Ultrafast emission from colloidal nanocrystals under pulsed X-ray excitation

Fast timing has emerged as a critical requirement for radiation detection in medical and high energy physics, motivating the search for scintillator materials with high light yield and fast time response. However, light emission rates from conventional scintillation mechanisms fundamentally limit the achievable time resolution, which is presently at least one order of magnitude slower than required for next-generation detectors. One solution to this challenge is to generate an intense prompt signal in response to ionizing radiation. In this paper, we present colloidal semiconductor nanocrystals (NCs) as promising prompt photon sources. We investigate two classes of NCs: two-dimensional CdSe nanoplatelets (NPLs) and spherical CdSe/CdS core/giant shell quantum dots (GS QDs). We demonstrate that the emission rates of these NCs under pulsed X-ray excitation are much faster than traditional mechanisms in bulk scintillators, i.e. 5d-4f transitions. CdSe NPLs have a sub-100 ps effective decay time of 77 ps and CdSe/CdS GS QDs exhibit a sub-ns value of 849 ps. Further, the respective CdSe NPL and CdSe/CdS GS QD X-ray excited photoluminescence have the emission characteristics of excitons (X) and multiexcitons (MX), with the MXs providing additional prospects for fast timing with substantially shorter lifetimes

Detectors in Medicine and Biology

The invention by Crookes at the end of the nineteenth century of a device called spinthariscope, which made use of the scintillating properties of Lead Sulfide allowed Rutherford to count α particles in an experiment, opening the way towards modern dosimetry. When at the same time Wilhelm C. Roentgen, also using a similar device, was able to record the first X-ray picture of his wife’s hand 2 weeks only after the X-ray discovery, he initiated the first and fastest technology transfer between particle physics and medical imaging and the beginning of a long and common history