First-principles study of luminescence in Ce-doped inorganic scintillators

Luminescence in Ce-doped materials corresponds to a transition from an excited state where the lowest Ce 5$d$ level is filled [often called the (Ce${}^{3+}$)${}^{*}$ state] to the ground state where a single 4$f$ level is filled. We have performed theoretical calculations based on density functional theory to calculate the ground-state band structure of Ce-doped materials as well as the (Ce${}^{3+}$)${}^{*}$ excited state. The excited-state calculations used a constrained occupancy approach by setting the occupation of the Ce 4$f$ states to zero and allowing the first excited state above them to be filled. These calculations were performed on a set of Ce-doped materials that are known from experiment to be scintillators or nonscintillators to relate theoretically calculable parameters to measured scintillator performance. From these studies, we developed a set of criteria based on calculated parameters that are necessary characteristics for bright Ce-activated scintillators. Applying these criteria to about 100 new materials, we developed a list of candidate materials for new bright Ce-activated scintillators. After synthesis in powder form, one of these new materials (Ba${}_{2}$YCl${}_{7}$:Ce) was found to be a bright scintillator. This approach, involving first-principles calculations of modest computing requirements, was designed as a systematic, high-throughput method to aid in the discovery of new bright scintillator materials by prioritization and down-selection on the large number of potential new materials.