Nano Organic Co-Crystal Scintillator for X-ray Imaging

Traditional-metal-containing scintillators are widely used in X-ray imaging due to their efficient X-ray absorption and output of visible light. However, they suffer from heavy-metal toxicity, environmental stability, harsh preparation, and afterglow. Metal-free organic scintillators show a rising momentum, especially organic-halogen-containing molecules. Halogens are introduced to improve their X-ray absorption, but the resulting increase in spin-orbit coupling leads to significant delayed fluorescence or phosphorescence, affecting the response speed to X-rays. Moreover, there is still insufficient practice in fabricating microstructured organic scintillators for high spatial resolution of imaging. Herein, the preparation of nano organic co-crystals (t-Bpe-IFB co-crystal, abbreviated as BIC, t-Bpe for trans-1,2-bis(4-pyridyl)ethylene, and IFB for 1,3,5-trifluoro-2,4,6-triiodobenzene) and its application in X-ray imaging are explored. In contrast to previous single organic-halogen-containing molecules, BIC generates nanosecond-scale fluorescence through the charge-transfer state of the donor-acceptor. Its high iodine content ensures large X-ray absorption, strong radioluminescence, and a low detection limit of 85 nGy(air) s(-1). The composite film made of nano-sized BICs and polydimethylsiloxane exhibits a high spatial resolution of 16.7 lp mm(-1). Herein, the application of organic co-crystals is expanded and ideas are provided for the development of new scintillators.