Abnormal site occupancy and high performance in warm WLEDs of a novel red phosphor, NaHF2:Mn4+, synthesized at room temperature

Abstract

A novel red phosphor, NaHF₂:Mn⁴⁺ (NHF:Mn), was obtained via substituting Na⁺ located at the center of the octahedron coordinated with six F⁻ ions with Mn⁴⁺ in the host lattice of NHF. The phase purity and the exact composition of the obtained NHF:Mn were confirmed by X-ray powder diffraction (XRD), Rietveld refinement, energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and infrared (IR) spectroscopy, respectively. The luminescence intensity of NHF:Mn was enhanced by optimizing the synthetic conditions. A series of warm white light-emitting diodes (WLEDs) with a color rendering index (CRI) higher than 88.0 and correlated color temperatures (CCT) between 3146 and 5172 K were obtained by encapsulating the as-prepared red phosphor NHF:Mn with the yellow one Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) on blue chips. The advantage of the synthetic strategy to obtain NHF:Mn can be extended to develop novel Mn⁴⁺ doped red phosphors via substituting for central ions with unequal electric charge in the centers of octahedra.