Lead-free perovskite-inspired metal halides are rapidly emerging as a powerful platform for next-generation optoelectronics, offering chemical tunability, rich structural diversity, and reduced toxicity compared to their lead-based counterparts. [1, 2] Yet, fully exploiting their potential requires a mechanistic understanding of how structural dimensionality, lattice distortion, and dopant chemistry dictate their broadband emission and exciton dynamics. In this presentation, I will highlight our recent efforts to establish these structure–composition–property relationships and translate them into design principles for high-performance lead-free light emitters and sensing materials. [3-5]

We first examine the role of structural dimensionality using a family of antimony (Sb)-doped Indium (In)-based halides that possess 0-dimensional (0D) electronic structures but feature 3D, 2D, 1D, and 0D connectivity at the molecular level. [6] As the dimensionality decreases, the broadband emission redshifts continuously from about 500 to 660 nm (Fig. 1a). Through detailed structural and spectroscopic analyses, we reveal that the distortion of [SbCl₆]^3- octahedra drives this tunability (Fig. 1b). We further demonstrate that solvent coordination during crystallization provides an additional handle to tailor emission: by crystallizing [SbCl₆]^3- frameworks from hydrochloric acid (HCl), dimethylformamide (DMF), methanol (MeOH), acetonitrile (ACN) and dimethylacetamide (DMAC). We uncover solvent-dependent structural motifs where coordinated organic molecules modulate the local metal halide structures and resulting different photoluminescence. [7] Extending these principles, we introduce a broader design strategy that couples ns² ion doping with controlled lattice distortion to achieve tunable broadband emission spanning the UV–visible–NIR range within a single host.

Beyond compositional and structural design, we further probe the fundamental mechanisms governing exciton relaxation in low-dimensional lead-free metal halides, particularly their strong temperature-dependent broadband emission. Using a 1D hybrid organic–inorganic Tin (Sn) halide as a model system, we investigate how exciton–phonon coupling and lattice dynamics regulate broadband emission. Temperature-dependent femtosecond transient absorption (Fig. 1c) measurements provide direct insight into the exciton relaxation pathways, revealing a thermally activated phonon-assisted nonradiative channel. [8] We further investigate the functional role of dimensionality to exciton-phonon coupling and exciton self-trapping.

Together, these results advance the fundamental understanding of lead-free perovskite-inspired materials and establish mechanistic guidelines for their use in broadband LEDs, low-threshold lasers, and temperature-responsive photodetectors.