Photoluminescence Enhancement through Anion Sublattice Engineering in (dien)In(Cl 1– x Br x ) 6 Hybrid Halides

High Resolution Image Download MS PowerPoint Slide Indium-based hybrid halides are emerging as promising lead-free highly efficient luminescent materials, yet the relationship among their composition, structure, and emission mechanism remains poorly understood. Here, we synthesized and characterized a complete (dien)In(Cl 1– x Br x ) 6 (0 ≤ x ≤ 1) (dien─diethylenetriamine) solid-solution series to elucidate the origin of their photoluminescence (PL) behavior. Pristine (dien)InCl 6 exhibits organic impurity-related emission at 430 nm and lower-energy self-trapped exciton (STE) emission, while even minor Br incorporation (as low as 3.7%) induces a sharp red shift of emission to 580 nm. Structural analysis reveals a sequence of phase transformations accompanied by halide site preference redistribution and anionic substructure ordering. Combined spectroscopic and DFT analyses show that PL originates from ligand-to-metal charge transfer (LMCT) transitions followed by radiative recombination between self-trapped excitons and halide nonbonding states. The systematic evolution of PL and PLE spectra, decreasing Stokes shift, and nonmonotonic PLQY trend, which reaches a maximum of 57% at x = 0.744, are rationalized by suppression of the impurity-associated emission and increasing orbital overlap upon bromide substitution. These results establish the emission mechanism in (dien)In(Cl 1– x Br x ) 6 and demonstrate how subtle structural and electronic changes govern radiative processes in indium halide hybrids, offering design principles for efficient lead-free luminescent materials.