yielding blue emission with narrow bandwidth; this threshold is critical for maintaining color purity in display applications.
• • At x ≥ 0.2, defect-assisted trapping pathways emerge, causing broadband white-light emission with photoluminescence quantum yields (PLQY) up to 12%—a 3-fold increase over undoped PEA2PbBr4, enabling single-material white LEDs.
• • Temperature-dependent PL reveals detrapping activation energies of 45–60 meV for intrinsic STEs and 80–100 meV for defect-mediated traps, providing a quantitative framework for predicting thermal stability in optoelectronic devices.
• • Transient absorption spectroscopy confirms carrier lifetimes of 1.2 ns (intrinsic) vs. 4.5 ns (defect-assisted), indicating that defect engineering can extend exciton lifetimes by 275%, beneficial for scintillator response times.