Warm Warm White Light-emitting Diodes Research Articles

High-efficiency RbASiF6:Mn4+ (A = K, Cs) phosphors obtained by one-step green synthesis method

Red-emitting Mn4+-doped fluoride phosphors are recognized as promising materials for high-performance warm white light-emitting diodes (WLEDs). However, the extensive use of toxic hydrofluoric acid in traditional synthesis methods hinders their development and commercialization. Furthermore, the traditional solid-phase method often has cumbersome sintering steps, high temperature, long holding time, and certain safety hazards, so it is very necessary to develop a green synthesis method with simple steps and low energy consumption. In this study, a low-temperature solid-state method is proposed to synthesize RbASiF6:Mn4+ (A = K, Cs) phosphors by one step. Optimal emission intensities were observed at Mn4+ concentrations of 1.2 % in RbKSiF6 and 2.1 % in RbCsSiF6. These phosphors demonstrated high thermal stability. At 423 K, the photoluminescence intensities of RbKSiF6:1.2 %Mn4+ and RbCsSiF6:2.1 %Mn4+ reached 114 % and 87 % of their respective values at room temperature. Meanwhile, the chromaticity shifts were almost negligible, and high color purity was achieved for both phosphors. The electro-optical performance of WLED devices utilizing these phosphors, in combination with YAG:Ce3+ and GaN chips, showed high color rendering indices (CRI) and low correlated color temperatures (CCT) across varying currents. Specifically, under a driving current of 20 mA, the device incorporating RbKSiF6:1.2 %Mn4+ exhibited a CRI of 94 and a CCT of 3732 K, with a luminous efficacy of 61 lm/W. These findings highlight the potential of green-synthesized RASFM phosphors in advancing the application of warm WLEDs.

Synthesis and luminescence characterization of Dy3+/Sm3+ Co-doped Y2MgTiO6 double-perovskite phosphors for warm WLED

Y2MgTiO6:Dy3+/Sm3+ double-perovskite phosphors were synthesized using the high-temperature solid-state reaction method, and their luminescence properties were examined through various techniques, including Rietveld refinement, excitation and emission spectra, Commission Internationale de l'Eclairage (CIE) analysis, and band gap simulation. Ab initio calculations were performed to analyze the band gap and density of states, allowing for the prediction of the effect of Dy3+ and Sm3+ doping on emission intensity. The emission spectra of Y2MgTiO6 (YMTO) doped with Sm3+ and Dy3+ exhibited maximum peaks at 602 nm and 575 nm, respectively, when excited at 325 nm. Both YMTO:Sm3+ and YMTO:Dy3+ demonstrated excellent thermal stability. The CIE coordinates of YMTO doped with 1 mol% Dy3+ were determined to be (0.3771, 0.3804), with a correlated color temperature (CCT) of 4115 K, confirming its suitability for warm white light applications. Introducing 1 mol% and 3 mol% of Sm3+ ions into the Dy3+/Sm3+ co-doped YMTO allowed for adjustable CCT values of 3719 K and 3302 K, respectively, further enhancing their potential for use in warm white light-emitting diodes (WLEDs).

Novel Mn4+-activated fluoride red phosphors induced by alkaline metal ions replacement: Green synthesis, luminescence enhancement, high stability and application in warm WLED

Red-emitting Mn4+-doped fluoride phosphors are promising fluorescent material for use in high-performance warm white light emitting diodes (WLEDs). However, low stability and non-green synthesis method limit the development and commercialization of such phosphor. Herein, a series of novel (Li/Na/Cs)0.4Ba0.8SiF6:Mn4+ phosphors with optimized fluorescence properties induced by alkaline metal ions replacement are successfully synthesized via a green and eco-friendly approach. Under the irradiation of 460 nm blue light, Cs0.4Ba0.8SiF6:Mn4+ red phosphor with narrow band emission peak has the best optical performance. The optimal doping concentration of Mn4+ in Cs0.4Ba0.8SiF6 host and the reason for concentration quenching are systematically analyzed. Furthermore, the moisture resistance and thermal stability of this phosphor are discussed. After being soaked in deionized water for 90 min, the PL intensity of Cs0.4Ba0.8SiF6:Mn4+ phosphor can maintain at 40% of that in air, which is 4 times higher than commercial K2SiF6:Mn4+. At the operating temperature of LED (423 K), Cs0.4Ba0.8SiF6:Mn4+ red phosphor can exhibit stable light output intensity and color. A warm WLED with low correlated color temperature of 4336 K, high color rendering index of 88.4 and high lumen efficiency of 105.96 lm/W is fabricated via using Cs0.4Ba0.8SiF6:Mn4+ phosphor as a component of red-light, and the warm WLED can maintain stable output even at high driving currents. Overall, the alkali metal ion replacement and green synthesis strategies have opened up a new perspective for the synthesis of efficient Mn4+-doped fluoride phosphors, which has dual benefits for optimizing the performance of WLED and environmental protection.

Hydrothermal synthesis of orange fluorescent carbon dots and their application in fabrication of warm WLEDs and fluorescent ink

Herein, we are reporting the synthesis of orange fluorescent carbon quantum dots (OFCDs) using o-phenylenediamine and semicarbazide by hydrothermal method and the synthesized OFCDs were applied for warm white light emitting diodes (WLEDs) and fluorescent ink applications. The fluorescence emission spectrum of OFCDs shows the emission maximum at 625 nm with an excitation wavelength of 540 nm. The quantum yield of OFCDs was calculated to be 23%. We have prepared warm WLED device by coating PVA-OFCDs polymer matrix on near UV LED light (λem: 420 nm). The OFCDs based warm WLED device exhibits chromaticity coordinate (0.42, 0.48), Colour Correlated Temperature (CCT) 2500 K and Color Rendering Index (CRI) value 82. We also prepared the highly stable fluorescent ink using the same PVA-OFCDs for security information encryption and anti-counterfeiting applications. This OFCDs and their WLEDs device would be an efficient one in optoelectronics and forensic fields.

Continuous production of K2SiF6:Mn4+ red phosphor by green route synthesis method for warm WLEDs application

The K2SiF6:Mn4+ red phosphor has caused widespread concern in warm white light-emitting diodes (WLEDs) due to its unique broadband blue light absorption and narrow-band red emission. However, commercial K2SiF6:Mn4+ red phosphor inevitably needs to use extremely corrosive HF as a raw material, which will cause great harm to the environment and human beings. In this work, the K2SiF6:Mn4+ phosphor with highly uniform particle shape and size was successfully synthesized without using HF solution through microfluidic technology. The structure, morphology and photoluminescence properties of the K2SiF6:Mn4+ phosphors prepared in this work were systematically investigated and analyzed. The K2SiF6:Mn4+ phosphors synthesized by microfluidic technology are all cubic particles. The sample was the most uniform with a particle size of about 4.14 μm when the pipe diameter was 4 mm and the injection speed was 1000 μL/min, and the number of active Mn4+ in this sample is the largest according to the calculation results, resulting in its maximum luminous intensity. Finally, a warm WLED with low CCT (3379 K) and high CRI (Ra = 89.7) was fabricated by combining the as-prepared red K2SiF6:Mn4+ phosphor with yellow phosphor YAG:Ce3+ and blue LED chip. The results indicate that the K2SiF6:Mn4+ phosphor prepared by the proposed green continuous route is suitable for WLEDs.

Embedding red-emitting dyes in robust hydrogen-bonded organic framework for application in warm white light-emitting diodes

Broadband yellow-emitting phosphors are very attractive for warm white light-emitting diodes (WLEDs) used in solid-state lighting, backlight display, and related fields. In this work, we describe a room temperature, solution processable yellow-emitting phosphors for warm WLEDs using the chemically stable nanoscale hydrogen-bonded organic framework (HOF) PFC-1 as the host. By embedding the red-emitting dyes of rhodamine B (RhB), rhodamine 6G (Rh6G), 4-( p -dimethylaminostyryl)-1-methylpyridinium (DSM), and 4-(dicyanomethylene)-2-methyl-6-( p -dimethylaminostyryl)-4H-pyran (DCM) in the green-emitting nano PFC-1, respectively, four types of single-matrix yellow-emitting nanocomposites were obtained. Due to the spectral combination of host PFC-1 and guest dyes, the obtained nanocomposites show broader emission spectra than that of the commercial yellow phosphor. Specifically, RhB@PFC-1 has a promising quantum yield of 17.8%. By coating the nanophosphors on the commercial blue LED chips (450 nm), bright sources of warm-white light were realized. It was found that the RhB@PFC-1 coated LED has an excellent color rendering index (CRI) of 85.6 and a correlated color temperature (CCT) of 4669 K at a drive current of 300 mA, while Rh6G@PFC-1 coated LED shows warm white light with a low CCT of 3100 K and a promising CRI of 75.4 K. This Dye@HOF strategy opens an avenue to developing yellow-emitting phosphors for the use in high color rendering warm WLEDs. • A series of yellow-emitting Dye@PFC-1 nanophosphors were reported. • The Dye@PFC-1 nanocomposites show a broader emission band than that of YAG:Ce 3+ . • Bright sources of warm white light were achieved by coating the nanocomposites on blue LED chips. • The WLED coated with RhB@PFC-1 exhibits a CRI of 85.6 and a CCT of 4669 K at a 300 mA driven current.

A red phosphor of Ba3In2F12:Mn4+ with enhanced moisture stability for warm WLED application

Although fluoride phosphors have distinguishing feature in luminescence spectra such as narrow band red light emission and broad band blue light excitation, the instability of [MnF6]2- limits their commercial applications. In this regard, we use weak reducing agents such as citric acid (CA) and oxalic acid (OA) for surface modification of a novel red phosphor Ba3In2F12:Mn4+ (BIF:Mn). A protective homogeneous passivation layer is formed on the surface of the phosphor particles with reduced Mn4+ content to improve the moisture resistance of Mn4+ doped fluoride phosphor BIF:Mn. In addition, their crystal structures, morphologies, photoluminescence characteristics, and the mechanism of luminescence enhancement are also described in details. By using near-ultraviolet or blue light-emitting diodes (LEDs) to excite it, an efficient red emission has been achieved with a maximum peak at 631 nm. In order to verify their application value, a warm white LED (WLED) with a color rendering index (CRI = 81.4) and a correlated color temperature (CCT = 4779 K) has fabricated with the as-prepared BIF:Mn and commercial yellow phosphor (YAG:Ce) on blue GaInN chip.

Near-unity blue-orange dual-emitting Mn-doped perovskite nanocrystals with metal alloying for efficient white light-emitting diodes

The tunable dual-color emitting Mn2+ doped CsPbCl3-xBrx nanocrystals (NCs) with near-unity photoluminescence quantum yield (PL QY) were synthesized through post-treatment of metal bromide at room temperature for fabrication of efficient warm white light-emitting diodes (WLEDs). Especially, the CdBr2 treated blue-orange emitting Mn doped NCs with various Mn/Pb molar feed ratios exhibit higher PL QY of 97% and longer Mn2+ PL lifetime of 0.9 ms. It is surprisingly found that the X-ray diffraction peak at 31.9° is almost not changed with increasing Br composition, meaning formation of metal alloying due to incorporation of amount of divalent cation in NCs. The strong and stable Mn2+ PL at temperature ranging from 80 K to 360 K are revealed and the temperature-dependent energy transfer efficiencies in Mn2+ doped CsPbCl1.5Br1.5 NCs are obtained. The enhancement mechanism of Mn2+ PL QY was attributed to improved energy transfer from exciton to Mn2+ d–d transition and suppressed defect state density after post-treatment. The efficient warm WLEDs with color rendering index of 90 and luminous efficacy of 92 lm/W at 10 mA were fabricated by combining blue-orange dual-emitting Mn2+ doped CsPbCl3-xBrx@SiO2 and green emissive CsPbBr3@SiO2 NCs with violet GaN chips.

New Mg2+/Ge4+-Stabilized Gd3MgxGexAl5-2xO12:Ce Garnet Phosphor with Orange-Yellow Emission for Warm-White LEDs (x = 2.0-2.5).

By stabilization of the Gd3Al5O12 garnet by replacing 80% or more of Al3+ with Mg2+/Ge4+ pairs, a series of new orange-yellow-emitting Gd3MgxGexAl5-2xO12:Ce (x = 2.0-2.5) phosphors were successfully developed for potential application in warm-white-light-emitting diodes (WLEDs). Rietveld structure refinement proved that Mg2+ first substitutes the octahedral Al3+ ion, followed by the replacement of the tetrahedral Al3+ together with Ge4+. The band structure of the x = 2.0 typical garnet was analyzed via density functional theory (DFT) calculations. The incorporation of an increasing content of Mg2+/Ge4+ was experimentally shown to narrow the band gap and expand the unit cell of the garnet host and blue shift the emission/excitation wavelength and shorten the fluorescence lifetime of Ce3+. The photoluminescence behaviors were rationalized by considering the influence of Mg2+/Ge4+ on the crystal structure, band structure, and local coordination. An LED lamp fabricated by combining the (Gd2.97Ce0.03)Mg2Ge2AlO12 optimal phosphor with a 450 nm-emitting InGaN blue LED chip exhibited a color-rendering index of 71.6, luminous efficacy of 16.1 lm/W, and a low correlated color temperature of 2201 K under a driving current of 20 mA, indicating that phosphor may have potential application in warm WLEDs.

A novel reddish-orange-emitting cationic iridium(III) complex containing a carbazole-triazine bipolar unit: Synthesis and application in neutral/warm white light-emitting diodes

A reddish-orange-emitting cationic iridium(III) complex [(dfppy) 2 Ir(EPTC)]PF 6 (dfppy: 2-(2,4-difluorophenyl)pyridine, EPTC: 9-ethyl-3-(3-(pyridin-2-yl)-1,2,4-triazin-5-yl)-9 H -carbazole) containing a carbazole-triazine bipolar unit was synthesized. The thermal decomposition temperature ( T d ) of the complex was 355 °C, its relative emission intensity at 100 °C was 78.6% of that at 20 °C, which was enough for it to be used in LEDs. Mainly due to the bipolar unit, [(dfppy) 2 Ir(EPTC)]PF 6 can efficiently absorb and be excited by blue light (λ em,max = 457 nm) of GaN chips. Excited by blue-emitting GaN chips, the complex can be used for fabricating reddish-orange LEDs, moreover, together with yellow-emitting Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce), neutral and warm white light-emitting diodes (WLEDs) can be obtained with good performances. When [(dfppy) 2 Ir(EPTC)]PF 6 was blended in silicone at 1.0, 1.5 and 2.0 wt% respectively, all together with YAG:Ce at 4.0 wt%, three efficient neutral WLEDs were obtained. Their correlate color temperatures (CCT) were 4874 K, 4312 K and 3665 K, color rendering indexes (CRI) were 80.2, 78.3 and 76.4, luminous efficiencies ( η L ) were 88.5 lm·W −1 , 83.6 lm·W −1 and 67.4 lm·W −1 , Commission International de I'Eclairage (CIE) values were (0.34, 0.32), (0.36, 0.33) and (0.38, 0.33) respectively. When blending concentration of [(dfppy) 2 Ir(EPTC)]PF 6 was increased to 2.5 wt% together with YAG:Ce still at 4.0 wt%, a warm WLED was obtained, its CCT was 3282, CRI was 73.9, η L was 63.0 lm·W −1 , and CIE value was (0.40, 0.35). • A reddish-orange-emitting cationic iridium(III) complex containing a carbazole-triazine bipolar unit. . • The complex can be efficiently excited by blue-emitting GaN chips mainly due to the effect of the bipolar unit. • Together with Y 3 Al 5 O 12 :Ce 3+ as phosphors, neutral and warm white light-emitting diodes can be obtained with good performances.

Highly luminescent water-soluble AgInS2/ZnS quantum dots-hydrogel composites for warm white LEDs

Ternary Ⅰ-Ⅲ-Ⅵ quantum dots (QDs) have become promising color-conversion materials for warm white light-emitting diodes (WLEDs) because of their broad emission, large stokes shift, high luminescence and low-toxicity. In this work, AgInS2/ZnS (AIS/ZnS) core/shell QDs were synthesized via a facile microwave-assisted aqueous method. The PL emission can be tuned from 540 to 622 nm by varying the Ag/In ratio and the maximum quantum yield can reach 58.27%. Flexible luminescent films were obtained by embedding AIS/ZnS QDs in polyacrylamide hydrogel, which were combined with blue InGaN chips to fabricate remote-type warm WLEDs. The as-prepared LEDs exhibit a relatively high color rendering index (CRI) of 87.5 and a correlated color temperature (CCT) of 3669 K, indicating that water-soluble AIS/ZnS QDs are competitive color-conversion materials for warm WLEDs.

Green route synthesis and optimized luminescence of K2SiF6:Mn4+ red phosphor for warm WLEDs

As the unique broadband blue light absorption and narrow-band red emission, the Mn4+-doped fluoride red phosphors have aroused tremendous attention for warm white light-emitting diodes (WLEDs). However, to prepare such phosphors, it is inevitable to use the hypertonic HF as solvent, which may be harmful to the environment. In our work, the K2SiF6:Mn4+ was prepared by using low toxicity (NH4F + HNO3/HAc/H3PO4) to replace HF. The structure, morphology and element composition have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometers (EDS) in detail, respectively. Upon 466 nm blue light excitation, the K2SiF6:Mn4+ can emit red light at near 632 nm. The influence of potassium sources and surfactants on luminescent properties of K2SiF6:Mn4+ were investigated. In addition, the concentration quenching mechanism was discussed. Moreover, the crystal field strength and emission mechanism of Mn4+ in K2SiF6 host were also analyzed. Finally, using K2SiF6:Mn4+ as red component, a warm WLED with low color temperature (CCT = 3816 K), high color rendering index (CRI, Ra = 87.7) and luminous efficiency (LE) of 139.51 lm/W was achieved, suggesting the K2SiF6:Mn4+ is an excellent red phosphor for warm WLEDs.

A Mn4+-doped oxyfluoride phosphor with remarkable negative thermal quenching and high color stability for warm WLEDs

Abstract Red-emitting phosphors composed of Mn4+-activated fluorides have attracted considerable interest for their applications in warm white light-emitting diodes (WLEDs). However, in addition to moisture instability, the unsatisfactory thermal stability of these phosphors limits their industrial applications. In this study, a novel red phosphor of CsMoO2F3:Mn4+ was synthesized via simple coprecipitation. This red phosphor exhibits an orthorhombic structure with a bandgap of ~3.43 eV. The Mn4+ ions occupy Mo6+ sites at the centers of [MoO2F4]2− octahedrons. This phosphor shows narrow emission around ~633 nm excited by 450 nm blue-chip with high color purity of 99.58%. Satisfactorily, this phosphor exhibits excellent thermal stability and a strong negative-thermal-quenching. The total PL intensity of CsMoO2F3:3.88%Mn4+ phosphor at 275 K strengthens to ~540% relative to that at 25 K, and its relative emission intensity preserves about 129.3% when the temperature rises from room temperature to 423 K (150 ℃). It also shows admirable color stability with a slight chromaticity shift (ΔE) of only ~ 33.9 × 10 - 3 in the temperature region from 298 to 473 K. Furthermore, a warm WLED was fabricated by the mixture of red-emitting CsMoO2F3:3.88%Mn4+ and the yellow-emitting YAG:Ce3+ phosphors with a blue-emitting InGaN LED chip. The device exhibits low correlated color temperature (3983 K) and high color-rendering index (Ra = 81.3). With the increasing drive current from 20 mA to 120 mA, the chromaticity coordinate variation (CCV) is only (−0.0163, 0.0202). All these results indicate that the CsMoO2F3:Mn4+ phosphor holds tremendous potential for practical applications in high-power lighting and display with high-performance WLEDs.

Ammonium salt conversion towards Mn4+ doped (NH4)2NaScF6 narrow-band red-emitting phosphor

Mn4+-activated fluoride red phosphors have a bright prospect for improving the warm white light-emitting diodes (W-LEDs) performances, whereas there remains some challenges in synthesis, such as reducing the consumption of toxic HF and improving Mn4+ doping efficiency. Herein, a new phosphor (NH4)2NaScF6:Mn4+ (NNSFM) was synthesized by an ammonium salt conversion method, which can effectively reduce HF consuming, enhance reaction rate and doping efficiency. The synthesis mechanism, luminescence properties and W-LEDs performances of the as-synthesized NNSFM have been investigated. Moreover, the lattice structure and doping position have been investigated in detail by the density functional calculations (DFT), which show that Mn4+ could occupy the Sc3+ crystallographic site in this structure and simultaneously produce a Na vacancy (VNa') for charge compensation. Using the NNSFM as red-light component, a warm W-LED device with a high color rendering index (CRI, Ra = 80.6) and low correlated color temperature (CCT = 3006 K) has been achieved. This work presents a new Mn4+ doped fluoride red phosphor and also develops an environmentally friendly strategy for synthesizing Mn4+ doped fluoride phosphors.

Enhancement of zero phonon line for Na2TiF6:Mn4+, Li+ phosphors induced by Li+

Red light purity of red emitting phosphor is an important factor for using in warm white light-emitting diodes (WLEDs). In order to obtain red emitting phosphor with good red light purity, a series of Na2TiF6:0.08Mn4+, xLi+ samples were prepared with the cation exchange method. Phenomena of zero phonon line as the strongest peak and strong enhancement induced by Li+ were observed. The mechanisms of the phenomena are discussed and proposed. From the result of temperature-dependent behavior measurement and stability test, it can be known that the optimal sample exhibited good thermal stability and color stability under WLEDs working conditions. Finally, prototype WLEDs was fabricated with the optimal sample and Y3Al5O12:Ce3+ (YAG:Ce3+) based on InGaN chip. Warm white light with low correlated color temperature (CCT = 4393 K) and high color rendering index (Ra = 90.5 and R9 = 89) was obtained, making it had potential application for blue light-based warm WLEDs.

A red-emitting Mn4+ activated phosphor with controlled morphology and two-dimensional luminescence nanofiber film: Synthesis and application for high-performance warm white light-emitting diodes (WLEDs)

Mn4+ activated fluoride red phosphors, Na2GeF6:Mn4+, with controllable morphology and size, were successfully synthesized through simple coprecipitation method. Using the hollow Na2GeF6:Mn4+ particles, we successfully fabricated two-dimensional red-emitting nanofiber film via electrospinning technology. The phase purity, morphology and composition of the samples were confirmed via X-ray powder diffraction (XRD), scanning electron microscope (SEM) and energy-dispersive X-ray spectrometer (EDS), respectively. Different surfactants were introduced into the experimental process, which successfully controlled the sample morphology. The broad excitation band from 300 nm to 550 nm matches well with commercial blue light emitting diodes, and narrow band emission red light can be observed in the range of 575–675 nm because of spin-forbidden 2Eg - 4A2g energy level transition of Mn4+ ion. The effect of doping concentration on luminescence and the mechanism of concentration quenching were discussed. On the basis of the experimental excitation (PLE) and emission (PL) spectra, the crystal field strength of the Mn4+ occupation environment was estimated and the nephelauxetic effect was researched for the Mn4+ ions in the Na2GeF6 host. Temperature-dependent properties of Na2GeF6:Mn4+ particles and nanofiber film were systematically analysed. Moreover, the Na2GeF6:Mn4+ particles and nanofiber film can significantly change the performance of white light-emitting diodes (WLEDs), the nanofiber film is a more appropriate candidate than Na2GeF6:Mn4+ particle for warm WLED applications.

Synthesis and photoluminescence properties of a novel BaGe4O9:Eu3+ red emitting phosphor for warm white LEDs

Novel BaGe4O9:Eu3+ red-emitting phosphors were synthesized by a high-temperature solid-state reaction. The crystal structures, morphological properties, elements analysis, optical properties and fluorescence decay time were investigated systematically. In contrast, the optimal Eu3+-doping concentration is 30 mol% when monitored at 591 nm with a 394 nm excitation. The energy transfer of Eu3+ ions in BaGe4O9 host lattice is dominated by the exchange interaction with the critical distance (Rc) of 5.28 Å. As expected, the red-emitting phosphor BaGe3.7O9:0.3Eu3+ exhibited a better quantum yield (QY) of 57.9% and an excellent lifetime of 2.25 ms. Consequently, the red-emitting phosphors BaGe3.7O9:0.3Eu3+ revealed a promising performance in warm WLED device with the CIE coordinates of (0.4365, 0.4130), the color temperature (Tc) of 3079 K and the color rendering index (Ra) of 85.8 under a driven current of 20 mA. These results indicate that the BaGe4O9:Eu3+ phosphors are prospective candidates as red-light component for warm white light-emitting diodes (WLEDs) devices.

Room-temperature synthesis, optimized photoluminescence and warm-white LED application of a highly efficient non-rare-earth red phosphor

Non-rare-earth red phosphors as alternative to commercial (oxy) nitride phosphors have attracted considerable attention for energy-efficient warm white light-emitting diodes (WLEDs). An excellent narrow-band red emission K2GeF6:Mn4+ product was successfully obtained through co-precipitation method. The crystal structure, morphology, composition and optical properties of K2GeF6:Mn4+ samples were investigated in details via X-ray powder diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive spectrometry (EDS) and photoluminescence spectra, respectively. Mn4+ activated K2GeF6 red phosphor possesses two strong and wide absorption bands in the region of 300–500 nm, which can be applied to UV and blue LED chips and bright intense red light (635 nm) with high color purity. Simultaneously, mechanisms of concentration and temperature quenching were systematically elucidated. After a systematic investigation, the luminescence properties of K2GeF6:Mn4+ have been optimized by changing synthetic conditions, such as the doping concentration, the concentration of HF, the potassium source, the amount of KF and the addition of surfactant. The red phosphor K2GeF6:Mn4+ was packaged via mixing commercial YAG:Ce yellow phosphor, an outstanding warm WLED with low CCT (3882 K), high CRI (Ra = 90.4) and high luminous efficacy (LE) of 125.84 lm/W has been obtained, implying that K2GeF6:Mn4+ is the potential red phosphor for warm WLEDs.

Synthesis and improved photoluminescence of a novel red phosphor LiSrGaF6:Mn4+ for applications in warm WLEDs.

Red phosphors composed of Mn4+-activated complex fluorides have attracted considerable attention for applications in warm white light-emitting diodes (WLEDs). In the present study, we report a facile strategy to synthesize a novel red phosphor LiSrGaF6:Mn4+ (LSGF:Mn) at room temperature, and we also discuss its formation mechanism. Mn4+ ions occupy Ga3+ sites located at the centers of distorted [GaF6]3- octahedrons and emit intense red luminescence when excited by UV or blue light. The effects of synthesis conditions such as the type of strontium salts, the concentrations of K2MnF6 and NH3·H2O, and the reaction temperature have been investigated. The luminescence intensity of the phosphor LSGF:Mn has been improved by optimizing the synthetic parameters. The as-prepared phosphor LSGF:Mn exhibits broad and intense absorption in the blue region and bright luminescence in the red region, which indicate that it is promising for applications in warm WLEDs.

Luminescent Properties of a Cs3AlF6:Mn4+ Red Phosphor for Warm White Light-Emitting Diodes

Mn4+ activated fluoride phosphors have been considered as highly promising red component for warm white light-emitting diodes (WLEDs) in recent years. In this work, a novel nonequivalent doping Cs3AlF6:Mn4+ red-emitting phosphor were synthesized via a co-precipitation method and its crystal structure, morphology, and luminescent properties were investigated in detail. The Cs3AlF6:Mn4+ phosphor with a sheet morphology have broad band absorption in blue light region (∼467 nm) and narrow bandwidth emissions in red region (∼634 nm). The WLED fabricated with Cs3AlF6:Mn4+ red phosphor, YAG:Ce3+ yellow phosphor and a blue InGaN LED chip demonstrates intense warm light with good luminescence performance of low related color temperature (CCT, Tc = 3659 K) and high color rendering index (CRI, Ra = 86.2). These results indicate the Cs3AlF6:Mn4+ red phosphor can be a potential candidate for warm WLEDs.