Crystal growth and scintillation properties of new ytterbium-activated scintillators Cs4CaI6:Yb and Cs4SrI6:Yb

Abstract Yb2+ was investigated as a potential alternative activator for Cs4SrI6 and Cs4CaI6 scintillators for the first time, as opposed to the previously studied Eu2+ activator. Single crystals with nominal Yb2+ concentrations of 0.5 mol%, 1 mol%, and 3 mol% were grown in O7 mm ampoules using the vertical Bridgman method. Luminescence and scintillation properties were evaluated as a function of Yb2+ concentration and host compound. The 5d → 4f electronic transition of Yb2+ was observed for both the Sr- and Ca-containing compositions. X-ray induced radioluminescence emission was centered between 449 nm and 463 nm depending on Yb2+ concentration and host compound. Both the spin-allowed and spin-forbidden transitions were observed in photoluminescence emission spectra and were centered at 446 nm and 476 nm, respectively, for both compounds. The best scintillation performance was achieved with Cs4CaI6:Yb 1 mol%, which had a 3.5% energy resolution at 662 keV and 43,000 ph/MeV light yield. To our knowledge this is the best energy resolution ever reported for a Yb2+-doped scintillator. Additional Cs4CaI6:Yb 1% crystals were grown in O12 mm ampoules to investigate the size dependence of scintillation properties, as well as crystal homogeneity.