Charge carrier and exciton dynamics in LaBr3:Ce3+ scintillators: Experiment and model

The scintillation yield and decay time of LaBr3 doped with 0.2%, 0.5%, and 5% cerium were studied between 80 K and 600 K. LaBr3:5%Ce3+ on a photomultiplier tube shows at 300 K a very high scintillation yield of 22 800 photoelectrons per MeV (64 000 photons per MeV) with a decay time of 16 ns. At 600 K the yield decreases by similar or equal to 15%. The scintillation yield of LaBr3:0.2%Ce3+ is 19 800 photoelectrons per MeV (56 000 photons per MeV) at 300 K with a decrease by similar or equal to 50% at 600 K and a main scintillation decay time around 30 ns. The appearance of slow components in the Ce emission indicates a relatively slow energy transfer from the host crystal to Ce. The presence or absence of slow components depends on both concentration and temperature. The results are analyzed and interpreted with a model that comprises prompt charge carrier trapping by Ce and delayed excitation of Ce by means of thermally activated transport of self-trapped exciton defects. The results of the study provide detailed information on the scintillation mechanism. Besides presenting experimental data, the different energy transfer processes are quantified.