Crystal growth and characterization of high performance KSr₂Br_xI_5-x:Eu scintillators

In this work we investigated the effects of replacing some of the matrix iodine atoms in KSr₂I₅:Eu with bromine, forming new solid solutions of KSr₂Br_xI_(5-x):Eu (where 0.05 ≤ x ≤ 1). Transparent 15 and 22mm diameter single crystals of KSr₂Br_xI_(5-x):Eu were grown via the vertical Bridgman technique using a two-zone transparent furnace. The scintillation properties of the mixed compounds were investigated and compared to the non-mixed parent compound, KSr₂I₅:Eu. The addition of bromine blue-shifted the x-ray excited emission from 450 to 446 nm, increased the light yield by ~11% and decreased the scintillation decay time by suppressing its secondary component (≥3 μs), while maintaining energy resolutions comparable to the reference crystal. Thermoluminescence glow curves showed that the addition of bromine modified the shallow traps located between 25 and 55 K, suggesting that these traps are responsible for lengthening KSI's decay time. In large sizes (10.3 cm³), KSr₂Br_0.10I_4.90:Eu 2% had light yields up to 79,000 ph/MeV and energy resolutions as low as 3.2% at 662 keV.