Tricolor Phosphors Research Articles

Selective Extraction of Red Phosphor (Y2O3:Eu3+) Constituents from Waste Fluorescent Lamps Phosphor Using Acid Leaching

Modern fluorescent lamp phosphor powder contains tricolor phosphor. This tricolor phosphor consists of three different types of rare earth phosphors: red (YOX), green (CMAT/LAP) and blue (BAM); mixed in varying proportions. The exact separation of these three rare earth phosphors is essential in order to precisely recover the contained rare earth elements from waste lamps phosphor. In this present work, we reported an efficient methodology for the separation of these three tricolor phosphors and the selective extraction of predominantly presented red phosphor (YOX) constituents using acid leaching. The waste phosphor powder was leached with different acids: both organic and inorganic type. The 3 M H2SO4 leaching was found to be most suitable for the selective extraction of red phosphor constituents, i.e. Y and Eu. The recovered phosphor powder was analyzed with SEM/EDS and XRD analysis. The obtained XRD pattern was refined using Rietveld refinement method for the quantification of phases present. Recovered red phosphor powder contained three main crystalline phases Y2O3, Eu2O3 and Y2OS2. KEYWORDS: Waste Lamp Phosphor; Tricolor Phosphor; Rare Earth Elements; Acid Leaching

Efficient Blue-emitting Phosphor SrLu2O4:Ce3+ with High Thermal Stability for Near Ultraviolet (~400\u2009nm) LED-Chip based White LEDs

Blue-emitting phosphors for near ultraviolet (NUV) based tri-color RGB phosphor blend converted white light emitting diodes (LEDs) have been extensively investigated in the past few years. LED chip peaked near 400 nm is the most efficient among the NUV chips currently. However, most of blue phosphors show inefficient excitation around 400 nm. Herein, a novel blue phosphor SrLu2O4:Ce3+ matching well with near 400 nm chip and showing high thermal stability has been developed. The photoluminescence spectrum presents a broad emission band peaking at 460 nm with a bandwidth of nearly 90 nm. By optimizing the Ce3+ concentration, an internal quantum efficiency (IQE) as high as 76% was achieved. Furthermore, 86% of the room-temperature emission intensity is still maintained at 150 °C, indicating a good thermal stability and practicality. A series of white LEDs were fabricated based on 405 nm chips coated with a blend of the new blue phosphor with the commercial yellow and red phosphors. High color rendering indexes (≥90) were achieved while the correlated color temperature was tuneable in the range of 3094 to 8990 K. These results suggest that SrLu2O4:Ce3+ can be utilized as a blue-emitting phosphor in NUV based white LEDs.

The impact of local structure variation on thermal quenching of luminescence in Ca3MoxW1−xO6:Eu3+ solid solution phosphors

Near-ultraviolet (NUV, 365–410 nm) excitable white light emitting diodes require intense absorption in the NUV region for the tri-color phosphors (red, green, and blue). Optional red phosphor Ca3MoO6:Eu3+ meets the requirement of NUV absorption but suffers from severe quenching, while Ca3WO6:Eu3+ has good resistance to thermal quenching but could not absorb NUV light efficiently. It is requisite to investigate the candidate Ca3MoxW1−xO6:Eu3+ to balance the both effects. Results indicate that thermal quenching turns to be worse with an increase in Mo contents in the solid solutions with inevitable distortions or defects, especially when exciting the charge transfer band of WO6 and MoO6 groups. Temperature-dependent Raman spectroscopy is utilized to reveal the impact of structural variation in the quenching process since the variations influence the energy transfer between WO6/MoO6 groups and Eu3+ ions or among Eu3+ ions. Results show that the tilting or distortion of the Ca/W/MoO6 octahedral framework and weakened Eu3+-O bonds have large impacts on thermal quenching performance of Eu3+ luminescence in the solid solutions. The research would benefit the design of novel red phosphors.

Bright and High-Color-Rendering White Light-Emitting Diode Using Color-Tunable Oxychloride and Oxyfluoride Phosphors

White lighting converted by tricolor phosphor and near-ultraviolet light-emitting diode demonstrates great potential in general lighting. However, a major problem with this approach is the lower luminous efficiency of the resulting white lighting by the reabsorption among tricolor phosphors. In this work, we propose a general but effective method for achieving high-efficacy white light-emitting diodes (WLEDs) by using two-color phosphors having the same host that can lower energy loss by reabsorption. Color-tunable Sr7.95Si4O12Cl8:0.05Eu2+ (SSO_Cl:0.05Eu2+) phosphors are synthesized by cationic substitution strategy, and the emission colors can be tuned from blue-greenish to blue/yellow by Sr → Mg/Ca substitution. The red-shifted emission is attributed to the increased Eu2+ d-orbital splitting owing to the smaller size of Ca2+, whereas blue-shifted Eu2+ emission is unusual in Mg-substitution for Sr2+. WLEDs with luminous efficacies (ηL) of 28.9–56 lm/W and CRIs of 79–90.2 are demonstrated using the two-co...

KLaSr3(PO4)3F (Re=Tb3+/Eu3+/Eu2+): Promising Multi-Color Luminescence Phosphors forn-UV/UV White LEDs

Among inorganic phosphors used in solid-state lighting, the warm white light phosphors have drawn significant attention because of their high color rendering (CRI) and appropriate warm correlated color temperature (CCT). Herein, novel green emission KLa0.90Tb0.10Sr3(PO4)3F and red emission KLa0.90Eu(3+)0.10Sr3(PO4)3F phosphors were successfully synthesized for the first time. Besides, the phase constitution and photoluminescence properties were investigated in detail. The KLa0.90Tb0.10Sr3(PO4)3F phosphor shows a green emission with a maximum at 545 nm under excitation of 231 nm, while KLa0.90Eu(3+)0.10Sr3(PO4)3F displays a red emission centered at 617 nm excited at 393 nm. Temperature-dependent emission spectra reveal that these phosphors have better thermal stability and color stability. What is more, the white light emission phosphor can be generated by mixing three kinds of KLaSr3(PO4)3F:Re phosphors (Re=Eu2+, Tb3+, and Eu3+), exhibiting a CRI of ∼85 and a warm CCT of ∼3946 K. All the results indicated that the white light emission phosphor with high color rendering and appropriate warm correlated color temperature could be reached by combining these tri-color phosphors with proper ratio.

Development of YK3B6O12:RE (RE = Eu3+, Tb3+, Ce3+) tricolor phosphors under near-UV light excitation

Polycrystalline phosphors YK3B6O12:RE3+ (RE = Eu, Ce, Tb) were prepared by the solid-state synthesis. The single crystal-phases of the samples were confirmed by X-ray powder diffraction (XRD) measurements and the structural refinements. The field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and electron dispersive X-ray (EDX) measurements were applied to analyze the morphologies of the phosphors. The photoluminescence excitation spectra (PLE) and emission (PL) spectra, decay curves and lifetimes were investigated. Under the near-UV light excitation, YK3B6O12:Eu3+, YK3B6O12:Ce3+, and YK3B6O12:Tb3+ phosphors exhibit the characteristic emission transitions from Ce3+ (5d→4f transitions in blue color), Eu3+ (5D0→7F2, red color), and Tb3+ (5D4→7F5, green color), respectively. The luminescence internal quantum efficiency (QE), the optimal doping level and the thermal stability with the activation energy (ΔE) were measured. The result in this work could be useful for the further applications of this new host as a potential phosphor.

Luminescence of Eu3+ in a Mullite-Type Host Material Bi2Ga2Al2O9

The escalating energy demand coupled with limited conventional energy resources led to a widening gap between supply and demand, making it inevitable to look for novel energy efficient technologies. Solid state lighting is one of the promising areas where a significant amount of energy consumed can be conserved without compromising on the sophistications of conventional lighting. Solid state lighting kindled the interest of researchers owing to their impressive energy efficiency, longer life time, greater reliability, eco-friendly nature and the reasonable ease of fabricating the white light emitting diodes (WLEDs). Typically blue light emitting chip in combination with yellow light emitting phosphor1, Y3Al5O12:Ce3+ (YAG:Ce3+) have been used to produce the white light. However, the obtained white light has poor light quality and low color rendering index (CRI >80), due to lack of red component in the obtained white light spectrum. Tricolor phosphors (red, green and blue) in combination with near ultra violet (NUV) emitting source (InGaN chip) were considered to be an alternative to get better lighting properties and the generated white light by this technique has similarity to sun light and a good CRI value2 , 3. The commercially used red phosphor Y2O2S:Eu3+ is sensitive towards moisture and decomposed under high temperature which is harmful to the environment. Nitrides, CaAlSiN3:Eu2+ can be used as a substitute but its preparation needs greater care and highly controlled preparation conditions. Therefore, the red phosphors with thermal, chemical stability and high luminous intensity became an essential need for lighting industries. Recently, mullite and mullite-type ceramics have attracted attention because of their interesting optical properties4, high thermal and chemical stability5. In this context, we report Eu3+ activated mullite-type Bi(1-x)2Ga2Al2O9:xEu3+ (x = 0.00, 0.025, 0.05, 0.10, 0.20 and 0.30) solid solution which were prepared by simple solid state method. The prepared samples were characterized by x-ray diffraction and luminescence properties were measured under near UV and blue light excitation. The europium dopped Bi2Ga2Al2O9 (BGAO) showed characteristic excitation peaks between 250 nm and 500 nm. The chromaticity coordinates (0.61, 0.37) calculated under blue light excitation for 20% Eu3+ doped BGAO, located in orange-red region of chromaticity graph. The coordinates were close to the reference red phosphors and the results indicate that it have potential application in the field of lighting and displays under blue LED excitation.

Synthesis and photoluminescence properties of red-emitting Y6WO12:Eu3+ phosphors

For a system of white-light-emitting diodes (WLEDs) fabricated using near-ultraviolet (UV) LED chips coated with RGB tri-color phosphors, the most important issue is enhancing the efficiency of the red phosphor. Y6WO12:Eu3+ phosphor is a potential material that can emit red color under near-UV excitation. This work investigated the luminescence properties of Y6WO12:Eu3+ under UV light excitation. The photoluminescence (PL) emission intensity of EuxY6–xWO12 (x = 0.1–1.0) phosphor from the 5D0→7F2 transition increased with Eu3+ content until x = 0.9. For x > 0.9, the PL emission intensity decreased due to concentration quenching. The decay time of EuxY6–xWO12 (x = 0.1–1.0) phosphor for the 5D0→7F2 transition was about 0.6–0.7 ms and did not decrease obviously, which means that there was no nonradiative energy transfer in the phosphor. The asymmetry ratio (5D0 → 7F2/5D0 → 7F1) of EuxY6–xWO12 (x = 0.1–1.0) was about 2, which caused the PL emission intensity of EuxY6–xWO12 (x = 0.1–1.0) phosphor from the 5D0→7F2 transition to be higher than that from the 5D0→7F1 transition. The chromaticity coordinates of the EuxY6–xWO12 (x = 0.1–1.0) phosphor were close to the chromaticity coordinates of the standard red color. The EuxY6–xWO12 (x = 0.9) phosphor showed the highest quantum efficiency.

A single Eu2+-activated high-color-rendering oxychloride white-light phosphor for white-light-emitting diodes.

Single-phased, high-color-rendering index (CRI) white-light phosphors are emerging as potential phosphor-converted white-light-emitting diodes (WLEDs) and as an alternative to blends of tricolor phosphors. However, it is a challenge to create a high CRI white light from a single-doped activator. Here, we present a high CRI (Ra = 91) white-light phosphor, Sr5(PO4)3-x(BO3)xCl:Eu2+, composed of Sr5(PO4)3Cl as the beginning member and Sr5(BO3)3Cl as the end member. This work utilized the solid-solution method, and tunable Eu2+ emission was achieved. Color-tunable Eu2+ emissions in response to structural variation were observed in Sr5(PO4)3-x(BO3)xCl solid solutions. This was further confirmed using X-ray Rietveld refinement, electron paramagnetic resonance spectroscopy, and in the photoluminescence spectra. The color-tunable emissions included the white light that originated from the combination of the blue emission of Sr5(PO4)3Cl:Eu2+ and an induced Eu2+ yellow emission at approximately 550 nm in the solid solution. Importantly, the white-light phosphors showed a greater R9 = 90.2 under excitation at 365 nm. This result has rarely been reported in the literature and is greater than that of (R9 = 14.3) commercial Y3Al5O12:Ce3+-based WLEDs. These findings demonstrate the great potential of Sr5(PO4)3-x(BO3)xCl:0.04Eu2+ as a white-light phosphor for near-UV phosphor-converted WLEDs. These results also provide a shortcut for developing a high CRI white-light phosphor from a single Eu2+-doped compound.

Enhancing the photoluminescence intensity of CaTiO3:Eu3+ red phosphors with magnesium

Red phosphors MgxCa1–xTiO3:Eu3+ (0<x<0.5) were synthesized by solid-state reaction method. The crystalline structure and morphology of the as-prepared samples were confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The luminescence property was measured using photoluminescence excitation and photoluminescence emission spectra. Results showed that spherical particles appeared in the phosphor bodies and size of the phosphor particles were uniformly distributed in the range of 600–800 nm when the Mg2+ concentration was about 40 mol.%. It could readily be seen that the strongest PL emission was located at 617 nm monitored at 398 nm, which well matched with the near ultraviolet (NUV, 395–400 nm) GaN-LEDs. More importantly, PL emission intensity (617 nm) of phosphor Mg0.4Ca0.6TiO3:0.03Eu3+ was 4.26 times of that of phosphor CaTiO3:0.03Eu3+. Based on these results, it implied that the PL intensity of phosphorCaTiO3:0.03Eu3+ could be significantly enhanced by introducing Mg2+ into CaTiO3 host lattices and the phosphor Mg0.4Ca0.6TiO3:0.03Eu3+ might be the promising red-emitting phosphor in making tricolor phosphor converted white-LEDs.

Red light emitting BaNb2O6:Eu3+ phosphor for solid state lighting applications

Europium doped barium niobate (Eu3+:BaNb2O6) phosphors were successfully synthesized by conventional solid state reaction method. Thermogravimetric analysis–differential scanning calorimetry (TGA–DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterization techniques have been used to disclose thermal, structural and morphological properties of the synthesized phosphors. X-ray diffraction pattern for the synthesized phosphor calcined at 1200°C confirms the formation of pure orthorhombic phase for BaNb2O6. In addition to the above mentioned characterizations, photoluminescence properties were also investigated for the BaNb2O6 phosphor under near-UV/blue excitations. Intense red emission observed at 611nm due to 5D0→7F2 transitions of Eu3+ under the excitations of both 394nm (7F0→5L6) and 466nm (7F0→5D2). The CIE chromaticity coordinates evaluated from the emission spectra are falling in the pure red region of the CIE 1931 diagram, which are very much close to the commercial red phosphor (Y2O2S:Eu3+). The above results indicate that Eu3+ doped BaNb2O6 phosphors may be potential candidates to use in white LEDs in which tricolor (red/green/blue) phosphors are excited by near ultraviolet light.

Gd3B(W,Mo)O9: Eu3+ red phosphor: From structure design to photoluminescence behavior and near-UV white-LEDs performance

The photoluminescence behavior of a high efficient red phosphor Gd3B(W,Mo)O9:Eu3+ designed according to crystal structure and electronic structure is presented in detail. The substitution of isolated WO6 group by MoO6 makes the absorption band edge extend from 360nm to 440nm, as designed to fit the excitation of near ultraviolet (NUV) LED chip, which could be interpreted by the density functional theory calculations. The extreme low symmetry (C1) of Eu3+(Gd3+) site enables Eu3+ ion to show dominant electronic dipole transition 5D0→7F2 (∼616nm) with five apparent splitting peaks according to group theory, which is almost 10 times stronger than that of commercial Y2O2S:Eu3+ upon ∼385nm excitation. The outstanding thermal stability of photoluminescence of this phosphor up to 523K may probably be owed to the energy transfer from isolated MoO6 groups to the well-dispersed Eu3+ ion separated by BO3 groups. The performance of NUV white-LEDs package fabricated with a blue, green and this red phosphor is also demonstrated. It shows high color stability of the white light (CIE coordinate (0.320, 0.349), CCT 6031K, at 20mA) under the DC drive current varied from 20mA to 350mA, verifying the potential application of the red phosphor in tri-color phosphors coated white-LEDs.

Phase transition and multicolor luminescence of Eu2+/Mn2+-activated Ca3(PO4)2 phosphors

Intense blue-green-emitting Eu2+: Ca3(PO4)2 and tunable multicolor-emitting Eu2+/Mn2+: Ca3(PO4)2 phosphors are prepared via a solid-state reaction route. Eu2+-doped orthorhombic Ca3(PO4)2 phosphor exhibits a broad emission band in the wavelength range of 400–700nm with a maximum quantum yield of 56.7%, and the emission peak red-shifts gradually from 479 to 520nm with increase of Eu2+ doping content. Broad excitation spectrum (250–420nm) of Eu2+: Ca3(PO4)2 matches well with the near-ultraviolet LED chip, indicating its potential applications as tri-color phosphors in white LEDs. Interestingly, Mn2+ co-doping into Eu2+: Ca3(PO4)2 leads to its phase transition from orthorhombic to rhombohedral, and subsequently generates tunable multi-color luminescence from green to red via Eu2+→Mn2+ energy transfer, under 365nm UV lamp excitation.

Cyan emission of phosphor Sr6BP5O20:Eu2+ under low-voltage cathode ray excitation

A series of Eu2+ doped Sr6BP5O20 phosphors were prepared by a traditional high temperature solid state reaction method. Their photoluminescence under ultraviolet (UV) light and low-voltage electron beam excitation were investigated. Cyan emission band with a maximum wavelength at about 480nm can be observed. The chromaticity coordinates reveal the phosphor can evidently enlarge the gamut compared with tricolor phosphors. The results show that Sr6BP5O20:Eu2+ may be a potential candidate for field emission displays (FEDs).

Development of a single-phased Ca3SnSi2O9: Bi3+, Dy3+, Eu3+ phosphor with tri-colors for white light-emitting diodes

The bright blue emission at 420nm, originating from the charge transfer transition of the self-activated SnO6 octahedron, was observed in Ca3SnSi2O9 host matrix. Bi3+, Dy3+ and Eu3+ exhibited their characteristic emission under ultraviolet excitation when these activators were doped into Ca3SnSi2O9, respectively. The emission intensity located at the blue–yellow and red region of Dy3+ and Eu3+ could be further improved when Bi3+ was co-doped in Dy3+, Eu3+ doped Ca3SnSi2O9. Furthermore, a tunable color emission, especially the white light, was realized in Ca3SnSi2O9: Bi3+, Dy3+, Eu3+ phosphors by adjusting the relative concentration of the activators. It demonstrates that Bi3+, Dy3+, Eu3+ codoped Ca3SnSi2O9 could potentially be used as a tricolor phosphor for the fabrication of phosphor-converted light emitting diodes (pc-LED).

Tricolor emission Ca3Si2O7:Ln (LnCe, Tb, Eu) phosphors for near-UV white light-emitting-diode

Tricolor emission in a same Ca3Si2O7 host with independent Ln (LnCe3+, Eu2+, Tb3+) dopants is demonstrated to construct a near-UV white light emitting diode (LED). The luminescence properties and thermal quenching properties, as well as the applications in near-UV white LED are investigated. These phosphors show typical blue, red, and green, three-basal-color, luminescence in the CIE chromaticity diagram for Ce3+, Eu2+ and Tb3+ dopants, respectively. Thermal quenching properties show that the luminescence thermal stability strongly depends on the different dopant types; better thermal quenching property of Ce3+ and Tb3+ is recorded in comparison with that of Eu2+. The white LED prototype fabricated with near-UV chip and as-prepared tricolor phosphors exhibits acceptable CIE chromaticity coordinates (0.32, 0.30) with a CCT of 6000K and a CRI of 87, indicating the potential application of Ca3Si2O7:Ln phosphors in near-UV white LED.

Ba1−xSrxMgSiO4:Eu2+,Mn2+: A novel tunable single-matrix tricolor phosphor for W-LED

The Ba1−xSrxMgSiO4:Eu2+,Mn2+ phosphors were prepared by solid-state reaction. Their photoluminescence properties were investigated with fluorescence spectrum and CIE chromaticity. The emission color of Eu2+ in Ba0.98−xSrxMgSiO4:0.02Eu2+ could be tuned from green to blue by adjusting the content of Sr2+. The blue emission of Eu2+ overlapped well with the excitation spectra of Mn2+, leading to an efficient energy transfer from Eu2+ to Mn2+ in Ba0.98−xSrxMg1−ySiO4:0.02Eu2+,yMn2+. Ba0.93Sr0.03Mg1−ySiO4:0.02Eu2+,yMn2+ could emit three efficient broad bands at 440, 530 and 640 nm. The emission color of Ba0.93Sr0.03Mg1−ySiO4:0.02Eu2+,yMn2+ could be tuned from greenish blue to yellowish white by increasing the content of Mn2+ from 0 to 0.1. By changing the content of Sr2+/Mn2+, white-light with different hues could be conveniently obtained in the Ba1−xSrxMgSiO4:Eu2+,Mn2+ phosphors. The results showed that Ba1−xSrxMgSiO4:Eu2+,Mn2+ is a promising single-phased tricolor phosphor in the fabrication of W-LED.

PDP用发光材料的研究进展

At present,the commercial tri-color phosphors for PDP application are(Y,Gd)BO3∶ Eu3+(red phosphor),Zn2SiO4∶Mn2+,BaAl12O19∶Mn2+ or(Gd,Y)BO3∶Tb3+(green phosphors) and BaMgAl10O17∶Eu2+(blue phosphor).However,there exists a common problem in the above tri-color phosphors,that is,their luminescence efficiency is low.Moreover,they also present the disadvantages as follows which restrict their luminescence properties: the color purity of(Y,Gd)BO3∶Eu3+ is poor;the decay lifetimes of Zn2SiO4∶Mn2+ and BaAl12O19∶Mn2+ are long;the luminescence intensity of(Gd,Y)BO3∶Tb3+ is insufficiency,while BaMgAl10O17∶Eu2+ presents poor stability when treated by heating or VUV irradiation.Aiming at these problems,this paper summarizes the recent research progresses on the VUV luminescence mechanism and the improvement of luminescence properties for the tri-color phosphors.Meanwhile,the research progress on the exploring of novel VUV phosphors is also involved.

Separation of red (Y2O3: Eu3+), blue (Sr, Ca, Ba)10(PO4)6Cl2: Eu2+ and green (LaPO4: Tb3+, Ce3+) rare earth phosphors by liquid/liquid extraction

A novel process for separation of red (Y2O3: Eu3+), blue (Sr, Ca, Ba)10(PO4)6Cl2: Eu2+ and green (LaPO4: Tb3+, Ce3+) fine tricolor phosphor powders was established. First, the green phosphor was extracted and separated from three phosphor mixtures in heptane/DMF(N, N-Dimethylformamide) system using stearylamine or laurylamine (DDA) as the cationic surfactant. Then, after being treated with 99.5% ethanol, the blue and red phosphors could be separated in Heptane/DMF system in presence of 1-octanesulfonic acid sodium salt as the anionic surfactant. Satisfactory separation results have been achieved through two steps extractions with their artificial mixtures. The grades and recovery of separated products reached respectively as follows: red product was 95.3% and 90.9%, blue product was 90.0% and 95.2%, and green product was 92.2% and 91.8%.

Luminescence enhancement of BaMgSiO 4:Eu 2+ by adding borate as flux

The luminescence of Eu 2+ in BaMgSiO 4 with BaB 2O 4 as flux was studied. The emission spectrum of the phosphor consisted of two bands, peaking at about 398 nm and 515 nm, which were attributed to the emissions from different Eu 2+ sites in the lattice. When the BaB 2O 4 flux was applied, the intensity of the 398 nm emission was not clearly affected, but the intensity of the 515 nm emission was enhanced by about ten times. Gaussian fitting showed that the emission band at around 515 nm could actually be resolved into two bands with peak wavelengths of 499 nm and 521 nm, respectively. The assignments of the emission bands to the cation sites were carried out according to the values of bond valence. The overlapping of the 398 nm emission band on the excitation band of 515 nm emission implied that energy transfer could occur from the luminescent center related to the 398 nm emission to the center related to the 515 nm emission, and the energy transfer process remarkably enhanced the intensity of the 515 nm emission band. The phosphor had strong excitation at around 350-400 nm and emitted a bright green luminescence. Thus it could have applications as a green component in solid-state lighting devices assembled by near-UV Light Emitting Diodes (LED) combined with tricolor phosphors.