The electronic structure of K2SiF6 from GW calculations and photoelectron spectroscopy.

Ultrafast scintillators based on ternary hexafluorides are promising for next-generation radiation detectors, which can be used in time-of-flight positron emission tomography. To gain a detailed understanding of the scintillation mechanism in these materials, accurate knowledge of the electronic band structure is required. In this study, photoelectron spectroscopy, density-functional theory, and G0W0 calculations were used to investigate the electronic structure of K2SiF6. The G0W0 calculations predict a wide band gap of 12.4 eV reflecting the strongly ionic character of the bonding. In contrast to predictions from semi-local or hybrid density-functional theory calculations, the large band gap predicted by G0W0 suggests that Auger-Meitner decay of K 3p holes is energetically not allowed and that scintillation via cross-luminescence is possible in this material. However, the poor light-yield observed experimentally indicates that the exclusion of Auger-Meitner decay is not sufficient for good scintillation performance, and cross-luminescence competes with other decay channels.