Electrospinning, optical properties and white LED applications of one-dimensional CaAl₁₂O₁₉:Mn⁴⁺ nanofiber phosphors

Non-rare-earth, red-emitting CaAl₁₂O₁₉:Mn⁴⁺ nanofiber phosphors have been successfully prepared by an electrospinning technique followed by an annealing process. The as-prepared precursor fibers have smooth surfaces with an average diameter of 5 µm. After annealing at high temperature, the diameter of the fibers gradually reduces due to the decomposition of the organic polymers. The photoluminescence and crystalline properties of the fibers were investigated as a function of Mn⁴⁺ concentration and the annealing temperature. Under ultraviolet and blue light excitation, CaAl₁₂O₁₉:Mn⁴⁺ exhibits a characteristic red emission at 655 nm with three satellite peaks due to the ²E→⁴A₂ transition of Mn⁴⁺. The highest PL intensity is achieved at a 0.5% Mn⁴⁺ concentration and a firing temperature of 1400 °C. In comparison to CaAl₁₂O₁₉:Mn⁴⁺ prepared by a usual solid-state reaction, the luminescence of the as-prepared nanofiber phosphors in the present work has been strongly enhanced by optimizing the morphology and improving the crystallinity and phase purity. The absorption band in the blue region and a bright emission in the red region make the CaAl₁₂O₁₉:Mn⁴⁺ nanofiber phosphor a candidate for achieving high color rendering in YAG:Ce-based WLEDs. A warm WLED with a high CRI of 88.5 at a CCT of 4553 K has been successfully achieved by coating YAG:Ce with CaAl₁₂O₁₉:Mn⁴⁺ nanofiber phosphors on blue InGaN chips.