Improvement of Energy Resolution and Neutron–Gamma Discrimination of NaI:Tl,⁶Li Single Crystal Scintillators by Ca²⁺ and Sr²⁺ Co-Doping

NaI:Tl,6Li single crystals, due to low use cost and an efficient gamma ray ( $\gamma$ ) and neutron ( $n$ ) detection capability, have been regarded as promising $n/\gamma $ scintillators. In this work, NaI:Tl,6Li single crystals co-doped with different Ca $^{2+}$ and Sr $^{2+}$ concentrations were grown by the multiampoule Bridgman method. Their $\gamma $ -ray energy resolution and $n/\gamma $ discrimination were improved. The $\gamma $ -ray energy resolution at 662 keV was improved from 7.0% to 6.0% by Ca $^{2+}$ or Sr $^{2+}$ co-doping, despite at the expense of scintillation yield by around 20%. The pulse shape discrimination (PSD), expressed as figure-of-merits (FoMs) for neutron and $\gamma $ -ray, was enhanced from 4.65 for NaI:Tl,6Li to 5.85 for Ca $^{2+}$ co-doping and 5.72 for Sr $^{2+}$ co-doping. This work not only highlights the effectiveness of the co-doping strategy on the improvement of NaI:Tl,6Li single crystal scintillator but also makes the crystal more competitive toward neutron and $\gamma $ -ray detection applications.