Tuning Coordination Environments of Dopants through Topochemical Reaction Enables Substantial Enhancement of Luminescence in Mn⁴⁺-Doped Perovskite

Synthesizing highly luminescent active iondoped phosphors is desirable for many related applications but, remains challenging when a conventional solid-state reaction method is used for this purpose. In this contribution, we demonstrate the transformation of a poorly luminescent phase with a photoluminescence quantum yield (PLQY) of 3.1% to highly luminescent cousins with a PLQY of 58.9%, through a postsynthetically topochemical reaction treatment, as illustrated in a Mn4+-doped Sr3WO6 model system. Detailed structural analyses, combined with spectroscopic results, revealed that the highly luminescent treated samples have larger W-O distances, and the volume of the [(W/Mn)O-6] octahedron in the structure was expanded with respect to the precursor, as a result of the formation of oxygen vacancies. We find that topochemical reduction causes the conversion of W6+ ions to W5+, while it does not impact the oxidation state of Mn(4+)( )ions. These changes lead to the release of the chemical pressure around the Mn4+ ions, resulting in significant suppression of non-radiative recombination and thus greatly enhanced luminescence. We believe that our concept proposed here has the potential to be extended to tuning the properties of other functional materials that are sensitive to the local crystal environments of dopants.