Band structure calculations of cerium activated inorganic scintillators

Abstract

Trivalent cerium has been used extensively in recent years as an activator in crystalline hosts for fast scintillators. The scintillation efficiencies have been found to vary greatly, however. For example, no scintillation is observed from Ce-doped Y2O3 and Lu2O3, the efficiency is low for CeF3, whereas the efficiency is very high for Lu2SiO5:Ce. This behavior has been attributed in large part to the location of the ground 4f and excited 5d levels of Ce3+ with respect to the fundamental band gap of the host. We have performed band structure calculations to predict the band gaps and the location of the Ce and Lu 4f and 5d levels in the fluoride host CeF3 and in the oxide host LuAlO3. Calculations were made using a full-potential linear muffintin orbital (FP-LMTO) approach. We find that Ce 4f levels in CeF3 are several eV above the top of the valence band (VB), thus reducing the probability of hole capture. The Lu 4f levels in LuAlO3 are predicted to be several eV below the top of the VB. Both of these results are in agreement with experiment. Preliminary calculations on LuAlO3:Ce locate the Ce 4f energy levels approximately 3 eV above the VB (O2p) which is not consistent with the high scintillation efficiency of LuAlO3:Ce.