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.     

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.     

High luminescent thermal stability and water resistance of K2SiF6:Mn4+@CaF2 red emitting phosphor

K₂SiF₆:Mn⁴⁺ (KSF:Mn⁴⁺), as an efficient red-emitting phosphor, has a promising application in WLEDs (white light-emitting diodes). However, poor moisture resistance performance still hinders its deeper commercialization. Here, KSF:Mn⁴⁺@ CaF₂ with high water resistance and luminescent thermal stability has been prepared though H₂O₂-free hydrothermal method and surface coating process. Both KSF:Mn⁴⁺ and KSF:Mn⁴⁺@CaF₂ all have high luminescent thermal stability, due to negative thermal quenching (NTQ) effect. Mechanism of the NTQ has been discussed and suggested as thermal-light energy conversion mechanism. Compared with KSF:Mn⁴⁺, water resistance of KSF:Mn⁴⁺@CaF₂ is greatly improved by coating of CaF₂, because the outer shell of CaF₂ can effectively prevent the [MnF₆]^2- group on the surface of the phosphor from being hydrolyzed into MnO₂. The results of water resistance test shows that after immersing in water for 360 min (6 h), luminescent intensity of the uncoated product drops to 41.68% of the initial one, while that of the coated product remains to have 88.24% of its initial one. Warm white light with good luminescent performances (CCT = 3956 K and Ra = 89.3) is got from prototype WLEDs assembled by using the optimal coated sample. The results suggest that the optimal coated sample has potential application in blue-based warm WLEDs.     

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.     

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.     

Zero-thermal-quenching of LiAl5O8: Eu2+, Mn2+ phosphors by energy transfer and defects engineering

The photoluminescence behavior of inorganic phosphors is generally influenced by thermal stability, which determines the luminescence efficiency of the corresponding devices. Here, a series of Eu²⁺, Mn²⁺ co-doped LiAl₅O₈ blue-green-emitting phosphors with thermal robust are successfully fabricated. The concentration-dependent emission spectra and the decay curves of the as-obtained LiAl₅O₈: Eu²⁺, Mn²⁺ samples manifest the occurrence of the energy transfer from Eu²⁺ to Mn²⁺ ions via dipole-dipole interaction, and the corresponding emitted colors are gradually modulated from blue to green under the excitation of 310 nm. Moreover, the zero-thermal-quenching luminescence is observed when the operation temperature is up to 423 K, which is attributed to the energy release from the trapping centers to emitting centers (Eu²⁺ and Mn²⁺) at high temperature. Furthermore, a warm white light-emitting diodes (WLEDs) device with correlated color temperature of 5061 K, a color rendering index of 80.6 and long-term stability is fabricated by combining UV LED chip (λ_ex = 310 nm), as-obtained LiAl₅O₈: Eu²⁺, Mn²⁺ phosphor, commercially available red phosphor and green phosphor. These results prove the potential application of the as-obtained LiAl₅O₈: Eu²⁺, Mn²⁺ phosphor for UV-pumped WLEDs devices.     

An efficient far-red emission Sr2InSbO6:Mn4+, M (M = Li+, Na+, and K+) phosphors for plant cultivation LEDs

High-efficiency and far-red light phosphors based on Mn⁴⁺-doped inorganic luminescence materials are beneficial to plant cultivation. However, Mn⁴⁺-doped oxide phosphors have a common problem of low quantum efficiency. Alkali metal ion codoping can effectively improve the luminescence properties of Mn⁴⁺-activated oxide phosphors. Herein, a series of Sr₂InSbO₆:Mn⁴⁺, M (SISO:Mn⁴⁺, M) (M = Li⁺, Na⁺, and K⁺) far-red-emitting phosphors codoped alkali metal ions were first synthesized. Density functional theory calculation indicated that SISO is a kind of indirect bandgap material with a bandgap of ∼1.60 eV. The SISO:Mn⁴⁺ samples showed a far-red light at 698 nm upon 365 nm, which perfectly matched the absorption spectrum of the far-red-phytochrome (Pfr) of plants. The doping concentration of the SISO:Mn⁴⁺ samples was optimized to be 0.006 mol. The concentration quenching mechanism was defined as dipole–dipole interaction by combining the Dexter theory and the Inokuti–Hirayama model. Optimizing the sintering temperature and codoped with alkali metal ions (Li⁺, Na⁺, and K⁺) could improve the luminescent intensity of SISO:Mn⁴⁺. The optimum sintering temperature was 1300°C. The internal quantum efficiencies of SISO:0.006Mn⁴⁺ and SISO:0.006Mn⁴⁺, 0.006Li⁺ phosphors are 22.67% and 60.56%, respectively. SISO:Mn⁴⁺, Li⁺ phosphors-based plant growth light-emitting diodes (LEDs) demonstrate excellent optical stability and long lifetime. Thus, these phosphors are promising candidates for plant cultivation LEDs.     

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.     

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.     

Enhanced luminescence of manganese in singly doped white light zinc phosphate glass

On the basis of a kind of zinc phosphate oxynitride glass matrix with a broadband blue light, a series of manganese single-doped glasses were obtained. A broader red emission with the higher intensity belonging to the Mn²⁺ ion was observed in this glass matrix. The mechanism of the emission from Mn²⁺ ions was clarified through Mn³⁺ as an “energy acquisition probe” to replace complex dynamic luminescence discussion, which was a fit explanation for the differences in luminescence behavior of Mn ions in prepared glasses at different degrees of redox. The research results indicated that the prepared manganese-doped glass was a potential candidate as phosphor-converted white-light-emitting diodes. An encapsulated white-light-emitting diode device based on this glass with 276 nm ultraviolet chip was achieved. It showed the CIE values of (0.33, 0.35), high CRI (Ra = 86), and low color temperature (5228 K).     

Orderly‐Layered Tetravalent Manganese‐Doped Strontium Aluminate Sr4Al14O25:Mn4+: An Efficient Red Phosphor for Warm White Light Emitting Diodes

Searching for an efficient non rare earth‐based oxide red phosphor, particularly excitable by light in the wavelength from 380 to 480 nm and unexcitable by green light, is essential for the development of warm white light emitting diodes (WLEDs). Here, we report a promising and orderly‐layered candidate: Sr₄Al₁₄O₂₅:Mn⁴⁺ with CIE color coordinates (0.722, 0.278). It has higher luminescence efficiency particularly upon blue excitation and is much cheaper than the commercial red phosphor 3.5MgO·0.5MgF₂·GeO₂:Mn⁴⁺ (MMG:Mn⁴⁺). In sharp contrast to Eu²⁺‐doped (oxy)nitrides, the phosphor can be synthesized by a standard solid‐state reaction at 1200°C in air. The effects of flux boron content, environment, and preparation temperature, sintering dwelling time as well as Mn concentration have been systematically investigated for establishing the optimal synthesis conditions. The low temperature emission spectra reveal that there are at least three types of Mn⁴⁺ ions in Sr₄Al₁₄O₂₅:Mn⁴⁺ due to the substitution for the distorted octahedral Al³⁺ sites. The AlO₆ layers where Mn⁴⁺ prefers to reside are well separated from one another by AlO₄ tetrahedra in one dimension parallel to axis a. This scenario can efficiently isolate Mn⁴⁺ ions from local perturbations, thereby enabling the high efficiency of luminescence. The energy transfer rates and mechanism are discussed.     

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.     

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.     

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.     

Solution growth of millimeter-scale Na2SiF6 single crystals for Mn4+-doping as red phosphor

The cation exchange method has been demonstrated to be efficient in doping Mn⁴⁺ ions into various fluorides to synthesize the red-emitting LED phosphors. This paper, however, reports the challenge in using this method to dope Mn⁴⁺ into the Na₂SiF₆ single crystals, to prepare the fluoride phosphor in single-crystal form, a state-of-the-art study in the white LED lighting field. The millimeter-sized Na₂SiF₆ single crystals with a uniform columnar morphology (2–3 mm in length) were successfully grown in solution by a slow cooling process after optimizing the precursors. Then, the crystals were soaked in the HF solution dissolved with K₂MnF₆ to implement Mn⁴⁺-doping via the cation exchange process. Evaluation of the Mn⁴⁺-doping behavior reveals that the Mn⁴⁺ ↔ Si⁴⁺ cation exchange is less efficient in the case of single crystal host compared with the polycrystalline powdery ones and by-reactions also occur which generates new phases. The Na₂SiF₆ single crystals doped with Mn⁴⁺ exhibit a series of discrete sharp peaks with intense zero phonon line emission at 617 nm under 450 nm blue irradiation. This study may trigger the exploration of new single crystal fluoride phosphor.     

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.     

Synthesis,Structure, and Performance of Efficient Red Phosphor LiNaGe4O9:Mn4+ and Its Application in Warm WLEDs

For phosphor‐converted warm white light‐emitting diodes (WLEDs), it is essential to find highly efficient red oxide phosphors, which are better chemically stable and benign to environment and can be prepared in a much milder condition. Here, we report a red phosphor LiNaGe₄O₉:Mn⁴⁺ with a quantum yield up to 78% after systematic optimization in synthesis temperature, dopant concentration of Mn⁴⁺, and sintering time. Best performance of the phosphor can be reached when it is synthesized in a mild reaction condition, that is, at 850°C for 3 h in air. The integrated emission intensity is more than four times stronger than commercial red phosphor 3.5MgO·0.5MgF₂·GeO₂:Mn⁴⁺ (MFG:Mn⁴⁺) under a blue light excitation at 470 nm. Crystal structural analysis reveals that the high efficiency Mn⁴⁺ exhibits in the compound is mainly due to the well separation of GeO₆ groups from each other by GeO₄ tetrahedra in the neighborhood and the ideal substitution of octahedral Ge⁴⁺ site by Mn⁴⁺ in view of both size and charge matches. The high performance of the phosphor encourages us to apply the blue absorbing red phosphor to WLED, which is based on combination of a blue LED chip and YAG:Ce³⁺, and the warm perception WLED is therefore achieved with a color temperature of 3353 K.     

LED-pumped intense red luminescence based on Ba2LaTaO6: Mn4+ double perovskite phosphor

Non-rare earth Mn⁴⁺ ion-doped red oxide phosphors have great potential for applications in warm white light-emitting diodes (wLEDs) due to their low cost and stable physicochemical properties. Herein, a series of Ba₂LaTaO₆ (BLTO): Mn⁴⁺ phosphors were successfully synthesized by the high-temperature solid-state method. The theoretical values of the band gap calculated by the density functional theory are close to the experimental values obtained by the absorption spectroscopy. In addition, the phosphors have a broad excitation band in the wavelength range of 280–550 nm and emit red light at the peak wavelength of 681 nm under excitation. The concentration quenching of the BLTO: Mn⁴⁺ phosphor was caused by dipole-dipole interactions. The activation energy and the average decay lifetimes of the samples were calculated. Meanwhile, the effects of synthesis temperature and Li⁺ ion doping on the luminescence performance of the samples were also investigated. Satisfactorily, the color purity and internal quantum efficiency of the phosphor reached 98.3% and 26.8%, respectively. Further, the samples were prepared as red-light components for warm wLEDs. The correlated color temperature, color rendering index, and luminous efficiency of the representative devices driven by 60 mA current were 5190 K, 83.3, and 81.59 lm/W, respectively. This work shows that the BLTO: Mn⁴⁺ red phosphor with excellent luminescence performance can be well applied to warm wLEDs.     

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

A series of Cs₂BF₆:Mn⁴⁺ (B = Ge, Si, Ti, Zr) red phosphors were synthesized by a precipitation-cation exchange route. The phase purity, morphology, and constituent were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Optical properties were investigated by photoluminescence (PL) spectra and high-resolution PL. Temperature-dependent PL examination at the range of both 273-573 K and 10-300 K was performed to investigate the emission mechanism of Mn⁴⁺ in these fluorides. The intensity for both zero-phonon lines (ZPLs) and vibration coupled emission of Mn⁴⁺ in these four systems with different crystal structures was investigated systematically. These phosphors present bright red emission under blue light (467 nm) illumination, among which Cs₂GeF₆:0.1Mn⁴⁺ shows the highest emission intensity with ultrahigh quantum efficiency of 94%. The white light-emitting diodes (WLEDs) fabricated with this sample, blue InGaN chips and commercial YAG:Ce³⁺ phosphor exhibited high luminous efficacy beyond 100 lm/w with high color rendering index (~88.6) and low color temperature (~3684 K).