Enhanced Quantum Efficiency in Ca _2−2x Na _x Gd _x MgWO ₆ :Mn ⁴⁺ Phosphors: Allosteric Substitution to Disrupt Local Symmetry for Plant Cultivation Application

Abstract Light‐converting films enhance photosynthesis, yet most phosphors’ low quantum efficiency restricts their application. This work finds that the co‐substitution of Na ⁺ and Gd ³⁺ for Ca ²⁺ in Ca ₂ MgWO ₆ :Mn ⁴⁺ (CMWO: Mn ⁴⁺ ) 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 Mn ⁴⁺ d‐orbitals distribution under cation substitution. This work designs a unique reflection‐typed sunlight‐conversion fluorescent membrane using Ca _0.8 Na _0.6 Gd _0.6 MgWO ₆ : Mn ⁴⁺ (CNGMWO: Mn ⁴⁺ ), 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: Mn ⁴⁺ holds promise for plant cultivation.