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.
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Greenhouse owners highly value the hemispherical light transmittance (THEM) of roofing materials because sunlight rarely projects at a perpendicular angle, especially in high-latitude regions. With growing interest in research of advanced multi-functional greenhouse roofing, a compact and efficient THEM characterization system for lab-scale samples is needed to promote research in the horticulture field. In this study, we developed a tabletop system capable of characterizing THEM of lab-scale samples with a size one-third of that required by the current characterization system. Key designing parameters, such as the beam cross-section area, port area, and port edge thickness were systematically varied to evaluate their impact on THEM characterization. The results indicated that the total port area should be limited to under 1% of the sphere surface area with minimized edge thickness since reflection from the edge area can not be corrected by a double-beam measurement. Furthermore, the collimated beam cross-section area should exceed the port area by a factor of 1.5 to ensure that THEM remains unaffected by the sphere rotation center. The system provides a consistent and reliable method for THEM measurement and offers essential guidelines for future users to construct a similar setup. ... Read more

A study on Er ³⁺ and Yb ³⁺ luminescence excitation in Cs ₃Y ₂I ₉, Cs ₂NaYBr ₆, Cs ₃Lu ₂Br ₉, YCl ₃, YBr ₃, and YI ₃ is presented. The focus is on determining the energy of the charge transfer band, i.e., the energy needed to transfer an electron from the halide anion (Cl, Br, I) to either Yb ³⁺ or Er ³⁺. Those energies together with published spectroscopic information on other lanthanides in the compounds are used to construct vacuum referred binding energies (VRBE) schemes by employing the chemical shift model. Also, VRBE schemes of seven other halide compounds are constructed based on available spectroscopic data. The systematics in the binding energy at the valence band top and conduction band bottom of the thirteen compounds with changing type of halide and with changing compound composition is discussed. ... Read more