Improving the Scintillation Performance of KSr2I5:Ce3+ through Exploration of Activator Concentration and Growth Conditions

Potassium strontium iodide (KSr₂I₅ or KSI) has been previously discovered and investigated as a high energy resolution scintillator for national security applications. Activators were investigated in hopes to improve some of the less desirable characteristics associated with typical Eu²⁺-doping, like decay time and slightly higher emission wavelength. Cerium-3+ was identified as one of the most promising alternatives, but challenges with crystal growth and poor crystal quality have made investigation more challenging due to an inability to obtain high quality single crystals. A series of KSr₂I₅:Ce crystals with varying concentrations of Ce³⁺ were grown and characterized via the Bridgman-Stockbarger method for the purpose of this research. Crystal quality was noticeably improved after investigation into interface control parameters and adjusting the thermal gradient in the growth furnace. Other experiments were conducted to investigate further improvements in crystal quality, specifically at higher Ce-dopant concentrations. The maximum achievable scintillation performance of each crystal was measured with small samples (0.5 - 1 cm³). Light yields of all KSr₂I₅:Ce have been consistent, achieving up to 50,000 photons/MeV. Energy resolution values as low as 3.1% at 662 keV have also been observed and appear to be loosely correlated to Ce³⁺-concentration and overall crystal quality. Other factors contributing to energy resolution of scintillators and the overall performance of grown crystals are discussed in relation to applicability for security applications.