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.