Enhanced Quantum Efficiency in Ca2−2xNaxGdxMgWO6:Mn4+ Phosphors: Allosteric Substitution to Disrupt Local Symmetry for Plant Cultivation Application

Light-converting films enhance photosynthesis, yet most phosphors' low quantum efficiency restricts their application. This work finds that the co-substitution of Na+ and Gd3+ for Ca2+ in Ca2MgWO6:Mn4+(CMWO: Mn4+) significantly enhances the deep red emission by nearly tenfold. The phosphor can emit red light with a peak at 688 nm under near-ultraviolet excitation, and an external quantum efficiency of 51.5%. The luminous intensity of phosphor stored at 85 °C and 85% humidity for 1000 h is about 95.36% of that at room temperature. Analyses of X-ray Absorption Fine Structure (XAFS), Rietveld, and electron density distribution reveal a unique mechanism of breaking parity-forbidden d-d transitions induced by the symmetry breaking through a big change of Mn4+ d-orbitals distribution under cation substitution. This work designs a unique reflection-typed sunlight-conversion fluorescent membrane using Ca0.8Na0.6Gd0.6MgWO6: Mn4+(CNGMWO: Mn4+), which enables highly efficient directing of deep red toward crops. The actual growth of lettuce and mini-tomatoes is examined, and the fresh weights of lettuce and mini-tomatoes are increased by 57 ± 15% and 30 ± 20%, respectively, compared with the blank control group. Remarkably, the conversion membrane contributes to a +81% increase in the dry weight of lettuce. The results show that the deep red phosphor CNGMWO: Mn4+ holds promise for plant cultivation.