Crystal Growth Scale-Up and Stability of RbSr ₂ X ₅ :Eu Scintillators

The discovery and development of new scintillation materials support national security needs. In these applications, large volumes of scintillator crystals are needed to achieve efficient screening for contraband. Therefore, one important step in the discovery of new scintillator compositions is testing their feasibility for scale-up and their stability. In this work, high-quality Ø22 mm crystals of two new scintillators RbSr2Br5:Eu and RbSr2I5:Eu were grown via the Vertical Bridgman method, and their scintillation properties were characterized. The Ø22 mm RbSr2I5:Eu crystals could be grown with fast translation rates up to 3.5 mm/h. Both RbSr2Br5:Eu and RbSr2I5:Eu had high scintillation performance, including light yields of 46,000 and 61,000 ph/MeV,respectively, for Ø22 × 35 mm crystals. Additionally, properties related to physical stability were investigated, including the coefficients of thermal expansion via high-temperature X-ray diffraction (HTXRD) as well as moisture sensitivity. HTXRD confirmed the absence of solid–solid phase transitions and showed that RbSr2Br5 had minimal thermal expansion anisotropy compared to RbSr2I5 and some other inorganic metal halide scintillators, which favors the growth of large-sized crystals.