Recently, we proposed a concept for a new class of near infrared (NIR) scintillators by employing efficient Eu²⁺ → Sm²⁺ energy transfer. In this article we investigate the optical spectroscopy of Sm²⁺ in BaBrI, CsSrI₃, and CsBa₂I₅ halide hosts. A criterion was derived for fast Sm²⁺ 5d → 4f emission and a list of new potential NIR scintillators is proposed.

The concept of quantum-dot-in-perovskite solids pioneered by Ning and co-workers introduces a useful class of solution-processed type I heterostructures for optoelectronics applications. Concurrent searches for solution-processable detectors of ionizing radiation have focused on lead-halide perovskites. As described in this issue of ACS Nano, Cao et al. examined CsPbBr₃ nanocrystals imbedded in Cs₄PbBr₆ as a wider gap host and determined its performance and possibilities as a scintillator for X-ray imaging. In this Perspective, we describe issues and research opportunities on ionizing radiation imaging and spectroscopy based on the CsPbBr₃@Cs₄PbBr₆ composite and other perovskite-dot-in-host combinations in which the dot may be of lower dimensionality than 3, and we explore ionizing radiation detectors using halide perovskites.

Scintillators are materials that absorb a high energy particle (α,β,γ radiation) and downconvert it into a short pulse of visible or near-visible light. As determined by photon detection statistics, the ultimate energy resolution for γ-photon detection can only be approached for materials that show a perfect proportional response with γ-energy. A large amount of research has resulted in the discovery of highly proportional materials, such as SrI₂:Eu²⁺ and CsBa₂I₅:Eu²⁺. However, the resolution is still limited because of unavoidable self-absorption of Eu²⁺ emission, especially when large-sized scintillators are to be used. By co-doping with Sm²⁺, the emission of Eu²⁺ can be efficiently shifted to the far-red by exploiting nonradiative energy transfer. Herein, this new idea is applied to CsBa₂I₅, and Sm co-doped CsBa₂I₅:Eu²⁺ can be considered as the first “black scintillator” with an emission wavelength around 755 nm, a remarkable high energy resolution of 3.2% at 662 keV gamma excitation, and a scintillation decay time of 2.1 μs. The proposed double-doping principle can be used to develop an entirely new class of near-infrared (NIR) scintillators.

In this article we present a method of characterizing scintillating materials by digitization of each individual scintillation pulse followed by digital signal processing. With this technique it is possible to measure the pulse shape and the energy of an absorbed gamma photon on an event-by-event basis. In contrast to time-correlated single photon counting technique, the digital approach provides a faster measurement, an active noise suppression, and enables characterization of scintillation pulses simultaneously in two domains: time and energy. We applied this method to study the pulse shape change of a CsI(Tl) scintillator with energy of gamma excitation. We confirmed previously published results and revealed new details of the phenomenon.