Significantly conquering moisture-induced luminescence quenching of red line-emitting phosphor Rb2SnF6:Mn4+ through H2C2O4 triggered particle surface reduction for blue converted warm white light-emitting diodes

Abstract

Mn⁴⁺ 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 Rb₂SnF₆:Mn⁴⁺, which, estimated by the single crystal X-ray diffraction data, crystallizes in the trigonal space group Pm1 with the lattice parameters a = b = 6.0323(12) Å, c = 4.7880(8) Å, and V = 150.89(7) ų. The Rb₂SnF₆:Mn⁴⁺ 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 Mn⁴⁺. A treatment solution with appropriate reducing ability is emphasized to obtain Rb₂SnF₆:Mn⁴⁺ with simultaneous high brightness and water resistance. The results show that the low concentration of H₂C₂O₄ solution treated Rb₂SnF₆:Mn⁴⁺ 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 H₂C₂O₄ treated Rb₂SnF₆:Mn⁴⁺ 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 Rb₂SnF₆:Mn⁴⁺ phosphor that can be used for high performance warm WLEDs but also provides a deep insight into how to well address moisture-induced Mn⁴⁺ luminescence quenching through appropriate reduction of Mn⁴⁺, opening up new opportunities for future solid-state lighting purposes.