Potassium strontium iodide: A new high light yield scintillator with 2.4% energy resolution

A new ternary metal halide scintillator, potassium strontium iodide, activated with divalent europium (KSr₂I₅:Eu) has been discovered. This material has a monoclinic crystal structure with a density of 4.39 g/cm³. Differential scanning calorimetry indicates a congruent melting point of 471°C and suggests that this compound has no solid-solid phase transitions. As is the case with most metal halides, the material is hygroscopic, and it has some internal radioactivity due to the presence of ⁴⁰K. Single crystals of 13 and 25 mm diameter of KSr₂I₅ doped with 4% Eu²⁺ were grown in evacuated quartz ampoules via the Bridgman technique. X-ray excited emission consisted of a single peak at ~452 nm due to the 5d-4f transition in Eu²⁺. The measured light yield is ~94,000 photons/MeV with an energy resolution of 2.4% at 662 keV.