Lead halide perovskites are reportedly a very promising group of materials for scintillation due to their fast sub-nanosecond exciton luminescence, small band-gaps, and high theoretical light yield. Unfortunately, they only show emission at cryogenic temperatures. In this work single crystals of CsPbBr₃ and CsPbCl₃ are studied at cryogenic temperatures. Upon comparing the 10 K emission spectra measured under X-ray and UV–vis excitation, a new near-infrared emission was found for both CsPbBr₃ and CsPbCl₃ only present under X-ray excitation. The integral light yields of CsPbBr₃ and CsPbCl₃ at 10 K are estimated to be 34,000 and 2,200 photons/MeV under 40 keV X-ray excitation, respectively. The main components of the light yield of CsPbBr₃ at 10 K are the near band-gap free exciton emission that suffers from self-absorption and the broad near-infrared emission that falls outside the typical detection range of a photo-multiplier tube. Due to the combination of the two aforementioned effects it was not possible to measure a γ-ray pulse height spectrum for CsPbBr₃ at 10 K. Despite all the suitable properties, like the fast decay, a small band-gap, and the positive prospects of 3D perovskite based scintillators, we conclude that these materials perform poorly as scintillation crystals.

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NaI is the most commonly used host lattice for scintillators, which makes it interesting to further improve its scintillation properties. Many alternative activators have been tried instead of the conventionally used Tl+. In this work, Sm2+ is used as an near-infrared emitting activator for NaI to study whether it is suitable for readout with silicon based photodetectors. NaI single crystals (co-)doped with 0-0.2% Tl+ and 0.2%–2% Sm2+ were grown by the vertical Bridgman technique. The emission of the samples was studied under optical and X-ray excitation. It is shown by photoluminescence decay studies that Tl+ works as a sensitiser for Sm2+. The samples indicate the formation of multiple (at least 5) different Sm2+ emission sites. Annealing the samples changes their emission intensity and scintillation properties. NaI:Sm2+ shows great similarities with its Eu2+-doped counterpart. Finally, it is demonstrated that NaI:Sm2+ can be read out with silicon photomultipliers and an energy resolution of 11% has been attained.@en

Small bandgap scintillators have gained significant attention in recent years. Especially Cs4PbBr6 is an interesting material, mitigating the small Stokes shift-related problem of perovskites like CsPbBr3. In this work, optical and scintillation properties of Cs4PbBr6 single crystals are investigated as a function of temperature, with a detailed focus at 10 K. The Cs4PbBr6 single crystals were grown using the vertical Bridgman method. Due to incongruent melting, CsPbBr3 inclusions are formed, generating a 540 nm emission band. Prepairing Cs4PbBr6 via solid-state synthesis yields CsPbBr3-inclusion-free material, showing no green 540 nm emission band. In Cs4PbBr6 samples with and without CsPbBr3 inclusions, a new emission band at 610 nm ascribed to an unknown defect was found. Based on the presented experiments, an emission mechanism is proposed for Cs4PbBr6. This shows that both defects and CsPbBr3 inclusions play a role in the emission behavior of Cs4PbBr6 but only the CsPbBr3 inclusions are responsible for the 540 nm emission.@en

Recent research activity on Sm²⁺-doped compounds has significantly increased the amount of available data on 4f⁵5d → 4f⁶ decay times. This enabled the systematic comparison of spectroscopic and time resolved luminescence data to theoretical models describing the interplay between the 4f⁵5d and 4f⁶[⁵D₀] excited states on the observed decay time. A Boltzmann distribution between the population of the excited states is assumed, introducing a dependence of the observed 4f⁵5d → 4f⁶ decay time on the energy gap between the 4f⁵5d and 4f⁶[⁵D₀] levels and temperature. The model is used to interpret the origin of the large variation in reported 4f⁵5d → 4f⁶ decay times through literature, and links their temperature dependence to applications such as luminescence thermometry and near-infrared scintillation. The model is further applied to the analogous situation of close lying 4f^n-15d and 4fⁿ states in Eu²⁺ (⁶P_7/2) and Pr³⁺ (¹S₀).

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Currently only Eu²⁺-based scintillators have approached the light yield needed to improve the 2% energy resolution at 662 keV of LaBr₃:Ce³⁺,Sr²⁺. Their major limitation, however, is the significant self-absorption due to Eu²⁺. CsCu₂I₃ is an interesting new small band gap scintillator. It is nonhygroscopic and nontoxic, melts congruently, and has an extremely low afterglow, a density of 5.01 g/cm³, and an effective atomic number of 50.6. It shows self-trapped exciton emission at room temperature. The large Stokes shift of this emission ensures that this material is not sensitive to self-absorption, tackling one of the major problems of Eu²⁺-based scintillators. An avalanche photo diode, whose optimal detection efficiency matches the 570 nm mean emission wavelength of CsCu₂I₃, was used to measure pulse height spectra. From the latter, a light yield of 36 000 photons/MeV and energy resolution of 4.82% were obtained. The scintillation proportionality of CsCu₂I₃ was found to be on par with that of SrI₂:Eu²⁺. Based on temperature-dependent emission and decay measurements, it was demonstrated that CsCu₂I₃ emission is already about 50% quenched at room temperature. Using temperature-dependent pulse height measurements, it is shown that the light yield can be increased up to 60 000 photons/MeV by cooling to 200 K, experimentally demonstrating the scintillation potential of CsCu₂I₃.

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The benefits of doping Cs₄EuBr₆ and Cs₄EuI₆ with Sm²⁺ are studied for near-infrared scintillator applications. It is shown that undoped Cs₄EuI₆ suffers from a high probability of self-absorption, which is almost completely absent in Cs₄EuI₆:2% Sm. Sm²⁺ doping is also used to gain insight in the migration rate of Eu²⁺ excitations in Cs₄EuBr₆ and Cs₄EuI₆, which shows that concentration quenching is weak, but still significant in the undoped compounds. Both self-absorption and concentration quenching are linked to the spectral overlap of the Eu²⁺ excitation and emission spectra which were studied between 10 K and 300 K. The scintillation characteristics of Cs₄EuI₆:2% Sm is compared to that of the undoped samples. An improvement of energy resolution from 11% to 7.5% is found upon doping Cs₄EuI₆ with 2% Sm and the scintillation decay time shortens from 4.8 s to 3.5 s in samples of around 3 mm in size.

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