Multilayer Metascintillators Based on High Light Yield Nanocomposites Enable Ultrafast Time Coincidence Resolution

Fast and highly emissive scintillators are requested for many advanced applications where high signal-to-noise ratio is required in a short time window. For example, to detect high rate events avoiding pile up in high energy physics experiments at the energy and intensity frontiers, coping with the challenges of unprecedented event rate and severe radiation environment; or to quickly acquire high quality images at low dose in medical applications, like in time-of-flight positron emission tomography (TOF-PET) imaging technique, where coincidence time resolution (CTR) of tens of picoseconds time resolutions are desired. Plastic scintillators fulfill the requirement of fast emission but unfortunately, their low density results into a low stopping power of high energy radiation as well as into an inadequate scintillation light yield - the ratio between the number of emitted photons and the energy deposited in the system – that is lower than the one of top inorganic scintillators. This, detrimentally limits the collected light output and consequently the detector sensitivity, especially in those applications where small detectors are required. A common strategy to improve their is the loading of polymeric scintillators with high Z elements or dense nanoparticles (NPs) to enhance the stopping power of liquid and polymeric conjugated scintillators. [1] [2] [3] Here a composite polymeric scintillator consisting in a scintillating polymeric PVT matrix embedding the BBQ scintillating dye and loaded with hafnium oxide NP is presented. By exploiting the localized radiosensitization effect of the heavy NPs, [1] we finely selected and tuned the material composition and the component properties in order to maximize the radiation’s energy deposition, its harvesting and its conversion to emissive molecular excitons. The system properties have been investigated by means of steady state and time resolved photoluminescence and scintillation spectroscopy. In the best configuration, the nanocomposite shows a = 60000 ph MeV^-1, which surpasses any commercial plastic scintillator, and fast scintillation with 0.15 ns and 1.6 ns of rise and decay time, respectively. [5]<br/><br/>This fast and highly scintillating nanocomposite has been coupled to bismuth germanate oxide (BGO) realizing a prototype multilayer heterostructured scintillator pixel of 3x3x3 mm³ of TOF-PET imaging. [4] Upon interaction with 511 keV g-rays, the energy sharing between the dense BGO, which stops the radiation, and the lighter nanocomposite is observed. This process activates the nanocomposite’s fast emission enabling an excellent ultrafast coincidence time resolution (CTR) of 120 ps full width half maximum (FWHM), [5] which is about half of the one given by BGO and other crystals used in commercial scanners.<br/><br/>[1] Villa et al. <i>Nano Letters</i>, accepted.<br/>[2] Orfano et al. <i>Nature Photon. </i>17, 672–678 (2023)<br/>[3] Gandini et al. <i>Nature Nanotechnol</i>. 15, 462–468 (2020)<br/>[4] Orfano at al. <i>Adv. Mater. Technol</i>. 2024, 2302075<br/>[5] Villa et al. in preparation