Tailored Mn2+-Activated Zinc Halides for Enhanced X-ray Imaging via Ligand Modulation

Abstract

Lead-free organic–inorganic metal halides have emerged as promising candidates for X-ray imaging applications owing to their intrinsic radioluminescence, solution processability, and economic viability. However, their development remains largely empirical, with limited understanding of the structure–property relationships governing radioluminescence efficiency and stability. Herein, we address this challenge using two zero-dimensional (0D) mixed-metal Mn-Zn bromide systems with distinct organic spacers (T = C9H14BrN and D = C6H12N2), enabling controlled modulation of organic spacer length and metal–metal separation. Although both systems exhibit near-unity photoluminescence quantum yields (PLQYs), they display markedly different scintillation responses. The larger metal–metal separation in Mn0.5Zn0.5Br4T, induced by the longer organic cation T, suppresses nonradiative interactions, leading to enhanced radioluminescence efficiency and operational stability. The optimized system, Mn0.5Zn0.5Br4T, achieves a high light yield of 76,000 photons MeV–1, excellent stability, and an ultralow detection limit of 112 nGy s–1—approximately 50 times lower than standard medical diagnostic dose rate (5.5 μGy s–1). Flexible large-area scintillators further demonstrate high-resolution X-ray imaging capability. This work establishes a structure–property relationship linking organic spacer modulation, mixed-metal composition, and scintillation efficiency, enabling a rational design framework for scalable, high-performance X-ray scintillators.