Heavy-Metal-Free ZnSeTe Quantum Dots-Based Liquid Scintillators for Scalable X-Ray Imaging

Quantum dot (QD)-based scintillators show promise for use as flexible X-ray imaging screens due to their high performance and scalable characteristics. However, conventionally used QD-based scintillators face severe limitations, including poor chemical stability and unavoidable toxic issues arising from heavy metals such as cadmium (Cd) or lead (Pb). Herein, a Cd/Pb-free liquid scintillator based on ZnSeTe-based core-shell QDs and an energy transfer donor molecule of 2,5-diphenyloxazole (PPO) is reported, which offers high efficiency and scalability. By adjusting the Te/Se ratios of ZnSeTe, an optimal balance between X-ray absorption and radioluminescence efficiency of ZnSeTe-based core-shell QDs is achieved, resulting in a blue-emitting scintillator with a light yield of 11 222 (±2%) photons MeV^-1 beyond commercial Bi₃Ge₄O₁₂. Furthermore, halogen passivation effectively eliminates trap states on the surface of ZnSeTe-based core-shell QDs, doubling the X-ray-excited fluorescence intensity. Consequently, the composite liquid scintillator, fabricated using PPO-composited ZnSeTe-based QDs, achieves a high light yield of 33 450 (±5%) photons MeV^-1 and a low detection limit of 788.4 nGy s^-1. High-performance X-ray imaging with a spatial resolution of 6.7 line pairs (lp) mm^-1 is achieved. This work introduces a novel approach for the development of eco-friendly QD-based scintillators with structural and optical modulation for high-performance X-ray imaging.