Assessment of Sm²⁺-doped SrI₂, EuI₂, and YbI₂ for near-infrared scintillator applications

Abstract

SrI₂:Eu²⁺ and CaI₂:Eu²⁺ are two of the brightest known scintillators, but they both suffer from self-absorption. Their respective undoped isostructural compounds EuI₂ and YbI₂ are not suitable for scintillation due to the additional problem of concentration quenching. These compounds can however be doped with Sm²⁺ to turn them into near-infrared emitting scintillators, with the additional benefit that the self-absorption probability of the Sm²⁺ emission is low. Here, the scintillation properties of SrI₂:1%Sm²⁺, EuI₂:4%Sm²⁺, and YbI₂:1%Sm²⁺ single crystals are assessed which were grown by the vertical Bridgman technique. SrI₂:1%Sm²⁺ and EuI₂:4%Sm²⁺ fall within the ideal wavelength range for detection with silicon based photodetectors and are spectroscopically very similar to each other. However, the key difference is that the scintillation decay time of EuI₂:4%Sm²⁺ is 1.1μs, much shorter than the 1.8μs of SrI₂:1%Sm²⁺. Both SrI₂:Sm²⁺ and EuI₂:Sm²⁺ are identified as interesting candidates for further optimisation in the development of near-infrared emitting scintillators.