Warm WLEDs Research Articles

A novel red phosphor of BaGe(1−x)TixF6:Mn4+ solid solution: facile hydrothermal controlled synthesis, microstructures and luminescent properties

A series of BaGe(1−x)TixF6:Mn4+ solid solution phosphor crystals have been successfully synthesized by a facile hydrothermal method. The obtained BaGe(1−x)TixF6:Mn4+ can be a promising candidate as the red phosphor used in warm WLEDs.

Samarium(iii) and terbium(iii) ion-doped NaLa(MoO4)2 phosphors for versatile applications

The Sm3+ and Tb3+ ion-doped NaLa(MoO4)2 can be used for optical temperature sensors, safety signs, and warm WLEDs.

Mn4+ nonequivalent-doped Al3+-based cryolite high-performance warm WLED red phosphors

Mn4+ nonequivalent-doped Al3+-based cryolite red phosphors with controlled morphology and optimized luminescence properties for high-performance warm WLEDs.

Design of a novel scandium silicate based blue-emitting phosphor with high efficiency and robust thermal stability for warm WLEDs and field emission displays

A novel blue-emitting phosphor is synthesized, and its luminescence properties and potential application for WLEDs and FEDs are explored.

Synthesis, luminescence properties and nephelauxetic effect of nano stick phosphors K3AlF6:Mn4+ for warm white LED

The high uniformity of the phosphors may help to improve their luminescent properties, emission intensities and quantum efficiencies. In order to achieve this goal, a series of nano stick K3AlF6:xMn4+ samples with regular morphology are prepared in this paper. These samples show high photoluminescence quantum yields. Nano stick sample is obtained after recrystallization with vapor diffusion method. Furthermore, color purity, analyses of crystal-field and nephelauxetic effect, the critical distance and the related type of multipolar interaction for the samples were also discussed. The calculation results show that the Mn4+ ions are located at a site of a strong crystal field, and the concentration quenching of Mn4+ in the samples K3AlF6:xMn4+ may be dominated by dipole-quadrupole interactions. Decay lifetime and the photoluminescence QY (quantum yield) of the optimal nano stick sample are 2.50 ms and 89.34%, respectively. The chromaticity coordinates of the optimal nano stick sample are x = 0.6872 and y = 0.3126, which are very close to the NTSC (the national television systems committee) standard values for red color (x = 0.67, y = 0.33). Employing the as-prepared nano stick K3AlF6:xMn4+ as a red component, a high-performance WLEDs with a lower correlated color temperature (CCT = 4170 K) and a high color rendering index (CRI = 85.6) was obtained. It suggests the as-prepared K3AlF6:xMn4+ is a potential commercial red component for warm WLEDs.

A novel far red-emitting phosphor SrMgAl10O17: Cr3+ for warm w-LEDs

Cr3+ -activated SrMgAl10O17 (SAM) far red-emitting phosphors were prepared by high temperature solid state reaction. The phases and luminescent properties of the samples were measured and characterized by X-ray diffraction (XRD) and the fluorescence spectrometer, respectively. Under excitation at 396 nm, SAM:xCr3+ phosphors exhibited narrow-band ultraviolet emission peaking at 695 nm in the range 650–750 nm. The thermal stability of SAM:Cr3+ was excellent (I423K /I273K=34.49%). The CRI, CCT and LE value of the packaged light emitting diode (LED) were calculated following as: CRI=40.7, CCT=7455 K, LE=90.4 lm/W. Importantly, the IQE value of SAM:Cr3+ samples reached 44.12%. All the results indicated that this phosphor has the application prospect in the plant growth LED light.

Ce3+-activated CaSr2Al2O6 green-emitting phosphors: Potential application as color converter for warm WLEDs

In this work, green-emitting Ce3+-activated CaSr2Al2O6 (CSA) phosphors were successfully synthesized by solid-state reaction at high temperature and their phase purity, crystal structure, morphologies, photoluminescence properties, as well as the thermal stability were also investigated at length. The CSA:Ce3+ phosphors exhibited an intense broad green emission band in the 450–650 nm range centered at 545 nm under 375 nm near-ultraviolet light excitation. The full width at half maximum was about 94 nm. And the optimal doping concentration of Ce3+ ions in Ca1-xSr2Al2O6:xCe3+ was x = 0.01 (namely, 1 mol%). The CIE chromaticity coordinates of CSA:0.01Ce3+ samples were calculated to be (0.3553, 0.5541) with the corresponding internal quantum efficiency determined to be about 31%. Besides, the CSA:0.01Ce3+ phosphors possessed a high thermal stability. The green emission showed slight blue-shift at high-temperature, while its emission intensity at 423 K still maintained 71.3% of the initial value at 303 K. A prototype white light-emitting-diode (LED) lamp with a superb color rendering index (CRI = 92) and a low correlated color temperature (CCT = 3671 K) was successfully fabricated by combining a 365 nm near-ultraviolet-emitting LED chip with the CSA:0.01Ce3+ as a green component, BaMgAl10O17:Eu2+ as a blue component, and CaAlSiN3:Eu2+ as a red component.

A green synthetic route to K2NbF7:Mn4+ red phosphor for the application in warm white LED devices

Lack of red-light of current w-LEDs restricts their applications in the field of high color rendering index warm solid-state lighting. Fluoride phosphors doped with Mn4+ provide an efficient way to resolve the problem. Unfortunately, these excellent Mn4+ activated fluoride red phosphors are generally synthesized in highly toxic HF solution. In this paper, we report a novel green synthetic route to prepare a non-rare-earth and nonequivalent doping type of K2NbF7:Mn4+ red phosphor with micro-rod-like morphology. The results of XRD and its Rietveld refinement reveal that all the samples possessed only a single phase with monoclinic P21/c structure and the Mn4+ ions were successfully incorporated into the crystal lattice. The Mn4+ ions in K2NbF7 matrix have a highly distorted octahedral environment, which strengthen the intensity of zero phonon line (ZPL). The strongest absorption and excitation bands appear in blue region of diffuse refection spectra (DRS) and the photoluminescence excitation (PLE) of K2NbF7:Mn4+ sample, which demonstrates the product perfectly match with the most popular GaN-based blue chip. Under blue light illumination, the as-prepared K2NbF7:Mn4+ sample exhibits intense sharp-line red fluorescence (∼628 nm) with internal quantum yield (QY) of 71.3%, an extreme narrow full width at half-maximum (FWHM) of ∼2.8 nm, and an ultra-high-color purity of 99.2%. Impressively, by incorporating K2NbF7:Mn4+ as a red component, a warm w-LED with high CRI of 83.8, low color temperature of 3010 K and high luminous efficiency of 115.91 lm/W is obtained, demonstrating great validity of K2NbF7:Mn4+ red phosphor for white LED devices.

Green synthesis of K2TiF6:Mn4+ using KHF2 as accessory ingredient: A novel airtight solid-state strategy

In this work, an airtight solid-state strategy was developed for the synthesis of K2TiF6:Mn4+ phosphor without the usage of high concentration HF solution. By heating K2TiF6, K2MnF6 and KHF2 in a sealed container at 474 K for hours and then washing the as-synthesized samples several times, K2TiF6:Mn4+ phosphor was obtained. The microstructure, luminescent properties of the phosphor were investigated systemically. The reaction mechanism were investigated and discussed in detail. KHF2 is the key role to obtain the red phosphor, which provides additional pressure and HF gas atmosphere, works as reaction intermediate and contributes to Mn4+ doping into K2TiF6 host. By using as-prepared K2TiF6:Mn4+ phosphor as a red componet for warm W-LEDs, the high color rendering index (Ra = 84) and low color temperature (CCT = 3621 K) device performance proved that this environmental friendly synthesis method would be an efficient way to produce red fluoride phosphor for W-LEDs.

Chromaticity-Tunable and Thermal Stable Phosphor-in-Glass Inorganic Color Converter for High Power Warm w-LEDs.

In this work, an aluminate silicate garnet phosphor, Y2Mg2Al2Si2O12:Ce3+ (YMASG:Ce3+), exhibiting strong and broad yellow-orange emission, was successfully synthesized. Attributed to the double cation substitution of YAG:Ce3+, which led to a compression effect, a redshift was observed with respect to YAG:Ce3+. More importantly, a transparent phosphor-in-glass (PiG) sample was obtained by incorporating the phosphor YMASG:Ce3+ into a special low-melting precursor glass. The energy dispersive spectrometer (EDS) mapping analysis of the as-prepared PiG sample indicates that YMASG:Ce3+ was successfully incorporated into the glass host, and its powders were uniformly distributed in glass. The photoluminescence intensity of the PiG sample was higher than that of the powder due to its relatively high thermal conductivity. Additionally, the combination of the PiG sample and a blue high-power chip generated a modular white LED with a luminous efficacy of 54.5 lm/W, a correlated color temperature (CCT) of 5274 K, and a color rendering index (CRI) of 79.5 at 350 mA.

A novel rare-earth free red-emitting Li3Mg2SbO6:Mn4+ phosphor-in-glass for warm w-LEDs: Synthesis, structure, and luminescence properties

Developing a novel non-rare-earth activated oxide red phosphor with admirable luminescent performance and low cost is still of great interest in the field of energy-saving warm white light-emitting diodes (w-LEDs) illumination. Here, Li3Mg2SbO6:Mn4+ (LMSO:Mn4+) red-emitting phosphor has been successfully prepared with cheap raw materials via a traditional solid-state method. Crystal structure, morphology, composition as well as optical properties are studied in detail. The prepared LMSO:Mn4+ phosphor exhibits a broad and deep red emission band in the range of 600–750 nm with the maximum centered at 666 nm, which is ascribed to the Mn4+:2Eg→4A2g transition in [SbO6] octahedral environment. Moreover, the nephelauxetic effect of Mn4+ in the LMSO matrix is evaluated by investigating the crystal field strength (Dq) and Racah parameters (B and C). Importantly, LMSO:0.01Mn4+ phosphor demonstrates good thermal stability and high quantum efficiency. By embedding LMSO:Mn4+ and Y3Al5O12:Ce3+ phosphors with various ratios in the TeO2-based glass host, a series of phosphors-in-glass(PiG) composites are achieved and demonstrate to remain the original optical properties of phosphors. Remarkably, by coupling PiG color converters with a blue LED chip, high-power w-LEDs devices with tunable optoelectronic parameters are constructed, with the correlated color temperature evolving from cool white (6783 K) to warm one (4014 K) and the color rendering index increasing from 72.2 to 88.7.

Photoluminescence and energy transfer of a color tunable phosphors: Sr3La(BO3)3:Ln3+ (Ln = Dy, Eu, Tb) for warm white light UV-excited WLEDs

A series of color tunable Sr3La(BO3)3:Ln3+(Ln = Dy, Eu, Tb) phosphors were prepared via solid-state reaction method. The characterizations of X-ray diffraction (XRD), photoluminescence properties, the decay curves and energy transfer mechanism were investigated in detail. The color temperature of Sr3La(BO3)3:Dy, Eu was lower than Sr3La(BO3)3:Dy. The emission color of Sr3La(BO3)3:Tb, Eu was tunable from green to white and orange since the energy transfer of Tb3+ → Eu3+ in phosphors. The energy transfer efficiency reached 53.18% when y = 0.10. The phosphor Sr3La(BO3)3:0.04Tb, 0.04Eu could emit white light, and its correlated color temperature was 3929 K. Under 375 nm excitation, Sr3La(BO3)3:Tb, Eu, Dy emitted white light. What’s more, the chromaticity coordinate of Sr3La(BO3)3:0.04Tb, 0.06Eu, 0.04Dy was (0.365,0.338) which was close to the standard white chromaticity coordinate, and its correlated color temperature was 4155 K. Those results indicated that Sr3La(BO3)3:Tb, Eu, Dy may be a potential warm white-emitting candidate for w-LEDs under n-UV excitation.

Eu3+‐doped CsPbBr1.5I1.5 quantum dots glasses: A strong competitor among red fluorescence solid materials

AbstractCsPbBr1.5I1.5 quantum dots (QDs) glasses are synthesized by traditional melting and thermal treated method, CsPbBr1.5I1.5 QDs glasses show vast potential as red fluorescence component in warm WLED applications due to their moderate emission wavelength as well as good opacity property. However, the quantum yield of QDs glasses is still low, therefore, Eu3+ ions is chosen to introduce into CsPbBr1.5I1.5 QDs, the quantum yield is enhanced to 64.7%. After a sequence of testing operations, we find that 6.5%CsPbBr1.5I1.5:0.28%Eu3+ QDs glasses is a strong competitor among red fluorescence solid materials.

Mn-doped CsPbCl3 perovskite quantum dots (PQDs) incorporated into silica/alumina particles used for WLEDs

Recently, more and more scholars synthesised the Mn-doped CsPbX3 (X = Cl, Br, I) inorganic perovskite quantum dots (PQDs), which exhibited a strong dopant luminescence characteristic of d-d transition of Mn2+ and dual-color emission. However, Mn-doped CsPbCl3 PQDs suffer from the instability, which hindered the application of PQDs in optoelectronic devices. Here, we resolve this problem with SiO2/Al2O3 monolith (SAM) through a simple sol-gel process and obtained a robust luminescent PQDs-SiO2/Al2O3 monolith (PQDs-SAM) with surprising high stability. This is an easy one-pot operation and can be done with large quantities. The composites not only maintain the PQDs remarkable optical properties, but also improve their stability, which is significantly. The Mn-doped CsPbCl3 PQDs-SAM in powder form is easily mixed into the resins and applied as color-converting layer with curing on blue light-emitting diodes (LED). And above all, the orange PQDs-SAM composite is used as red phosphor and stack on the Ce3+:YAG phosphor-in-glass (Ce-PiG) via screen-printing technology (Ce-PiG&R-PQDs-SAM). Whereafter, warm WLED is constructed by blending the Ce-PiG&R-PQDs-SAM materials with the InGaN blue chips. And the constructed WLEDs generate a warm white with an optimal luminous efficacy (LE) of 80.91 l m/W, a high CRI of 83.8, and a low CCT of 4082 K.

Double perovskite Ca2GdNbO6:Mn4+ deep red phosphor: Potential application for warm W-LEDs

A novel Mn4+-doped Ca2GdNbO6 (CGN) phosphor was prepared by high-temperature solid-state reaction. The crystal structure was investigated by X-ray diffraction patterns and unit cell structure. Mn4+ replaced the location of Nb5+ in the CGN lattice, and the value of energy gap (Egap) decreased from 2.16 eV to 1.13 eV, indicating that Mn4+ ions play a great influence on the absorption of CGN hosts. The broad excitation band from 250 nm to 550 nm matches well with commercial near-UV light emitting diodes, and the emission peak centered at 680 nm is due to 2E→4A2g transition in Mn4+ ions. The CIE chromaticity coordinates (0.698, 0.303) of CGN:Mn4+ phosphor was close to standard red color coordinates (0.666, 0.333). These investigations demonstrate CGN:Mn4+ phosphor as an efficient red phosphor for potential applications.

A Phosphine-Free Route to Size-Adjustable CdSe and CdSe/CdS Core-Shell Quantum Dots for White-Light-Emitting Diodes.

The selenium dioxide was used as the precursor to synthesize wide-size-ranged CdSe quantum dots (2.4-5.7 nm) via hot-injection route. The CdSe quantum dots are featured with high crystalline, monodisperse, zinc blende structure and wide emission region (530-635 nm). In order to improve the stability and quantum yield, a phosphine-free single-molecular precursor approach is used to obtain CdSe/CdS core/shell quantum dots. The CdSe/CdS quantum dots are highly fluorescent with quantum yield up to 65%, and persist the good monodispersity and high crystallinity. Moreover, the quantum dots white light-emitting-diodes are fabricated by using the resultant red emission core/shell quantum dots and Y3Al5O12:Ce3+ yellow phosphors as color-conversion layers on a blue InGaN chip. The prepared light-emitting-diodes show good performance with CIE-1931 coordinated of (0.3583, 0.3349), an Ra of 92.9, and a Tc of 4410 K at 20 mA, which indicate that the combination of red-emission QDs and yellow phophors as a promising approach to obtain warm WLEDs with good color rendering.

Correction: Dye-embedded YAG:Ce3+@SiO2 composite phosphors toward warm wLEDs through radiative energy transfer: preparation, characterization and luminescence properties.

Correction for 'Dye-embedded YAG:Ce3+@SiO2 composite phosphors toward warm wLEDs through radiative energy transfer: preparation, characterization and luminescence properties' by Guo-Hui Pan, Jiahua Zhang et al., Nanoscale, 2018, DOI: 10.1039/c8nr07360k.

Efficient rare-earth free red-emitting Ca2YSbO6:Mn4+,M(M = Li+, Na+, K+, Mg2+) phosphors for white light-emitting diodes.

Owing to its low-cost and satisfactory luminescent-emission performance in warm white light-emitting diodes (w-LEDs), the non-rare-earth Mn4+-activated red phosphor has become a promising competitor of commercial rare-earth doped phosphor. In this study, a series of novel red-light emitting phosphors based on Ca2YSbO6:Mn4+ have been developed successfully by a conventional solid-state reaction. The structural and luminescent properties of these phosphors are systematically investigated. The as-prepared Ca2YSbO6:Mn4+ product exhibits a broad excitation band ranging from 250 to 600 nm and an abnormal intense deep-red emission centered at 680 nm with a full width at half maximum (FWHM) of ∼46 nm. The optimal Mn4+ doping concentration is about 0.3 mol%, and the concentration quenching mechanism is determined to be a dipole-dipole interaction. Impressively, the Ca2YSbO6:0.003Mn4+ phosphor shows an outstanding quantum efficiency of 62.6% and an excellent thermal stability. In addition, the effect of Li+, Mg2+, Na+ and K+ dopants on the luminescent properties of Mn4+-doped Ca2YSbO6 phosphors is elucidated. Furthermore, by employing the as-prepared Ca2YSbO6:Mn4+ as a red component, a warm w-LED with high color rendering index (Ra = 87.5) and low correlated color temperature (CCT = 3255 K) can be acquired. It is believed that the present phosphor has a potential application as a supplement of the red component for warm w-LEDs.

Dye-embedded YAG:Ce3+@SiO2 composite phosphors toward warm wLEDs through radiative energy transfer: preparation, characterization and luminescence properties.

The most common yellow phosphor for wLEDs, Y3Al5O12:Ce3+ (YAG:Ce3+), suffers from a deficiency of red in its spectral content of light. In this paper, a new strategy is provided to tailor the Ce3+ spectral profile through surface-located dye molecules of ATTO-Rho101, which feature intense, broad absorption in the green-yellow spectral region of Ce3+ emission as well as bright red emission. Sphere-shaped and highly dispersed micrometer and nanometer-sized YAG:Ce3+ (micro/nano-YAG:Ce3+) was synthesized through a modified solvothermal method. Surface SiO2 coating and simultaneous dye embedding were performed on the solvothermally derived YAG:Ce3+, heat-treated micro-YAG:Ce3+ and commercial phosphors. Efficient radiative transfer/reabsorption from Ce3+ in the inner core of YAG to the dye molecules in the SiO2 outer shell, irrespective of the size of the phosphors, was demonstrated in the accumulated YAG:Ce3+@SiO2 + dye powder upon blue light excitation; this enhanced its red emission. Fluorescence microscopy was demonstrated to be a powerful tool to identify the reabsorption phenomenon of the powdered materials. Packaging the heat-treated micro-YAG:Ce3+@SiO2 + dye phosphors on blue LED chips yielded a warm wLED (Ra∼ 93), but an Ra of only ∼79 was obtained for the wLED with commercial YAG:Ce3+@(SiO2 + dye)5 due to the low concentration of phosphors dispersed in the epoxy resin and the resulting decreased reabsorption by dye molecules. Surface-protonated amine species were found to induce Ce3+→ Ce4+ oxidation upon activation by heating or photoirradiation and then quench the photoluminescence (PL) of micro-YAG:Ce3+ even after surface modification by SiO2, YAG or being embedded in an epoxy resin matrix. High calcination temperatures greatly improved the PL stability of micro-YAG:Ce3+ through the removal of surface-capped species. The dye in the silica matrix showed high stability against heating and irradiation due to the so-called "caging effects"; however, decreased photo-stability was found in commercial YAG:Ce3+@(SiO2 + dye)5 due to the incomplete and/or loose SiO2 layer grown during multiple surface modifications.

Highly efficient rare-earth-free deep red emitting phosphor La2Li1−ySb1−xO6:xMn4+,yMg2+: application in high-power warm w-LEDs

A highly efficient La2Li1−ySb1−xO6:xMn4+,yMg2+ red phosphor with enhanced photoluminescence and the corresponding PiG-based high-power warm w-LEDs were investigated.