Warm White Light-emitting Diodes Research Articles

Zero-Dimensional Hybrid Antimony Chloride with Near-Unity Broad-Band Orange-Red Emission toward Solid-State Lighting.

Zero-dimensional (0D) hybrid metal halides are attractive owing to their distinctive structure as well as photoluminescence (PL) characteristics. To discover 0D hybrid metal halides with high photoluminescence quantum yield and good stability is of great significance for white light-emitting diodes (LEDs). Herein, a novel hybrid antimony chloride (CTP)2SbCl5 is synthesized, which shows a bright broad-band orange-red emission peaking at 620 nm under the low energy excitation (365 nm), achieving an excellent photoluminescence quantum yield of 96.8%. In addition, (CTP)2SbCl5 shows an additional emission peaking at 470 nm when excited at high energy (323 nm). PL spectra and density functional theory results demonstrate that the observed dual-band emission originates from the singlet and triplet self-trapped excitons confined in isolated [SbCl5]2- square pyramids. Moreover, (CTP)2SbCl5 presents relatively superior air stability, and the PL intensity still maintains 78% of the initial PL intensity when exposed to the air for above 2 weeks. Benefiting from high-efficiency PL emission and good stability of (CTP)2SbCl5, a stable warm white LED device with a 92.3% color rendering index was prepared by coating blue phosphor BaMgAl10O17:Eu2+, green (Sr,Ba)2SiO4:Eu2+, and orange-red (CTP)2SbCl5 on a 365 nm LED chip. This work provides an efficient luminescent material and also demonstrates the potential application of 0D hybrid antimony chloride in solid-state lighting.

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).

Thermally stable Dy2O3/Sm2O3 co-doped glass ceramics containing La2Sn2O7 crystal with tunable luminescence

By using the melt crystallization process, Dy2O3/Sm2O3 co-doped glass ceramics (GCs) containing La2Sn2O7(LSO) crystal were successfully prepared. By using X-ray diffraction (XRD), the sample's phase was determined, and scanning electron microscopy (SEM), the sample's morphology was examined. The optimal heat treatment condition of glass ceramics was determined to be 650 °C/1.5 h. Under 362 nm excitation, the energy transfer of Dy3+→Sm3+ was observed in Dy2O3/Sm2O3 co-doped glass ceramic samples from the emission spectrum. Electric dipole-electric dipole interaction is identified as the mechanism of energy transfer from Dy3+ to Sm3+ according to the Dexter formula for energy transfer. The emission spectra of 0.5%Dy2O3-0.4%Sm2O3 co-doped glass ceramic samples in a range from 298 K to 458 K show that the samples have high thermal stability, and the thermal quenching activation energy at 575 nm has been estimated to be 0.265 eV. According to chromaticity coordinates and correlated color temperature, warm white light emission may be achieved by co-doping Dy2O3/Sm2O3 glass ceramics. The findings demonstrate Dy2O3/Sm2O3 co-doped glass ceramics containing La2Sn2O7 crystal have a potential application prospect in warm white light-emitting diodes (w-LEDs).

Green, pollution-free and low-cost semiconductor luminescent material based on CuAlInS quantum dots

In recent years, CuInS2 quantum dots have shown great potential for various applications due to their wide excitation wavelength range, symmetric emission wavelength range, long fluorescence lifetime and optical stability. However, the high cost of indium (In) limits its commercialization. In this study, we partially substituted the expensive In element with more affordable and abundant aluminum (Al) to reduce the cost of CuInS2 quantum dots. CuInS2, CuAlInS, CuInS2/ZnS and CuAlInS/ZnS core/shell quantum dots were synthesized using one-pot method. Due to the incorporation of Al, their photoluminescence (PL) spectra exhibit a blue shift of about 5 nm. A time-resolved PL measurement indicated that the PL lifetime of the quantum dots was a characteristic feature of three dominating transitions from the conduction band to surface defect level, from the conduction band to an acceptor level, and from the donor level to an acceptor level. The temperature-dependent PL proves that after the introduction of Al, the FWHM of quantum dots does not show significant broadening with increasing temperature. Finally, CuInS2/ZnS and CuAlInS/ZnS quantum dot phosphor LEDs are produced. The brightness of the CuAlInS/ZnS quantum dot phosphor LED is slightly higher than that of CuInS2/ZnS quantum dot phosphor LEDs. The red-emitting CuAlInS/ZnS quantum dot phosphor LED with easy fabrication and no need for encapsulation can compensate for the lack of red light in warm white LED applications in future research.

Seeing green: phototactic responses for management of Rove beetle Paederus fuscipes

Paederus fuscipes Curtis (Coleoptera: Staphylinidae) is a medical pest due to its attraction to bright light sources from human residential premises. This study aims to investigate the phototactic response on light wavelengths and colour preferences by P. fuscipes. Paedarus fuscipes showed positive responses to all types of light sources (fluorescent, LED, and incandescent) presented in the light and dark choice test, which indicates their attractiveness towards light presented in human habitation. However, most beetles showed a higher preference towards fluorescent and cool white LED. Paedarus fuscipes showed consistent preferences for white, blue and green, with the exception of red. Remarkably, green light elicited the strongest positive phototactic response compared to other colours. Overall, our results showed that P. fuscipes beetles prefer the range of 550 nm wavelength. Warm light colours such as yellow (warm white LED) with red illumination can be recommended to avoid infestation and in innovative management of Paedarus.

Mn4+-doped organometallic hafnium hexafluoride phosphors: Achieving near-unity quantum yield to elevate LED performance

Mn4+-activated fluoride phosphors with high luminous efficacy and short decay lifetimes are essential in realizing high-quality warm white-light-emitting diode (WLED) lighting. In this work, Mn4+-activated narrow-band red (∼630 nm) phosphor [(CH3)4N]2HfF6 was successfully synthesized by introducing an organic cationic group (tetramethylammonium) into the [HfF6]2- system using a mild chemical co-precipitation method. The sample structure was confirmed using various characterization techniques such as scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Powder particles with diameters ranging from 10 to 20 um and double pyramidal structures were prepared by adjusting the anti-solvent temperature to control the crystal growth rate. The investigation of the morphology, structure and photoluminescence properties of Mn4+-doped [(CH3)4N]2HfF6 phosphors at different anti-solvent temperatures deepened our understanding of the correlation between structure and luminescence. Ultimately, phosphors with optimal performance (external quantum efficiency, ∼92.2%, and decay lifetime, ∼3.6 ms) were obtained. The samples were mixed with polydimethylsiloxane organosilicon to prepare a red light-conversion flexible film, and the (TMA)2HfF6:Mn4+ red phosphor and commercially available YAG:Ce3+ yellow-green phosphor was thoroughly mixed with transparent silica to form a stable paste, and then coated on a blue LED bead to prepare warm white LEDs, which significantly optimized the performance of the white LEDs (correlated color temperature, ∼5564 K). These experimental results indicate that the materials prepared by the mild solution method have important applications in the domains of display and lighting.

Ultra-Stable ITO-Free Organic Solar Cells and Modules Processed from Non-Halogenated Solvents under Indoor Illumination.

Organic Photovoltaics (OPV) is a very promising technology to harvest artificial illumination and power smart devices of the Internet of Things (IoT). Efficiencies as high as 30.2% have been reported for OPVs under warm white light-emitting diode (LED) light. This is due to the narrow spectrum of indoor light, which leads to an optimal bandgap of ≈1.9eV. Under full sunlight, OPV devices often suffer from poor stability compared to the established inorganic PV technologies such as crystalline silicon. This study focuses on a potentially very cost-effective Indium Tin Oxide (ITO) free cell stack with absorber materials processed from non-halogenated solvents. These organic solar cells and modules with efficiencies up to 21% can already achieve remarkable stabilities under typical indoor illumination. Aging under 50,000lux LED lighting leads to very little degradation after more than 11000h. This light dose corresponds to more than 110years under 500lux. For modules encapsulated with a flexible barrier, extrapolated lifetimes of more than 41years are achieved. This shows that OPV is mature for the specific application under indoor illumination. Due to the large number of potential organic semiconducting materials, further efficiency increase can be expected.

Efficient broadband yellow-emitting Mg2.5Lu1.5Al1.5Si2.5O12:Ce3+ garnet phosphors for blue-light-pumped white light-emitting diodes

The discovery of yellow-emitting phosphors with higher luminescence intensity and wider bandwidth than the commercial Y3Al5O12:Ce3+ (YAG:Ce3+) phosphor upon blue light excitation remains one of the significant challenges for establishing human-centered warm white light-emitting diode towards high-performance illumination. Herein, we innovatively synthesized a novel Ce3+-activated broadband yellow-emitting garnet phosphor of Mg2.5Lu1.5Al1.5Si2.5O12:Ce3+ (MLASO:Ce3+) via conventional high-temperature solid-state reaction method. The as-prepared MLASO:10%Ce3+ garnet sample possesses a cubic structure with Ia3‾d space group and lattice parameters of a = b = c = 11.85098 Å and V = 1664.421(0.044) Å3. Luminescence spectroscopy tests indicates that the optimal MLASO:10%Ce3+ yellow-emitting phosphor features 1.2 times higher relative integral luminescence intensity and an impressive full width at half maximum (FWHM) of up to 145 nm with respect to the most extensively available commercial YAG:Ce3+ phosphor (FWHM = 122 nm) under the identical blue light irradiation, which can provide more red-components for improving color rendering index. Additionally, the CIE color coordinates and a satisfactory internal quantum efficiency are determined to be (0.4751,0.5028) and 74%, respectively. More importantly, the representative optimal sample can preserve 77% luminescence emission intensity at a 423 K high temperature thermal treatment environment compared to the ambient temperature. As a result, this study sheds light on newly discovered broadband yellow-emitting MLASO:10%Ce3+ garnet phosphor containing more of the red chromatic spectrum can sever as one of the promising color-conversion-materials in high-performance white LEDs with high color rendering index for healthy solid-state lighting.

The developments of cyan emitting phosphors to fulfill the cyan emission gap of white-LEDs.

Future generations of solid-state lighting (SSL) will prioritize the development of innovative luminescent materials with superior characteristics. The phosphors converted into white light-emitting diodes (white LEDs) often have a blue-green cavity. Cyan-emitting phosphor fills the spectral gap and produces "full-visible-spectrum lighting." Full-visible spectrum lighting is beneficial for several purposes, such as light therapy, plant growth, and promoting an active and healthy lifestyle. The design of cyan garnet-type phosphors, like Ca2LuHf2Al3O12 (CLHAO), has recently been the subject of interest. This review study reports a useful cyan-emitting phosphor based on CLHAO composition with a garnet structure to have a cyan-to-green emitting color with good energy transfer. It could be employed as cyan filler in warm-white LED manufacturing. Due to its stability, ability to dope with various ions suitable for their desired qualities, and ease of synthesis, this garnet-like compound is a great host material for rare-earth ions. The development of CLHAO cyan-emitting phosphors has exceptionally high luminescence, resulting in high CRI and warm-white LEDs, making them a viable desire for LED manufacturing. The development of CLHAO cyan-emitting phosphors with diverse synthesis techniques, along with their properties and applications in white LEDs, are extensively covered in this review paper.

Green and warm-white light-emitting diodes enabled by zero-dimensional green-emitting Mn(II) bromide complex with record high efficiency

Green and warm-white light-emitting diodes enabled by zero-dimensional green-emitting Mn(II) bromide complex with record high efficiency

Broadband emission characteristics and WLED application of self-activated YMZn3AlO7 (M=Ca, Sr, Ba) phosphors

In this study, a non-activated ion-doped full-spectrum emission phosphor for white light-emitting diode (WLED) lighting is proposed using oxygen defect engineering. The YMZn3AlO7 (M = Ca, Sr, Ba) phosphors with "114″ structure were prepared via a high-temperature solid-state reaction. Under excitation with 373 nm ultraviolet (UV) light, YSrZn3AlO7 in YMZn3AlO7 (M = Ca, Sr, Ba) exhibited the highest emission intensity and formed a wide yellow emission band centred at 563 nm. The full width at half maximum of the YSrZn3AlO7 phosphor was 172.6 nm. A theoretical model based on the designed oxygen vacancies was proposed to determine the self-activated luminescence mechanism. Density functional theory calculations revealed that oxygen vacancies lead to the generation of new energy levels. Electron paramagnetic resonance experiments further confirmed that the luminescence originated from oxygen vacancies. Eventually, a warm WLED device ((x, y) = (0.4057, 0.4359)) with a correlated color temperature of 3814 K and a relative color rendering index of 83 was successfully prepared using the YSrZn3AlO7 phosphor and a 365 nm UV LED chip. These results suggest that YSrZn3AlO7 is a promising WLED phosphor and provide new insights into the application of self-activated phosphors in WLED.

Synthesis and luminescence properties of oxyapatite-type ZnLa4(SiO4)3O:Eu3+ phosphor for high CRI w-LEDs, latent fingerprints, and security ink

The Eu3+-doped oxyapatite-type ZnLa4(SiO4)3O (ZLSO) phosphors with a strong red emission were successfully synthesized. The pure phase of the phosphors with the hexagonal system was verified through X-ray diffraction. The band gap energy of the ZLSO was calculated using Materials Studio and measured using the diffuse reflection spectra. Attributed to the 7F0→5L6 transition of Eu3+ at 394 nm, the prepared phosphors showed a more intense emission at 614 nm than at 590 nm, due to their asymmetric position. The optimized doping concentration of the ZLSO:xEu3+ sample was 20 mol%, and the relevant mechanism of concentration quenching was dipole-quadrupole interaction. Notably, the ZLSO:Eu3+ phosphors exhibited preferable thermal stability, with an activation energy of 0.289 eV. The fabricated warm white light-emitting diodes (w-LEDs) with ZLSO:Eu3+ phosphors presented a high average colour rendering index (Ra = 95, CCT = 5233 K). Meanwhile, the level 1–3 structures of latent fingerprints (LFPs) were distinctly displayed by ZLSO:Eu3+ samples, and security ink was successfully used to encrypt information. In summary, the highly efficient oxyapatite-type ZLSO:20 mol%Eu3+ phosphors have attractive application potential in multiple application fields, such as w-LEDs, LFPs, and security ink.

Tunable luminescence and energy transfer in Tb3+,Eu3+ co-doped Gd2Zr2O7 phosphors with high thermal stability for WLEDs

Red phosphors with good thermal stability, high color temperature and color purity are critical in high power warm white LED devices. Herein, a series of single and co-doped Tb3+,Eu3+ polychromatic phosphors with pyrochlore structure based on Gd2Zr2O7 have been prepared for the first time by a conventional solid phase reaction method. Compared to single doped Eu3+ phosphors, Tb3+,Eu3+ co-doped phosphors possess following advantages: improved UV absorption, increased photoluminescence intensity, extended luminescence range and improved thermal stability. At room temperature, the Gd2Zr2O7:Tb3+,Eu3+ phosphors exhibited a gradual shift from yellow-green emission at 544 nm to orange-red emission at 613 nm with increasing doping of Eu3+ ions. Energy transfer efficiency has been evaluated to be 71% by analyzing the fluorescence lifetime of Tb3+ ions. The concentration quenching mechanism under different conditions was analyzed in detail and it was concluded that the quenching of Tb3+ is caused by dipole-dipole interaction. In addition, the activation energy (ΔEa) of the Gd1.92Zr2O7:0.03Tb3+,0.05Eu3+ phosphor was calculated to be as high as 0.2674 eV compared to other Tb3+, Eu3+ co-doped phosphors, demonstrating its high thermal stability. WLEDs devices based on Gd1.92Zr2O7:0.03Tb3+,0.05Eu3+ phosphors have been prepared, which have low correlated color temperature (CCT) (5283 K), high color rendering index Ra = 85.5 K) and CIE coordinates chromaticity coordinate (0.3371,0.3333). All of the results show that Gd2Zr2O7:Tb3+,Eu3+ phosphors provide a new avenue to develop high quality red emission and high thermal stability phosphors for 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.

Preparation and photoluminescence properties of high thermal stability Sr3Ga2Sn1.5Si2.5O14:Eu3+ red phosphors for high-power light-emitting diodes application

A series of Sr3Ga2Sn1·5Si2·5O14:xEu3+ (SGSSO:xEu3+) phosphors with excellent thermal stability were prepared by the solid-state reaction method. The phase and luminescence properties of the sample were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy, and photoluminescence (PL) spectra. Under the excitation of 395 nm, the SGSSO:Eu3+ phosphor exhibits strong red emission at 618 nm, which is attributed to the 5D0 → 7F2 transition of the Eu3+ ions. When monitoring the 618 nm emission peak, the excitation spectrum contains several excitation peaks with a maximum value of 395 nm, which is well matched with the commercial violet LED chips. In addition, the emission spectra of SGSSO:Eu3+ at different temperatures have also been studied. Pleasantly, the luminous intensity of the SGSSO:Eu3+ sample at 150 °C still maintains 80.2% of that at room temperature, demonstrating its good thermal stability and application potential in high-power LEDs. The mechanism for the high thermal stability of the as-prepared phosphor was also discussed. Moreover, the photoluminescence quantum yield of the optimized SGSSO:0.06Eu3+ phosphor can reach 62.7%. Finally, a warm white LED device with high color rendering index and low color temperature was prepared using the prepared SGSSO:Eu3+ phosphor as a red component, verifying the application potential of SGSSO:0.06Eu3+ in LEDs.

Thiogallate phosphor for white LEDs with water-resistance and green light-emitting capability

The application of sulfide phosphor in the field of phosphor-converted white light-emitting diodes (pc-WLEDs) and wide-gamut displays has been limited by its poor water resistance. Herein, a water-resistant green emission phosphor, LiGaS2:Eu2+ (LGSE), has been developed using a chalcogenometallate LiGaS2 (LGS) as the luminescent host. First-principles calculation was utilized to identify the electronic structure of LGS and the optimal site for the Eu2+ dopant. Upon stimulation by 450 nm light, the LGSE phosphor exhibits a brilliant green emission with a photoluminescence emission (PL) maximum at 544 nm and a quantum efficiency of 55.3%. The exceptional luminance characteristics of this green-emitting phosphor were revealed by diffuse reflection spectra, steady-state PL spectra, and temperature-dependent PL measurements. The LGSE phosphor retains at least 94% of its initial emission even after 20 days of water immersion. The integration of LGSE with a commercial red-emitting K2SiF6:Mn4+ phosphor on a 450 nm blue LED chip produced a warm white light LED device, in which the color rendering index was Ra = 80.3 and CCT = 5128 K. This development represents a significant advancement in the field of water-resistant sulfide phosphors.

Luminescence properties of Eu2+/3+ co-activated La6Sr4(SiO4)6F2 polychromatic phosphors towards white light-emitting diodes and anti-counterfeiting

To obtain emitting color regulation, series of Eu2+/3+-coactivated La6Sr4(SiO4)6F2 phosphors were synthesized. The crystal structure, morphology, elemental compositions and luminescence performances of the final products were discussed. Excited by 365 nm, all of the studied samples can emit the characteristic emissions of Eu2+ and Eu3+, in which their fluorescence intensities have various responses to doping content. Specially, as the dopant content increases, the emitting color is changed from green to yellow. Moreover, via changing the excitation wavelength, tunable emissions are also realized in the studied samples. On the basis of the temperature dependent emission spectra, it is found that Eu2+/3+-coactivated La6Sr4(SiO4)6F2 phosphors possess good thermal stability. Through selecting the designed phosphors as yellow emitting components, a warm white light-emitting diode (white-LED) was packaged, in which its electroluminescence properties are hardly altered at high injection current. When the working current is 100 mA, the color coordinate, correlated color temperature and color rendering index of the fabricated white-LED are (0.358,0.358), 4580 K and 87.39, respectively. In addition, using the resultant compounds as luminescent labels, different patterns were prepared for the application in information encryption. The results demonstrated that Eu2+/3+-coactivated La6Sr4(SiO4)6F2 phosphors with multicolor emissions and outstanding thermal stability are suitable for white-LED and optical anti-counterfeiting as emitting components.

A porous Eu-PTA/Tb-SSA/ZrO2/ZnZrO3 light color adjustable phosphor: Luminescent property and application of warm white LED

Light emitting diode (LED) is the fourth generation lighting source, but it has some shortcomings such as complex chip packaging process and the unbalanced light color of phosphor in long-time application. In this study, a kind of Eu-terephthalic acid/Tb-sulfosalicylate/ZrO2/ZnZrO3 (Eu-PTA/Tb-SSA/ZrO2/ZnZrO3) phosphor with warm white light emission properties was prepared, and the warm white light LED (w-WLEDs) was successfully prepared by encapsulating Eu-PTA/Tb-SSA/ZrO2/ZnZrO3 phosphors together with 270 nm UV-chip. The ZrO2/ZnZrO3, Tb-SSA/ZrO2/ZnZrO3 and Eu-PTA/ZrO2/ZnZrO3 samples show blue emission, green emission and red emission under deep ultraviolet (UV, 270 nm) excitation, respectively. The Tb-SSA and Eu-PTA are co-doped into ZrO2/ZnZrO3 matrix with blue emission to achieve the warm white light emission, and the light color can be adjusted by controlling the doping amount of Eu3+ and Tb3+. Through the excitation method of single-component phosphor by the single chip, the complex chip packaging process of w-LED can be solved. By doping rare earth organic complexes into porous ZrO2/ZnZrO3 matrix, the problems of the light color unbalanced of phosphor and the low luminescence intensity of rare earth doped metal oxides composites can be solved.

Synthesis of an efficient Mn4+-doped fluoride red phosphor with excellent fluorescence stability by green synthesis method for warm WLED

Currently, Mn4+-doped fluoride phosphors have become a research hotspot, which can help compensate for the missing red component in cold white light-emitting diodes (WLEDs). However, significant synthesis defects limit the development of such fluorescent powders due to the use of highly toxic solvent HF. To improve this situation, a simple green synthesis method should be explored to synthesize Mn4+-activated fluoride phosphor. In this study, a series of red-emitting Mn4+-activated BaTiF6 phosphors are successfully synthesized via the non-toxic reaction system (HNO3/HCl + NH4F). Its crystal structure, morphology, optical characteristics and thermal stability are systematically evaluated. Under blue light excitation, BaTiF6:Mn4+ exhibits a bright narrow-band red emission with exceptional correlated color temperature (3909 K) and color purity (90%). Additionally, the critical concentration of Mn4+ is determined to be 0.03 and the concentration quenching mechanism is also systematically discussed. By calculating the crystal field strength (Dq), Racah parameters (B and C) and nephelauxetic effect ratio parameter β1, it is confirmed that BaTiF6 host can provide a strong crystal field environment for Mn4+. Moreover, these results are compared with other matrix materials. Intriguingly, the optimal sample exists satisfactory thermal stability, whose fluorescence intensity at 423 K retains 49% of that at 298 K and the activation energy reaches up to 0.925 eV. In addition, the chromaticity shift and chromaticity coordinate variation are calculated as 17 × 10−3 and (−0.0063, 0.0063), respectively. Meanwhile, the feasibility of the as-fabricated WLEDs for interior illumination is examined. A high-performance warm WLED with low correlated color temperature (CCT = 4470 K) and high color rendering index (Ra = 88.3) is achieved by using BaTiF6:Mn4+ as a red-emitting material, moreover, WLED exhibits strong output stability under high driving current. The findings of this work provide a comprehensive understanding for rational design of high-performance Mn4+-activated fluoride red phosphors through a simple green synthesis method.

Narrow-Band Deep-Blue Emission and Superior Thermal Stability of Fluoroaluminate Phosphor Based on Tungsten Bronze-Type Mineral Structure.

Screening novel narrow-band phosphors inspired by natural mineral structures is urgently demanded for improving the performance of phosphor-converted light-emitting diodes. In this work, a novel narrow-band deep-blue-emitting tungsten bronze-type KCaAl2F9:Eu2+ phosphor with superior thermal stability is successfully synthesized. Structural analysis shows that the representative KCaAl2F9:0.013Eu2+ phosphor crystallizes in an orthorhombic space group C2221 with a rigid network. The rigid [AlF6]3- octahedrons are linked together by sharing corners to build endless [AlF6]3-∞ chains, further stacking with each other in a highly cross-linked way to establish the rigid network of the KCaAl2F9 host. Benefiting from the rigid microenvironment, the developed phosphor not only shows a narrow-band deep-blue emission with a full width at half maximum of 45 nm and a high color purity of 92%, but it also exhibits the superior thermal stability with an emission loss of only 10% at 423 K, demonstrating its application potential in bridging the deep-blue spectral cavity toward sunlight-like full-spectrum lighting. In addition, the concentration/temperature quenching behaviors of KCaAl2F9:Eu2+ phosphor are systematically investigated. By revealing the specific structure-property relationship of tungsten bronze-type KCaAl2F9:Eu2+ phosphor, the present study provides a significant guide for identifying the novel narrow-band deep-blue-emitting component applicable to full-spectrum warm white light-emitting diode devices.