CsBa 2 I 5 :Eu 2+ ,Sm 2+ ‐ The First High Energy Resolution Black Scintillator for γ ‐ray Spectroscopy

Scintillators are materials that absorb a high energy particle (alpha,beta,gamma 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 gamma-photon detection can only be approached for materials that show a perfect proportional response with gamma-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 mu s. The proposed double-doping principle can be used to develop an entirely new class of near-infrared (NIR) scintillators.