Oxygen-Vacancy-Driven Persistent Luminescence in Mn2+-Doped MgGeO3: Insights from X-Ray Absorption Fine Structure Spectroscopy

Abstract

Mn²⁺-doped MgGeO₃ (MMGO) is a near-infrared-emitting persistent luminescence (PersL) phosphor. Its low luminescence decay has been linked to vacancies within the MgGeO₃ host, likely associated with Ge, although no direct correlations have been confirmed. In this study, the Ge K-edge X-ray absorption fine structure (XAFS) spectroscopy is employed to investigate a series of MMGO submicron-sized particles with varying afterglow durations. These samples are synthesized using a recently developed hydrothermal method, where it is found that the PersL duration is related to the annealing temperature and the presence of codopants. It is first demonstrated that the XAFS spectra obtained using an in-house XAFS spectrometer are comparable in quality to those acquired at synchrotron facilities. Analysis of the local Ge environment of the MMGO shows that the PersL duration is directly related to the Ge–O coordination number. Additionally, the introduction of Li⁺ extends the PersL duration of MMGO but does not alter the Ge–O coordination. The findings provide insights into the structural mechanisms driving luminescence and highlight the capability of in-house XAFS systems to deliver high-quality data for advanced materials research.