Study of Annihilation Photon Pair Coincidence Time Resolution Using Prompt Photon Emissions in New Perovskite Bulk Crystals

Semiconductor-based radiation detectors can typically achieve better energy and spatial resolution when compared to scintillator-based detectors. However, if used for positron emission tomography (PET), semiconductor-based detectors normally cannot achieve excellent coincidence time resolution (CTR), due to the relatively slow charge carrier collection time limited by the carrier drift velocity. If we can collect prompt photons emitted from certain semiconductor materials, there are possibilities that the CTR can be greatly improved, and time-of-flight (ToF) capability can be achieved. In this paper, we studied the prompt photon emission (mainly Cherenkov luminescence) property and fast timing capability of cesium lead chloride (CsPbCl₃) and cesium lead bromide (CsPbBr₃), which are two new perovskite semiconductor materials. We also compared their performance with thallium bromide (TlBr), another semiconductor material that has already been studied for timing using its Cherenkov emissions. We performed coincidence measurements using silicon photomultipliers (SiPMs), and the full-width-at-half-maximum (FWHM) CTR acquired between a semiconductor sample crystal and a reference lutetium-yttrium oxyorthosilicate (LYSO) crystal (both with dimensions of 3 × 3 × 3 mm³) is 248 ± 8 ps for CsPbCl₃, 440 ± 31 ps for CsPbBr₃, and 343 ± 16 ps for TlBr. Deconvolving the contribution to CTR from the reference LYSO crystal (around 100 ps) and then multiplying by the square root of 2, the estimated CTR between two of the same semiconductor crystals was calculated as 324 ± 10 ps for CsPbCl₃, 606 ± 43 ps for CsPbBr₃ and 464 ± 22 ps for TlBr. This ToF capable CTR performance combined with an easily scalable crystal growth process, low cost and toxicity, as well as good energy resolution lead us to the conclusion that new perovskite materials such as CsPbCl₃ and CsPbBr₃ could be excellent candidates as PET detector materials.