Radioluminescence and recombination processes in BaF2 : Ce

In this paper we report measurements of x-ray- and vacuum UV-excited lumine scence, luminescence excitation spectra and rime profiles, low temperature thermoluminescence and isothermal decays as well as x-ray- and gamma-excite d scintillation time profiles and scintillation light yields at various tem peratures on BaF2:Ce and, for reference, on undoped BaF2, two well known sc intillator materials. For the first time we find that all these results can be consistently interpreted in the frame of a model that includes Ce-relat ed recombination centres and several charge 'traps'. The charge trapping at most of these 'traps' has its origin in self-trapping and trapping of hole s at regular (V-k) and interstitial (H) fluorine sites. Pie have identified and characterized two different modes of thermally activated V-k release t hat precede radiative recombination at Ce sites. These two modes are respon sible for a 7 ns rise rime and a slower 114 ns components in the scintillat ion time profile at room temperature (297 K) that produce about 67% of the scintillation light detected within a 0.5 mu s time window. The remaining 3 3% is due to a prompt component decaying with the Ce3+ radiative lifetime o f about 30 ns that originates from the direct recombination of charge carri ers at Ce3+ ions. We also estimate that scintillation light loss due to eve n slower components, at 23.1 mu s (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 mu s time window. Therefore in addition to their well known role as de fect centres actively participating in the formation of stable radiation da mage 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.