Deciphering Anomalous Luminescence in Highly Doped Transition‐Metal Phosphors: Spin‐Exchange, Unusual Site Occupancy, and Trace Impurities

ABSTRACT Anomalous luminescence in phosphors highly doped with transition‐metal ions (e.g., , ) has attracted significant interest for multifunctional optical materials and devices. However, rational optimization and materials design have been hindered by controversial mechanisms. Here, we establish a unified analytical framework for deciphering such complex emissions across a diverse range of host systems. Our framework categorizes the possible origins into distinct classes— transition‐metal dimers or clusters, configuration‐associated isolated transition‐metal centers, and impurities. We demonstrate that the various anomalous luminescence phenomena observed in highly doped transition‐metal phosphors cannot be explained by exchange‐coupled dimers alone, but instead arise from a variety of configuration‐dependent effects that arise at high doping levels (e.g., unusual site occupancy, defect‐dopant complexes, or alternative valence states), or trace impurities. In particular, the intervalence charge transfer transition in transition‐metal dimers is expected to be predominantly non‐radiative due to the large structural relaxation energy involved. This study provides a generalizable framework for deciphering complex luminescence in highly doped systems, reconciling long‐standing controversies and offering a mechanistic foundation for interpreting broadband near‐infrared emissions in highly doped phosphors for multifunctional optical applications.