Significantly conquering moisture-induced luminescence quenching of red line-emitting phosphor Rb ₂ SnF ₆ :Mn ⁴⁺ through H ₂ C ₂ O ₄ triggered particle surface reduction for blue converted warm white light-emitting diodes

Mn ⁴⁺ doped fluoride phosphors have attracted tremendous attention in the solid-state lighting field due to the outstanding feature of efficient narrow band red emission. However, poor resistance against moisture-induced luminescence quenching is a recognized obstacle for realizing their wider commercial use. Herein, we design and fabricate a highly stable red phosphor based on previously unnoticed Rb ₂ SnF ₆ :Mn ⁴⁺ , which, estimated by the single crystal X-ray diffraction data, crystallizes in the trigonal space group P3m1 with the lattice parameters a = b = 6.0323(12) Å, c = 4.7880(8) Å, and V = 150.89(7) Å ³ . The Rb ₂ SnF ₆ :Mn ⁴⁺ as expected exhibits highly efficient red emission upon excitation by UV and blue light. Significantly, the poor water resistance is conquered by constructing a protective deactivated layer with surface reduction of Mn ⁴⁺ . A treatment solution with appropriate reducing ability is emphasized to obtain Rb ₂ SnF ₆ :Mn ⁴⁺ with simultaneous high brightness and water resistance. The results show that the low concentration of H ₂ C ₂ O ₄ solution treated Rb ₂ SnF ₆ :Mn ⁴⁺ preserves a bright red-emitting color analogous to its initial color and >95% of its initial emission intensity when immersing in water at room temperature (RT) and in boiling water for 3 h. Lastly, by employing H ₂ C ₂ O ₄ treated Rb ₂ SnF ₆ :Mn ⁴⁺ as a red phosphor, a high quality WLED with a CRI of 90, CCT of 3936 K and luminous efficacy of 106.24 lm W ^-1 is fabricated. This work not only experimentally fabricates a new efficient and stable Rb ₂ SnF ₆ :Mn ⁴⁺ phosphor that can be used for high performance warm WLEDs but also provides a deep insight into how to well address moisture-induced Mn ⁴⁺ luminescence quenching through appropriate reduction of Mn ⁴⁺ , opening up new opportunities for future solid-state lighting purposes.