Highly efficient and water-resistant K3ZrF7:Mn4+ red-emitting phosphors

Abstract

Mn4+ activated fluorides are promising red phosphors to be used in warm white light emitting diodes and liquid crystal display (LCD) backlighting due to their unique narrow-band red emission and broad band absorption in blue wavelength region. However, the instability in humid environment of these phosphors limited their practical application. In this work, we developed a facile co-precipitate method to prepare Mn4+ doped K3ZrF7 phosphors with good water-resistant properties. The crystal structure of K3ZrF7 was analyzed by XRD Rietveld refinement. The photoluminescence intensity was maintained at 95% after being immersed in water for 40 min in comparison with only 39.8% for Mn4+ doped K2TiF6 phosphors. The intrinsic seven coordination environment of Mn4+ in K3ZrF7 crystal was proposed as the main reason contributing to the good water resistance of the sample. The internal quantum efficiency and external quantum efficiency of optimized K3ZrF7:Mn4+ was measured to be 70.8% and 19.5% respectively. The thermal stability of the obtained phosphors was studied. A warm white light LED device with color temperature of 4074 K and color rendering index of 76.5 was fabricated by combining a mixture of K3ZrF7:Mn4+ and Y3Al5O12:Ce3+ with a blue InGaN chip.