Mn 4+ -activated oxyfluoride K 3 TaOF 6 red phosphor with intense zero phonon line for warm white light-emitting diodes.

The intense zero phonon line (ZPL) of the Mn 4+ : 2 E→ 4 A 2 transition can further promote the color rendering and luminous efficiency for high-quality white-emitting diodes (w-LEDs). In this article, a Mn 4+ -activated K 3 TaOF 6 oxyfluoride red phosphor was synthesized via a facile two-step method. Its phase and morphology were characterized by X-ray diffraction, SEM and TEM. The as-prepared K 3 TaOF 6 :Mn 4+ exhibits an intense absorption of blue light and a strong emission band peaking at 628 nm with a color purity as high as 96.4%. Attributed to the distorted octahedral coordination environment of Mn 4+ ions, an intense ZPL emission was detected at 620 nm. By theoretical calculation, Mn 4+ ions in the K 3 TaOF 6 host experience a strong crystal field. In addition, the temperature-dependent PL and thermoluminescence (TL) spectra suggest that thermal ionization dominates the thermal quenching phenomenon in this phosphor.