Halogen Substitution in Zero‐Dimensional Mixed Metal Halides toward Photoluminescence Modulation and Enhanced Quantum Yield

Abstract Zero‐dimensional (0D) organic−inorganic hybrid metal halides haveunprecedented degrees of freedom for structural tunability and photoluminescence modulation. Here, the 0D isomorphic hybrid metal mixed halides (C₉NH₂₀)₉Pb₃Zn₂Br_19(1−x)Cl_19x (x = 0–1) with continuous halogen contents control, exhibiting tunable emission and enhancement of photoluminescence quantum yield (PLQY) are reported. The competitive bromine to chlorine substitution process in (C₉NH₂₀)₉Pb₃Zn₂Br_19(1−x)Cl_19x occurs first in [ZnBr_4−xCl_x]²⁻ tetrahedron before the [Pb₃Br_11−xCl_x]⁵⁻ trimer. The increasing Cl content in samples from x = 0 to 1 results in an expected blue shift of emission peak from 565 to 516 nm, and meanwhile a strikingly room temperature PL quantum yield increase from 8% to 91%. Combined experimental characterizations and theoretical calculations indicate that the blue shift of interband transition energy is responsible for the emission peak shift. Moreover, with the increasing Cl content, the enhanced electron−phonon interaction and the weakened thermal‐assisted nonradiative recombination result in more efficient radiative transition channels and ultimately enhanced PLQY. The impact of halogen substitution on electronic structures and optical properties in 0D hybrid metal halides is emphasized in this work as a new strategy to promote the future development of new luminescent materials.