Particle-size dependent light yield of scintillating polymeric nanocomposites

Scintillating composites consisting of a dye-doped matrix loaded with dense nanoparticles areintensively studied to overcome the performance limitations of polymeric scintillators used for fasttiming detection, dosimetry, /neutron discrimination, and other medical, technical, and researchapplications. Here we investigate for the first time the scintillation efficiency of a series of compositesloaded with hafnium oxide nanoparticles of different sizes, but where the total mass of added densematter is kept constant. The best composition, counterintuitively, is the one with particles of thelargest employed size (~50 nm) and consequently with the lowest concentration. Spectroscopyexperiments and Monte Carlo modelling of the light/matter interaction show that the presence of largenanoparticles induces a significantly more localized generation of diffusing ionized charges withrespect to the unloaded system. This locally-enhanced charge density favours their recombination togenerate emissive states, thus increasing the composite scintillation yield above that one of manycommercially available polymeric systems. Notably, this happen without affecting the time responseof the material. The obtained results demonstrate that a controlled and finely designed inhomogeneityof the system stopping power, through the loading with low concentration and size-tailorednanoparticles, is a still unexplored and promising strategy to improve the performance of polymericscintillators.