Giant Enhancement of Luminescence from Phosphors through Oxygen‐Vacancy‐Mediated Chemical Pressure Relaxation

Abstract Relaxing chemical pressure in phosphors with large‐size‐mismatched dopants, aiming at attaining high‐efficiency luminescence and a higher dopant concentration, remains a challenging subject of continuous research effort. Originally seen as undesirable and detrimental to the performance of luminescent systems, this study demonstrates that the formation of a tiny amount of oxygen vacancies favors chemical pressure relaxation (CPR), resulting in topotactic transformation of poorly luminescent parent phases to highly luminescent cousins, as exemplified by a model system of Bi³⁺‐doped Lu₂O₃. The integration of experimental observations with theoretical calculations reveals that the emergence of oxygen vacancies adjacent to Bi³⁺ can expand its size of coordination geometry, thus releasing the chemical pressure and significantly influencing the emission characteristics. Importantly, it is illustrated that the concept of oxygen‐vacancy‐mediated CPR is sufficiently general to allow the optimization of luminescence from other classes of foreign‐ion‐doped phosphors plagued by size mismatch. It is suggested that this concept can be applied to an array of optical materials in various forms, and also provides unique opportunities for tuning other properties of functional materials that are sensitive to local coordination environments of dopants.