Hydrothermal preparation and photoluminescent property of LiY(MoO4)2:Pr3+red phosphors for white light-emitting diodes

Praseodymium doped lithium yttrium molybdate Li Y1-8x Pr x(Mo O4)2(x=0.005–0.025) phosphors were successfully prepared by the hydrothermal method. The phase, morphology, and luminescent property of the prepared phosphors were investigated by X-ray diffraction and scanning electron microscopy. The results indicated that doping of Pr3+ ions did not change the main phase of the phosphors. The samples emitted red luminescence upon excitation at 453 nm and the strongest emission peak corresponding to the characteristic transition of the Pr3+ ion: 3P0→3F2 was observed at 657 nm. Li Y(Mo O4)2:Pr3+ red phosphors could be effectively excited by blue light emitting-diodes to emit red light; thus, acting as potential candidates for compensating the red light deficiency of cerium doped yttrium aluminum garnet yellow phosphor.     

Luminescent properties and application of Eu3+ -activated Gd2(MoO4)3 red-emitting phosphor with pseudo-pompon shape for solid-state lighting

Eu3+ -activated Gd2(MoO4)3 pseudo-pompon-like red-emitting phosphors were prepared by solid-state method.The structure,morphology,and luminescent properties of these powder samples were investigated by X-ray diffraction (XRD),scanning electron microscopy(SEM),and fluorescent spectrophotometry,respectively.The as-obtained phosphors were single crystalline phase with orthorhombic unit cell.The particles of the powder samples had the length of 5-12 μm and width of 3-7 μm with flake shape and large surface area,which is suitable for manufacture of white LEDs.The phosphor could be efficiently excited by the incident light of 348-425 nm,well matched with the output wavelength of near-UV (In,Ga)N chip,and re-emitted an intense red light peaking at 615 nm.By combing this phosphor with a～395 nmemitting (In,Ga)N chip,a red LED was fabricated,so that the applicability of this novel phosphor to white LEDs was confirmed.It is considered to be an efficient red-emitting conversion phosphor for solid-state lighting based on (In,Ga)N LEDs.     

Luminescence properties of YAl3（BO3）4 phosphors doped with Eu^3＋ ions

YAl3 （BO3）4： Eu^3＋ phosphors were prepared by the conventional solid state reaction. The phase structure and morphology were investigated by X-ray diffraction （XRD） and scanning electron microscope （SEM）. Doping YAl3（BO3）4： Eu^3＋ phosphors with concentration of Eu^3＋ ions of 0, 2, 5, 8 and 10 mol% were studied and their luminescent properties at room temperature were discussed. The excitation spectrum of Y0.95Eu0.05Al3（BO3）4 was composed of a broad band centered at about 252 nm and a group of lines in the longer wavelength region. In the emission spectra, the peak wavelength was about 614 nm under a 252 nm UV excitation. The optimal doping concentration of Eu^3＋ ions in YAl3（BO3）4： Eu^3＋ phosphors was 8 mol%.     

Photoluminescent properties of Ca2Gd8（SiO4）6O2： Dy^3＋ phosphor films prepared by sol-gel process

There are growing interests on phosphor thin films owing to their potential application in high-resolution devices such as cathode ray tubes and flat panel display devices. The solution-based sol-gel method is one of the most important techniques for the synthesis of various functional coating films. Compounds with the apatite structure are very suitable host lattices for various luminescent ions. Ca2RE8（SiO4）6O2 （ RE=Y, Gd, La ） is a kind of ternary rare-earth-metal silicate with oxyapatite structure, which has been used as host material for the luminescence of various rare earth and mercury-like ions. In this article, Ca2Gd8（SiO4）6O2：Dy^3＋phosphor films were dip-coated on quartz glass substrates through the sol-gel process. X-ray diffraction （XRD）, atomic force microscopy （AFM）, photoluminescence （PL） spectra, as well as lifetimes were used to characterize the resulting films. AFM study revealed that the phosphor films consisted of homogeneous particles. The Dy^3＋ showed its characteristic emission in crystalline phosphor films, i.e., ^4F9/2-^6H15/2 and ^4F9/2-^6H13/2.     

Luminescent properties of Ca2SiO4：Eu^3＋ red phosphor for trichromatic white light emitting diodes

The luminescent properties of Eu^3＋doped Ca2SiO4 red phosphors synthesized by the flux fusion reaction method were investigated. It was found that the excitation spectrum included two regions： the weak excitation band below 325 nm and strong narrow peaks above 325 nm. The main peak of the excitation band was located at 400 nm. The peaks located at 290 nm were assigned to the combination of the charge transfer transition of O-Eu, peaks above 325 nm （325, 385, 400, 470, 511, and 539 nm） were assigned to the f-f transitions of Eu^3＋. The emission spectrum was dominated by the red peak located at 612 nm due to the electric dipole transition of ^5D0-^7F2. In addition, the effects of the Eu^3＋ content and charge compensators of Li^＋, Na^＋, K^＋, and Cl^- ions on the emission intensity were investigated. The experiment results suggested that the strongest emission was obtained when the concentration of the Eu^3＋ ions was 0.3 mol^-1, and Li^＋ ions gave the best improvement to enhance the emission intensity. Ca2SiO4：Eu^3＋, Li^＋ was thus suitable for low-cost trichromatic white light emitting diodes （WLED） based on UV InGaN chip.     

Synthesis and luminescence properties of a novel red-emitting phosphor SrCaSiO_4：Eu~（3＋） for ultraviolet white light-emitting diodes

A novel red phosphor based on Eu3+-activated SrCaSiO4 was successfully synthesized by conventional solid state reaction method and the photoluminescence properties were investigated. X-ray diffraction (XRD) patterns indicated that SrCaSiO4:Eu3+ phosphors belong to orthorhombic crystal system (space group=Pmnb). The photoluminescence (PL) excitation spectrum showed broad-band absorption and the strongest excitation peak at 397 nm contributed to the 7F0→5L6 transition which matched well with the emission of a...     

Temperature effects on photoluminescence of YAG:Ce phosphor and performance in white light-emitting diodes

The well crystalline YAG:Ce³⁺ phosphor was synthesized by solid-state method, and the temperature dependence of excitation and emission spectra of YAG:Ce³⁺ phosphor were investigated in the temperature range from room temperature to 573 K. With temperature increasing, it was noted that the emission intensity of as-prepared phosphors decreased considerably more rapidly when pumped by 460 nm than by 340 nm. The temperature-intensity curves under different excitation wavelengths were obtained using an Arrhenius function, and the corresponding activation energies were also obtained respectively. Thus, the experimental phenomenon was discussed in terms of nonradiative decay rate. The effects of as-prepared phosphors on the performance of the white LED with changing temperature were also studied.     

Luminescence properties of YAl3(BO3)4 phosphors doped with Eu3+ ions

YAl3(BO3)4: Eu3+ phosphors were prepared by the conventional solid state reaction. The phase structure and morphology were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). Doping YAl3(BO3)4: Eu3+ phosphors with concentration of Eu3+ ions of 0, 2, 5, 8 and 10 mol% were studied and their luminescent properties at room temperature were discussed. The excitation spectrum of Y0.95Eu0.05Al3(BO3)4 was composed of a broad band centered at about 252 nm and a group of lines in the longer wavelength re-gion. In the emission spectra, the peak wavelength was about 614 nm under a 252 nm UV excitation. The optimal doping concentration of Eu<3+ ions in YAl3(BO3)4: Eu3+ phosphors was 8 mol%.     

Luminescent properties of Ca2SiO4:Eu3+ red phosphor for trichromatic white light emitting diodes

The luminescent properties of Eu3 doped Ca2SiO4 red phosphors synthesized by the flux fusion reaction method were investigated. It was found that the excitation spectrum included two regions: the weak excitation band below 325 nm and strong narrow peaks above 325 nm. The main peak of the excitation band was located at 400 nm. The peaks located at 290 nm were assigned to the combination of the charge transfer transition of O-Eu, peaks above 325 nm (325, 385, 400, 470, 511, and 539 nm) were assigned to the f–f transitions of Eu3 . The emission spectrum was dominated by the red peak located at 612 nm due to the electric dipole transition of 5D0–7F2. In addition, the ef- fects of the Eu3 content and charge compensators of Li , Na , K , and Cl– ions on the emission intensity were investigated. The experiment results suggested that the strongest emission was obtained when the concentration of the Eu3 ions was 0.3 mol–1, and Li ions gave the best improvement to enhance the emission intensity. Ca2SiO4:Eu3 , Li was thus suitable for low-cost trichromatic white light emitting diodes (WLED) based on UV InGaN chip.     

Luminescent properties of Ba3Gd（BO3）3：Eu^3＋ phosphor for white LED applications

Luminescent material Ba3Gd(BO3)3 doped with Eu3+ ion was prepared by high temperature solid-state method. The preparing conditions, luminescent properties, and particle morphology of Ba3Gd(BO3)3:Eu3 + phosphor were studied with X-ray diffraction (XRD), fluorescence spectroscopy, and scanning electron microscopy (SEM). The results obtained by XRD showed that pure phase of Ba3Gd(BO3)3 was obtained at 1000℃. Images from SEM displayed that the particles of Ba3Gd(BO3)3:Eu3+ phosphor had a spherical shape with an average diameter of about 200-400 nm. The luminescence spectra showed that Ba3Gd(BO3)3:Eu3+ phosphor was effectively excited by the near ultraviolet (UV) light (396 nm) and blue light (466 nm). The main emission peaks of Ba3Gd(BO3)3:Eu3+ phosphor were assigned to the supersensitive transition 5D0-7F2 (611 and 616 nm) of Eu3+ ion when samples were excited at 255 and 396 nm, respectively, and the luminescent intensity of Ba3Gd(BO3)3:Eu3+ at 611 and 616 nm reached to the maximum when the doped content of Eu3+ ion was 10mol.%. Therefore, this phosphor could be a promising red component for possible applications in the field of white LED.     

EXAFS investigation and luminescent properties of nanosized Tb: Lu2O3 phosphors

Nanosized terbium doped Lu2O3 phosphors were synthesized via a modified co-precipitation processing.The as-prepared Tb:Lu2O3 phosphors was consisted of well crystallized nanosized sphere particles with a diameter of about 30 nnx Local structure of Tb ions in Lu2O3 lattice was investigated by an analytical approach based on Fourier transformation of the extended X-ray absorption fine structure(EXAFS) data.X-ray near edge structure (XANES) spectra suggested that all Tb ions doped were tervalonce.EXAFS results indicated that Tb ions have entered the Lu2O3 cubic lattice by means of solid solution.The coordination number and first shell Tb-O distance dropped with the increasing of Tb concentration.Emission spectra of the phosphors was shown to be typical for Tb3+ with main components at 542,550 and 490 nm,derived from irradiative relaxation of 5D4 level.The emission intensity decreased severely with the increasing of Tb concentration from 1 mol.% to 15 tool.%,suggesting a significant concentration quenching above 1 mol.% Tb.The reduction of emission intensity was interpreted by higher distortion derived relaxation among the surface state resident Tb3+ ions.     

Photoluminescent properties of Ca2RE8（SiO4）6O2：A （RE=Y,Gd; A=Pb^2＋, Mn^2＋） phosphor films prepared by sol-gel process

Ca2RE8（SiO4）6O2：A （RE=Y, Gd; A=Pb^2＋, Mn^2＋） phosphor fdms were dip-coated on quartz glass substmtes through the sol-gel process. X-ray diffraction （XRD）, photoluminescence （PL） spectra as well as lifetimes were used to characterize the resulting films. Under short wavelength UV excitation, the film showed a red emission with medium intensity. The decay curve of Mn^2＋ luminescence in Ca2Gd8（SiO4）6O2：Pb Mn film could be fitted into a single exponential function. The lifetime of Mn^2＋ was 10.21 ms in Ca2Gd8（SiO4）6O2.     

Vacuum ultraviolet excited photoluminescence properties of Gd2O2CO3：Eu^3＋ phosphor

The Gd2O2CO3：Eu^3＋ with type-Ⅱ structure phosphor was successfully synthesized via flux method at 400 ℃ and their photoluminescence properties in vacuum ultraviolet （VUV） region were examined. The broad and strong excitation bands in the range of 153-205 nm owing to the CO3^2- host absorption and charge transfer （CT） of Gd^3＋-O2^- were observed for Gd2O2CO3：Eu^3＋. Under 172 nm excitation, Gd2O2CO3：Eu^3＋ exhibited strong red emission with good color purity, indicating Eu^3＋ ions located at low symmetry sites and the chromaticity coordination of luminescence for Gd2O2CO3：Eu^3＋ was （x=0.652, y=0.345）. The photoluminescence quenching concentration of Eu^3＋ excited by 172 nm for Gd2O2CO3：Eu^3＋ was about 5%. Gd2O2CO3：Eu^3＋ would be a potential VUV-excited red phosphor applied in mercury-free fluorescent lamps.     

Preparation and Luminescence of SrAi2O4:Eu2+, Dy3+ Nano-Particle

SrAl2O4: Eu2 , Dy3 nano-particle luminescence material was prepared by sol-gel method. Influences of synthesis conditions on the particle size and luminescence properties of SrAl2O4: Eu2 , Dy3 were studied. The synthesis process and the properties of the samples were analyzed by DTA, TGA, XRD, SEM. The result suggested that the formation of SrAl2O4: Eu2 , Dy3 sol is a slow heat release process beginning at 500 ℃ and peaking at 759 ℃.SrAl2O4: Eu2 ,Dy3 crystalline was formed at 1100 ℃. The luminescence properties of the SrAl2O4: Eu2 , Dy3 nanoparticle were compared with the conventional SrAl2O4: Eu2 , Dy3 particles. The average particle size of the product is about 30 nm. The excitation spectrum of the sample shows a broad band with peaks at 240, 330, 378 and 425 nm. The emission spectrum is a broadband spectrum with a peak at 523 nm.     

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 Ra and correlated color temperature(Tc) 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 photoluminescence properties of novel red-emitting Ca14Mg2(SiO4)8:Eu3+/Sm3+ phosphors

Novel red-emitting Eu3+, Sm3+ singly doped and co-doped Ca14Mg2(SiO4)8 phosphors were prepared by conventional solid- state reaction. Powder X-ray diffraction patterns were employed to confirm phase pu...     

Luminescent properties of SrSi2N2O2:Ce3+,Tb3+-a potential phosphor for white light emitting diodes

Ce3+ and Tb3+ co-doped SrSi2N2O2 phosphors were prepared by solid-state reaction. The X-ray diffraction pattern exhibited that the phosphor consisted mainly of oxygen-rich SrSi2N2O2. The optical properties of SrSi2N2O2:Ce3+, SrSi2N2O2:Tb3+ and SrSi2N2O2:Ce3+,Tb3+ were studied, respectively. The emission intensity of Tb3+ at 541 nm was remarkably enhanced by Ce3+ in SrSi2N2O2:Ce3+,Tb3+ phosphor, which was attributed to the energy transfer from Ce3+ to Tb3+. The chromaticity coordinates of phosphors were investigated as a function of Tb3+ concentration. When the Ce3+ and Tb3+ concentrations were 0.02 and 0.18 mol per formula unit, respectively, the chromaticity coordinate was (0.257, 0.337) in the CIE 1931 chromaticity diagram. SrSi2N2O2Ce3+,Tb3+ phosphors could be used for white light emitting diodes.