Core–Valence-Luminescence Cs–M–Cl (M = Zn, Mg) Scintillators for Photon-Counting X-ray Detectors

X-ray photon-counting detectors (PCDs) are a rapidly developing technology used in medical imaging. Current PCDs are based on room-temperature semiconductors, such as CdTe and CZT, directly converting incident X-ray photons into electrical pulses. An alternative to this approach is the use of ultrafast scintillators in combination with silicon photomultipliers. A very interesting class of materials potentially suitable for this application is scintillators exhibiting core–valence luminescence (CVL), which typically has a decay time between 0.5 and 2 ns. In this work, two families of Cs–Cl-based compounds, Cs–Zn–Cl and Cs–Mg–Cl, are investigated for their potential application in PCDs. These families of compounds are especially interesting because most members exclusively show CVL at room temperature, resulting in a fast scintillation pulse containing no slow components. Additionally, several approaches to tailor the scintillation properties of these materials, i.e., doping with Br– and Zn2+, are studied. Unfortunately, all compounds show a strong drop in the CVL response in the diagnostic energy range (25–150 keV), the operational range of a PCD. PCDs based on these materials will thus be able to handle the high X-ray fluence rate of an imaging task but will not be able to sufficiently discriminate the energies of incident X-ray photons. In addition to the Cs–Zn–Cl and Cs–Mg–Cl compounds, the nonproportional response of the CVL component of BaF2 is studied utilizing fast digitization of individual scintillation pulses in order to discriminate between processes related to the CVL and self-trapped exciton emission of BaF2.