Photoluminescence enhancement of red-emitting GdVO4：Eu and YVO4：Eu phosphors by adding zinc

We synthesized the rare-earth activated R0.94-xEu0.06ZnxVO4 (R: Gd and Y; 0≤x≤0.08) phosphors with a spherical morphology and a smooth surface by the ultrasonic spray pyrolysis. The annealed R0.94-xEu0.06ZnxVO4 crystallized in the tetragonal zircon type structure, belonging to the space group of I41/amd. The incorporation of a small amount of Zn to R0.94Eu0.06VO4 improved the emission characteristics. The emission intensities of the Gd0.88Eu0.06Zn0.06VO4 and Y0.9Eu0.06Zn0.04VO4 phosphors at 619 nm were 72% and 21% stronger than those of the Gd0.94Eu0.06VO4 and Y0.94Eu0.06VO4 phosphors, respectively. We demonstrated that the addition of Zn to R0.94Eu0.06VO4 was quite effective for improving the photoluminescent properties.     

Luminescence Properties of Green-Emitting Phosphor （Ba1- x, Srx ） 2 SiO4 ： EU^2＋ for White LEDS

The （Ba1- x, Srx ） 2 SiO4 ： EU^2＋ green-emitting phosphors were synthesized by conventional solid-state reaction in a CO-reductive atmosphere, and their luminescent properties were investigated. The XRD data show that the Ba/Sr ratio not only affects the lattice parameters, but also influences the emission peak. The excitation spectra indicate that this phosphor can be effectively excited by UV light from 370 to 470 nm. The emission band is due to the 4f^65d^1→4f^7 transition of the Eu^2＋ ion. With an increase in x, the emission band shifts to longer wavelength and the reason was discussed. The emission spectra exhibit a satisfactory green performance under different excitation wavelength（380,398,412,420,460 nm）. （Ba1- x, Srx ） 2 SiO4 ： EU^2＋ is a promising phosphor for green white-lighting-emission diode by ultraviolet chip.     

Broadband downconversion in YVO4：Tm3＋,Yb3＋ phosphors

An efficient near-infrared (NIR) downconversion (DC) by converting broadband ultraviolet (UV) into NIR was demonstrated in YVO4:Tm3+,Yb3+ phosphors. The phosphors were extensively characterized using various methods such as X-ray diffraction, photoluminescence excitation, photoluminescence spectra and decay lifetime to provide supporting evidence for DC process. Upon UV light varying from 260 to 350 nm or blue light (473 nm) excitation, an intense NIR emission of Yb3+ corresponding to transition of 2F5/2→2F7/2 peaking at 985 nm was generated. The visible emission, the NIR mission and the decay lifetime of the phosphors of various Yb3+ concentrations were investigated. Experimental results showed that the energy transfer from vanadate group to Yb3+ via Tm3+ was very efficient. Application of the broadband DC YVO4:Tm3+,Yb3+ phosphors might greatly enhance response of siliconbased solar cells.     

A novel synthesis method and up-conversion properties of hexagonal-phase NaYF4:Er nano-crystals

A novel synthesis method for hexagonal(β)-phase NaYF4:Er nano-crystals(NCs)which showed up-conversion(UC)from infrared to visible spectral region was developed.The NaYF4:Er NCs were synthesized in oleic acid(OA)and 1-octadecene(ODE)with Y2(CO3)3· xH2O,Er2(CO3)3· xH2O,Na2CO3 and NH4F as precursors.This proposed method was simple and less toxic compared with generally used method so far.The XRD results showed that the molar ratio of OA/ODE and the temperature were key factors for phase control of NaYF4:Er NCs.The UC emission spectra were obtained with the emission wavelength at about 980 nm(4I11/2→4I15/2),800 nm(4I9/2→4I15/2),660 nm(4F9/2→4I15/2)and 540 nm(4S3/2→4I15/2)from Er3+ ions,by excitation wavelength of 1550 nm.The slope values,n,in the pump-power dependence,showed that the emission at 980 and 800 nm were generated by 2-step UC and at 660 nm and 540 nm were 3-step UC.The optical process for the UC excitation was discussed.     

Luminescent Properties of SrGa2S4 :Eu and Its Application in Green-LEDs

Phosphor SrGa2S4Eu2 was synthesized with a high temperature solid state reaction.Its absorption spectrum, photoluminescence spectra, and fluorescence lifetime were studied in details.The excitation spectrum extended from UV to visible light region, and matched the emission of GaN chip.(Sr1-xEux)Ga2S4 emits strong green light and the concentration quenching did not occur; while the thermal quenching was evident.The emission peak shifted to long wavelength with increasing Eu2 concentration because of the changing of the crystal field strength.The lifetime of Eu2 ion was in the order of microsecond, which was reasonable for d→f transition.The electroluminescence spectrum of as-fabricated PC-LED at IF=20 mA was measured and most of the blue light of blue-LED chip at 460 nm was absorbed by the phosphor and simultaneously down-converted into an intensive green light at 540 nm.The color coordinate was (0.32, 0.63).SrGa2S4Eu2 was a promising phosphor for GaN-based green LEDs.     

Photoluminescent properties of LaF3：Eu^3＋ and GdF3：Eu^3＋ nanoparticles prepared by co-precipitation method

LaF₃:Eu³⁺ and GdF₃:Eu³⁺ nanoparticles were prepared by a co-precipitation method in the presence of the chelating agent, citric acid. The structural properties of the products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The average crystallite size was estimated from the full-width at half-maximum (FWHM) of the diffraction peaks by the Scherrer equation. The sizes of the nanoparticles were 12 nm for LaF₃:Eu³⁺ and 17 nm for GdF₃:Eu³⁺. The luminescent properties of the nanoparticles were investigated by excitation and emission spectra. Energy transfer from Gd³⁺ to Eu³⁺ was observed.     

Influence of Molten Salt on Luminescent Intensity and Particle Size of Y2O3 ：Eu^3＋ Phosphor

The Y-Eu oxalate precursor was prepared with a homogeneous precipitation method. And the additives, Na2CO3, S, NaCl or their combination, were introduced into the precursor to prepare Y2O3 ：Eu^3＋ red phosphors at 1000 1300 ℃ for 2 h. The effect of molten salts on particle size and luminescent intensity was studied. The experimental results showed that the complex molten salt （Na：CO3 ＋ S ＋ NaCl） was conductive to enhance the luminescent intensity of Y2O3 ：Eu^3＋. The emission intensity of the phosphor prepared with these additives at 1300 ℃ was about 45% higher than that of the one prepared without molten salt, and about 11% higher than that of the corresponding commercial phosphor. Meanwhile, the particle size of Y2O3 ：Eu^3＋ phosphor was controlled effectively with the molten salt.     

Preparation and luminescent properties of MgTiO3：Eu3＋ phosphor for white LEDs

A novel red phosphor Eu3+ doped magnesium titanate (MgTiO3) was synthesized via sol-gel method. The X-ray diffraction patterns (XRD) revealed that a pure MgTiO3 phase was obtained. Its excitation spectrum consisted of a broad band (<350nm) and a series of narrow bands in the long wavelength, and the strongest excitation peak at 465nm might be exited by GaN-chip to emit red light for white LED. The phosphors showed strong emission at 614nm which could be attributed to the 5D0→7F2 emission of Eu3+ . The emission intensity of MgTiO3:Eu3+ phosphor reached the maximum at the Eu3+ concentration of 3.5mol.%. The luminescent properties (such as emission intensity and decay times) were further improved by introducing Al3+ as a charge compensator, demonstrating potential applications in white LED.     

Phase structure and temperature dependent luminescence properties of Sr2LiSiO4F: Eu2+ and Sr2MgSi2O7: Eu2+ phosphors

Green-emitting Sr2LiSiO4F:Eu2+ and blue-emitting Sr2MgSi2O7:Eu2+ phosphors were synthesized by the conventional high temperature solid-state route,respectively.Their structures and photoluminescenee properties were comparatively investigated.It was found that the mixture phases of Sr2MgSi2O7 and SrF2 were obtained when a part of Sr2+ in Sr2LiSiO4F was replaced by some amount of Mg2+ in order to design the possible SrMgLiSiO4F:Eu2+ phosphor.Based on the photoluminescence analysis,Sr2LiSiO4F:Eu2+ phosphor exhibited a green broad emission band of main peak at 513 nm under the excitation of 365 nm,while the Sr2MgSi2O7:Eu2+ and SrMgLiSiO4F:Eu2+ phosphor showed blue emission centered at 467 nm.The temperature dependent photoluminescence properties and room temperature decay time for the three kinds of phosphors were also discussed in this paper.     

Novel phosphors of Eu^3＋, Tb^3＋ or Tm^3＋ activated LaBGeO5

Rare earth borogermanates as a group of stable compounds provided various potential properties important for modern sciences. Among the properties of interests, luminescence was manifested due to the variability of rare earth elements and the compounds constituted an important group of potential candidate. In this work, novel phosphors of Eu³⁺, Tb³⁺ or Tm³⁺ doped LaBGeO₅ with the stillwellite type structure were synthesized by the solid state reaction method. Their X-ray and UV excitation luminescent properties showed that LaBGeO₅ was an excellent host lattice for the luminescence of Eu³⁺, Tb³⁺ and Tm³⁺. The LaBGeO₅:Eu³⁺, LaBGeO₅:Tb³⁺ and LaBGeO₅:Tm³⁺ presented bright red, green and blue emission light for both UV and X-ray excitation.     

Characterization of Superfine Sr2CeO4 Powder Prepared by Microemulsion-Heating Method

Powder phosphor of Sr2CeO4 is prepared by microemulsion-heating method and a film of the phosphor on ITO glass is formed by electrophoretic deposition. Field emission scanning electron microscopy (FE-SEM) images show that the powder fired at 850 ℃ for 4 h has a spherical shape with an average diameter of 70 ～ 80 nm whereas the powder sintered at 900 ℃ for 4 h and 1000 ℃ for 4 h have shuttle-like and spherical shapes, respectively, with both sizes less than 1 μm.X-ray diffraction (XRD) patterns indicate that the superfine Sr2CeO4 exhibits an orthorhombic crystal structure. Roomtemperature photoluminescence (PL) measurements show that there are three excitation peaks located at around 262, 280and 341 nm, and all the Sr2CeO4 samples display an intense blue emission at 470 nm with CIE coordinate of (x, y) =(0.176, 0.283). The quantum yield of phosphor is high up to 0.47 ± 0.04. Compared with Sr2CeO4 samples prepared with traditional high-temperature heating, the phosphor synthesized with this method has a smaller size, lower calcination temperature, and shorter calcination time, and the main excitation and emission bands are blue shifted about 30 and 12 nm respectively. The startup voltage for Sr2CeO4 film on ITO glass shifts from 2700 to 4000 V with increasing thickness of the film.     

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%.     

Hydrothermal synthesis and luminescent properties of Li_xEu_xSr_（1-2x）MoO_4 red phosphor

LixEuxSr1-2xMoO4 red phosphors were synthesized via a facile hydrothermal method with various reaction time and ion contents of Eu3+ and Li+.As-synthesized samples were characterized by X-ray diffraction(XRD),thermogravimetry(TG),field emission scanning electron microscopy(FE-SEM) and fluorescence spectrophotometry.The XRD results revealed the formation of scheelite-like phosphor structures.The excitation spectra indicated the presence of two main excitation peaks located at 396 and 466 nm,suggesting that t...     

Luminescence enhancement of BaMgSiO4：Eu^2＋ by adding borate as flux

The luminescence of EU^2＋ in BaMgSiO4 with BaB2O4 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 BaB2O4 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.     

Flux and concentration effect on Eu^3＋ doped Gd2（MoO4）3 phosphor

A novel red emitting phosphor Gd2（MoO4）3：Eu^3＋ was prepared by solid reaction, using Gd2O3, Eu2O3 and WO3 as starting matedals and NH4F as flux. The effects of flux content and Eu^3＋ concentration on the crystal structure, morphology and luminescent properties were investigated using XRD, SEM and fluorescent spectrum measurement. The XRD patterns showed that the resultants had the monoclinic structure. With the increase in flux amount, their crystallization significantly improved. The SEM images indicated that the mean size of the phosphor particles was around 2 μm, and agglomeration of the phosphor particles appeared while introducing higher flux amount. The excitation spectra exhibited more intense f-f transitions originating from ground state 7^F0 to upper states 5^L6 and 5^D2 than the charge transfer band. The concentration quenching of Eu^3＋ emission indicated that energy transfer from Eu^3＋ to molybdate host existed even at lower Eu^3＋ concentration.     

Investigation on luminescence of red-emitting Mg3Ca3(PO4)4:Ce3+,Mn2+ phosphors

To realize red emission, the Ce3+-Mn2+ activated Mg3Ca3(PO4)4 phosphors were synthesized by solid-state reaction. The phase and luminescence properties of the as-prepared samples were characterized by ...     

Electronic structure of the SrAl2O4：Eu^2＋ persistent luminescence material

The electronic structure of the strontium aluminate (SrAl₂O₄:Eu²⁺) materials was studied with a combined experimental and theoretical approach. The UV-VUV synchrotron radiation was applied in the experimental study while the electronic structure of the non-optimized and optimized crystal structure were investigated theoretically by using the density functional theory. The structure of the valence and conduction bands as well as the band gap energy of the material together with the position of the Eu²⁺ 4f^{7 8}S_7/2 ground state were calculated. The calculated band gap energy (6.4 eV) agreed well with the experimental value of 6.6 eV. The valence band consisted mainly of oxygen states whereas the bottom of the conduction band of strontium states. In agreement with the experimental results, the calculated 4f^{7 8}S_7/2 ground state of Eu²⁺ lies in the energy gap of the host. The position of the 4f⁷ ground state depended on the Coulomb repulsion strength. The position of the 4f⁷ ground state with respect to the valence and conduction bands was discussed using theoretical and experimental evidence available.     

Luminescence Properties of Green-Emitting Phosphor (Ba1-x,Srx)2SiO4:Eu2+ for White LEDS

The (Ba1-xSrx)2SiO4∶Eu2 green-emitting phosphors were synthesized by conventional solid-state reaction in a CO-reductive atmosphere, and their luminescent properties were investigated. The XRD data show that the Ba/Sr ratio not only affects the lattice parameters, but also influences the emission peak. The excitation spectra indicate that this phosphor can be effectively excited by UV light from 370 to 470 nm. The emission band is due to the 4f65d1→4f7 transition of the Eu2 ion. With an increase in x, the emission band shifts to longer wavelength and the reason was discussed. The emission spectra exhibit a satisfactory green performance under different excitation wavelength(380, 398, 412, 420, 460 nm). (Ba1-xSrx)2SiO4∶Eu2 is a promising phosphor for green white-lighting-emission diode by ultraviolet chip.     

Preparation and characterization of flower-like SrAl2O4:Eu2+,Dy3+ phosphors by sol-gel process

A flower-like Eu2+ and Dy3+ co-doped SrAl2O4 long-lasting phosphorescent (LLP) phosphor was synthesized via the inorganic- salt-based sol-gel method.The crystal structure,morphology and optical properties of the composite were characterized.X-ray diffraction diffu-sion (XRD) data and DSC-TG curves of the phosphor revealed that the SrAl2O4 crystallites have been formed after the precursor was calcined at 900 °C and to be single-phase SrAl2O4 at 1100 °C.The SEM photographs indicated that the sample exhibited ...     

A green-yellow emitting β-SreSiO4：Eu^2＋ phosphor for near ultraviolet chip white-light-emitting diode

Sr2SiO4：xEu^2＋ phosphors were synthesized through the solid-state reaction technique. The crystal phase of Sr2SiO4：xEu^2＋ phosphor manipulated by Eu^2＋ concentration was studied. The phase transited from β to α＇ in Sr2SiO4：xEu^2＋ phosphor with increasing europium concentration. The single β phase was formed as x≤005 and changed α＇ phase when x〉0.01. The emission spectrum of the β-Sr2SiO4：Eu^2＋ phosphor consisted of a green-yellow broadband peaking at around 540 nm and a blue band at 470 nm under near ultraviolet excitation. The white LEDs by combining near ultraviolet chips with β-Sr2SiO4：Eu^2＋ phosphors were fabricated. The luminous efficiency （15.7lm/W） was higher than α＇-Sr2SiO4：Eu^2＋ phosphor white LED.