Micro-Raman imaging of SrI3⁻ anions in SrI2:Eu scintillator crystals

Europium-doped strontium iodide (SrI₂:Eu) crystals are reported to be high light yield scintillator materials with good energy resolution, the best energy resolution of SrI₂:Eu at 662 keV having reached 2.6%. To improve the crystals growth quality and to protect the crystals from hydration, it is practical to distinguish the pure crystals from impurity and structural defects by Raman spectroscopy. In this report, SrI₂:Eu crystals grown from the vertical Bridgman method have been characterized with the polarized Raman spectroscopy. Orientations of the crystals were determined with the spectroscopy assisted with the polarized optical microscopy. The crystals are highly hygroscopic, the intensity of new peak at 87 cm^-1 associated with SrI₃^- anions continues to increase with time even the samples are kept in mineral oil or encapsulated in parylene. Micro-Raman mapping on the distributions of SrI₃^- anions in SrI₂ crystals stored in mineral oil are reported.