Highly Regular, Uniform K₃ScF₆:Mn⁴⁺ Phosphors: Facile Synthesis, Microstructures, Photoluminescence Properties, and Application in Light-Emitting Diode Devices

Abstract

A new generation of red phosphors of complex fluoride matrices activated with Mn has gained a broad interest in getting high color quality and low color temperature of solid-state white light-emitting diodes (WLEDs). However, besides their instability toward moisture, the extremely irregular and nonuniform morphologies of these phosphors have limited their practical industry applications. In the present study, a novel type of KScF:Mn red phosphor with highly regular, uniform, and high color purity was obtained successfully through a facile coprecipitation route under mild conditions. The crystal structure was identified with aids of the powder X-ray diffraction, Rietveld refinement, and density functional theory calculations. The prototype crystallizes in the space group Fm3 m with a cubic structure, and the lattice parameters are fitted well to be a = b = c = 8.4859(8) Å and V = 611.074(2) Å. The Mn ions occupy Sc sites and locate at the centers of the distorted ScF octahedrons. A wide band gap of approximately 6.15 eV can provide sufficient space to accommodate impurity energy levels. Unlike most other Mn ion-activated fluoride phosphors, the as-prepared KScF:Mn phosphors demonstrate highly uniform and regular morphologies with shapes transforming from cube to octahedron with increasing Mn ion concentration. Under blue light excitation, the as-prepared KScF:Mn sample exhibits intense sharp-line red fluorescence (the strongest peak located at 631 nm) with high color purity. An excellent recovery in luminescence upon heating and cooling processes implies high stability of KScF:Mn. Furthermore, a warm WLED fabricated with blue GaN chips merged with the mixture of KScF:Mn and the well-known commercial YAG:Ce yellow phosphors exhibits wonderful color quality with lower correlated color temperature (3250 K) and higher color-rendering index ( R = 86.4). These results suggest that the KScF:Mn phosphor possesses stupendous potentiality for practical applications.

Surface Passivation toward Highly Stable Mn4+‐Activated Red‐Emitting Fluoride Phosphors and Enhanced Photostability for White LEDs

“…For this issue, red‐emitting phosphors have been extensively investigated to improve CRI of WLEDs . Most recently, the Mn 4+ ‐activated narrow‐band red‐emitting fluorides phosphors, such as A 2 XF 6 :Mn 4+ (A = Li, Na, K, Rb, and Cs; A 2 = Ba, Zn; X = Si, Ge, Sn, Ti, Zr, and Hf), A 3 MF 6 :Mn 4+ (M = Al, Ga, Sc), and A 2 NF 7 :Mn 4+ (N = Nb, Ta), have gained increasing attention because of their broadband absorption in the blue region, good thermal stability, and suitable spectral profile in the red region . Moreover, the narrow‐band red component can improve the luminous efficiency of the final WLEDs device except for the contribution in the enhanced CRI.…”

Engineering cation vacancies to improve the luminescence properties of Ca14Al10Zn6O35: Mn4+ phosphors for LED plant lamp

“…Presently, the Eu 2+ ‐doped phosphors with red emission are widely studied by many researchers due to the excellent optical properties, including high luminescence efficiencies and thermal stability. Nevertheless, the Eu 2+ ‐doped phosphors are further hindered for indoor plant growth because rare‐earth materials are expensive and the far‐red region in the spectra is insufficient . Alternatively, Mn 4+ with 3d 3 electronic configurations can be excited effectively by blue light and exhibit far‐red emitting due to the spin‐forbidden 2 E → 4 A 2 transition .…”

“…Nevertheless, the Eu 2+ -doped phosphors are further hindered for indoor plant growth because rare-earth materials are expensive and the far-red region in the spectra is insufficient. [10][11][12] Alternatively, Mn 4+ with 3d 3 electronic configurations can be excited effectively by blue light and exhibit far-red emitting due to the spin-forbidden 2 E → 4 A 2 transition. [13][14][15][16][17][18] Many researches on Mn 4+ -doped phosphors mainly focus on fluorides and oxides.…”

Comparative analysis on the photoluminescence properties of Cs2BF6:Mn4+ (B = Ge, Si, Zr, Ti) red phosphors for WLEDs

“…The Mn 4+ ‐activated fluoride phosphors have been attracted more and more attentions recently . Mn 4+ is a transition metal ion with 3d 3 external electronic structure.…”

“…10 The Mn 4+ -activated fluoride phosphors have been attracted more and more attentions recently. 7,[11][12][13][14][15][16][17] Mn 4+ is a transition metal ion with 3d 3 external electronic structure. The broad excitation and narrow emission band of Mn 4+ as the consequence of its unique electronic configuration makes it proper for red phosphors.…”