Nanocrystalline Lead Halide Perovskites to Boost Time-of-Flight Performance of Medical Imaging Detectors

Time-of-flight (TOF) technique, traditionally used in high energy physics (HEP) and positron emission tomography (PET), is now being explored for lower energy applications like computed tomography (CT). Regardless of the application, pushing the current boundaries in time resolution calls for novel technologies and materials exhibiting ultra-fast time response. Semiconductor nanocrystals like cesium lead halide perovskites (CsPbBr3), benefiting from quantum confinement effects, feature ultra-fast decay and, when combined with a suitable bulk scintillator following a heterostructure concept, can also provide the necessary stopping power. In this work, thin films of CsPbBr3 on top of BGO, LYSO:Ce, and GAGG:Ce,Mg wafers are fabricated to test their impact on the single crystal scintillator time resolution under soft X-rays excitation (about 10 keV). It is demonstrated that the CsPbBr3 layer significantly improves the overall time resolution in all cases, achieving up to a tenfold improvement with BGO and GAGG:Ce,Mg. Under 511 keV gamma-rays, a proof-of-concept of the heterostructure design for TOF-PET using CsPbBr3 thin film deposited on GAGG:Ce,Mg bulk crystal is successfully tested. Shared events depositing energy in both materials are identified, resulting in more than twofold improved coincidence time resolution: 118 +/- 4 ps full-width-at-half-maximum (FWHM) compared to the 272 +/- 8 ps of solely GAGG:Ce,Mg. Cesium lead bromide thin films were deposited on GAGG, BGO, and LYSO to improve their timing performances. The time resolution of the resulting heterostructures was measured under X-ray and 511 keV gamma-ray irradiation, achieving tenfold and twofold improvement over the standard scintillator in the two measurements respectively. This demonstrates great potential for time-of-flight X-ray (TOF-X-ray) and positron emission tomography (TOF-PET) applications. image