The Influence of Cation Impurities on the Scintillation Performance of ${{\hbox {SrI}}_2}$ (Eu)

To better identify the influence of cation impurities on the scintillation performance of SrI2(Eu), SrI2 crystals were grown, each co-doped with 4 mol% Eu^{2 +} and 0.2 mol% of one of the following: Mg^{2 +}, Ba^{2 +}, Cs⁺, Ca^{2 +}, Fe^{2 +}, Cu⁺, Na⁺, and Sn^{2 +}. Four 10 mm diameter crystals were grown at a time by the vertical Bridgman-Stockbarger method. The segregation behavior and the scintillation performance of 10 mm dia.×6 mm cylinders and 7 mm×6 mm×2 mm cuboids were characterized. Mg^{2 +}, Cs⁺, Fe^{2 +}, and Cu⁺ impurities did not adversely affect scintillation properties, and segregated during growth. However, Na⁺, Ba^{2 +}, and Ca^{2 +} did not segregate well and degraded light yield and energy resolution, especially at the larger sample size. Sn^{2 +} proved to be the most detrimental to light yield and produced a secondary emission peak at 600 nm, but did not affect the non-proportionality response. The results of this study suggest that SrI2(Eu) can tolerate a surprisingly large amount of cation impurities. These findings suggest that the purity requirements for starting materials can be relaxed, and purification efforts may be adjusted to target only the most harmful impurities.