Photoluminescence enhancement of Mn4+-doped Rb2NaAlF6 single-crystal phosphors via heterovalent co-doping for wide gamut displays

Abstract

Mn⁴⁺ activated fluorides are crucial for lighting and displays, owing to their unique narrowband red emission and broadband blue light excitation. However, designing target red phosphors that simultaneously possess appropriate chromaticity coordinates, short fluorescence lifetimes, and high quantum efficiencies (QEs) remains a significant challenge. Herein, by employing a synergistic strategy of the growth of single-crystal phosphors combined with a heterovalent co-doping approach, shorter fluorescence lifetimes (4.93 ms), excellent chromaticity coordinates (0.7001, 0.2998), and high external QE (EQE, 50.91%) are first achieved in the Rb₂NaAlF₆:Mn⁴⁺,Mg²⁺ (RNAFMM-C) single-crystal red phosphor. The significant increase in EQE (from 13.19% to 50.91%) is attributed to the single-crystal morphology with defect-rare and low surface energy, and the increased distortion of the [MnF₆]²⁻ octahedron, which breaks the partial parity-forbidden transition selection law. Additionally, the crystal samples of RNAFMM-C exhibit superior moisture resistance. More importantly, combining the RNAFMM-C, commercial green phosphor β-SiAlON:Eu²⁺ and blue InGaN chip, an emitting device with a high luminous efficiency of 118.48 lm W⁻¹ and a wide color gamut of 109.20% National Television Standards Committee (NTSC) is further demonstrated, and it shows good potential in projectors. RNAFMM-C is a promising red-light component for the next generation of wide gamut displays.