<p>Two-dimensional metal halide perovskites (2D MHPs) have garnered significant attention for their promising optoelectronic properties, driven by strong excitonic effects and structural tunability. Their photoelectric properties are directly determined by their exciton behavior. Here, we investigate the impact of halogen doping on exciton dynamics and emission characteristics in PEA₂Pb(Br_1−<i>x</i>Cl_<i>x</i>)₄. Systematic Cl-doping engineering induces a remarkable spectral evolution, characterized by a transition from blue emission to white-light emission. This transformation correlates with a unique switching behavior between extrinsic and intrinsic self-trapped exciton (STE) states, as revealed through combined analysis of excited-state transitions and carrier dynamics. Temperature-dependent photoluminescence studies coupled with lattice distortion analysis demonstrate that doping induces subtle structural perturbations within the inorganic framework. These minimal lattice modifications fundamentally reconfigure excitonic behavior. The doping-dependent competition between intrinsic polaronic self-trapping and defect-mediated trapping mechanisms accounts for the observed spectral broadening. Specifically, Cl incorporation below 0.2 preferentially enhances intrinsic STE formation through lattice softening, while higher doping levels introduce defect-assisted trapping pathways. This dual-channel trapping model, validated by temperature-activated detrapping kinetics and transient absorption spectroscopy, provides new insights into defect engineering strategies for tailoring emission characteristics in low-dimensional hybrid perovskites.</p>