Extending Afterglow of Ga₂O₃ Nanocrystals by Dy³⁺ Dopant-Induced Carrier Trapping: Toward Design of Persistent Colloidal Nanophosphors

Design and preparation of persistently luminescent nanostructured phosphors are of a significant interest in lighting, photonic, and photovoltaic technologies. However, afterglow generally occurs in bulk phosphors synthesized by high-temperature solid-state reactions. Here, we report the synthesis of colloidal Dy3+-doped γ-phase Ga2O3 nanocrystals and demonstrate an extension of the lifetime of nanocrystal emission arising from native-defect-based donor–acceptor pair recombination, relative to undoped nanocrystals. Using temperature-dependent photoluminescence measurements, we show that Dy3+ dopants reside in the vicinity of nanocrystal surfaces and generate trap states that are significantly shallower than donor states originated by the presence of oxygen vacancies in Ga2O3 nanocrystals. This defect configuration allows for thermal reactivation of electrons trapped in Dy3+-derived excited states, resulting in an increase in the nanocrystal emission intensity and an extension of the afterglow lifetime with temperature. These results are supported by kinetic Monte Carlo simulation based on the probability of different electron transfer processes. The results of this work demonstrate a pathway to extending afterglow emission in metal oxide nanocrystals and designing persistent nanophosphors.