Structural Design Strategies of Lead-Free Ternary Metal Halide Scintillators for Advanced X-ray Imaging

Conspectus The ever-increasing demand for advanced X-ray detection technologies calls for a revolution in conventional inorganic scintillators. In recent years, ternary metal halides (TMHs) have attracted extensive attention from both the scientific and industry communities owing to their strong X-ray absorption, high luminescence efficiencies, and structurally tunable characteristics, positioning them as promising candidates for next-generation scintillation materials. Generally, the performance of TMHs is governed by the synergistic interplay between metal halide structural units and organic components (ions or coordinated ligands), wherein the diverse assembly of organic and inorganic moieties affords a unique platform for rational materials design. To date, owing to the strong X-ray absorption arising from the high atomic number of Pb, lead-based TMH (Pb-TMH) scintillators represent the most explored materials for X-ray detection and imaging. However, Pb-TMHs suffer from severe self-absorption, inherent lead toxicity, and poor environmental stability, which critically impede their practical deployment. Encouragingly, lead-free TMH scintillators, particularly those based on Cu(I), Mn(II), and Sb(III), have demonstrated scintillation performances comparable to or even surpassing those of lead-based scintillators. Given this great progress, the key to advancing TMH scintillators toward practical applications lies in developing strategies for designing structural units that achieve optimal balance among scintillation performance, long-term stability, and processing compatibility. In this Account, we present a material design paradigm that employs TMH structural units as modular building blocks to construct high-performance scintillators for advanced X-ray imaging. It begins by introducing the structural types and underlying luminescence mechanisms of Mn(II)-, Cu(I)-, and Sb(III)-based TMHs, followed by a systematic discussion of the structural design strategies developed for these three systems with particular emphasis on organic ligand functionalization and inorganic polyhedral configuration modulation. Following this route, we emphasize the approaches for enhancing scintillation performance through cation engineering, core geometry modulation, coordination framework rigidity modulation, and guest molecule incorporation based on the structure–property relationships established across these three material systems. We further demonstrate that these well-designed TMH scintillators meet the diverse demands of X-ray imaging in various scenarios, including flexible curved-surface imaging, underwater imaging, dynamic imaging, and computed tomography. In addition, we highlight our unique insights into the development of advanced X-ray detection and imaging technologies, including the construction of an omnidirectional X-ray detection device and the establishment of a novel X-ray imaging mode with long-term archival storage and rewritable readout capabilities. Lastly, we point out the remaining challenges and future research directions in this field. We hope that this Account provides novel insights into the key parameters governing the scintillation performance of lead-free TMHs and inspires further design of advanced X-ray imaging materials with tailored properties.