On the use of CdSe scintillating nanoplatelets as time taggers for high-energy gamma detection

R M Turtos,S Gundacker,I Moreels,C Dujardin,S Omelkov,B Mahler,M Kirm,Z Meng,A Vasil’Ev,J Saaring,A H Khan,P Lecoq,E Auffray

doi:10.1038/s41699-019-0120-8

Abstract

The technological challenge imposed by the time resolution essential to achieve real-time molecular imaging calls for a new generation of ultrafast detectors. In this contribution, we demonstrate that CdSe-based semiconductor nanoplatelets can be combined with standard scintillator technology to achieve 80 ps coincidence time resolution on a hybrid functional pixel. This result contrasts with the fact that the overall detector light output is considerably affected by the loss of index-light-guiding. Here, we exploit the principle of 511 keV energy sharing between a high-Z, high stopping power bulk scintillator, and a nano-scintillator with sub-1 ns radiative recombination times, aiming at a breakthrough in the combined energy and time resolution performance. This proof-of-concept test opens the way to the design and study of larger size sensors using thin nanocomposite layers able to perform as efficient time taggers in a sampling detector geometry of new generation.

Highlights

The possibility of reaching real-time molecular imaging for cancer diagnosis using time-of-flight positron emission tomography scanners (TOF-PET) calls for well dedicated efforts along this line of research.[1]Benefits would extend beyond a 10-fold sensitivity, and spread to areas like neonatal imaging and theranostics, just to mention a few.[2]
In order to increase the prompt photon emission yield, we propose to replace the usual bulk scintillator pixel by a sampling configuration, so that the recoil electron from a photoelectric conversion created in the dense host scintillator can eventually reach a fast emitting nano-scintillator layer.[12]
As presented in the sections above, CdSe/CdS nanoplatelets exhibit a red-shifted RL emission with a binding energy of 35 meV, characteristic of biexcitons in 1.5 nm thick CdSe platelets. This confirms biexcitonic emission under X-ray excitation, which have associated decay times of ~100 ps, a promising route to pursue for fast timing applications

Summary

Introduction

The possibility of reaching real-time molecular imaging for cancer diagnosis using time-of-flight positron emission tomography scanners (TOF-PET) calls for well dedicated efforts along this line of research.[1]Benefits would extend beyond a 10-fold sensitivity, and spread to areas like neonatal imaging and theranostics, just to mention a few.[2]. The possibility of reaching real-time molecular imaging for cancer diagnosis using time-of-flight positron emission tomography scanners (TOF-PET) calls for well dedicated efforts along this line of research.[1]. PET scanner are at the level of 215 ps using Lu2−xYxSiO5 crystals and silicon photomultiplier (SiPM) readout.[3] Time resolution achieved with current state-of-the-art scintillators featuring standard photon emission mechanisms, i.e., minimum decay times of tens of nanoseconds and maximum light yield of. 100,000 ph/MeV, is largely limited by their associated photon-time density.[4,5,6] harvesting prompt photons from quantum confined direct band-gap semiconductors would highly impact the time resolution of state-of-the-art scintillating detectors.[4]

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Methods

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Conclusion