Unlocking Intense and Near‐Full‐Spectrum Photoluminescence in Cd‐Based Metal Halides Via Pressure and Doping Engineering

ABSTRACT 2D Cd‐based metal halides combine exceptional air stability with reduced toxicity, rendering them promising alternatives to Pb‐based perovskites for optoelectronic applications. Nevertheless, achieving highly efficient and tunable multicolor photoluminescence (PL) in these materials remains a formidable challenge. Herein, BDACdBr 4 (BDA = 1,4‐butanediamine) exhibits intense, near‐full‐visible PL through the synergistic application of high‐pressure tuning and ionic substitution. Upon compression, pronounced octahedral distortions, intralayer deformation, and interlayer contraction are induced, collectively restricting excited‐state relaxation, strengthening electron‐phonon coupling, and lowering reorganization energy. These effects substantially promote radiative recombination of self‐trapped excitons (STEs) while suppressing nonradiative decay, leading to intense PL emission under pressure. Simultaneously, the widened bandgap, reduced Stokes shift, and reduced degeneracy of STE states contribute to an obvious blueshift in emission, ranging from natural white to blue. Furthermore, partial ionic substitution with Pb 2+ and Sb 3+ enables pressure‐tunable emission spanning from deep‐blue to orange‐red. This dual approach, combining pressure and doping engineering, provides a versatile strategy for designing efficient, multicolor emissive metal halides, highlighting their potential for next‐generation pressure sensors and solid‐state lighting technologies.