Investigation of Sm 2+ as a near-infrared emitting activator for NaI scintillators

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, Sm 2+ 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% Sm 2+ 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 Sm 2+ . The samples indicate the formation of multiple (at least 5) different Sm 2+ emission sites. Annealing the samples changes their emission intensity and scintillation properties. NaI:Sm 2+ shows great similarities with its Eu 2+ -doped counterpart. Finally, it is demonstrated that NaI:Sm 2+ can be read out with silicon photomultipliers and an energy resolution of 11% has been attained. • At least 5 different emitting Sm 2+ sites have been identified. • Co-doping NaI with Tl + and Sm 2+ quenches the emission of Tl + , but not of Sm 2+ . • Energy transfer from Tl + to Sm 2+ takes place. • Annealing of NaI:Sm 2+ more than doubles its light yield. • Even at room temperature, high ionic mobility creates precipitates containing Sm 2+ .