Highly Stable K₂SiF₆:Mn⁴⁺@K₂SiF₆ Composite Phosphor with Narrow Red Emission for White LEDs

Abstract

Poor water resistance and nongreen synthesis remain great challenges for commercial narrow red-emitting phosphor AMF:Mn (A = alkali metal ion; M = Si, Ge, Ti) for solid-state lighting and display. We develop here a simple and green growth route to synthesize homogeneous red-emitting composite phosphor KSiF:Mn@KSiF (KSFM@KSF) with excellent water resistance and high efficiency without the usage of toxic and volatile hydrogen fluoride solution. After immersing into water for 6 h, the as-obtained water-resistant products maintain 76% of the original emission intensity, whereas the emission intensity of non-water-resistant ones steeply drops down to 11%. A remarkable result is that after having kept at 85% humidity and at 85 °C for 504 h (21 days), the emission intensity of the as-obtained water-resistant products is at 80-90%, from its initial value, which is 2-3 times higher than 30-40% for the non-water-resistant products. The surface deactivation-enabled growth mechanism for these phosphors was proposed and investigated in detail. We found that nontoxic HPO/HO aqueous solution promotes the releasing and decomposition of the surface [MnF] ions and the transformation of the KSFM surface to KSF, which finally contributes to the homogeneous KSFM@KSF composite structure. This composite structure strategy was also successfully used to treat KSFM phosphor prepared by other methods. We believe that the results obtained in the present paper will open the pathway for the large-scale environmentally friendly synthesis of the excellent antimoisture narrow red-emitting AMF:Mn phosphor to be used for white light-emitting diode applications.

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

“…To clarify the mechanism of this H 2 O 2 ‐passivated strategy for improving the moisture resistance of Mn 4+ ‐doped fluoride phosphors, we should first understand the general deposition and solubility equilibrium in water for most of hexafluoride . The main chemical reactions of fluoride complexes in water are derived from many references, and the general expression of K 2 XF 6 :Mn 4+ phosphors were corrected as K 2 X 1− a Mn a F 6 . All of the ionization and hydrolysis process is described in Equations – and the stepwise hydrolysis process is also listed in Equation (S1) of the Supporting Information…”

“…Besides, Murphy et al developed a washing process to reduce surface active manganese from KSF using K 2 SiF 6 and hydrofluoric acid (HF) saturated solutions or H 2 SiF 6 solutions . And core–shell‐structured KTF was successfully prepared by Huang et al Wang and co‐workers further synthesized K 2 SiF 6 :Mn 4+ @K 2 SiF 6 composites without the consumption of toxic HF solution, and prepared new reductive dl‐mandelic acid loaded K 2 GeF 6 :Mn 4+ (KGF) phosphor . These strategies can evidently improve the moisture resistance of fluoride red phosphors, while most of the surface modification procedures are relatively complex, and it is a big challenge to enhance the stability with the surface protective layer.…”

Narrow‐Band Red‐Emitting Phosphor K2SiF6:Mn4+: HF‐Free Synthesis, Surface Modification, and Application for Warm White LEDs

“…Therefore, it is quite necessary to render red‐emitting fluoride phosphors doped with Mn 4+ phosphors good chemical stability based on the green synthetic route. Wang et al., developed a facile and green synthesis strategy to prepare red‐emitting composite phosphor K 2 SiF 6 : Mn 4+ @ K 2 SiF 6 not involved HF solution. The emission intensity of as‐prepared phosphor was measured to maintain 76% of the original state after immersed in distilled water for 6 hours.…”

Mn4+-activated BaLaMgSbO6 double-perovskite phosphor: a novel high-efficiency far-red-emitting luminescent material for indoor plant growth lighting

“…Recently, red-emitting luminescent materials doped with rareearth ions (such as Eu 3+ , Eu 2+ , Ce 3+ ) and transitional metal ions (such as Mn 4+ and Cr 3+ ) have attracted much attention due to their promising applications in lighting and displays. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Mn 4+ ion with a 3d 3 electron conguration belongs to the transitional metal ion, and in recent years Mn 4+activated red-emitting phosphors have been widely reported for warm-white light-emitting diodes (LEDs) towards general lighting applications. [15][16][17][18][19] Generally, Mn 4+ ions can substitute for W 6+ , Sn 4+ , Sb 5+ , Al 3+ , Ge 4+ , Ta 5+ , and Ti 4+ ions in the octahedral or distorted octahedral systems.…”