Synthesis and luminescence property of Sr3SiO5:Eu2+ phosphors for white LED

Sr3SiO5:Eu2+ yellow phosphors for white LEDs were synthesized by high temperature solid state reaction method under a reductive atmosphere. The crystalline phases were examined with X-ray diffraction (XRD). Luminescence properties were studied, and effects of various fluxing agents BaCl2, MgF2, CaF2 and BaF2 on the emission spectra were also studied. The optimal Eu2+ concentration and flux were determined. Sr3SiO5: Eu2+ was obtained by firing the sample on optimal composition and fabrication process. The sa...     

Luminescence properties of Eu2＋ -doped Ba3Si6O12N2 green phosphor： concentration quenching and thermal stability

The efficient Eu2+ -doped Ba3 Si6O12N2 green phosphors were prepared by a traditional solid state reaction method under N2 /H2 atmosphere at a temperature up to 1350 oC for 12h. Photoluminescence (PL) properties showed a broad emission band with a peak of 525 nm and the full width of half-emission maximums (FWHM) of 70 nm under 460 nm light irradiation. The X-ray diffraction patterns (XRD) and scanning electron microscope (SEM) images of the synthesized powder demonstrated its pure phase and excellent crystallization. Quenching concentration in this phosphor was found to be 0.3. The mechanisms of concentration quenching and redshift of emission peak with increasing concentration of Eu2+ were studied. The temperature dependence measurement of this green phosphor revealed excellent thermal quenching property compared to silicate green phosphor. It is believed that Ba3 Si6O12N2 :Eu2+ is an excellent green phosphor for UV or blue chip based white LEDs.     

Synthesis and photoluminescent properties of Sr2Si5N8：Eu^2＋red phosphors for white light-emitting diodes

Highly efficient Sr2Si5N8：Eu^2＋red emitting phosphor was successfully synthesized by a cost-effective direct silicon nitrida-tion and gas-reduction method. The effects of synthesis parameters, including reaction temperature, heating rate and gas species, on the crystal structure and photoluminescence of the prepared phosphors were studied. Single-phase Sr2Si5N8：Eu^2＋phosphor was ob-tained at 1500℃ with a heating rate of 300℃/h under NH3-1 vol.%CH4 atmosphere using starting silicon and oxide powders. Silicon powder and high heating rate favored the achievement of the pure Sr2Si5N8 phase. Under near-UV to blue light excitation, the obtained Sr2Si5N8：Eu2＋phosphor showed a board red emission band centered at about 625 nm, which agreed well with the phosphors prepared by the conventional solid-state reaction. The possible reaction mechanism was also proposed based on the experimental observations.     

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.     

Photoluminescence and thermal quenching properties of tunable green-emitting oxynitride (Ca_xSr_(1–x))_6Si_(25.6)Al_(6.4)N_(41.6)O_(4.4):Eu~(2+) phosphors

Green emitting Eu~(2+) doped(Ca_xSr_(1–x))_6Si_(25.6)Al_(6.4)N_(41.6)O_(4.4) phosphors with x value ranging from 0 to 0.1 were synthesized by the solid state reaction method under nitrogen atmosphere.The X-ray diffraction(XRD)patterns of the phosphors with different Ca~(2+) concentrations indicated that pure sialon phases were obtained.Crystal structure of these sialon phases was estimated to be a commensurate composite network stacking by two different types of layers.Intense and tunable green emissions with a slight red shift from 515 to 520 nm were observed with varying Ca/Sr ratios.The emission intensity decreased gradually because of the increase of the crystal splitting effect.Thermal quenching properties of the phosphors with different Ca~(2+) saturation were also discussed.The thermal stability became worse as more Ca~(2+) ions substituted for Sr~(2+) ions according to a larger Stokes shift.The solid solution phosphors could be a promising candidate for white LEDs for their interesting photoluminescence properties when the thermal stability would be improved.     

Rare earth （Eu2＋,ce3＋） activated BaAIESi2O8 blue emitting phosphor

Blue emitting rare earth（Eu2＋,Ce3＋） doped BaAl2Si2O8 phosphors were synthesized by combustion methods at 600 oC. BaAl2Si2O8： Eu2＋ phosphor showed isolated broad blue emission band at 455 nm, when it was excited with the wavelength of 329 nm. Whereas BaAl2Si2O8：Ce3＋ phosphor exhibited blue emission band at 442 nm, under 303 nm excitation wavelength. These observed emission bands of Eu2＋ and Ce3＋ ions corresponded to 5d-4f allowed transitions. The position of emission band was calculated by using the equationE=Q[1-〔V/4〕^1/V）]× 10 （nEar/80）Also the spin orbit splitting difference in the ground state levels of Ce3＋ ion was studied by Gaussian curve fitting. Broad absorption and emission bands in blue regions made prepared phosphors a promising blue host for the white-LEDs.     

Effect of SiN substituting for AI-O bonds on luminescence properties of Sr3AIO4F：Ce3＋ phosphor

Cerium-doped Sr3（A11-x,Six）O4-xNxF oxynitride phosphors with different x values were synthesized by solid-state reaction. The structure and optical properties of these phosphors were investigated by X-ray diffraction （XRD）, energy dispersive spectroscopy （EDS） and photoluminescence （PL） spectra. The XRD results showed that SiN substitution for Al-O） did not change the structure of Sr3A104F host and there was no impurity for x〈0.6. With the increasing ofx values, the absorption of phosphors at the blue region was enhanced and the emitting band varied from 519 to 529 nm under the 460 nm blue light excitation. The red shift of the emission band was associated with an increase in the crystal-field splitting and the covalence, which arose from the incorporation of N. More- over, the incorporation of N also improved the thermal quenching properties and the external quantum efficiency with a maximum value up to 43.3%, indicating that this phosphor is a promising candidate for white LEDs application.     

Synthesis of Long Afterglow Phosphor CaAl2Si2O8 ：Eu^2＋, Dy^3＋ via Sol-Gel Technique and Its Optical Properties

The long afterglow phosphor CaAl2Si2O8：Eu^2＋ , Dy^3＋ was prepared by a sol-gel method. The sol-gel process and the structure of the phosphor were investigated by means of X-ray diffraction analysis （XRD）. It is found that the single anorthite phase formed at about 1000 %, which is 300 % lower than that required for the conventional solid state reaction. The obtained phosphor powders are easier to grind than those of solid state method and the partical size of phosphor has a relative narrow distribution of 200 to 500 nm. The photoluminescence and afterglow properties of the phosphor were also characterized. An obvious blue shift occurs in the excitation and emission spectra of phosphors obtained by sol-gel and solid state reaction methods. The change of the fluorescence spectra can be attributed to the sharp decrease of the crystalline grain size of the phosphor resulted from the sol-gel technique.     

Synthesis and Characterization of Cerium-Doped Lutetium Aluminum Garnet Phosphors by Nitrate-citrate Sol-Gel Combustion Process

Nanosized cerium-doped lutetium aluminum garnet （LuAG：Ce） phosphors were prepared by nitrate-citrate solgel combustion process using 1：1 ratio of the citrate：nitrate. The prepared LuAG：Ce phosphors were characterized by XRD, TEM, photoluminescence and radioluminescence spectra excited by UV and X-ray, respectively. The purified crystalline phase of LuAG：Ce was obtained at 900 ℃ by directly crystallizing from amorphous materials. The resultant Lu- AG：Ce phosphors were uniform and had good dispersivity with an average particle size of about 30 urn. Both photoluminescence and radioluminescence were well-known Ce^3＋ emissions located in the range of 470 -600 nm consisting of two emission bands because of the transition from the lowest 5d excited state （2D） to the 4f ground state of Ce^3＋, which matched well with the sensitivity curve of the Si-photodiode. There was a little red shift for the emission components from the UV-excited emission spectrum to the X-ray-excited emission spectrum. The fast scintillation decay component of 26 ns satisfies the requirements of fast scintillators.     

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）.     

New Rare-Earth Containing （Sr1- yEuy）2 Al2Si10S14O4 Phosphors for Light-Emitting Diodes

Remarkable progress was made in the development of white-light-emitting diodes （LEDs）. White LEDs provided a light element having a semiconductor InGaN light-emitting chip （blue or UV LEDs） and luminescent phosphors. Here we reported the sialon s-phase of （Sr,Eu）2A12Si10N14O4. Eu^2＋ activator ions that were substituted for the strontium site represented a new type of yeUow-green phosphor that could be excited by blue LEDs used for application in the fabrication of white 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%.     

Photoluminescence properties of Ca-doped BaMg Al10O17）：Eu2＋,Mn2＋ blue phosphor using BaF2 and CaF2 as co-flux

Ca-doped Ba Mg Al10O17：Eu2＋,Mn2＋（BAM） blue phosphors were synthesized by flux assisted solid-state reaction method using Ca F2 and Ba F2 as co-flux.Good dispersity and particle size homogenization of hexagonal pure phase BAM were obtained by sintering at 1400 ℃.The effects of the Ca2＋ ions content on the structure, morphology and photoluminescence properties of the phosphors were studied.The results indicated that the incorporation of Ca could decrease the lattice constant, improve the homogeneity and dispersity and enhance the photoluminescence（PL） intensity of the phosphor effectively.The optimum Ba0.86Ca0.04Mg0.97Al10O17：0.1Eu2＋,0.03Mn2＋ PL intensity was enhanced for about 30% and relative brightness was improved about 4%.Furthermore, the synthesized BAM and commercial BAM phosphors were annealed for 30 min at 600 oC in air.The Ca-doped phosphors had stronger emission intensity, higher brightness and better chromaticity stability than that of the commercial phosphor.These results indicated that Ca-doped blue phosphors had good potential applications in the commercial tricolor fluorescent lamps as well as in other display and lamps.     

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%.     

Luminescence properties of nitride red phosphor for LED

Eu^2＋-doped ternary nitride phosphor, Sr2Si5N8：Eu^2＋, was synthesized using the high temperature solid-state method. The X-ray diffraction （XRD） pattern showed that Sr2Si5N8 single phase was obtained. The lattice parameters shrank because the radius of Eu^2＋ was smaller than that of Sr^2＋. The emission spectra showed a broad emission band. With an increase in Eu^2＋ concentration, the emission peak position was redshifted. The excitation spectra showed two excitation bands originating from the host and the 4f^7→4f^6 5d^1 transition of Eu^2＋ ions Compared with the luminescent characteristic of Sr2Si5N8：Eu^2＋ and CaS：Eu^2＋ phosphors, at different temperatures, it was noted that the intensity of the two phosphors reduced gradually with an increase in temperature. The intensity of Sr2Si5N8：Eu^2＋ phosphor was stronger than that of CaS：Eu^2＋, which indicated that the luminescent characteristic of the former was better than that of the latter.     

A green-yellow emitting β-Sr2SiO4:Eu2+ phosphor for near ultraviolet chip white-light-emitting diode

Sr2SiO4:xEu2 phosphors were synthesized through the solid-state reaction technique. The crystal phase of Sr2SiO4:xEu2 phosphor manipulated by Eu2 concentration was studied. The phase transited from β to α′ in Sr2SiO4:xEu2 phosphor with increasing europium concentration. The single β phase was formed as x≤0.005 and changed α′ phase when x>0.01. The emission spectrum of the β-Sr2SiO4:Eu2 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:Eu2 phosphors were fabricated. The luminous efficiency (15.7 lm/W) was higher than α′-Sr2SiO4:Eu2 phosphor white LED.     

Photoluminescence properties of Ce3+ doped YSiO2N blue-emitting phosphors

Oxonitridosilicate phosphors with compositions of Y 1-x Ce x SiO 2 N (x=0-0.1) were synthesized by a new synthetic route based on a solid state reaction among YSi, CeSi, SiO 2 and Y 2 O 3 compounds at high temperature and high pressure. The photoluminescence properties dependent on Ce concentration and temperature were investigated. Concentration quenching occurred when the doped Ce 3+ concentration was more than 3 mol.%. The emission spectra showed red shifts from 430 to 447 nm with the increased Ce concentration from 0.5 mol.% to 10 mol.%. The quenching temperature was estimated as ～380 K. The chromaticity coordinates of the excitation and emission spectra were stable against the temperature. This study showed these YSiO 2 N:Ce 3+ phosphors the potential applications in the three-RGB phosphor-converted white LEDs.     

Synthesis and luminescence properties of Sr3-z（AlxSi1-x）O5-xFx：zCe^3＋phosphors

Sr3-z(Alx,Si1-x)O -5-xFx:zCe3+ phosphors were synthesized by high-temperature solid-state reaction.The structure and luminescence properties of phosphors with various Al/Si ratios and Ce3+ concentrations were characterized using various methods such as X-ray diffraction,photoluminescence excitation and photoluminescence spectra.XRD result displayed that a complete solid solution between Sr3AlO4F and Sr3SiO5 was formed.With the increasing of x value,a broader excitation band and stronger absorption appeared in the blue light region.Moreover,the emission band shifted to a shorter wavelength and the emission intensity reached a maximum at x=0.6.By adjusting the concentration of Ce3+,a widely tunable range of emission wavelength under the excitation of 460 nm was obtained from the green to yellow regions.In addition,the concentration and thermal quenching were also discussed.     

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.     

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 inves-tigated 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 ef-ficient energy transfer from Eu2+ to Mn2+ in Ba0.98-xSrxMg1-ySiO4:0.02Eu2+,yMn2+. Ba0.93Sr0.03Mg1-ySiO4:0.02Eu2+,yMn2+ could emit three ef-ficient 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.