High-Purity Narrow-Band Green Light KAl₁₁O₁₇: Eu²⁺, Mn²⁺ Phosphor Prepared Based on Energy Transfer Effect

A narrow-band green-emitting phosphor KAl₁₁O₁₇(KAO): Eu²⁺, Mn²⁺, was synthesized via a high-temperature solid-state reaction to evaluate its potential for use in high-quality backlight displays. Structural refinement reveals that Eu²⁺ and Mn²⁺ ions preferentially occupy distinct crystallographic sites: Eu²⁺ resides at K⁺ sites in the conductive layer, whereas Mn²⁺ substitutes for tetrahedral Al³⁺ sites within the spinel block. This spatial separation facilitates efficient energy transfer (ET) from Eu²⁺ to Mn²⁺. Spectroscopic analysis of the optimally doped composition, KAO: 0.07Eu²⁺, 0.04Mn²⁺, indicates that the ET proceeds predominantly via a dipole - quadrupole (d-q) mechanism. The resulting phosphor exhibits bright green emission centered at 510 nm with an exceptionally narrow full width at half maximum (FWHM) of 8.13 nm, a high color purity of 98%, and an internal quantum efficiency (IQE) of 65.41%. Moreover, the material demonstrates excellent thermal stability, retaining 93.11% of its initial luminescence intensity at 423 K, corresponding to a thermal activation energy of 0.2917 eV. To demonstrate its practical utility, a white LED device was fabricated by combining the optimized green phosphor (KAO: 0.07Eu²⁺, 0.04Mn²⁺) with a blue phosphor (BaMgAl₁₀O₁₇ (BAM): Eu²⁺), a red phosphor (Ca₉KMn(PO₄)₇: Eu²⁺), and a 365 nm near-ultraviolet chip. The resulting device achieves a wide color-gamut covering 107.8% of the NTSC standard. Collectively, these results demonstrate that precise control of site occupancy and energy transfer enables the design of green phosphors that simultaneously exhibit narrow-band emission, high color purity, and robust thermal stability-properties that are essential for wide color-gamut WLED backlight displays.