Tailoring Self‐Trapped Exciton Emission in 0D Indium‐Based Perovskites by Solvent‐Induced Crystal Structure Engineering

Abstract 0D indium‐based all‐inorganic metal halide perovskites offer great potential for multifunctional applications but face the challenges of poor structural adjustability and an incomplete dynamic picture of self‐trapped exciton (STE) emissions. Here, a novel 0D Cs 4 InCl 7 single crystal is developed as a solvation bridge for phase transformations to either 0D Cs 2 InCl 5 ·H 2 O via water or into 0D Cs 3 InCl 6 by methanol. The diversified crystal structures not only enrich the emission colors but also the difference in the coordination number and symmetry of Cs + , laying foundations for comprehending the influence of A‐site on STE emissions. Steady‐state and transient spectroscopy together with density functional theory simulations, reveal that low coordination geometry and charge symmetry of octahedron facilitate excited state distortions, leading to strong second‐order Jahn‐Teller (SOJT) effect for large Stokes shift of STE emissions. Multicolor tuning in Sb 3+ ‐doped Cs 4 InCl 7 under solvent and heat stimuli enables the extended optical applications in anti‐counterfeiting, temperature sensing, and solvent sensors. The work offers an improved understanding of SOJT manipulation via atomic engineering of A‐site in 0D lead‐free perovskites and sheds light on their broad practical applications.