Design of luminescence in(Sr,Gd)Li(Al,Mg)_(3)N_(4):Eu^(2+)deep red phosphors via crystal field engineering for full-spectrum WLEDs

Red phosphor,with longer wavelength,is highly desirable for full-spectrum WLEDs.Targeted deep red phosphors(Sr,Gd)Li(AI,Mg)_(3)N_(4):Eu^(2+)were designed from the initial model of SrLiAl_(3)N_(4):Eu^(2+)by structural modification.The correlations among structural evolution,crystal-field environment,and luminescence properties were elucidated.Replacing Sr^(2+)with Gd^(3+)in(Sr,Gd)LiAl_(3)N_(4):Eu^(2+)leads to the enhanced crystal field splitting,larger Stokes shift,and increased structural polyhedron distortion differences,consequently resulting in spectral red-shift and broadening.For further spectral tuning,Mg,with lower electronegativity,was also introduced to modify the local crystal structure,consequently resulting in a further red-shift towards 675 nm and enhanced photoluminescence intensity in(Sr,Gd)Li(AI,Mg)_(3)N_(4):Eu^(2+).What’s more,w-LEDs were fabricated by using blue LED chip,blue,green,red and deep red((Sr,Gd)Li(Al,Mg)_(3)N_(4):Eu^(2+))phosphors whose color rendering index were Ra 96.0 and R997.7.All above results demonstrate that the partial replacements of Sr^(2+)by Gd^(3+)and Al^(3+)by Mg^(2+)are effective methods for spectral modulation and(Sr,Gd)Li(AI,Mg)_(3)N_(4):Eu^(2+)phosphors are suitable for highquality full-spectrum WLEDs.

Photoluminescence properties of Sm^(3+)-doped LiY(MoO_4)_2 red phosphors

A series of novel Sm3＋-doped LiY（MoO4）2 red phosphors under the UV excitation were synthesized by solid state reaction at 800 ℃ for 7 h. The data measured by X-ray diffraction （XRD） indicated that the samples were all pure phases of LiY（MoO4）2. Their excitation spectra had a broad band ranging from 250 to 350 nm and several sharp peaks. The centers of the peaks were located at about 365 nm （6H5/2→4D3/2）, 378 nm （6H5/2→rp7/2）, 406 nm （6H5/2→4FT/2）, 420 nm （6H5/2→6ps/2）, 442 nm （6H5/2→4Gg/2）, 471 nm （6H5/2→4I13/2） and 482 nm （6H5/2→419/2）, respectively. The strongest emission was excited by 406 nm, and the main emissions were located at 568 nm （4G5/2→6Hs/2）, 610 nm （4Gs/2→rH7/2）, 649 nm （4G5/2→6H9/2） and 710 nm （4Gs/2→6HII/2）. Photoluminescence prop- erties were determined for various concentrations of Sm3＋-doped LiY（MoO4）2 host, and the luminescence intensity had the best value when x=0.02 in LiYix（MoO4）2：xSm3＋.

Preparation,structure and luminescence properties of deep red phosphors SrSiN2:Eu^2+

This paper reported a novel synthetic route to Eu2＋ doped SrSiN2 deep red phosphors for white light-emitting diodes. A series of single-phased and high-efficiency SrSiN2：Eu2＋ red phosphors were synthesized based on this method. Their structure, morphology, luminescence, quantum efficiency （QE） and thermal quenching properties were investigated and compared with those of SrSiN2： Eu2＋ prepared by the conventional route. It was found that the addition of a small amount of Si3N4 could promote the formation of SrSiN2 from Sr2SisN8 phase. A highly uniform rod-shaped morphology was obtained based on this method. The X-ray powder diffraction and the Rietveld refinement analysis identified the preferential crystalline orientation growth. Under the blue light excitation, Eu2＋ doped SrSiN2 phosphors showed excellent optical properties. Compared with those prepared by the conventional approaches, the external QE of SrSiN2：Eu2＋ phosphor was greatly improved, allowing it a promising phosphor for white LEDs.

Enhanced luminescence performances of Mn^(4+)-activated Sr_(4)Al_(14)O_(25)red phosphors by doping with Sc^(3+)ions

A series of non-rare earth Mn^(4+)-activated strontium aluminate phosphors Sr_(4)Al_(14)O_(25):Mn^(4+)co-doped with Sc^(3+)ions were successfully synthesized by a high-temperature solid-state reaction method.XRD result reveals that there is no introduction of additional phase but expansion of lattice with incorporation of Sc34 ions.Excitation and emission spectrum measurement shows that the synthesized phosphors can be efficiently excited by near-ultraviolet and blue light,and a deep red emission centered at 652 nm with a narrow full width at half maximum(FWHM)can be obtained,which is attributed to the transition^(2)E→^(4)A_(2)of Mn^(4+)ions.In addition,the crystal field strength parameter(Dq)and Racah parameters(B,C)and energies of states were calculated based on experimental data.Moreover,the luminous intensity of Sr_(4)Al_(14-x)SCxO_(25):Mn^(4+)is enhanced and increased by 60%compared with Mn^(4+)single incorporated sample at x=0.06.A phenomenon of redshift is observed in the excitation spectrum and discussed systematically.Finally,the mechanism of the positive effects with Sc^(3+)ions incorporated into lattice is discussed in detail.All the results suggest that the Sr_(4)Al_(13.94)Sc_(0.06)O_(25):Mn^(4+)phosphor will become one of the great candidates for backlight of LCD.

Synthesis and Luminescence Properties of(Y, Gd)(P, V)O_4:Eu^(3+), Bi^(3+) Red Nano-phosphors with Enhanced Photoluminescence by Bi^(3+), Gd^(3+) Doping

A series of(Y_(1-y), Gdy)_(0.95-x)(P_y, V_(1-y))O_4 :0.05Eu^(3+), xBi^(3+)+phosphors have been successfully prepared by a subsection method. The crystal structure, surface morphology and luminescence properties were investigated. It was found that the sintered samples crystallized in a tetragonal crystal system with space group I_(41)/amd(a = b = 0.7119 nm, c = 0.6290 nm). The products presented rod-like morphology with length of 100-150 nm and width of 50-100 nm. A maximum peak at 619 nm(~5D_0 →~7F_2) was observed in emission spectrum of the phosphors. It was also found that co-doping of Bi^(3+)+, P5+and Gd^(3+)ions into YVO_4:Eu^(3+)can not only made the right edge of the excitation band shift to the long-wavelength region, but also increased the emission intensity at 619 nm sharply and decreased the lifetime of fluorescence decay. These results may expand the application scope of the phosphors.

High temperature stability of Eu^(2+)-activated nitride red phosphors

The novel nitride-based luminescent materials have received much attention since the end of the last century. In this paper, the commercial Eu2＋-activated nitride red phosphors, Sr1.95Si5N8：Eu0.05, Sr1.85Si5N8：Eu0.15 and Ca0.99AlSiN3：Eu0.01 phosphors were an-nealed at different temperatures （beyond 300 oC） to investigate the dependence of their luminescence performance and structure vari-ability on the temperature. By photoluminescence spectra, X-ray diffraction （XRD） and thermogravimetry-differential scanning calo-rimetry （TG-DSC） analysis, the high temperature stability of the hosts and activator of the three samples were disclosed. With the an-nealing temperature increasing, the activator Eu2＋ions were firstly oxidized and then host in Sr1.95Si5N8：Eu0.05 and Sr1.85Si5N8：Eu0.15, but for Ca0.99AlSiN3：Eu0.01, only the oxidation of the host could be observed, which would lead to the luminescence degradation and even failure of these phosphors. The activator Eu2＋ions were much more stable in CaAlSiN3：Eu than Sr2Si5N8：Eu due to their crystal surroundings, and its concentration also influenced the temperature stability of Sr2Si5N8：Eu.

Luminescent properties of red phosphors K_2Ba(MoO_4)_2:Eu^(3+) 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 red phosphors Ca_(10)Li(PO_4)_7:Eu^(3+)

A series of red phosphors Ca10Li （PO4）7：Eu3＋ were synthesized by high temperature solid-state reaction method. Their luminescence properties were characterized by means of photoluminescence excitation and emission spectra,CIE chromaticity and quantum efficiency. Results indicated that the phosphors could be effectively excited by the near ultraviolet （NUV） light （393 nm）. The main emission peaks of the phosphor were ascribed to the transition 5D0–7F2 （613 and 617 nm） of Eu3＋ ion when samples were excited by 393 nm. The CIE chromaticity （x,y） of Ca9.9Li （PO4）7：0.10Eu3＋ was x=0.638,y=0.361 and the quantum efficiency of this phosphor was 75% excited by 393 nm. Therefore,this phosphor could be a promising red component for the applications in white LEDs.

Synthesis of LiEu_(1-x)Bix(MoO_4)_2 red phosphors by sol-gel method and their luminescent properties

The Bi3＋ doped molybdate-based red-emitting phosphors, LiEu1-xBix（MoO4）2, were successfully synthesized with a sol-gel method. The prepared LiEu1-xBix（MoO4）2 phosphors exhibited pure and intense red emission at 613 nm under the excitation of near-UV 394 nm. It was discussed in detail that the influence of the synthesis conditions such as the doping concentration of Bi3, the dose of citric acid, pH of the precursor solution and the sintering temperature on the emission intensity of the phosphors. According to the results, the optimal condition was obtained： the doping concentration of Bi3＋ was 15 mol.%, molar ratio of citric acid to metal ions was 1.5：1, pH of the precursor solution was 1.0 and the sintering temperature was 800 ℃. The X-ray diffraction （XRD） patterns of the LiEuo.85Bi0.15（MoO4）2 phosphor prepared under the optimal condition indicated that the phosphor was single phase with tetragonal scheelite structure. The Commission Intemationale de I＇E- clairage （CIE） chromaticity coordinates of LiEuo.85Bio.15（MoO4）2 were （x=0.655, y=0.345）, which were closer to the national television stan- dard committee （NTSC） standard values （x=0.670, y=0.330） than that of a commercial red phosphor of Y202S：Eu3＋（x=0.630, y=0.350）. This LiEuo.85Bi0As（MoO4）2 red phosphor is a promising candidate for the fabrication of white light-emitting diode （W-LED） with near-UV chips.

Enhanced photoluminescence of CaTiO_3:Eu^(3+) red phosphors prepared by H_3BO_3 assisted solid state synthesis

CaTiO3：Eu3＋ red phosphors were prepared using H3BO3 assisted solid state synthesis. The structure and morphology of the obtained sample were observed by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. And the luminescence property was measured using photoluminescence excitation （PLE） and photoluminescence （PL） spectra, respectively. In the excitation spectra, main excitation peaks of the prepared samples were centered at 397 and 465 nm, revealing that these phosphors could be excited by commercial GaN- and InGaN-typed light emitting diodes （LEDs）. Dominant emission peaks of the phosphors were located at 616 nm, owing to the transition of 5D0→7F2 of Eu3＋. In the optimum condition, CaTiO3：3%Eu3＋ phosphor was obtained at a sintering temperature of 1200 °C in air with a content of 20 mol.% H3BO3 addition. When excited by 397 nm irradiation, the PL intensity of as-prepared red phosphor was 2.2 times higher than that of samples obtained by traditional solid state synthesis, while the PL intensity was 3 times higher than that excited by 465 nm irradiation. The added H3BO3 improved the crystallinity, and increased the color purity, implying the potential to be a promising red phosphor in white light emitting diodes （WLEDs）.

Enhancing the photoluminescence intensity of CaTiO_3:Eu^(3+) 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 tmiformly 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, 395400 nm） GaN-LEDs. More importantly, PL emission intensity （617 nm） of phosphor Mg0.nCa0.6TiO3：0.03Eu3＋ 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.

Preparation and Long Persistence Red Luminescence of M_ (0.2)Ca_(0.8)TiO_3∶Pr ^(3+) (M=Mg^(2+), Sr^(2+), Ba^(2+), Zn ^(2+)

M 0.2Ca 0.8TiO 3∶Pr 3+(M=Mg 2+, Sr 2+, Ba 2+, Zn 2+) long persistence red phosphors were prepared by solid state reaction. The influence of the partially replacing Ca 2+ in CaTiO 3 with Mg 2+, Sr 2+, Ba 2+, Zn 2+ on the excitation spectra, the emission spectra and the long persistence properties were studied. The results suggest that certain quantity of Mg 2+, Sr 2+, Ba 2+, Zn 2+ which partially replace Ca 2+ can enhance the luminescent intensity and prolong the afterglow persistence of the samples. The intensity of Mg 0.2Ca 0.8TiO 3∶Pr 3+ is above all of the samples. Take Mg 0.2Ca 0.8TiO 3∶Pr 3+ as the basic sample, the influence of Pr 3+ concentrations (C(Pr 3+)) on the long afterglow properties were also studied. The results suggest that when the C(Pr 3+) is 0.10% (mol fraction) the intensity of the sample is the highest. The excitation spectra of all these samples show broad band spectra ranging from 300～500 nm peaking at about 342 nm. The emission spectra also exhibit a broad band peaking at 613 nm (CaTiO 3∶Pr 3+ is 612 nm). XRD research indicates that the crystalline phases change due to the replacement of divalent metal ions.The research on the thermoluminescence spectra of Mg 0.2Ca 0.8TiO 3∶Pr 3+ indicates that the peak is at 107.35 ℃ and the depth of the trap energy is about 0 852 eV.

Luminescence properties of red-emitting Ca_2Al_2SiO_7:Eu^(3+) nanoparticles prepared by sol-gel method

A series of red-emitting Ca2_xA12SiOT：xEu^3＋ （x = 1 mol.%-10 tool.%） phosphors were synthesized by the sol-gel method. The effects of annealing temperature and doping concentration on the crystal structure and luminescence properties of Ca2A12SiO7：Eu^3＋ phosphors were investigated. X-ray diffraction （XRD） profiles showed that all peaks could be attributed to the tetragonal Ca2A12SiO7 phase when the sample was annealed at 1000℃. Scanning electron microscopy （SEM） micrographs indicate that the phosphors have an irregularly rounded mor- phology with particles of about 200 nm. Excitation spectra showed that the strong broad band at around 258 nm and weak sharp lines in 350-490 nm were attributed to the charge transfer band of Eu^3＋-O^2- and f-f transitions within the 4f^6 configuration of Eu^3＋ ions, respectively. Emission spectra implied that the red luminescence could be attributed to the transitions from the ^5D0 excited level to the 7Fj （J = 0, 1, 2, 3, 4） levels of Eu3＋ions with the main electric dipole transition ^5D0→^7F2 （618 and 620 nm）, and Eu^3＋ ions prefer to occupy a lower symmetry site in the crystal lattice. Moreover, the photoluminescence （PL） intensity was strongly dependent on both the sintering temperature and doping concentration, and the highest PL intensity was observed at an Eu^3＋ concentration x = 7 mol.% after annealing at ll00℃. The obtained Ca2A12SiO7：Eu^＋3＋ phosphor may have potential application for the red lamp phosphor.

Luminescent properties of Ca_2SiO_4: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 Red Phosphor CaO:Eu^(3+)

Ca（NO3）2·4H2O, Eu（NO3）3 and H2C2O4·2H2O were adopted to synthesize CaO： Eu3＋ with the chemical co-precipitation method, and the effects of the calcination temperature and Eu3＋ doping concentration on the phosphor structure and its luminescent properties were investigated by TG-SDTA, XRD, and PL-PLE. The results confirm that the Eu3＋ ions as luminescent centers substi-tutes Ca2＋ sites without changing the crystal structure of cubic CaO. The optimum calcination tem-perature and the optimum concentration of Eu3＋ are 1 100 ℃ and 1 mol%, respectively, under which the best crystallinity and highest PL intensity appeared. The maximum emission wavelength is 592 nm （5D0→7F1） which is excited by xenon lamp with the wavelength of 200-280 nm, indicating that the Eu3＋ ion mainly locates in the symmetric position （Oh） in the crystal lattice of CaO.

A red oxide phosphor,Sr_2ScAlO_5:Eu^(2+) with perovskite-type structure,for white light-emitting diodes

Sr2ScAlO5：Eu^2＋, a red oxide phosphor with a perovskite-type structure, has been synthesized through a solid-state reaction and its luminescence properties have been investigated. An absorption band centering at 450 nm is observed from the diffuse reflection spectra and the excitation spectra, indicating that the phosphor can match perfectly with the blue light of InGaN light-emitting diodes. A broad red emission band at 620 nm is found from the emission spectra, originating from the 4f^65d-4f^7 transition of the Eu^2＋ ions. The best doping content of Eu in this material is about 5%. S Sr2ScAlO5：Eu^2＋ is a highly promising red phosphor for use in white light-emitting diodes.

Preparation and characterization of nanosized Gd_xBi_(0.95-x)VO_4:0.05Eu^(3+) solid solution as red phosphor

A complete solid solutions with monophasic zircon-type structure of vanadates of formula GdxBio.95-xVO4：0.05Eu3＋ （x = 04）.95） are synthesized by combined method of co-precipitation and hydrothermal synthesis. Their microstructures and morphologies are characterized by X-ray powder diffraction and transmission electronic microscope, and the results show that each of all the samples has a monophasic zircon-type structure. The absorption spectrum of the prepared phosphor shows a blue-shift of the fundamental absorption band edge with increasing the gadolinium content. Under UV-light and visible-light excitation, all the prepared phosphors show the typical luminescence properties of Eu3＋ in the zircon-type structure. The emission intensity of GdxBi0.95-xVO4：0.05Eu3＋ （x = 0.55） is strongest in all samples under UV-light and visible-light excitations. Finally, the mechanisms of luminescence of Eu3＋ in the GdxBi0.95-xVO4：0.05Eu3＋ （x = 0-0.95） solid solutions are analyzed and discussed.

Insights into structural and spectroscopic characterization of Sm^(3+)doped orange rich red emitting CsMgPO_(4)phosphors

In the present study,Sm^(3+)activated inorganic orthophosphate CsMgPO_(4)(CSMP)phosphors were prepared by adopting a solid-state reaction method.The structural phase purity and morphological features were studied by X-ray powder diffraction(XRD)and scanning electron microscopy(SEM),respectively.The molecular structure and vibrational modes were substantiated with the Fourier transform infrared spectroscopy(FTIR)and Raman spectroscopy characterization.The optical bandgap of the host and Sm^(3+)doped phosphors was deduced from the diffused reflectance(DR)spectra with a typical value of 5.72 eV and a small variation is observed with increasing concentrations.A systematic study of photoluminescence(PL)properties of Sm^(3+)doped CSMP phosphors was carried out.From the room temperature excitation and emission spectra,it is found that the phosphor emits in the orange rich red light under the suitable excitation of 402 nm in the UV region and concentration quenching occurs at x=0.02 doping level.The emission peaks observed at around 562,598 and 644 nm confirm the characteristic Sm^(3+)4 f-4 f transitions.The temperature-dependent photoluminescence(TD-PL)of the x=0.02(optimum doping)is recorded from 30 to 210℃,showing good thermal stability even at 150℃.The thermal quenching mechanisms are discussed based on the configuration coordinate model of excitation and emission.The prepared phosphors are found to exhibit near thermal stability compared to the commercially available red phosphors.PL decay time and quantum efficiency were measured.The colour coordinates are found to lie in the orangish-red region of the colour space.Thus the prepared phosphors CSMP:x Sm^(3+)can be useful as a red component in designing UV excitable chip-based phosphor-converted white LED applications.