Nanocrystal-based scintillators for TOF-PET with ultimate time resolution

The 10ps TOFPET challenge [1] requires a parallel effort on all the components of the detector chain (crystal, photodetector, readout electronics). Even with the best presently available SiPM photodetectors, the most popular scintillators for PET (L(Y)SO, L(G)SO, LaBr3) are limited in their timing performance at low energy and a mechanism to produce a few hundred prompt photons on top of the scintillation signal is necessary in order to reach 10ps coincidence time resolution (CTR) at 511keV.

This contribution describes our work for developing a metamaterial-based scintillator block having these characteristics. A quantitative justification will be given, based on our measurements, for a combination of L(Y)SO, in form of block, plates or fibers with:

• ZnO rods of different sizes
• CdSe nanoplatelets, taking advantage of the 1D quantum confinement, allowing coherent multi-excitonic emission with a <1ps rise time and 290ps decay time,
• ZnO:Ga quantum dots, with <1ps rise time and 504ps decay time,
• CsPbBr3 perovskite quantum dots showing a bright multiexcitonic emission with rise time of <1ps, and a decay time of 320ps (»50%) and 2.48ns (»50%).

Simulation results for different, but not yet optimized, geometrical configurations of the metamaterial structure show that an energy leakage from LYSO to the fast component of the metastructure of ≥ 100keV can be obtained for about 20% of the 511keV -rays fully converted in the metastructure, inducing the production of »250 prompt photons on CdSe nanoplatelets on top of the LYSO scintillation signal.

Evidence of this prompt emission has been obtained in our lab on a simple heterostructure made of 200micron thick LYSO plates covered by CdSe nanoplatelets layers deposited by drop casting. Results on more metastructures configurations will be given at the time of the conference.

[1] P. Lecoq, “Pushing the limits in Time-Of-Flight PET imaging”, IEEE Trans. Rad. Pl. Med. Sc., NOV. 2017. Volume: 1 Issue: 6, pp 473-485