Mn4+-activated oxyfluoride K3TaOF6 red phosphor with intense zero phonon line for warm white light-emitting diodes

Abstract

The intense zero phonon line (ZPL) of the Mn⁴⁺:²E→⁴A₂ transition can further promote the color rendering and luminous efficiency for high-quality white-emitting diodes (w-LEDs). In this article, a Mn⁴⁺-activated K₃TaOF₆ 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 K₃TaOF₆:Mn⁴⁺ 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 Mn⁴⁺ ions, an intense ZPL emission was detected at 620 nm. By theoretical calculation, Mn⁴⁺ ions in the K₃TaOF₆ 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.