A promising red phosphor MgMoO4:Eu for white light emitting diodes

Motivated by the need for new red phosphors for solid-state lighting applications Eu³⁺-doped MgMoO₄ was prepared by solid-state reaction and its excitation and emission spectra were measured at room temperature. In addition, the effects of firing temperature and Eu³⁺ doping concentration on the PL intensities were also investigated. Compared with Y₂O₂S:0.05Eu³⁺, the obtained Mg_0.80MoO₄:Eu³⁺_0.20 phosphor shows a stronger excitation band near 400 nm and intensely red-emission lines at 616 nm correspond to the forced electric dipole ⁵D₀ → ⁷F₂ transitions on Eu³⁺ under 394 nm light excitation. The CIE chromaticity coordinates (x = 0.651, y = 0.348) of Mg_0.80MoO₄:Eu³⁺_0.20 close to the NTSC (National Television Standard Committee) standard values, and therefore may find application on near UV InGaN chip-based white light emitting diodes.     

Hydrothermal synthesis and photoluminescence of SrWO4:Tb novel green phosphor

Tb³⁺-doped SrWO₄ phosphors with a scheelite structure have been prepared by hydrothermal reaction. X-ray powder diffraction, field-emission scanning electron microscopy, photoluminescence excitation and emission spectra and decay curve were used to characterize the resulting samples. Scanning electron microscopy image showed that the obtained SrWO₄:Tb³⁺ phosphors appeared to be nearly spherical and their sizes ranged from 1 to 3 μm. Photoluminescence spectra indicated the phosphors emitted strong green light centered at 545 nm under ultraviolet light excitation. Because 12 at.% SWO₄:Tb³⁺ phosphor exhibits intensive green emission under 254 nm excitation in comparison with the commercial green fluorescent lamp phosphor (LaPO₄:Ce,Tb), the excellent luminescence properties make it a new promising green phosphor for fluorescent lamps application.     

Luminescent characteristics of LiSrBO3:M (M = Eu, Sm, Tb, Ce, Dy) phosphor for white light-emitting diode

LiSrBO₃:M (M = Eu³⁺, Sm³⁺, Tb³⁺, Ce³⁺, Dy³⁺) phosphors which have been developed for white light-emitting diodes (LEDs) were synthesized by a normal solid-state reaction. The emission and excitation spectra indicate that these phosphors can be effectively excited by near-ultraviolet light-emitting diodes (UVLED), and exhibit satisfactory red, green and blue performances, respectively, nicely fitting in with the widely applied UV chip. Under the condition of doping charge compensation Li⁺, Na⁺ and K⁺, the luminescence intensities of these phosphors were increased.     

Preparation, characterization and luminescence of La2TeO6 phosphor doped with Eu

Phosphors of La₂TeO₆ doped with Eu³⁺ ions have been synthesized by the oxidation of the corresponding rare-earths oxytellurides of formula La_2−xEu_xO₂Te (x = 0.02, 0.06, and 0.1) at 1050 K. Powder X-ray diffraction confirms that the as prepared materials consist of the orthorhombic La₂TeO₆ as main phase. The photoluminescence (PL) of red-emitting La_2−xEu_xTeO₆ powder phosphors is reported. The emission spectrum, exhibits an intense emission peak due to ⁵D₀ → ⁷F₂ transition at 616 nm, which indicates that the Eu³⁺ ion occupies a non-centrosymmetric site in the host lattice. These materials could find application for use as lamp phosphors in the red region.     

Synthesis and photoluminescence of nano-Y2O3:Eu phosphors

We report nano-Y₂O₃:Eu³⁺ phosphors with particle size of about 50 nm and relatively high photoluminescence (PL) intensity which is close to the standard for application. The influences of the dope amount, the surfactant and the precipitation pH on the PL intensity, the particle size and the dispersion have been studied. It has been found that 4% is the best Eu³⁺ molar concentration to get the highest PL intensity for both nano- and micro-Y₂O₃:Eu³⁺. The addition of butanol as a surfactant inhibits the grain growth and the agglomeration of particles efficiently by reducing the oxygen bridge bonds. As the pH rises, the PL intensity and the particle size increase due to the formation of oxygen bridge bonds.     

Synthesis and optical properties of (Gd1−x,Eux)2O2SO4 nano-phosphors by a novel co-precipitation method

(Gd_1−x,Eu_x)₂O₂SO₄ nano-phosphors were synthesized by a novel co-precipitation method from commercially available Gd₂O₃, Eu₂O₃, H₂SO₄ and NaOH starting materials. Composition of the precursor is greatly influenced by the molar ratio of NaOH to (Gd_1−x,Eu_x)₂(SO₄)₃ (the m value), and the optimal m value was found to be 4. Fourier transform infrared spectrum (FT-IR) and thermal analysis show that the precursor (m = 4) can be transformed into pure (Gd_1−x,Eu_x)₂O₂SO₄ nano-phosphor by calcining at 900 °C for 2 h in air. Transmission electron microscope (TEM) observation shows that the Gd₂O₂SO₄ phosphor particles (m = 4) are quasi-spherical in shape and well dispersed, with a mean particle size of about 30-50 nm. Photoluminescence (PL) spectroscopy reveals that the strongest emission peak is located at 617 nm under 271 nm light excitation, which corresponds to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. The quenching concentration of Eu³⁺ ions is 10 mol% and the concentration quenching mechanism is exchange interaction among the Eu³⁺ ions. Decay study reveals that the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions has a single exponential decay behavior.     

Luminescent properties of Sr2P2O7:Eu,Mn phosphor under near UV excitation

The phosphors in the system Sr_2−x−yP₂O₇:xEu²⁺,yMn²⁺ were synthesized by solid-state reactions and their photoluminescence properties were investigated. These phosphors have strong absorption in the near UV region, which is suitable for excitation of ultraviolet light emitting diodes (UVLEDs). The orange-reddish emission of Mn²⁺ in these phosphors can be used as a red component in the tri-color system and may be enhanced by adjusting the Mn²⁺/Eu²⁺ ratio. The energy transfer from Eu²⁺ to Mn²⁺ is observed with a transfer efficiency of ∼0.45 and a critical distance of ∼10 Å. The results reveal that Sr_2−x−yP₂O₇:xEu²⁺,yMn²⁺ phosphors could be used in white light UVLEDs.     

Hydrothermal synthesis and photoluminescence properties of nano-crystalline GdBO3:Eu phosphor

Nano-crystalline GdBO₃:Eu³⁺ was prepared by a hydrothermal method and the effects of some processing variables such as pH, temperature were investigated. The as-synthesized powders were spherical shaped agglomerates of nanoparticles. The luminescent properties were compared with samples synthesized by conventional solid-state reaction method. Both the photoluminescence intensity and chromaticity were improved and a red-shift in the CT band was observed for the hydrothermally synthesized samples. Possible mechanisms of phase formation were investigated and explanations for the changes in optical properties are proposed.     

Luminescence characterization of (Ca1−xZnx)Ga2S4:Eu phosphors for a white light-emitting diode

We investigated the luminescence properties of (Ca_1−xZn_x)Ga₂S₄:Eu²⁺ phosphor as a function of Zn²⁺ and Eu²⁺ concentrations. The luminescence intensity was markedly enhanced by increasing the mole fraction of Zn²⁺ at Ca²⁺ sites. Lacking any Zn²⁺ ions, CaGa₂S₄:0.01Eu²⁺ converted only 18.1% of the absorbed blue light into luminescence. As the Zn²⁺ concentration increased, the quantum yield increased and reached a maximum of 24.4% at x = 0.1. Furthermore, to fabricate the device, the optimized green-yellow (Ca_0.9Zn_0.1)Ga₂S₄:Eu²⁺ phosphor was coated with MgO. White light was generated by combining the MgO-coated phosphor and the blue emission from a GaN chip.     

A novel broadband emission phosphor Ca2KMg2V3O12 for white light emitting diodes

A novel broadband emission phosphor Ca₂KMg₂V₃O₁₂ was first synthesized by solution combustion method. The X-ray diffraction showed that Ca₂KMg₂V₃O₁₂ phase can be obtained at 600-900 °C through combustion route. The crystal structure of this material was refined by Rietveld method using powder X-ray diffraction. It crystallizes in cubic system and belongs to space group Ia3d with z = 8, a = 0.12500 nm. The excitation band of Ca₂KMg₂V₃O₁₂ peaks at 320 nm in a region between 260 nm and 425 nm, and the emission spectrum exhibits an intense band centered at about 528 nm covering from 400 nm to 800 nm. The colour coordinates of samples prepared at different ignition temperatures are in a range of x = 0.323-0.339, y = 0.430-0.447.     

Novel red phosphors Na2CaSiO4:Eu for light-emitting diodes

Novel red phosphors Na₂CaSiO₄:xEu³⁺ were synthesized using high temperature solid-state reaction and their luminescence characteristics were investigated for the first time. The excitation spectra indicate that the Na₂CaSiO₄:xEu³⁺ phosphors can be effectively excited by ultraviolet (393 nm) light. The emission spectra of Na₂CaSiO₄:xEu³⁺ phosphors invariably exhibit four peaks assigned to the ⁵D₀-⁷F_J (J = 1, 2, 3 and 4) transitions of Eu³⁺ under 393 nm excitation. The Commission Internationale de l’Eclairage (CIE) chromaticity coordinates and quantum efficiency (QE) are (0.66, 0.34) and 58.9%, respectively. The good color saturation and high quantum efficiency indicate that Na₂CaSiO₄:Eu³⁺ phosphors are potential candidate for light-emitting diodes.     

Tunable color emission and afterglow in CaGa2S4: Eu, Ho phosphor

The tunable color emission and persistent luminescence lifetime in phosphor CaGa₂S₄: Eu²⁺, Ho³⁺ were achieved through the introduction of alkaline earth elements Mg, Sr and Ba, in which the Ca was partially replaced. The duration of the persistent luminescence of the material CaGa₂S₄: Eu²⁺, Ho³⁺ was remarkably shortened as Al was introduced, substituting for Ga. The luminescent properties were investigated via thermo-luminescence (TL) glow curves, phosphorescence spectra and decay time curves. These results show that vast changes in trap levels and charge density takes place with introduction of other alkaline earth elements or Al. Trap depths and the trap density were also evaluated by simple methodologies.     

A novel red long lasting phosphorescent (LLP) material β-Zn3(PO4)2:Mn, Sm

A novel red long lasting phosphorescent materials β-Zn₃(PO₄)₂:Mn²⁺,Sm³⁺ is firstly synthesized by high-temperature solid-state reaction. The influence of Sm³⁺ ions on luminescence and long lasting phosphorescence properties of Mn²⁺ in phosphor β-Zn₃(PO₄)₂:Mn²⁺,Sm³⁺ are systematically investigated. It is found that the red phosphorescence (λ = 616 nm) performance of Mn²⁺ ion such as brightness and duration is largely improved when Sm³⁺ ion is co-doped into the matrix in which Mn²⁺ ion acts as luminescent center and Sm³⁺ ion plays an important role of electron trap. Thermoluminescence spectrums show that there exists one peak in β-Zn₃(PO₄)₂:Mn²⁺,Sm³⁺, the depth of which is 0.33 eV, and that there are three peaks in β-Zn₃(PO₄)₂:Mn²⁺, among which the depth of the lowest temperature peak in β-Zn₃(PO₄)₂:Mn²⁺ is 0.37 eV. Such differences in the trap depth result in the improvement of red long lasting phosphorescence of Mn²⁺ in present matrix.     

Luminescent properties of Na3YSi3O9 doped with Eu under UV-VUV excitation

The luminescent properties of Na₃Y_1−xSi₃O₉:xEu³⁺ (0.05 ≦ x ≦ 0.80) powder crystals were investigated in UV-VUV region. The Eu³⁺-O²⁻ charge transfer band (CTB) was observed to be located at around 233 nm and the environmental parameter (h_e) was estimated to be about 0.730. The excitation spectrum monitoring the 613 nm red emission from Eu³⁺ ions reveals the host absorption band (HAB) to be around 145 nm. The calculated Commission Internationale de l’Eclairage (CIE) chromaticity coordinates indicate the emission by 233 nm rather than by 147 nm excitation has the better color purity and the possible mechanisms have been proposed. The Eu³⁺-emission showed high quenching concentration due to the isolated YO₆ octahedra in the host and the small h_e for the Eu³⁺ ions and the optimum concentration was determined to be as high as x = 0.65 and 0.30 with 233 and 147 nm excitation, respectively.     

Structure and luminescence properties of Mn-doped Zn2SiO4 prepared with extracted mesoporous silica

Zn₂SiO₄:Mn powders were prepared by solid-state reaction using extracted SBA-15 as silica source. The well crystalline willemite Zn₂SiO₄:Mn can be obtained at 800 °C, much lower than the conventional solid-state reaction temperature and lower than using the calcined SBA-15. This can be attributed to the high reactive activity of the extracted SBA-15 due to its high density silanol groups, large surface areas, and non-crystalline structure. Ultraviolet (UV) and vacuum ultraviolet (VUV) excitation spectra reveal the host lattice absorption band around 162 nm and the charge transfer transition band around 245 nm. The Zn₂SiO₄:Mn phosphor exhibits a strong green emission around 527 nm. The Zn₂SiO₄:Mn phosphor with an Mn doping concentration of 0.06, i.e., Zn_1.94Mn_0.06SiO₄, shows the highest relative emission intensity. Upon 147 nm excitation, the luminescence decay time of the green emission of Zn_1.94Mn_0.06SiO₄ around 527 nm is 8.87 ms.     

Structural, morphological and optical investigations on BaMgAl10O17:Eu elaborated by a microwave induced solution combustion synthesis

Blue-emitting Eu²⁺-doped barium magnesium aluminate (BaMgAl₁₀O₁₇:Eu²⁺) for advanced displays and lighting devices was prepared by a microwave induced solution combustion synthesis using urea as combustion fuel and nitrates as oxidizer. Purity control of as-synthesized blue phosphor particles was undertaken by modifying the fuel to oxidizer molar ratio. X-ray diffraction, scanning electron microscopy and photoluminescence were used to investigate powders crystallinity, particles size, morphology and luminescent properties, respectively. Fuel-rich urea reactions preferentially lead to pure phases compared to the powders synthesized with a stoichiometric fuel to oxidizer ratio. In both cases, we produce a nearly pure well-crystallized and nanostructured BaMgAl₁₀O₁₇:Eu²⁺. Photoluminescence measurements exhibit the characteristic blue emission of Eu²⁺ under UV light excitation however a weak red emission associated to Eu³⁺ is also detected.     

A potential Eu-activated Ca10K(PO4)7 red phosphor for white light-emitting diodes

New red Ca₁₀K(PO₄)₇:Eu³⁺, K⁺ phosphors were synthesized by solid state reaction and their photoluminescence properties as well as those by co-doping Mo⁶⁺ under near ultraviolet excitation were investigated. From the excitation spectra monitored at 611 nm, it can be seen that the strongest excitation peak is situated at 393 nm, well matching with the emission wavelength of near-ultraviolet chips for white LEDs. Upon 393 nm excitation, the brightness of Ca₉K(PO₄)₇:0.5Eu³⁺, 0.5 K⁺ with the optimal Eu³⁺-doping concentration is about 2.3 times stronger than that of the commercial red Y₂O₃:Eu³⁺ phosphor. The introducing of Mo⁶⁺, which results in a possible variety for the excited energy level of the host, can enhance the brightness of Eu³⁺ to be maximized by about 15%. The CIE chromaticity coordinates of Ca₉K(PO₄)₇:0.5Eu³⁺, 0.5 K⁺ are calculated to (0.654, 0.345), which are close to the (0.67, 0.33) standard of the National Television System Committee. All the above results indicate Eu³⁺-activated Ca₁₀K(PO₄)₇ is a potential candidate for white LEDs.     

Synthesis and photoluminescence properties of a new red emitting phosphor: Ca3(VO4)2:Eu; Mn

A new red emitting phosphor, Ca₃(VO₄)₂:Eu³⁺; Mn²⁺, was synthesized by a citric acid sol-gel combustion method and characterized by XRD, TEM and photoluminescence (PL) spectra. The red emission located at about 613 nm was ascribed to ⁵D₀-⁷F₂ transition of Eu³⁺. And the red luminescence intensity changed with annealing temperature and concentration of Eu³⁺. The effect of the co-doped Mn²⁺ was also investigated systematically.     

Investigation of Na3GdP2O8:Tb as a potential green-emitting phosphor for plasma display panels

The photoluminescent properties of a series of Tb³⁺-doped Na₃GdP₂O₈ phosphors excitable by vacuum ultraviolet and ultraviolet light are reported. The host related absorption, f-f and f-d transitions of Gd³⁺ and Tb³⁺, and charge transfer of O²⁻ → Gd³⁺ and O²⁻ → Tb³⁺ are assigned. Under 147 nm light excitation, Na₃GdP₂O₈:Tb³⁺ phosphors show efficient green emissions with a dominant peak at 545 nm. The optimal sample Na₃Gd_0.4Tb_0.6P₂O₈ shows a shorter decay time and a comparable brightness when compared with the commercial Zn₂SiO₄:Mn²⁺ green phosphor. These results demonstrate that it is a potential candidate for plasma display panels application.