Defect Engineering in SrI2:Eu2+ Single Crystal Scintillators

Eu2+-activated strontium iodide is an excellent single crystal scintillator used for gamma-ray detection, and significant effort is currently focused on the development of large-scale crystal growth techniques. A new approach of molten-salt pumping or so-called Melt aging was recently applied to optimize the crystal quality and scintillation performance. Nevertheless, a detailed understanding of the Muffle Furnace underlying mechanism of this technique is still lacking. The main purpose of this paper is to conduct an in-depth study of the interplay between microstructure, trap centers, and scintillation efficiency after melt aging treatment. Three SrI2:2 mol % Eu2+ single crystals with 16 mm diameter were grown using the Bridgman method under identical growth conditions with the exception of the melt aging time (e.g., 0, 24, and 72 h). Using energy-dispersive X-ray spectroscopy, it is found that the matrix composition of the finished crystal after melt aging treatment approaches the stoichiometric composition. The mechanism responsible for the formation of secondary phase inclusions in melt-aged SrI2:Eu2+ is discussed. Simultaneous improvement in light yield, energy resolution, scintillation decay-time and afterglow is achieved in melt-aged SrI2:Eu2+. The correlation between performance improvement and defect structure is addressed. The results of this paper lead to a better understanding of the effects of defect engineering in control and optimization of metal halide scintillators using the melt aging technique.