Charge carrier and exciton dynamics inLaBr3:Ce3+scintillators: Experiment and model

The scintillation yield and decay time of ${\mathrm{LaBr}}_3$ doped with 0.2%, 0.5%, and 5% cerium were studied between $80\mathrm{K}$ and $600\mathrm{K}$. ${\mathrm{LaBr}}_3:5\%{\mathrm{Ce}}^{3+}$ on a photomultiplier tube shows at $300\mathrm{K}$ a very high scintillation yield of $22800$ photoelectrons per MeV ($64000$ photons per MeV) with a decay time of $16\mathrm{ns}$. At $600\mathrm{K}$ the yield decreases by $\simeq 15\%$. The scintillation yield of ${\mathrm{LaBr}}_3:0.2\%{\mathrm{Ce}}^{3+}$ is $19800$ photoelectrons per MeV ($56000$ photons per MeV) at $300\mathrm{K}$ with a decrease by $\simeq 50\%$ at $600\mathrm{K}$ and a main scintillation decay time around $30\mathrm{ns}$. 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.