A novel red phosphor of Mn4+ ion-doped oxyfluoroniobate BaNbOF5 for warm WLED applications

Abstract

A red phosphor composed of Mn⁴⁺-activated oxyfluoroniobate BaNbOF₅ was synthesized from the starting materials BaF₂, Nb₂O₅, and K₂MnF₆ in an HF solution by using a method based on dissolution ion-exchange recrystallization. The BNOF:Mn phosphor particles transformed from micron-sized polyhedrons to rectangular blocks as the reaction temperature was increased from room temperature to 180 °C. The effects of the synthetic parameters, such as the concentration of K₂MnF₆ in the reaction system and the reaction temperature, on the luminescence intensity of BNOF:Mn were investigated by acquiring detailed experimental results. The as-prepared BNOF:Mn phosphor displayed a broad and intense absorption in the blue-light region and a bright luminescence in the red-light region with a color purity of 97.7% at the Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of x = 0.594, y = 0.390. The BNOF:Mn phosphor showed superior thermal stability and its activation energy E_a was determined to be 0.506 eV. The advantage of the synthetic strategy to obtain BNOF:Mn can be extended to developing oxyfluoroniobates based on Mn⁴⁺-doped red phosphors, which might have the advantages of both oxides and fluorides.