Luminescent properties of red phosphors K2Ba（MoO4）2：Eu3＋ for white light emitting diodes

K2Ba(MoO4)2:Eu3+ phosphors were synthesized by solid-state reaction. The emission and excitation spectra of K2 Ba(MoO4)2:Eu3+ phosphors exhibited that the phosphors could be effectively excited by near ultraviolet (394 nm) and blue (465 nm) light, and emitted red light at 616 nm. The influence of Eu3+concentration, sintering temperature and charge compensators (K+, Na+ or Li+ ) on the emission intensity were investigated. The results indicated that concentration quenching of Eu3+ was not observed within 30mol.% Eu 3+, 600 oC was a suitable sintering temperature for preparation of K2 Ba(MoO4)2:Eu3+phosphors, and K+ ions gave the best improvement to enhance the emission intensity. The CIE chromaticity coordinates of K2 Ba(MoO4)2:0.05Eu3+phosphor were calculated to be (0.68, 0.32), and color purity was 97.4%.     

Photoluminescence properties of M2ZnSi2O7:Eu2+（M=Sr,Ba）

The hardystonite phosphors of Eu2+ activated M2ZnSi2O7(M=Sr,Ba) were synthesized by combustion-assisted method.They were systematically characterized by photoluminescence excitation and emission spectra.The emission spectra of these two phosphors showed that the main emission peaks are at 475 and 503 nm due to 4f65d1→4f7 transition of Eu2+.Both phosphors could be efficiently excited in the wavelength range of 250-425 nm where the near ultraviolet light-emitting diode was well matched.The(x,y) color coordinates were determined with the emission values(x,y)=(0.41,0.21) and(0.16,0.45) for the M2ZnSi2O7:Eu2+(M=Sr,Ba) phosphors.     

Luminescent properties of Eu~（3＋） doped Gd_2WO_6 and Gd_2（WO_4）_3 nanophosphors prepared via co-precipitation method

Eu3+ doped Gd2WO6 and Gd2(WO4)3 nanophosphors with different concentrations were prepared via a co-precipitation method. The structure and morphology of the nanocrystal samples were characterized by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. The emission spectra and excitation spectra of samples were measured. J-O parameters and quantum efficiencies of Eu3+ 5D0 energy level were calculated, and the concentration quenching of Eu3+ luminescence in different matrixes were studied. The results indicated that effective Eu3+:5D0-7F2 red luminescence could be achieved while excited by 395 nm near-UV light and 465 nm blue light in Gd2WO6 host, which was similar to the familiar Gd2(WO4)3:Eu. Therefore, the Gd2WO6:Eu red phosphors might have a potential application for white LED.     

Luminescent properties of MMgP_2O_7：Eu~（3＋）（M=Ca,Sr,Ba） phosphor

A series of red phosphors Eu3+-doped MMgP2O7(M=Ca,Sr,Ba) were synthesized by solid-state reaction method.X-ray powder diffraction(XRD) analysis confirmed the formation of pure CaMgP2O7,SrMgP2O7 and BaMgP2O7 phase.Photoluminescence spectra of MMgP2O7(M=Ca,Sr,Ba):Eu3+ phosphors showed a strong excitation peak at around 400 nm,which was coupled with the characteristic emission(350-400 nm) from UV light-emitting diode.The CaMgP2O7:Eu3+,SrMgP2O7:Eu3+ and BaMgP2O7:Eu3+ phosphors showed strong emission bands peaking at 612,593 and 587 nm,respectively.Due to the difference of the ion sizes between Ba2+(0.142 nm),Sr2+(0.126 nm),Ca2+(0.112 nm),Mg2+(0.072 nm) and Eu3+(0.107 nm),Eu3+ ions were expected to substitute for different sites in CaMgP2O7,SrMgP2O7 and BaMgP2O7 lattice.     

Fabrication and luminescent properties of red phosphor M3BO6:Eu3+（M=La,Y）

A series of red phosphors M3BO6:Eu3+(M=La,Y) were synthesized at 1150 oC by conventional solid state reaction method and their luminescent properties were investigated.Structural characterization of the luminescent materials was carried out with X-ray powder diffraction(XRD) analysis.Photoluminescence measurements indicated that the La3BO6:Eu3+ phosphor exhibited bright red emission centered at about 612 nm 626 nm under UV excited.La3BO6:Eu3+ phosphor had better luminescent intensity than Y3BO6:Eu3+ phosphors under the same excitation and measuring conditions.It was shown that the 0.08 mol.% Eu3+ ions in La3BO6:Eu3+ phosphors was optimal.The color parameter indicated that La3BO6:Eu3+ phosphor was a preferable red phosphor for white LED.     

LiY1-xEux（MoO4）2 as a promising red-emitting phosphor of WLEDs synthesized by sol-gel process

A series of LiY1-xEux(MoO4)2 red-emitting phosphors were synthesized by sol-gel technique. The phase impurity and spectroscopic properties were characterized by X-ray diffraction (XRD) and photo-luminescence (PL) spectra respectively. The effect of Eu3+ doping con-centration, annealing temperature and the molar ratio of citric acid to the total metal cations (C:M) on the optical properties of the red phos-phors were studied and optimized. It was found that all the samples could be excited efficiently by blue light (465 nm), which was well coin-cident with the emission of GaN based LED chips. The luminescent intensity reached maximum when annealing temperature was 750 ?C and Eu3+ doping concentration was 5% with C:M=3:1.     

Properties of red-emitting phosphors Sr2MgSi2O7:Eu3+ prepared by gel-combustion method assisted by microwave

Novel red-emitting phosphors Sr2MgSi2O7:Eu3+ were prepared by gel-combustion method assisted by microwave. The phase struc-ture and luminescent properties of as-synthesized phosphors were investigated by XRD and fluorescence spectrophotometer, respectively. The results showed that the as-synthesized sample was Sr2MgSi2O7 with tetragonal crystal structure. The excitation spectrum of Sr2MgSi2O7:Eu3+ was composed of two major parts: one was the broad band between 200 and 350 nm, which belonged to the charge transfer of Eu3+-O2-; the other consisted of a series of sharp lines between 350 and 450 nm, ascribed to the f-f transition of Eu3+. The emission spec-trum consisted of two emission peaks at 593 and 616 nm, which was attributed to 5D0→7F1 and 5D0→7F2 of Eu3+, respectively. The concen-tration of Eu3+ (x) had great effect on the emission intensity of Sr2-xMgSi2O7:Eu3+x. When x varied in the range of 0.04-0.18, the intensity of emission peaks at 593 and 616 nm increased gradually with the concentration of Eu3+ increasing. It was interesting that no concentration quenching occurred. Moreover, the luminescent intensity could be greatly enhanced with incorporation of charge compensator Li+ ions.     

Synthesis and photoluminescence properties of Ca3R2-xWO9:xEu3+(R=Y,Gd) phosphors

Ca3R2–xWO9:xEu3+(R=Y, Gd) red-emitting phosphors were prepared by solid state reactions. These samples were characterized by differential scanning calorimetry and thermogravimetry analysis(DSC-TGA), X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), photoluminescence(PL) and field emission scanning electron microscopy(FE-SEM) analyses. The optimum sintering temperature for these phosphors was 1100 oC, and the optimum sintering time was 2 h. The optimum doped concentration of Eu3+3+ in Ca3Y2–xWO9:xEu and Ca3Gd2–xWO9:xEu3+ were x=1.5 and x=1.1, respectively. These phosphors could be excited by near-UV light of 394 nm and blue light of 465 nm, and showed strong red emission line at 612 nm(5D0→7F2), which indicated that Ca3R2–xWO9:xEu3+(R=Y, Gd) were promising red candidates for white LED.     

Synthesis and luminescence characteristics of Li2Y4-xEux（WO4）7-y（MoO4）y red-emitting phosphor for white LED

Li2Y4-xEux（WO4）7-y（MoO4）y red-emitting phosphors were synthesized by solid state reaction and characterized by powder X-ray diffraction （XRD） and photoluminescence （PL） spectrum. The excitation spectra showed that the phosphors could be efficiently excited by near-UV light of 395 nm. When the relative molar ratio of Mo/W was 7：0, and the optimum doped concentration of Eu3＋was 2.8 mol, the phosphor showed strong red emission lines at 615 nm corresponding to the forced electric dipole 5D0→7F2 transition of Eu3＋. Compared with Na2Y2Eu2（MoO4）7 and K2Y2Eu2（MoO4）7, the fluorescence intensity of Li2Y1.2Eu2.8（MoO4）7 phosphor was the strongest. The CIE chromaticity coordinates of Li2Y1.2Eu2.8（MoO4）7 phosphor was calculated to be （0.66, 0.34）.     

Eu2＋ and Dy3＋ codoped （Ca,Sr）7（SiO3）6Cl2 highly efficient yellow phosphor

Eu2+ and Dy3+ codoped(Ca,Sr)7(SiO3)6Cl2 yellow phosphors were successfully synthesized by self-flux method. The structure, morphology and photoluminescence properties were investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM) and photoluminescence spectra. The as-prepared phosphor showed a broad emission spectrum centered at 550 nm for Eu2+single-doped phosphor, while located at 548–544 nm for the Eu2+, Dy3+ codoped samples under excitation at 380 nm light. The emission intensity was greatly improved when Dy3+ was doped into the(Ca,Sr)7(SiO3)6Cl2:Eu2+ system. The composition-optimized sample with 3 mol.% of Dy3+ and constant 10 mol.% of Eu2+ exhibited a 220% PL enhancement compared to the phosphor with 10 mol.% Eu2+ single-doped. Meanwhile, it was found that the quantum efficiency of phosphor namely(Ca,Sr)7(SiO3)6Cl2:3 mol.% Dy3+, 10 mol.% Eu2+ could get up to 24.6%. The synthesized yellow-emitting(Ca,Sr)7(SiO3)6Cl2:Dy3+,Eu2+ is a promising candidate as high-efficiency yellow phosphor for NUV-excited white LEDs.     

Multi-site occupancies and luminescence properties of cyan-emitting Ca9-xNaGd2/3(PO4)7:Eu2+phosphors for white light-emitting diodes

Cyan-emitting Ca₉NaGd_2/3(PO₄)₇:Eu²⁺phosphors were synthesized via high temperature solid-state route.X-ray powder diffraction(XRD)and scanning electron microscopy(SEM)were used to verify the phase and morphology of the Ca₉NaGd_2/3(PO₄)₇:Eu²⁺(CNGP:Eu²⁺)phosphors.The as-obtained phosphor exhibits a broad excitation band of 250-420 nm,which is near the ultraviolet region.An intense asymmetric cyan emission at 496 nm corresponds to the 5 d-4 f transition of Eu²⁺.The multiplesite luminescent properties of Eu²⁺ions in CNGP benefit from versatile structure ofβ-Ca3(PO4)2 compounds.The effective energy transfer distance is 5.46 nm(through the spectral overlap calculation),validating that the resonant energy migration type is via dipole-dipole interaction mechanism.Compared to the initial one at room temperature,the luminescent intensity of CNGP:Eu²⁺phosphor can maintain 77%as it is heated up to 420 K.A white light-emitting diode(WLED)with excellent luminesce nt properties was successfully fabricated.Moreover,the CIE chromaticity coordinates of fabricated WLED driven by changing current just change slightly.     

Eu2+-doped Sr5(PO4)3Br blue-emitting phosphor with high color purity for near-UV-pumped white light-emitting diodes

Eu²⁺-doped bromophosphateapatite Sr₅(PO₄)₃Br phosphors were synthesized by the conventional high-temperature solid-state reaction. The crystal structure and luminescence properties of the phosphors, as well as their thermal stability and CIE chromaticity coordinates were systematically investigated. Photoluminescence spectra of Sr₅(PO₄)₃Br:Eu²⁺ exhibit a single blue emission at 450 nm under the excitation of 345 nm, which is ascribed to the 4f–5d transition of Eu²⁺. The phosphor shows very good thermal stability. The CIE color coordinates are very close to those of BaMgAl₁₀O₁₇:Eu²⁺ (BAM). All the properties indicate that the blue-emitting Sr₅(PO₄)₃Br:Eu²⁺ phosphor has potential application in white LEDs.     

Synthesis,structure and optical properties of novel thermally robust Dy~(3+)-doped Ca_9Sc(PO_4)_7 phosphors for NUV-excited white LEDs

The powder samples of Ca₉Sc(PO₄)₇:xDy^{^(3+})white emitting phosphors were prepared via a solid state reaction technique.The Ca₉Sc(PO₄)₇:Dy³⁺samples were researched by using the GSAS Rietveld refinement and X-ray diffraction(XRD) methods,and SEM images and elemental maps were recorded.Under 350 nm excitatio n,the emission spectra of Ca₉Sc(PO₄)₇:xDy³⁺samples have two obvious peaks and one weak peak at 484,572 and660 nm,corresponding to the characteristic electron transitions of(⁴F_9/2→ ⁶H_15/2,blue),(⁴F_9/2→ ⁶H_13/2,yellow) and(⁴F_9/2→ 6 H11/2,red),respectively.The concentration quenching effect,decay lifetime and thermal quenching of the as-synthesized Ca₉Sc(PO₄)₇:Dy³⁺samples were researched systematically.The Ca₉Sc(PO₄)₇:0.02 Dy³⁺phosphor possesses a good thermal stability,of which the emission intensity at 423 K can maintain 79% of the initial value(273 K).In addition,through the study of the chro maticity coordinates of the Ca₉Sc(PO₄)₇:0.02 Dy³⁺phosphor,it is found that it is located in the white region,and the Commission Internationalede L’Eclairage(CIE) chromaticity coordinates are(0.339,0.389),The above results show that Ca₉Sc(PO₄)₇:xDy³⁺phosphors can be excellent candidate material for applications in NUV-excited white LEDs.     

Spectral properties and Judd–Ofelt analysis of novel red phosphors Gd2InSbO7:Eu3+ with high color purity for white LEDs

Gd₂InSbO₇:Eu³⁺ red phosphors were successfully synthesized via high-temperature solid–state reaction. The phase purity, particle size, and luminescence properties of obtained phosphors were measured and analyzed in detail. The Gd₂InSbO₇ lattice possesses cubic structure with F_d-3m (227) space group. The phosphors emit bright red emission at 628 nm under 393 nm excitation, and this phenomenon is attributed to the ⁵D₀–⁷F₂ transition. The Judd–Ofelt parameters (Ω₂, Ω₄), transition ratio, and branching ratios (β) of Eu³⁺-doped Gd₂InSbO₇ phosphor were calculated on the basis of the emission spectra and decay lifetimes. The optimal content in Gd₂InSbO₇:xEu³⁺ is identified to be 15 mol%. The thermal quenching of Gd₂InSbO₇:Eu³⁺ is found to be over 500 K, and its activation energy is 0.26 eV. The Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of Gd₂InSbO₇:15%Eu³⁺ are (0.629, 0.371), which are close to ideal red chromaticity coordinates (0.670, 0.330). The fabricated w-LED exhibits good color rendering index (R_a) (86), correlated color temperature (CCT) (6997 K), and CIE chromaticity coordinates (0.302, 0.330). The obtained results demonstrate that Gd₂InSbO₇:Eu³⁺ phosphors have potential applications in white LEDs.     

A new oxyapatite red phosphor Eu3+-doped Ca3Y7(BO4)(SiO4)5O: Synthesis,structure and luminescence properties

A series of new oxyapatite red phosphors Ca₃Y₇(BO₄)(SiO₄)₅O doped with different concentrations of Eu³⁺ were successfully synthesized by high temperature solid state method. The X-ray diffraction (XRD) Rietveld refinement results show that the structure of the phosphor belongs to space group P6₃/m and Eu³⁺ ion replaces Y³⁺ ion. The emission spectrum consists of the characteristic emission peaks corresponding to Eu³⁺ under the excitation of 274 nm and the dominant emission peak is at 614 nm (⁵D₀→⁷F₂ of Eu³⁺). The concentration quenching effect occurs and the optimized Eu³⁺ concentration is 4.0 mol%. The energy level diagram for luminous mechanism is also given and the non-radiative energy transfer mechanism between Eu³⁺ is mainly exchange interaction. The CIE coordinate is close to the ideal red light and the color purity is higher than 99.79%. Moreover, the phosphor exhibits moderate thermal stability because the photoluminescence intensity at 423 K is still maintained at higher than 78.97% of that at room temperature. The internal quantum efficiency of Ca₃Y₇(BO₄)(SiO₄)₅O:4.0 mol%Eu³⁺ phosphor is 58.2%. A red light emitting diode (LED) device based on it can emit bright red light. The CCT values of the device are basically unchanged when driven by various bias current. The results show that Ca₃Y₇(BO₄)(SiO₄)₅O:Eu³⁺ is a new type of oxyapatite red fluorescent material with good comprehensive performances.     

Luminescence properties of phosphate phosphors Ba3Gd1−x(PO4)3:xSm3+

A series of reddish orange phosphors Ba_3Gd_(1-x)(PO_4)_3:xSm~(3+)(x = 0.02.0.04,...,0.12) were prepared by the high-temperature solid-state reaction. X-ray powder diffraction(XRD) and diffuse reflectance and photoluminescence spectra were utilized to characterize the structure and spectral properties of the phosphors. The phosphors have strong absorption in the near-UV region. CIE chromaticity coordinates of the phosphors are located in the reddish orange region since the strongest emission band is around 598 nm and related to the ~4 G_(5/2)→~6 H_(7/2) transition of Sm~(3+). Optimal concentration of Sm~(3+) in the phosphors is about 6.0 at%. The quantum yield of the Ba_3Gd_(0.94)(PO_4)_3:0,06 Sm~(3+) under excitation at 403 nm is about 52.07%. Temperature dependent photoluminescence spectra of the Ba_3Gd_(0.94)(PO_4)_3:0.06 Sm~(3+) were measured and the phosphor exhibits high thermal stability of emission. All the results show that the Ba_3Gd(PO_4)_3:Sm~(3+) phosphor may be a potential red phosphor for near-UV based white LEDs.     

Influence of reaction parameters on the luminescence properties of monodisperse NaGd(1−x−y)(WO4)2:xEu3+,yTb3+ phosphor by molten salt synthesis

Eu~(3+) activated and Eu~(3+), Tb~(3+) co-activated monodisperse sodium double tungstates NaGd(WO4)2 phosphors were prepared by molten salt method at 750 ℃ for 10 h using NaCl as a flux. The crystal structure and morphology of the as-synthesized phosphors were measured by XRD and SEM, respectively. The photoluminescence properties were characterized by PL spectra, decay lifetime and CIE. The presence of NaCl plays an important role in the morphology and luminescence properties. In this work,NaCl and one of the raw material Na_2 CO_3 in a certain proportion will form a low eutectic salt to decrease the reaction temperature and benefit the formation of monodisperse NaGd(WO_4)_2 crystals. The color of Eu~(3+) and Tb~(3+) co-doped NaGd(WO_4)_2 phosphors can be tuned from creamy white to orange, red and green by adjusting the doping concentration of rare earth ions, since the emission contain the broad blue-green emission origin from NaGd(WO_4)_2 host and characteristic red and green emission origin from Eu~(3+) and Tb~(3+) ions. The electroluminescent spectra and CIE measurement shows that the LED device with NaGd_((1-x))(WO_4)_2:xEu~(3+)(x = 0.24) phosphor can be excited by 365 nm and 380 nm LED chip, and their CIE coordinate is(x = 0.45, y = 0.45) and(x = 0.36, y = 0.37), Ra is 80.3 and 86.3, T_c is 3196 and4556 K, respectively. As a single-component phosphor, NaGd(WO_4)_2:Eu~(3+),Tb~(3+) have potential application in UV-pumped WLEDs.     

Intense blue-emitting Ca2PO4Cl:Eu2+ phosphor for near-ultraviolet converting white light-emitting diodes

A blue phosphor Ca₂PO₄Cl:Eu²⁺ (CAP:Eu²⁺) was synthesized by solid state reaction. The Ca₂PO₄Cl:Eu²⁺ exhibited high quantum efficiency and excellent thermal stability. The luminescent intensity of Ca₂PO₄Cl:Eu²⁺ was found to be 128% under excitation at 380 nm, 149% under 400 nm, and 247% under 420 nm as high as that of BaMgAl₁₀O₁₇:Eu²⁺. The optimal doping concentration was observed to 11 mol.% of CAP:Eu²⁺. The energy transfer between Eu²⁺ ions in CAP were occurred via electric multipolar interaction, and the critical transfer distance was estimated to be 1.26 nm. A mixture of blue-emitting Ca₂PO₄Cl:Eu²⁺, green-emitting (Ba,Sr)₂SiO₄:Eu²⁺ and red-emitting CaAlSiN₃:Eu²⁺ phosphors were selected in conjunction with 400 nm chip to fabricate white LED devices. The average color-rendering index R_a and correlated color temperature (T_c) of the white LEDs were found to be 93.4 and 4590 K, respectively. The results indicated that it was a promising candidate as a blue-emitting phosphor for the near-UV white light-emitting diodes.     

Synthesis and optical characterization of Eu2+,Tb3+-codoped Sr3Y(PO4)3 green phosphors

A series of Eu~(2+),Tb~(3+)-codoped Sr_3 Y(PO_4)_3(SYP) green phosphors were synthesized by hightemperature solid-state reaction. Several techniques, such as X-ray diffraction, UV-vis spectrum,and photoluminescence spectrum, were used to investigate the obtained phosphors. The present study investigates in detail photoluminescence excitation and emission properties, energy transfer between the two dopants, and effects of doping ions on optical band gap. SYP:0.05 Eu2+ phosphor shows an intense and broad excitation band ranging from 220 to 400 nm and exhibits a bright green emission band with CIE chromaticity coordinates(0.189, 0.359) under 350 nm excitation. Green emission of SYP:0.03 Tb3+ is intensified by codoping with Eu~(2+), and energy transfer mechanism between them is demonstrated to be a dipole-dipole interaction. Upon 350 nm excitation, SYP:Eu~(2+),Tb~(3+) phosphors exhibits two dominating bands peaking at 466 and 545 nm, which are assigned to 4 f~65 d~1→4 f~7 transition of Eu~(2+) ions and ~5 D_4→~7 F_5 transition of Tb~(3+) ions, respectively. Optimal doping concentrations of Eu~(2+) and Tb~(3+) in the SYP host are 5 mol% and 15 mol%, respectively. Results indicate that SYP:Eu~(2+),Tb~(3+) phosphors are potentially used as green-emitting phosphors for white light-emitting diodes.