Structure and Scintillation Properties of Cerium-Doped Barium Chloride Ceramics: Effects of Cation and Anion Substitution

Barium chloride has been doped with cerium chloride to form ceramic samples of composition Ba_1-xCe_xCl_2+x We find from the powder X-ray diffraction patterns that the compounds adopt the cubic fluorite structure for 0.06 <; x <; 0.33, not the usual orthorhombic BaCl₂ structure. The cation sublattice in this rare-earth stabilized cubic phase is disordered, whilst the additional chloride ions are accommodated at interstitial sites. Samples with x ~ 0.125 are translucent, and show a scintillation photopeak for ¹³⁷Cs gamma rays which can be used to compute a light yield of 7200 photons/MeV. The scintillation decay is characterized by a time constant of 50 ns, compared to a Ce³⁺ photoluminescence lifetime of 26 ns. We also report the structural effects of alternative cation dopants, including Gd, Lu, Sm and Y, and find that only Gd results in the same structural stabilization, but when additionally Ce doped the scintillation efficiency is only 2600 ph/MeV with a long afterglow. The effects of bromine substitution for chlorine in Ba_1-xCe_xCl_2+x to form Ba_1-xCe_xCl_2-2xBr_3x results in a material of near-cubic symmetry which is not transparent and does not show a photopeak, but for which the largest scintillation pulses correspond to an efficiency of 14,000 ph/MeV.