Electron traps and scintillation mechanism in LuAlO3:Ce

In this paper we report measurements of thermoluminescence in the temperature range of 20-370 K, isothermal decays, pulsed vacuum ultraviolet and gamma-excited luminescence time profiles at various temperatures on cerium-activated orthoaluminate (LuAlO3:Ce, LuAP), a new and promising scintillator material. We demonstrate that results of all these experiments can be consistently explained by assuming a recombination mechanism of scintination light production in the LuAP scintillator. Using a simple first-order kinetic model that includes Ce3+, ions as recombination centres and a number of electron traps, we extract from experimental data the basic trap parameters (energy depths and frequency factors). Consequently we identify nine traps that are responsible for undesired features of the LuAP scintillator, such as a reduced scintillation light output, a relatively long scintillation rise time and slow scintillation components (afterglow) at room temperature. We demonstrate that some of these traps are responsible for large variations of the scintillation light yield with temperature as reported earlier. Although the deepest traps do not alter scintillation time profiles, they are responsible for a significant scintillation light loss and are, therefore, detrimental to scintillation performance of the material. We observe that there is an apparent correlation between trap depths and frequency factors for at least five of the traps that may fit some more general pattern involving various groupings of all the traps. This, in turn, would indicate that traps in LuAP are not unrelated and are due, most likely, to a series of native defects in the LuAP crystal structure. Although the specific identity of traps remains unknown, the performance of the LuAP scintillator is now, in practical terms, fully understood and can be described numerically at any temperature using a model and a set of parameters given in this paper. It is clear that any major improvement of the material would require that traps are eliminated or that their influence on the scintillation process is minimized.