A coupled PL/OSL system to understand the dynamics of the metastable states

Metastable states form by charge (electron and hole) capture in defects in a solid. These play an important role in dosimetry, information storage, and many medical and industrial applications of photonics. Despite many decades of research, charge transfer across metastable states and its role in luminescence production is poorly understood. This is mainly because the measurement of luminescence from metastable states involves several processes such as detrapping, transport, competition, and electron-hole (henceforth e-h) recombination. Here we present a novel, coupled OSL/PL (optically stimulated luminescence/ photoluminescence) system in a natural aluminosilicate feldspar which comprises >50 % of the Earth crust, to understand the dynamics of the metastable states. Infrared PL (IRPL) in feldspar is capable of directly probing the trapped electrons. Whereas, OSL measures e-h recombination. Combining these two pieces of information, we develop here new analytical methods, and based on these elucidate for the first time the thermal dependence, diffusion, thermo-optical bleaching, and radiation-induced growth of electron and holes in feldspar. These results support a strong presence of localized recombination mechanisms in feldspar. These new methods and insights provide unique information for developing robust mathematical models that are crucial to the next generation applications of luminescence dosimetry in Earth and environmental sciences. We expect that this work will inspire a search of a similar coupled OSL-PL systems in other solid-state dosimeters and enrich our understanding of luminescence phenomena involving the metastable states.