The tetravalent-state stability of manganese is of primary importance for Mn4+ luminescence. Double perovskite-structured A2B′B″O6:Mn4+ has been recently prevalent, and the manganese ions are assumed to substitute for the B″(IV–VI)­O6 site to stabilize at the tetravalent charge state to generate far-red emissions. However, some Mn-doped A2B′B″O6-type materials show no or weak luminescence such as typical Ca2MgWO6:Mn. In this work, a cation-pair co-substitution strategy is proposed to replace 2Ca2+ by Na+–La3+ to form Ca2–2x Na x La x MgWO6:Mn. The significant structural distortion appears in the solid solution lattices with the contraction of [MgO6] but enlargement of [WO6] octahedron. We hypothesize that the site occupancy preference of Mn migrates from Mg2+ to W6+ sites. As a result, the effective Mn4+/Mn2+ concentration enhances remarkably to regulate nonluminescence to highly efficient Mn4+-related far-red emission. The optimal CaNa0.5La0.5MgWO6:0.9%Mn4+ shows an internal quantum efficiency of 94% and external quantum efficiency of 82%, reaching up to the top values in Mn4+-doped oxide phosphors. This work may provide a new perspective for the rational design of Mn4+-activated red phosphors, primarily considering the site occupancy modification and tetravalent-state stability of Mn.

As a universal sunlight-conversion agent for agricultural shed films, the green-to-red phosphor CaS:Eu 2+ suffers greatly from its poor moisture resistance. Unlike the conventional surface modifications upon application of postprocessing, this work proposes a one-step, two-additive strategy for synthesizing the CaS:Eu 2+ ,CaBr 2 ,CaF 2 composite phosphor. For the first time, we realize remarkable improvements in both the chemical stability and the luminescence intensity of a CaS:Eu 2+ -based material synchronously. The dual halide-modified composite phosphor maintains a stable phase composition against moist air and water immersion. The red emission of the as-obtained CaS:Eu 2+ ,CaBr 2 ,CaF 2 phosphor becomes 3 times as intense as that of nonmodified CaS:Eu 2+ . Moreover, the polymer film fabricated with the modified phosphor presents good weather resistance and brilliant lightconversion performance. Therefore, this one-step method gives the CaS:Eu 2+ ,CaBr 2 ,CaF 2 phosphor a great advantage as a long life light-conversion material for agricultural shed films.