Untangling the controversy on Ce3+ luminescence in LaAlO3 crystals

Abstract

Aluminum perovskites represent an important group of promising scintillation materials with excellent proportionality and energy resolution, but due to difficulties in crystal growth not much attention has been paid to them. We studied a Ce-doped LaAlO₃ lanthanum–aluminum perovskite (LaAP) because of its easy crystal growth facilitated by the large La³⁺ cations in the matrix. Moreover, recent observations of intense blue luminescence by some researchers show that the potential of this material could not be ruled out. On the other hand, some reports claim that Ce³⁺ luminescence is completely absent in the LaAP matrix. Therefore, we have decided to study this material in much greater detail using an extended set of correlated experiments to explain the observed discrepancies and underlying phenomena. Crystal growth by the micro-pulling-down method is reported together with the luminescence and scintillation properties. We demonstrate the influence of inclusions of other aluminate phases created during the crystal growth on the luminescence processes. The existence of the phases was simultaneously confirmed by observations using a scanning electron microscope, cathodoluminescence, energy-dispersive X-ray analysis and electron paramagnetic resonance (EPR), which were correlated with photoluminescence and scintillation studies. The EPR evidenced the incorporation of Ce ions in different environments comprising the LaAP matrix and inclusions. Based on these results, the luminescence mechanism is proposed and discussed and the low scintillation efficiency of the Ce-doped LaAP is explained together with the discrepancies in the literature.