Cross-luminescence in BaF2 crystals doped with M3+ and RE3+ ions: Hybrid density functional theory study

Radiation resistant inorganic materials emitting cross-luminescence are one of the most prospective candidates for new generation ultrafast detectors for medical tomography. Radiative transitions leading to cross-luminescence occur between valence and core states, and therefore calculations of the electronic structure of doped materials can explain ultrafast transitions and predict new cross-luminescent materials. In current work we demonstrate results of ab initio calculations of undoped and doped BaF${}_2$ by means of hybrid density functional theory. As a result of the work, the density of states (DOS) for nominally pure BaF${}_2$ and a whole series of BaF${}_2$ doped with various trivalent ions were obtained. The positions of the core energy levels of dopant ions lying between the Ba(5p) zone and the F(2s) zone, as well local geometries and formation energies were calculated. Our calculations show that the 5p states of impurity ions can be located below the 5p zone of barium by several eV. This opens up opportunities for transitions from the core 5p Ba zone to impurity 5p states, which might be involved in experimentally observed appearance of an ultrafast component in doped BaF${}_2$.