Formation mechanism and optimized luminescence of Mn4+‐doped unequal dual‐alkaline hexafluorosilicate Li0.5Na1.5SiF6

A novel red phosphor Li_0.5Na_1.5SiF₆:Mn⁴⁺ (LNSF:Mn) based on the unequal dual‐alkaline hexafluorosilicate with superior optical performances has been synthesized via ion‐exchange between [MnF₆]^2? and [SiF₆]^2? at room temperature. The composition and the crystal structure of the as‐obtained phosphor LNSF:Mn were determined by energy‐dispersive x‐ray spectroscopy (EDS) and x‐ray diffraction (XRD), respectively. The formation mechanism of the red phosphor LNSF:Mn has been discussed in detail. The phosphor LNSF:Mn exhibits good chromaticity properties and a quantum yield (QY) of 96.1%, which are better than the identified fluorosilicate phosphors Na₂SiF₆:Mn⁴⁺ (NSF:Mn) and K₂SiF₆:Mn⁴⁺ (KSF:Mn). A broad and intense absorption in the blue and a bright emission in red‐shifted wavelengths make the phosphor LNSF:Mn a desired candidate for applications in warm white light‐emitting diodes.     

Synthesis of K2SiF6:Mn4+ Phosphor from SiO2 Powders via Redox Reaction in HF/KMnO4 Solution and Their Application in Warm‐White LED

In this article, we propose a facile method for synthesis of K₂SiF₆:Mn⁴⁺ phosphor and discuss its promising application in warm‐white light emitting diodes (LED). The K₂SiF₆:Mn⁴⁺ was synthesized from SiO₂ powders through redox reaction in HF/KMnO₄ solution. The optical properties of LEDs containing different ratios of K₂SiF₆:Mn⁴⁺ phosphor and commercial Ce³⁺‐doped garnets (YAG‐40) yellow–green phosphor were studied. A warm‐white LED, with color temperature of 3510 K and color rendering index of 90.9 and efficacy of 81.56 lm/W was demonstrated.     

Mn4+ activated dodec-fluoride red phosphor Na3Li3In2F12:Mn4+ with excellent waterproof stability for WLEDs

Mn⁴⁺ activated fluoride red phosphors, as candidate red materials in white light-emitting diodes (WLEDs), have received widespread attention. However, the poor water stability limits their application. Herein, a novel dodec-fluoride red phosphor Na₃Li₃In₂F₁₂:Mn⁴⁺ with good waterproof stability was successfully synthesized by solvothermal method. The crystal structure, optical property, micro-morphology, element composition, waterproof property and thermal behavior of Na₃Li₃In₂F₁₂:Mn⁴⁺ phosphor were analyzed. Under the 468 nm blue light excitation, the Na₃Li₃In₂F₁₂:Mn⁴⁺ phosphor has narrow emission bands in the area of 590–680 nm. Compared with commercial red phosphor K₂SiF₆:Mn⁴⁺, the Na₃Li₃In₂F₁₂:Mn⁴⁺ phosphor possesses better waterproof stability. When soaked in water for 360 min, the PL intensity of the Na₃Li₃In₂F₁₂:Mn⁴⁺ phosphor remains at initial 80%. Finally, warm WLEDs with CRI of 87 and CCT of 3386 K have been fabricated using blue InGaN chip, YAG:Ce³⁺ yellow phosphor and Na₃Li₃In₂F₁₂:Mn⁴⁺ red phosphor.     

Hydrophobic surface modification toward highly stable K2SiF6:Mn4+ phosphor for white light-emitting diodes

K₂SiF₆:Mn⁴⁺ phosphor is well known for its excellent red emission performance which is vital for improving the color rendering of white light-emitting diodes. However, the poor moisture resistance limits its application in optical devices. In this paper, K₂SiF₆:Mn⁴⁺ phosphor is coated with an inorganic hydrophobic protective layer to obtain good moisture resistance. Chemical vapor deposition method was used to decompose acetylene at high temperature, and the generated nanoscale carbon layer worked as a hydrophobic protective coating on the surface of the phosphor. Microstructure, compositions and properties of the synthesized K₂SiF₆:Mn⁴⁺@C phosphor were investigated in detail. It is found that most of the deposited carbon is coated on the surface of phosphor crystals in amorphous state. The carbon atoms are bonded with the fluorine element in K₂SiF₆:Mn⁴⁺ phosphor, forming carbon-fluorine (C–F) covalent bonds. The moisture resistance of K₂SiF₆:Mn⁴⁺@C phosphor is improved owing to the protection of the hydrophobic carbon. The relative emission intensity of K₂SiF₆:Mn⁴⁺@C phosphor could maintain 73% of the initial luminous intensity after immersing in the aqueous solution at room temperature for 8 h, whereas K₂SiF₆:Mn⁴⁺ phosphor without carbon coating was only 0.7% remaining of the initial value under the same conditions.     

A novel Mn4+‐activated red phosphor for use in light emitting diodes,K3SiF7:Mn4+

Phosphors that exhibit a narrow red emission are particularly interesting due to the advantage of providing a more extensive color gamut and better rendering in LED applications such as displays and solid‐state lighting. Although some Eu²⁺‐activated nitridosilicates have been discovered in this regard, K₂SiF₆:Mn⁴⁺ phosphors are the only option in actual LED applications thus far. We discovered a novel phosphor, K₃SiF₇:Mn⁴⁺, with P4/mbm symmetry. The luminescent properties of K₃SiF₇:Mn⁴⁺ are almost identical to those of the K₂SiF₆:Mn⁴⁺ phosphor, but its materials identity is distinct due to a completely different crystallographic structure, which leads to reduced decay time. The fast decay is one of the most serious disadvantages of existing K₂SiF₆:Mn⁴⁺ phosphors. The K₃SiF₇:Mn⁴⁺ phosphor was examined in comparison to the K₂SiF₆:Mn⁴⁺ via density functional theory calculation, Rietveld refinement, X‐ray photoelectron spectroscopy, X‐ray absorption near‐edge structure spectroscopy, and time‐resolved photoluminescence.     

Deep-red-emitting SrLaLiTeO6: Mn4+ double perovskites: Correlation between Mn4+-O2− bonding and photoluminescence

Mn⁴⁺-activated deep red-emitting SrLaLiTeO₆ phosphors are investigated for indoor plant growth LED applications for the first time. The phosphors crystallize in monoclinic (P2₁/n) symmetry is isostructural with SrLaLiTeO₆ host. B-site substitution of Mn⁴⁺ ions is confirmed from the redshift of high energy phonon modes in both Raman and IR spectra. The phosphor exhibited a far-red emission centered at 696 nm corresponding to the ²E_g → ⁴A_2g spin-forbidden transition of the Mn⁴⁺ ions. Approximate crystal field parameters depict the weak influence of neighboring ligand fields on Mn⁴⁺ ions and the least covalence of Mn⁴⁺-ligand bonding compared to other double perovskite phosphors. Moreover, the phosphors exhibit excellent thermal stability with an activation energy of 0.23 eV. Phosphor parameters including CCT, color purity, and quantum yield are evaluated and their values meet the requirements of a red-emitting phosphor for LED applications. Furthermore, the PL emission spectrum of SrLaLiTeO₆: Mn⁴⁺ matches with the absorption spectrum of plant phytochromes denoting the prospects of this phosphor for indoor plant growth LED applications.     

A single‐phase full‐color emitting phosphor Na3Sc2(PO4)3:Eu2+/Tb3+/Mn2+ with near‐zero thermal quenching and high quantum yield for near‐UV converted warm w‐LEDs

A single‐phase full‐color emitting phosphor Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ has been synthesized by high‐temperature solid‐state method. The crystal structure is measured by X‐ray diffraction. The emission can be tuned from blue to green/red/white through reasonable adjustment of doping ratio among Eu²⁺/Tb³⁺/Mn²⁺ ions. The photoluminescence, energy‐transfer efficiency and concentration quenching mechanisms in Eu²⁺‐Tb³⁺/Eu²⁺‐Mn²⁺ co‐doped samples were studied in detail. All as‐obtained samples show high quantum yield and robust resistance to thermal quenching at evaluated temperature from 30 to 200°C. Notably, the wide‐gamut emission covering the full visible range of Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ gives an outstanding thermal quenching behavior near‐zero thermal quenching at 150°C/less than 20% emission intensity loss at 200°C, and high quantum yield‐66.0% at 150°C/56.9% at 200°C. Moreover, the chromaticity coordinates of Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ keep stable through the whole evaluated temperature range. Finally, near‐UV w‐LED devices were fabricated, the white LED device (CCT = 4740.4 K, Ra = 80.9) indicates that Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ may be a promising candidate for phosphor‐converted near‐UV w‐LEDs.     

HF-free molten salt route for synthesis of highly efficient and water-resistant K2SiF6:Mn4+ for warm white LED

It has been one of the hot issues to prepare the red-emitting Mn⁴⁺-doped fluoride phosphors with highly efficient and waterproofness for warm white-light-emitting diodes (WLEDs) by the green and environmentally friendly method. Herein, we design a novel green molten salt route to synthesize K₂SiF₆:Mn⁴⁺ red powder using molten NH₄HF₂ salt instead of HF liquor as the reaction medium. The results show that KMnO₄ and MnF₂ could produce Mn⁴⁺ in NH₄HF₂ molten salt through a reduction reaction, and the resulting Mn⁴⁺-doped K₂SiF₆ exhibited a bright red emission peaked at 632 nm under blue light excitation. The luminescence intensity of the as-obtained product after immersing into water for 24 hours maintain nearly 100% of that before soaking and emission peak shape remains unchanged. The thermal stability of the sample was evaluated by temperature-dependent luminescence spectral intensity during heating and cooling. Furthermore, a warm white-light-emitting diodes (WLEDs) with an excellent color rendering index (Ra = 87.1), lower correlated color temperature (CCT = 3536K), and high luminous efficacy (116.99 lm·W⁻¹) was fabricated based on blue chip and K₂SiF₆:Mn⁴⁺ and commercial yellow phosphor (Y₃Al₅O₁₂:Ce³⁺).     

Improvement of the luminescent thermal stability and water resistance of K2SiF6:Mn4+ by surface passivation

Mn⁴⁺-doped fluoride phosphors can solve the problem for lack of red emitting component in commercial white light-emitting diodes (WLEDs). However, its application is seriously hindered by its easy hydrolysis. Here, we propose to use sodium sulfite as a passivator to treat K₂SiF₆:Mn⁴⁺. After passivation, a Mn⁴⁺-rare K₂SiF₆ protective layer can be formed in situ on the surface of the phosphor, and lead to improved emission intensity, luminescent thermal stability and moisture resistance. When soaking in water for 6 h, the integrated fluorescent intensity of the passivated sample maintained 90.8% of the initial value, while the intensity of the un-passivated sample sharply decreased to 10.2% of the initial value. Mechanisms to improve the emission, water resistance and thermal stability of the luminescence are proposed and discussed. WLED was assembled with the passivated sample, and good performance of warm white light (CCT = 2963 K, Ra = 90.4) was obtained.     

Preparation,Design, and Characterization of the Novel Long Persistent Phosphors: Na2ZnGeO4 and Na2ZnGeO4:Mn2+

A novel blue‐emitting phosphor Na₂ZnGeO₄ and a novel green‐emitting phosphor Na₂ZnGeO₄:Mn²⁺ have been newly developed via high‐temperature solid‐state reaction. The crystal structure of Na₂ZnGeO₄ has been identified. Energy transfer from Na₂ZnGeO₄ host to Mn²⁺ ions was affirmed. Undoped and Mn²⁺‐doped Na₂ZnGeO₄ phosphors exhibit blue and green long persistent luminescence (LPL) with persistent duration more than 40 min and 4 h, respectively. The traps created in host lattice were clarified. The LPL mechanism in Na₂ZnGeO₄ and Na₂ZnGeO_4: Mn²⁺ was discussed briefly. This investigation provides two new and efficient long persistent phosphors (LPPs).     

Tunable Color of Eu2+/Mn2+ Coactivated Na5Ca2Al(PO4)4 via Energy Transfer

Eu²⁺ and Eu²⁺/Mn²⁺‐activated Na₅Ca₂Al(PO₄)₄ phosphors have been synthesized by the combustion method. X‐ray powder diffraction profiles, luminescence spectra, chromaticity variation, and energy transfer of Na₅Ca₂Al(PO₄)₄:Eu²⁺, Mn²⁺ were investigated as a function of the Eu²⁺ and Mn²⁺ concentrations in Na₅Ca₂Al(PO₄)₄. The Na₅Ca₂Al(PO₄)₄:Eu²⁺,Mn²⁺ phosphors can be effectively excited at wavelength ranging from 300 to 430 nm, which matches well with that for near‐ultraviolet (UV) light‐emitting diode (LED) chips. Under excitation at 354 nm, Na₅Ca₂Al(PO₄)₄:Eu²⁺,Mn²⁺ not only exhibits blue‐green emission band attributed to 4f⁶5d¹→4f⁷ of Eu²⁺ but also gives an orange emission band attributed to ⁴T₁→⁶A₁ of Mn²⁺. The emission color of the phosphor can be systematically tuned from blue‐green through white and eventually to orange by adjusting the relative content of Eu²⁺ and Mn²⁺ through the principle of energy transfer. The results indicated that Na₅Ca₂Al(PO₄)₄:Eu²⁺, Mn²⁺ may serve as a potential color‐tunable phosphor for near UV white‐light LED.     

A double-perovskite Sr2ZnWO6:Mn4+ deep red phosphor: Synthesis and luminescence properties

Novel double-perovskite Sr₂ZnWO₆:Mn⁴⁺(SZW:Mn⁴⁺) phosphor is synthesized by high-temperature solid-state reaction method in air. SZW:Mn⁴⁺ phosphor with excitation at 325 and 526 nm emits deep-red light, the chromaticity coordinate is (0.7315,0.2685), and the emission band peaking at ~702 nm within the range 640–760 nm is assigned to the ²E→⁴A₂ transition of Mn⁴⁺ ion. The influences of “Mn⁴⁺- ligand” bonding and crystal field strength to emission properties of Mn⁴⁺ ion are analyzed. The optimal Mn⁴⁺ ion concentration in SZW:Mn⁴⁺ phosphor is ~0.8 mol%. Lifetime of SZW:Mn⁴⁺ phosphor decreases from 554.77 to 401.35 μs with increasing Mn⁴⁺ ion concentration in the range of 0.2–1.0 mol%. The lifetime data and decay curves indicate that there is only a single type of Mn⁴⁺ ion luminescent center in SZW:Mn⁴⁺ phosphor. The luminous mechanism of SZW:Mn⁴⁺ phosphor is analyzed by Tanabe-Sugano energy level diagram of Mn⁴⁺ in the octahedron together with the simple energy level diagram. The experimental results are helpful to research the influences of the neighboring coordination environment around Mn⁴⁺ and host crystal structure to the luminescence properties of Mn⁴⁺ ion and to deeply understand other Mn⁴⁺-dopedmaterials.     

Key role of Nb5+ in achieving water-resistant red emission in K2Ta1-xNbxF7:Mn4+ phosphors

Mn⁴⁺-activated fluoride is one of the most important red phosphors for white light-emitting diodes (WLEDs) with high color rendering index (CRI). Due to a lack of water resistance, their potential applications are limited. Although surface coating strategies improve the waterproof stability of fluoride red phosphors, they have downsides. It was found that Nb⁵⁺ plays an important role in improving the water resistance of Mn⁴⁺-activated oxyfluorides by preventing the hydrolysis of [MnF₆]^2-. In this work, the influence of Nb⁵⁺ on the waterproof stability of Mn⁴⁺-activated fluorides was explored. A set of synthesized K₂Ta_1-xNb_xF₇:Mn⁴⁺ phosphors exhibit tunable and superior water resistance. The photoluminescence (PL) intensity of the representative sample K₂Ta_0.6Nb_0.4F₇:5%Mn⁴⁺ remains nearly 100% of its initial value even after being immersed in water for 60 min, which is significantly higher than the commercial K₂SiF₆:Mn⁴⁺ red phosphor (8.7%). Our findings open up new possibilities for the development of waterproof fluoride red phosphors.     

Surface modification of K2TiF6:Mn4+ phosphor with SrF2 coating to enhance water resistance

K₂TiF₆:Mn⁴⁺ is an attractive narrow-band red-emitting phosphor for warm white light-emitting diodes (LEDs). Nevertheless, the hexafluoride phosphor is liable to deliquesce in moist environments, which leads to a sharp deterioration performance of luminescence. Surface modification of K₂TiF₆:Mn⁴⁺ phosphor with SrF₂ coating has been introduced, with the aid of KHF₂ transition layer to moderate the lattice mismatch. The reaction mechanism is discussed in detail, as so as the influence of SrF₂ coating on the luminescence intensity. The SrF₂ coating is able to prevent the hydrolysis of internal [MnF₆]²⁻ group; thereby, the luminescence intensity retains over 90% of initial value after being immersed in distilled water for 2 h. The LED devices fabricated with commercial Y₃Al₅O₁₂:Ce³⁺ and as-modified K₂TiF₆:Mn⁴⁺ phosphors exhibit bright white light with tunable chromaticity coordinate, correlated color temperature, and color rendering index. It enlightens a convenient method to enhance the moisture resistance of Mn⁴⁺ doped fluoride phosphors for commercial application in the field of white LEDs.     

Rare-earth-free Li5La3Ta2O12:Mn4+ deep-red-emitting phosphor: Synthesis and photoluminescence properties

Li₅La₃Ta₂O₁₂:Mn⁴⁺ (LLTO:Mn⁴⁺) phosphors are prepared in air via high-temperature solid-state method and investigated for their crystal structures and luminescence properties. LLTO:Mn⁴⁺ phosphor under excitation at 314 nm shows deep-red emission peaking at 714 nm due to the ²E→⁴A₂ transition of Mn⁴⁺ ion. The excitation bands in the range 220 - 570 nm are attributed to the Mn⁴⁺ - O^2- charge-transfer band and the ⁴A_2g→⁴T_1g, ²T_2g, and ⁴T_2g transitions of Mn⁴⁺, respectively. The optimal Mn⁴⁺ ion concentration is ~0.4 mol%. The concentration quenching mechanism in LLTO:Mn⁴⁺ phosphor is electric dipole-dipole interaction. The luminous mechanism and temperature quenching phenomenon are explained by the Tanabe-Sugano energy level diagram and the configurational coordinate diagram of Mn⁴⁺ in the octahedron, respectively. The experimental results indicate that LLTO:Mn⁴⁺ phosphor has a potential application prospect as candidate of deep-red component in light-emitting diode (LED) lighting.     

Novel deep-red-emitting double-perovskite type Ca2ScNbO6:Mn4+ phosphor: Structure,spectral study,and improvement by NaF flux

A novel deep-red-emitting phosphor Ca₂ScNbO₆:Mn⁴⁺ is prepared via a high-temperature solid-state reaction and its luminescent properties are systematically investigated. The results show that Mn⁴⁺-activated Ca₂ScNbO₆ phosphors have broad absorption in ultraviolet region, and show bright deep-red emission at 692 nm. The optimal doping concentration, crystal-field strength, internal quantum efficiency, and mechanism of concentration and thermal quenching effects are discussed in detail. Moreover, NaF flux is screened out to improve both luminescent intensity and morphology of the phosphor. Finally, a red light-emitting diode (LED) lamp is fabricated with as-prepared Ca₂ScNbO₆:Mn⁴⁺ phosphors and a 365 nm LED chip. The electroluminescence spectra show a good overlapping with phytochrome P_R and P_FR absorbance. The results provided the as-synthesized Ca₂ScNbO₆:Mn⁴⁺ phosphors a great potential in plant growth lighting.     

Achieving highly efficient far-red emission from luminescence-ignorable Ca2MgTeO6:Mn4+ to Ca2-zLnzMgTe1-yWyO6:Mn4+ (Ln = La,Y, Gd) phosphors via solid solution and impurity doping strategies

The Mn⁴⁺-doped Ca2MgTeO6 (CMTO) far-red emitting phosphors with double perovskite-type structure were successfully synthesized. Upon near-ultraviolet (n-UV, 300 nm) light excitation, the as-prepared phosphors showed far-red light at 700 nm attributed to the ²E_g→⁴A_2g transition of Mn⁴⁺ ion. The doping concentration of the CMTO:xMn⁴⁺ samples was optimized to be 0.8 mol%. The relevant mechanism of concentration quenching was demonstrated as the dipole-dipole interaction. Furthermore, solid solution and impurity doping strategies were adopted to improve the far-red emission of the luminescence-ignorable CMTO:Mn⁴⁺ phosphor. Series of Ca₂MgTe_(1−y)W_yO₆:0.8 mol%Mn⁴⁺ (y = 0–100 mol%) solid solution and Ca_2−zLn_zMgTe_0.6W_0.4O₆:Mn⁴⁺ (Ln = La, Y, and Gd, z = 10 mol%) phosphors were synthesized through the above two strategies. The luminescence intensity of the optimal Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphor was 13.7 times that of the CMTO:Mn⁴⁺ phosphor and 2.51 times that of red commercial phosphor K₂SiF₆:Mn⁴⁺. Notably, both CMTO:Mn⁴⁺ and Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphors exhibited remarkable thermal stability compared with most Mn⁴⁺-doped phosphors. Finally, the highly efficient Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphor was successfully applied in fabricating the warm white light diode (w-LED). This working along both lines strategy exhibited great potential for luminescence optimization of Mn⁴⁺-doped oxide phosphors.     

Preparation and optical properties of a novel double-perovskite phosphor,Ba2GdNbO6:Mn4+, for light-emitting diodes

Red phosphors serve an important function as red components of warm white light-emitting diodes (WLEDs). Given their remarkable luminescent properties and low cost, Mn⁴⁺-doped phosphors are attracting significant attention. In this study, the novel red phosphor Ba₂GdNbO₆:Mn⁴⁺ was synthesized through high-temperature solid-state reaction. The host Ba₂GdNbO₆ with a double-perovskite structure was investigated. Scanning electron microscopy and thermogravimetric analysis were performed to evaluate the structure and thermal stability of the phosphor, respectively. PLE and photoluminescence spectra were further used to study the luminescence properties of the phosphor. Moreover, crystal field strength and Racah parameters were calculated to estimate the nephelauxetic effect of Mn⁴⁺ on the Ba₂GdNbO₆ host lattice. Thermal quenching characteristics were also analyzed. The fabricated red-emitting LED revealed its potential application in WLEDs.     

White‐Emitting Tuning and Energy Transfer in Eu2+/Mn2+‐Substituted Apatite‐Type Fluorophosphate Phosphors

Herein, a series of Eu²⁺&Mn²⁺substituted fluorophosphates Ca₆Gd₂Na₂(PO₄)₆F₂ phosphor with apatite structure have been synthesized and investigated by the powder X‐ray diffraction, photoluminescence spectra, fluorescence decay curves, thermal quenching, and chromaticity properties. Particularly, both Eu²⁺ and Mn²⁺ emissions at the two different lattice sites 4f and 6h in Ca₆Gd₂Na₂(PO₄)₆F₂ matrix have been identified and discussed. The dual energy transfer of Eu²⁺→Mn²⁺ and Gd³⁺→Mn²⁺ in Ca₆Gd₂Na₂(PO₄)₆F₂:Eu²⁺,Mn²⁺ samples have been validated and confirmed by the photoluminescence spectra. The dependence of color‐tunable on the activator concentration of Mn²⁺ was investigated to realize white light emission. By varying the doping concentration of the Mn²⁺ ion, a series of tunable colors including pure white light and candle light are obtained under the excitation of 350 nm. Moreover, the fluorescence decay curves have been fitted and analyzed using the Inokuti–Hirayama theoretical model to estimate the Eu–Mn interaction mechanism. We also investigated temperature‐dependent photoluminescence quenching characteristics according to the Arrhenius equation. Preliminary studies on the properties of the phosphor indicated that the obtained phosphors might have potential application as a single‐component white‐emitting phosphor for UV‐based white LEDs.     

Surface engineered environment-stable red-emitting fluorides for white light emitting diodes

Poor water stability is the main problem of commercialized Mn⁴⁺-doped fluorides for white light emitting diode (WLED) application. This work proposes a surface engineering strategy to rebuild a Mn⁴⁺-free fluoride shell on fluorides to effectively resist the destruction from water molecules. By simple processing using glyoxylic acid (GA) solution, the moisture resistance of the red-emitting fluorides can be significantly improved. The photoluminescence (PL) quantum efficiency (QE) of the surface-engineered K₂SiF₆:Mn⁴⁺ (KSFM-GA) still maintain 98.43% after water immersion for 360 h, in sharp contrary to the untreated one (its PLQE decreases to 59.79%). Additionally, PL intensity of the hydrolyzed KSFM can be recovered to 99.1% through the treatment of the reducing GA solution. By using the high-stability KSFM-GA red phosphor, the as-fabricated high-performance warm-WLED device can still maintain 84.6% in luminous efficacy, higher than that (79.6%) with the untreated KSFM, after 500 h of aging in a high temperature (85 °C) and high humidity (85%) environment.