Thallium-based scintillators for high-resolution gamma-ray spectroscopy: Ce3+- doped Tl2LaCl5 and Tl2LaBr5

Abstract In this paper we report on the crystallographic and scintillation properties of Tl2LaCl5:Ce 3 + and Tl2LaBr5:Ce 3 + , two novel thallium-containing high-resolution scintillators for gamma-ray spectroscopy. Crystals of Tl2LaCl5:Ce 3 + and Tl2LaBr5:Ce 3 + were grown by the Vertical Bridgman method up to 1-inch diameter and 1-inch long. Single crystals of Tl2LaCl5:Ce 3 + and Tl2LaBr5:Ce 3 + belong to the orthorhombic system with space group 62 and have a density of 5.16 and 5.98 g/cm3, respectively. The scintillators show high light yields of up to 68,000 photons/MeV, excellent gamma-ray energy resolution of ≤ 3% at 662 keV, a fast scintillation decay, and a proportional response over a wide range of energies from 32 keV up to 1275 keV. Density Functional Theory calculations show that the Ce 3 + energy levels are inside the bandgap despite the smaller bandgap of Tl2LaCl5 and Tl2LaBr5 compared to K2LaCl5 and K2LaBr5. A systematic Ce 3 + concentration study was performed for Tl2LaCl5:Ce 3 + and trends observed.