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

LaBr₃:Ce³⁺ is a compound with excellent scintillation properties, but its ultraviolet emission does not match well with the detection efficiency curves of silicon based photodetectors. In this work, Sm²⁺ is studied as an activator for LaBr₃ as its near-infrared emission can be detected with close to 100% efficiency by such photodetectors. LaBr₃:Sm²⁺ single crystals were grown with and without co-doping of Ce³⁺ or Pr³⁺. The samples were studied by means of X-ray excited and photoluminescence spectroscopy at temperatures between 10 K and 300 K. Their spectroscopic properties are compared to LaBr₃:Ce³⁺ and LaBr₃:Eu²⁺. The effect of using Ce³⁺ or Pr³⁺ as scintillation sensitiser for Sm²⁺ is assessed. It is found that energy transfer from host to Sm²⁺ greatly improves upon Ce³⁺ co-doping, but the quenching temperature of the Sm²⁺ emission decreases. The quenching mechanism of both the Ce³⁺ and Sm²⁺ emission in LaBr₃ is elaborated on. Furthermore, the effect of charge compensating defects on the light yield and spectroscopic properties is discussed.

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In this study, we systematically vary the Cl/Br and Br/I ratios in CsCaX₃:Tm²⁺ (X = Cl, Br, I) and hereby gradually shift the positions of the Tm²⁺ 4f¹²5d¹-levels as relative to the two 4f¹³ levels. At low temperatures up to five distinct Tm²⁺ 4f¹²5d¹→4f¹³ emissions and the 4f¹³→4f¹³ emission can be observed. As the temperature increases, most of the 4f¹²5d¹→4f¹³ emissions undergo quenching via multi-phonon relaxation (MPR) and at room temperature only the lowest energy 4f¹²5d¹→4f¹³ and the 4f¹³→4f¹³ emission remains. For all compositions a 4f¹³→4f¹³ risetime phenomenon is then observed whose duration matches the 4f¹²5d¹→4f¹³ decay time. It shows the feeding of the 4f¹³ state after 4f¹²5d¹ excitation. Surprisingly, the feeding time becomes longer from Cl→Br→I, while the related 4f¹²5d¹-4f¹³ energy gap becomes smaller. The temperature dependence of the 4f¹²5d¹→4f¹³ and 4f¹³→4f¹³ emission intensity shows a anticorrelation as earlier observed in other systems and confirms that the feeding process is thermally stimulated. However, the thermally stimulated activation energies that control the feeding process, increase from Cl→Br→I despite our observation that the 4f¹²5d¹-4f¹³ energy gap becomes smaller. An analysis reveals that the unexpected behaviour in risetime and activation energy, as a function of composition, cannot be explained by 4f¹²5d¹→4f¹³ feeding via interband crossing, but more likely via MPR where the electron–phonon coupling strength decreases from Cl→Br→I. No strong relation was found between composition and the quantum efficiency (QE) of the 4f¹³→4f¹³ emission, due to the presence of fluctuations that are likely caused by intrinsic differences in sample quality. Nevertheless, a 4f¹³→4f¹³ QE of up to 70% has been observed and the materials can therefore be used in luminescence solar concentrators.

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The luminescence and scintillation properties of SrI ₂ single crystals doped with 5% Eu ²⁺ and 0.05%, 0.2% and 0.5% Sm ²⁺ are evaluated. X-ray excited and photoluminescence measurements show energy transfer from excited Eu ²⁺ ions to Sm ²⁺ ions. At a concentration of 0.5% Sm ²⁺ , the luminescence consists almost entirely of 740 nm emission from Sm ²⁺ 5d-4f transitions. Co-doping SrI ₂ :5% Eu ²⁺ with Sm ²⁺ provides a novel method to bypass the self-absorption problem encountered in large SrI ₂ :Eu ²⁺ crystals and, at the same time, provides a unique near-infrared emitting scintillator with a light yield of approximately 40,000 photons/MeV.

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