Revealing trap depth distributions in persistent phosphors with a thermal barrier for charging

The performance of persistent phosphors under given charging and working\nconditions is determined by the properties of the traps that are responsible\nfor these unique properties. Traps are characterized by the height of their\nassociated barrier for thermal detrapping, and a continuous distribution of\ntrap depths is often found in real materials. Accurately determining trap depth\ndistributions is hence of importance for the understanding and development of\npersistent phosphors. However, extracting the trap depth distribution is often\nhindered by the presence of a thermal barrier for charging as well, which\ncauses a temperature-dependent filling of traps. For this case, we propose a\nmethod for extracting the trap depth distribution from a set of\nthermoluminescence (TL) curves obtained at different charging temperatures. The\nTL curves are first transformed into electron population functions via the\nTikhonov regularization, assuming first-order kinetics. Subsequently, the\noccupation of the traps as a function of their depth, quantified by the\nso-called filling function, is obtained. Finally, the underlying trap depth\ndistribution is reconstructed from the filling functions. The proposed method\nprovides a substantial improvement in precision and resolution for the trap\ndepth distribution compared with existing methods. This is hence a step forward\nin understanding the (de)trapping behavior of persistent and storage phosphors.\n