Synthesis and photoluminescence of Eu by co-doping Eu and Cl in Sr2P2O7 under air atmosphere

A novel phosphor Sr₂P₂O₇ co-doped with europium ion and chlorine ion was firstly synthesized by solid state reaction under air atmosphere. Its properties were systematically analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fluorescence spectra. The introduction of chlorine into the system was helpful and necessary to Eu³⁺ substitute Sr²⁺ site and subsequently to reduce Eu³⁺ to Eu²⁺, XPS results confirmed that some amount of Eu³⁺ ions could be reduced to Eu²⁺ ions under air atmosphere at high temperature. The reduction tendency of Eu³⁺ depends not only on the doping Cl⁻ content, but also on the sintering temperature and time. Photoluminescence spectra also revealed that europium ions were present in divalent as well as trivalent oxidation states, the emission peak at 415 nm is ascribed to the typical 5d-4f transition of Eu²⁺, 592 nm and 613 nm assigned to the characteristic transitions of ⁵D₀-⁷F_1,2 of Eu³⁺. Such abnormal reduction was attributed to the electronegative defects formed by nonequivalent substitution of Eu³⁺ on the Sr²⁺ sites in the investigated phosphors.     

Preparation and luminescent properties of Eu doped Sr3La(PO4)3 phosphor

Eu²⁺-doped Sr₃La(PO₄)₃ phosphors were synthesized by solid-state reaction method. Their luminescent properties were investigated. The phosphor could be excited by ultraviolet light effectively. The emission spectra exhibit two emission peaks located at 418 nm and 500 nm, respectively. These two peaks originated from two different luminescent centers, respectively. One is nine-coordinated Eu(I) center, other is six-coordinated Eu(II) center. It was found that the doping concentration of Eu²⁺ ions affected the shape of emission spectra. As the doping concentration increasing, Eu²⁺ ions are more likely to form Eu(I) luminescent centers and emit purple light.     

Optical properties of Si-N doped BaMgAl10O17:Eu, Mn phosphors for plasma display panels

The photoluminescence properties of Si-N doped BaMgAl₁₀O₁₇:Eu²⁺, Mn²⁺ phosphors were studied. Photoluminescence spectrum, powder X-ray diffraction and decay curves were used. The electronic structure of un-doped BaMgAl₁₀O₁₇ was investigated by using the density functional theory. It reveals that an ideal hexagonal shape and particle size in 3-5 μm are obtained by Si-N doping. Additionally, its photoluminescence and thermal stability are both improved. The energy transfer from Eu²⁺ to Mn²⁺ also enhanced by suitable Si-N doping. These are expected to be potentially applicable to industrial production of the phosphor in plasma display panels.     

Blue and green emissions with high color purity from nanocrystalline Ca2Gd8Si6O26:Ln (Ln = Tm or Er) phosphors

Blue and green light emissive nanocrystalline Ca₂Gd₈Si₆O₂₆ (CGS):Tm³⁺ and CGS:Er³⁺ phosphors with high color purity were prepared by solvothermal reaction method. The structural and morphological properties of these phosphors were evaluated by the powder X-ray diffraction (XRD) and scanning electron microscopy, respectively. From the XRD results, Tm³⁺:CGS and Er³⁺:CGS phosphors had the characteristic peaks of oxyapatite in the hexagonal lattice structure. The visible luminescence properties of phosphors were obtained by ultraviolet (UV) or near-UV light and low voltage electron beam (0.5-5 kV) excitation. The photoluminescence and cathodoluminescence properties were investigated by changing the variation of Tm³⁺ or Er³⁺ concentrations and the acceleration voltage, respectively. The CGS:Tm³⁺ phosphors exhibited the blue emission due to ¹D₂→³F₄ transition, while the CGS:Er³⁺ phosphors showed the green emission due to ⁴S_3/2→⁴I_15/2 transition. The color purity and chromaticity coordinates of the fabricated phosphors are comparable to or better than those of standard phosphors for lighting or imaging devices.     

Synthesis and photoluminescence properties of color-tunable BaLa2WO7:Eu phosphor

Color-tunable phosphors BaLa_2−xEu_xWO₇ were synthesized via a solid-state reaction. The absorption, excitation, emission and decay curves were obtained to study the luminescence properties. The experimental results indicate that BaLa_2−xEu_xWO₇ phosphors have two regions in the excitation spectra: one is assigned to the charge-transfer state (CTS) band at about 338 nm, and the other is assigned to the intra-4f transitions at 360-600 nm. The emission spectra of BaLa_2−xEu_xWO₇ phosphors excited at 395 nm exhibit a series of sharp peaks, which are attributed to the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions. Luminescence from higher excited states, such as ⁵D₁, ⁵D₂, and ⁵D₃, were also observed at low Eu³⁺ concentration. The optimal emission intensity of ⁵D₀ → ⁷F₂ red emission is at x = 0.4 (BaLa_1.6Eu_0.4WO₇). The chromaticity coordinates of BaLa_2−xEu_xWO₇ phosphors vary with Eu³⁺ content from white, orange-red, to red, making it a candidate for a white-light-emitting phosphor in UV-LEDs.     

Blue-emitting phosphor M2B5O9Cl: Eu (MSr, Ca) for white LEDs

Eu²⁺ doped M₂B₅O₉Cl (MCa, Sr) phosphors were prepared by a solid-state reaction method. Luminescent properties of as-synthesized phosphors were investigated under the excitation of near-ultraviolet (n-UV) light. Photoluminescence (PL) spectra revealed a blue emission band, and the emission band shifted to a longer wavelength region as Ca²⁺ substituted Sr²⁺. The photoluminescence excitation (PLE) spectra of M₂B₅O₉Cl: Eu²⁺ (MCa, Sr) showed broadband absorptions in the n-UV region. Moreover, the as-prepared phosphors were also compared with commercial BaMgAl₁₀O₁₇: Eu²⁺ (BAM) blue phosphor. The present phosphors showed a narrower full width at half-maximum and higher PL intensity than the reference BAM under the n-UV light excitation.     

Cr doping optimization in CaAl2O4:Eu blue phosphor

A new composition of phosphor material CaAl₂O₄:Eu²⁺ co-doped with Cr³⁺ was investigated. Various compositions with Eu²⁺ (1 and 2 mol%) and Cr³⁺ (0.05–0.1 mol%) were prepared by solid-state reaction method. These compositions show high brightness and longer persistent luminescence. Phase and crystallinity were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Excitation and emission spectra were taken to investigate the luminescence characteristics. Broad band UV excited luminescence of the CaAl₂O₄:Eu²⁺, Cr³⁺ was observed in the blue region (λ_max = 440 nm) due to transitions from 4f⁶5d¹ to the 4f⁷ configuration of the Eu²⁺ ion. Cr³⁺ ion co-doping generates deep traps which results in longer afterglow phosphorescence compared to parent phosphor.     

Synthesis and luminescence properties of Bi-doped YVO4 phosphors

YVO₄:Bi³⁺ phosphors have been prepared by a convenient high-temperature solid-state method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) technologies are used to study the luminescence properties of YVO₄:Bi³⁺ phosphors. The emission and excitation spectra of Bi³⁺ in the YVO₄ lattice have been investigated at room temperature. The excitation band peaks at 330 nm in a region among 250-400 nm, and the emission spectrum exhibits an intense yellowish-white broad emission centered at about 543 nm covering from 400 nm to 800 nm. The full width at half maximum (FWHM) is about 144 nm. The color coordinates of the as-synthesized YVO₄:Bi³⁺ phosphors are in a range of x = 0.358-0.374, y = 0.482-0.496. The dependence of the luminescence intensity on Bi³⁺ concentrations and heat treatment condition has also been discussed. In addition, we found that a little amount of flux NH₄Cl could enhance the Bi³⁺ luminescence intensity.     

Effects of RE^3＋（RE=La,Ce,Pr,Sm,Dy,Ho,Er,and Tm） on the luminescence of Sr2MgSiO5：Eu^2＋ phosphors

Sr2MgSiO5:Eu2+phosphors were synthesized through a high temperature solid state reaction method.The phase and luminescence properties of the samples were characterized by X-ray diffraction(XRD) and a luminescence spectrometer.The effects of RE3+(RE = La,Ce,Pr,Sm,Dy,Ho,Er,and Tm) on the luminescent properties of the samples were studied.The results show that the luminescence spectrum of Sr2MgSiO5:Eu2+ is a broad band composed of two emission peaks,at 460 and at 530 nm under near-ultraviolet excitation.Rare earth ions Re3+(RE = La,Ce,Pr,Sm,Dy,Ho,Er,and Tm) have great influence on the emission of Sr2MgSiO5:Eu2+ phosphors.The La3+ ion in Sr2MgSiO5:Eu2+ phosphors greatly enhances the emission at 460 and 530 nm.     

Preparation of Dy-activated strontium orthosilicate (Sr2SiO4:Dy) phosphors and its photoluminescent properties

Dy³⁺-activated β/α′-Sr₂SiO₄ phosphors were successfully prepared by solid-state reaction method with ammonium chloride (NH₄Cl) as the flux. The influences of calcination temperatures, amounts of NH₄Cl and the concentrations of Dy³⁺ on phase composition, morphology and the photoluminescent properties of as-prepared powders were investigated in detail. The β and α′ phases of Sr₂SiO₄ were obtained with 1 wt% and 2-5 wt% NH₄Cl, respectively, as the sintered condition was at 1000 °C for 4 h. With increasing the amount of NH₄Cl, the morphology of phosphors changed from needlelike to regular polyhedron shape and the colors of the Sr₂SiO₄:Dy³⁺ phosphors changed from blue-green to white. The luminescence intensity of ⁴F_9/2 → ⁶H_15/2 transition was slightly higher than that of ⁴F_9/2 → ⁶H_13/2 (ΔL = 2, ΔJ = 2) transition owing to the low-symmetry around Dy³⁺ ions. The optimum concentration of Dy³⁺ was 2.0 mol% and the concentration quenching were caused by the d-d interaction and a cross relaxation. The yellow-to-blue intensity ratio (Y/B) of Dy³⁺ emission did not to change with varying the Dy³⁺ concentration using Li⁺ ions for charge compensation. These indicate that this phosphor can be used as a potential candidate for the phosphor-converted white LEDs with a UV chip.     

Luminescence studies of Ba1−xMg2−y(PO4)2:xEu, yMn phosphor

The phosphors BaMg₂(PO₄)₂ doped with Eu²⁺ and Mn²⁺ solely or doubly were prepared by solid state reaction, and their luminescent properties were also investigated. Under the excitation of 322 nm, it has been observed a broad blue emission band centered at 417 nm and a red emission band centered at about 665 nm, resulting from Eu²⁺ and Mn²⁺, respectively. Resonance-type energy transfers from Eu²⁺ to Mn²⁺ were discovered by directly overlapping the emission spectra of Eu²⁺ and the excitation spectra of Mn²⁺. According to the changes of relative intensities of Eu²⁺ and Mn²⁺ emission, efficiencies of energy transfer were calculated. Based on the principle of energy transfer, the relative intensities of blue and red emission could be tuned by adjusting the contents of Eu²⁺ and Mn²⁺.     

Synthesis and luminescent properties of Ln3+ (Ln3+ = Eu3+, Dy3+) -doped Bi2ZnB2O7 phosphors

The new phosphors Bi2ZnB2O7:Ln3+ (Ln3+ =Eu3+,Dy3+) were synthesized by solid-state reaction technique.The obtained phosphors were investigated by means of X-ray powder diffraction (XRD),photoluminescence excitation and emission spectra with the aim of enhancing the fundamental knowledge about the luminescent properties of Eu3+ and Dy3+ ions in the Bi2ZnB2O7 host lattice.XRD analysis shows that all these compounds are of a single phase of Bi2ZnB2O7.The excitation and emission spectra of Bi2ZnB2O7:Ln3+ (Ln3+ =Eu3+,Dy3+) at room temperature show the typical 4f-4f transitions of Eu3+ and Dy3+,respectively.The hypersensitive transitions of 5D0→7F2 (Eu3+) and 4F9/2→ 6H13/2 (Dy3+) are relatively higher than those of the insensitive transitions in Bi2ZnB2O7.It is conceivable that the Bi2ZnB2O7 structure provides asymmetry sites for activators (Eu3+,Dy3+).The optimum concentrations of Eu3+ and Dy3+ ions in Bi2ZnB2O7 phosphors are both x =0.05.     

Influence of La and Dy on the properties of the long afterglow phosphor CaAl2O4: Eu, Nd

The long afterglow phosphor CaAl₂O₄:Eu²⁺,Nd³⁺ was prepared by the high temperature solid-state reaction method, and the influence of La³⁺ and Dy³⁺ on the properties of the long afterglow phosphor was studied by X-ray diffraction (XRD), photoluminescence (PL), and thermoluminescence (TL). The XRD pattern shows the host phase of CaAl₂O₄ is produced and no impurity phase appears. The peak wavelength of the phosphor does not vary with La³⁺ and Dy³⁺ doping. It implies that the crystal field, which affects the 5d electron states of Eu²⁺, is not changed dramatically after doping of La³⁺ and Dy³⁺. The TL spectra indicate that the phosphor doped with La³⁺ or Dy³⁺ produces different depths of trap energy level. In the mechanism of long afterglow luminescence, it is considered that La³⁺ or Dy³⁺ works as trap energy level. The decay time lies on the number of electrons in the trap energy level and the rate of the electrons returning to the excitation level.     

Photoluminescence and thermoluminescence studies of Mg2SiO4:Eu nano phosphor

Nanoparticles of Eu³⁺ doped Mg₂SiO₄ are prepared using low temperature solution combustion technique with metal nitrate as precursor and urea as fuel. The synthesized samples are calcined at 800 °C for 3 h. The Powder X-ray diffraction (PXRD) patterns of the sample reveled orthorhombic structure with α-phase. The crystallite size using Scherer's formula is found to be in the range 50-60 nm. The effect of Eu³⁺ on the luminescence characteristics of Mg₂SiO₄ is studied and the results are presented here. These phosphors exhibit bright red color upon excitation by 256 nm light and showed the characteristic emission of the Eu³⁺ ions. The electronic transition corresponding to ⁵D₀ → ⁷F₂ of Eu³⁺ ions (612 nm) is stronger than the magnetic dipole transition corresponding to ⁵D₀ → ⁷F₁ of Eu³⁺ ions (590 nm). Thermoluminescence (TL) characteristics of γ-rayed Mg₂SiO₄:Eu³⁺ phosphors are studied. Two prominent and well-resolved TL glows with peaks at 202 °C and 345 °C besides a shoulder with peak at ∼240 °C are observed. The trapping parameters-activation energy (E), order of kinetics (b) and frequency factor (s) are calculated using glow curve shape method and the results obtained are discussed.     

Photoluminescence and energy transfer studies on Eu and Ce co-doped SrCaSiO4 for white light-emitting-diodes

The luminescence of SrCaSiO₄:Eu²⁺, Ce³⁺ is studied as a potential ultraviolet light-emitting diodes (UV-LEDs) phosphor that is capable of converting the ultraviolet emission of a UV-LED into green light with good luminosity. There are two emissions peaks peaking at 420 and 500 nm, respectively. The two emissions come from d-f transitions of Ce³⁺ and Eu²⁺, respectively. Effective energy transfer occurs in Ce³⁺/Eu²⁺ co-doped SrCaSiO₄ due to a part of spectral overlap between the emission of Ce³⁺ and excitation of Eu²⁺. Co-doping of Ce³⁺ enhances the emission intensity of Eu²⁺ greatly by transferring its excitation energy to Eu²⁺. The Ce³⁺/Eu²⁺ energy transfer, thoroughly investigated by the diffuse reflection emission and excitation spectra, photoluminescence decay curves, is demonstrated to be in the mechanism of electric dipole-dipole interaction.     

Citric based sol-gel synthesis and luminescence characteristics of CaLa2ZnO5:Euphosphors for blue LED excited white LEDs

A novel class of orange-red phosphors namely CaLa₂ZnO₅ (CLZ) doped with Eu³⁺ ions were prepared by adopting citrate based sol-gel method. Those were thoroughly characterized by means of XRD, SEM, Tg-DTA, photoluminescent (PL) spectral profiles. PL studies reveal that its emission intensity strongly depends on sintering temperature as well as the dopant ion (Eu³⁺) concentration. Eu³⁺ ion doped CaLa₂ZnO₅ phosphor has a strong excitation at 468 nm, which correspond to the popular emission line from a GaN based blue light-emitting diode (LED) chip. The influence of the preparation method on the luminescence property was studied by comparing the emission performance of phosphors prepared by sol-gel and solid-state reaction methods along with a commercial red phosphor Y₂O₂S:Eu³⁺. Thus, the intense red emission (⁵D₀ → ⁷F₂) of the Eu³⁺ doped CLZ phosphors under blue excitation suggests them to be a potential candidate for the production of white light by blue LEDs.     

Luminescence properties of red-emitting Ca<Subscript>2</Subscript>Al<Subscript>2</Subscript>SiO<Subscript>7</Subscript>:Eu<Superscript>3+</Superscript> nanoparticles prepared by sol-gel method

A series of red-emitting Ca2-xAl2SiO7:xEu3+(x = 1 mol.%-10 mol.%) phosphors were synthesized by the sol-gel method.The effects of annealing temperature and doping concentration on the crystal structure and luminescence properties of Ca2Al2SiO7:Eu3+ phosphors were investigated.X-ray diffraction(XRD) profiles showed that all peaks could be attributed to the tetragonal Ca2Al2SiO7 phase when the sample was annealed at 1000℃.Scanning electron microscopy(SEM) micrographs indicate that the phosphors have an irregularly rounded morphology 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 Eu3+-O2-and f-f transitions within the 4f6 configuration of Eu3+ 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 Eu3+ 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 Eu3+ concentration x = 7 mol.% after annealing at 1100℃.The obtained Ca2Al2SiO7:Eu3+ phosphor may have potential application for the red lamp phosphor.     

Effect of surfactants on morphology and luminescent properties of CaMoO4: Eu red phosphors

Using polyethylene glycol (PEG), Tween-80, sodium dodecyl sulphonate (SAS) and cetyltrimethylammonium bromide (CTAB) as surfactants, CaMoO₄: Eu³⁺ red phosphors were prepared by co-precipitation method and their morphology, structure and luminescent properties were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD) and fluorescence spectrometer. The results showed that the introduction of surfactants did not change the crystal structure of CaMoO₄: Eu³⁺ phosphors, but greatly influenced their morphology. CaMoO₄: Eu³⁺ red phosphors were prepared with 5 wt% PEG20000 having small-sized and regularly spherical morphology, and there were greater improvement in the luminescent intensity than phosphors prepared with other surfactants.     

LaPO4:Eu, LaPO4:Ce, and LaPO4:Ce,Tb nanocrystals: Oleic acid assisted solvothermal synthesis, characterization, and luminescent properties

LaPO₄:Ln³⁺ (Ln = Eu, Ce, Tb) nanocrystals were successfully synthesized via a facile solvothermal process in the presence of oleic acid. The as-prepared crystals were well characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), optical spectra as well as the kinetic decay times, respectively. In the synthesis process, oleic acid as a surfactant has played a crucial role in confining the growth and size of the LaPO₄:Ln³⁺ phosphors. All the samples are well crystallized and assigned to the monoclinic monazite-type structure of the LaPO₄ phase. The prepared LaPO₄:Ln³⁺ phosphors present a narrow distribution with an average particle size of about 15 nm. Upon excitation by ultraviolet radiation, the LaPO₄:Eu³⁺ phosphors show the characteristic ⁵D₀-⁷F_1-3 emission lines of Eu³⁺, while the LaPO₄:Ce³⁺,Tb³⁺ exhibits the characteristic ⁵D₀-⁷F_3-6 emission lines of Tb³⁺. It is believed that these rare earth ion doped (Eu³⁺ ion or Ce³⁺ and Tb³⁺ ions co-doped) monoclinic monazite-type LaPO₄ nanocrystals could find potential application as future advanced optical materials.     

Luminescence properties of (Sr0.95?x?yMgxYy)Si2O2?yN2+y:Eu2+0.05 for novel LED conversion phosphors

By incorporating Mg and Y into SrSi₂O₂N₂:Eu²⁺ phosphor, we intended to improve the relatively high thermal quenching and poor efficiency of emission in conventionalSrSi₂O₂N₂:Eu²⁺ phosphors. MSi₂O₂N₂:Eu²⁺ _0.05 (M = Sr, Mg, Y) compounds were synthesized by ahigh-temperature solid-state reactionand were characterized using X-ray power diffraction as well as excitation and emission spectroscopy. As compared to the pure SrSi₂O₂N₂:Eu²⁺ _0.05, the emission intensity of the new MSi₂O₂N₂:Eu²⁺ _0.05 (M = Sr, Mg, Y) compound was increased by 65 %. Meanwhile, it was also possible to improve the ratio of thermal quenching up to 88 % by substituting the Sr with Mg and/or Y in the SrSi₂O₂N₂:Eu²⁺ _0.05 crystal structure. This improvement was mainly due to the intrinsic electronic negativity and size effect of Y³⁺, which leads to the shrinkage of the O/N ratioand the relaxation of local strain around the Eu²⁺ ion in the (Sr_0.95−x−yMg_xY_y)Si₂O_2−yN_2+y:Eu²⁺ _0.05 structure. Consequently, the (Sr_0.68Mg_0.27)Si₂O₂N₂:Eu²⁺ _0.05 phosphor is expected to be useful as a novel conversion phosphor with high thermal stability for white-light LEDs.