Radioluminescence and recombination processes in BaF2:Ce

In this paper we report measurements of x-ray- and vacuum UV-excited luminescence, luminescence excitation spectra and time profiles, low temperature thermoluminescence and isothermal decays as well as x-ray- and gamma-excited scintillation time profiles and scintillation light yields at various temperatures on BaF 2 :Ce and, for reference, on undoped BaF 2 , two well known scintillator materials. For the first time we find that all these results can be consistently interpreted in the frame of a model that includes Ce-related recombination centres and several charge `traps'. The charge trapping at most of these `traps' has its origin in self-trapping and trapping of holes at regular (V k ) and interstitial (H) fluorine sites. We have identified and characterized two different modes of thermally activated V k release that precede radiative recombination at Ce sites. These two modes are responsible for a 7 ns rise time and a slower 114 ns components in the scintillation time profile at room temperature (297 K) that produce about 67% of the scintillation light detected within a 0.5 µs time window. The remaining 33% is due to a prompt component decaying with the Ce 3+ radiative lifetime of about 30 ns that originates from the direct recombination of charge carriers at Ce 3+ ions. We also estimate that scintillation light loss due to even slower components, at 23.1 µs (H centres), 1.1 ms and 7 ms (V kA and V kA ' centres), exceeds at least threefold the amount of light emitted in the 0.5 µs time window. Therefore in addition to their well known role as defect centres actively participating in the formation of stable radiation damage centres these species are also involved in the radiative recombination process itself. The perspectives of improvements in performance of the BaF 2 :Ce scintillator are also briefly discussed.