Partial ligand exchange as a critical approach to the synthesis of transparent ytterbium fluoride-polymer nanocomposite monoliths for gamma ray scintillation

Partial ligand exchange is reported to be an effective approach to the synthesis of transparent bulk-size ytterbium fluoride-polyvinyl toluene (PVT) nanocomposites containing a high loading of YbF₃ nanoparticles. A bifunctional compound, bis[2-(methacryloyloxy)ethyl] phosphate (BMEP), is introduced to partially replace the oleic acid (OA) ligand on the surface of YbF₃ nanoparticles (NPs). The remaining OA helps retain a good dispersion of the nanoparticles in monomer vinyl toluene, while grafted BMEP enables the copolymerization of the nanoparticles with the polymer matrix. As a result, bulk transparent YbF₃/PVT nanocomposites with 1 mm thickness have been synthesized containing up to 63 wt% of YbF₃ nanoparticles (80 wt% if including the weight of the organic ligands and 47 wt% of the net Yb atoms) coupled with a transmission as high as ∼80%. Transmission electron micrographs show a uniform dispersion of the nanoparticles in the polymer matrix due to covalent bonding of the nanoparticles onto the polymer matrix via the BMEP ligand molecules, which overcomes the exclusion of the nanoparticles during the polymer chain growth. A monolith scintillator based on the transparent nanocomposite containing dissolved fluor compounds produces scintillation emission peaked at 416 nm with high light yield under 662 keV gamma ray irradiation.