Exploring growth conditions and Eu2+ concentration effects for KSr2I5:Eu scintillator crystals

• 13–22 mm dia. crystals of KSr2I5:Eu 4% were grown via the vertical Bridgman method.
• Effect of varying Eu2+ concentration on KSr2I5 was studied.
• Light yields of 88,000–96,000 ph/MeV were measured.
• Energy resolutions from 2.4% to 3.0% were measured at 662 keV.
• A new technique, micro-resolution X-ray mapping, was explored.

Our current research is focused on understanding dopant optimization, growth rate, homogeneity and their impact on the overall performance of KSr2I5:Eu2+ single crystal scintillators. In this work we have investigated the effects of Eu2+ concentration in the potassium strontium iodide matrix, and we found that the concentration needed to maximize the light yield was 4 mol%. In order to assess the effects of the pulling rate, we grew single crystals at 12, 24 and 120 mm/day via the vertical Bridgman technique. For the sample sizes measured (5×5×5 mm3), we found that the crystal grown at the fastest rate of 120 mm/day showed a light yield within ~7% of the more slowly grown boules, and no significant change was observed in the energy resolution. Therefore, light yields from 88,000 to 96,000 ph/MeV and energy resolutions from 2.4 to 3.0% (at 662 keV) were measured for KSr2I5:Eu 4% over a relatively wide range of growth conditions. In order to assess the homogeneity of KSr2I5:Eu 4%, a newly developed micro-resolution X-ray technique was used to map the light yield as a function of excitation position. In the crystals that we studied, we did not observe any significant inhomogeneity other than a smooth gradient due to light collection and self absorption effects.