Two new cerium-doped mixed-anion elpasolite scintillators: Cs2NaYBr3I3 and Cs2NaLaBr3I3

Abstract We recently discovered that mixed-anion Br–I elpasolite scintillators, Cs2NaYBr3I3: Ce and Cs2NaLaBr3I3: Ce, have promising performance. Ce concentration of these compounds was optimized in terms of light yield. Cs2NaLaBr3I3 with 5% Ce (by mole) has a light yield of 58,000 ph/MeV, and excellent energy resolution of 2.9% at 662 keV. It is better than both endpoint compounds of the Br–I solid solution. Cs2NaYBr3I3 with 2% Ce doping shows energy resolution of 3.3% at 662 keV, despite a relatively modest light yield of 43,000 ph/MeV. Non-proportionality of the mixed Br–I compounds was measured using gamma ray sources ranging in energy from 14 keV to 835 keV. The electronic band gaps of undoped Cs2NaLaBr3I3 and Cs2NaYBr3I3 were determined from optical transmittance and absorbance measurements. The band gaps of the compounds are 4.4 ± 0.1 eV, and 4.3 ± 0.1 eV, respectively. The crystal structures of Cs2NaLaBr3I3: Ce and Cs2NaYBr3I3: Ce are tetragonal and cubic respectively. The high symmetry leads to fewer cracks during crystal growth and minimizes light scattering at grain boundaries. The ease of crystal growth is promising for the scale-up of the growth process to larger sizes.