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A series of Eu-doped LaSr 2 AlO 5 phosphors were synthesized by high-temperature solid state reactions under oxidative and reductive atmospheres, respectively. The photoluminescence properties, fluorescence quenching mechanism and valence-change behavior of europium ions in the phosphor have been studied. For the samples prepared in oxidative atmosphere, the Eu 3+ ions occupy the La 3+ sites and exhibit characteristic sharp lines(500–750 nm) originating from the 5 D 1 and 5 D 0 levels to 7F transitions. With the increase of Eu 3+ concentration, the chromaticity coordinates of La 1− x Sr 2 AlO 5 : x Eu 3+ phosphors are turned from (0.479, 0.453) for x =0.005 to (0.621, 0.358) for x =1.0. The quenching process of 5 D 1 → 7 F 1 (533 nm) emission is attributed to cross-relaxation as the Eu 3+ concentration reaches 5 mol%. The dominant line emission 5 D 0 → 7 F 2 (619 nm) is quenched due to the exchange interaction as the Eu 3+ concentration reaches 75 mol%. For the sample prepared in reductive atmosphere, it shows the presence of both Eu 3+ and Eu 2+ . The Eu 2+ in LaSr 2 AlO 5 host lattice can be excited by a blue light with an intense broad red emission band centered at 610 nm (a full width at half maximum of 110 nm) with color coordinates of (0.611, 0.368). The internal quantum efficiency was measured to be ~42%, indicating that this phosphor has a great potential in blue-chip pumped white light emitting diodes (WLEDs). The conditions for the reduction process of Eu 3+ to Eu 2+ in solid state compounds were discussed. From the X-ray diffraction and Gaussian fitting of the emission spectra, we propose that Eu 3+ ions occupy the La 3+ sites while Eu 2+ ions occupy the two different Sr 2+ sites. [ABSTRACT FROM AUTHOR]

Abstract: Single-phase broad-band red-emitting Ca3Si2O7:Eu2+ phosphors, with photoluminescence features that qualify them as candidates for white light-emitting diodes applications, were successfully synthesized via a modified solid-state reaction method that employed H3BO3 as a flux. The phosphors produced have an intense broad red emission band, with a peak at 603nm, a full width at half maximum of 110nm, and color coordinates of (0.550, 0.438). Concentration quenching occurred at 0.01mol Eu2+. The discussion of the results shows that Eu2+ ions should be accommodated at the Ca-sites of the lattice, dipole–dipole interactions should predominantly govern the energy transfer mechanism among them, and the critical distance between them is ∼31Å. [Copyright &y& Elsevier]

Abstract: Ce3+/Eu2+ co-doped Li2SrSiO4 phosphor yields two emission bands consisted of blue and yellow components, which shows great potential as single host white phosphor for white LEDs. Effective energy transfer occurs in Ce3+/Eu2+ co-doped Li2SrSiO4 due to large 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 their absorption, excitation and photoluminescence decay behaviors, is demonstrated to be in the mechanism of electric dipole–dipole interaction. [Copyright &y& Elsevier]

Abstract: Eu2+ and Mn2+ co-doped SrSi2O2N2 green-phosphors, with promising luminescent properties (examined by their powder diffuse reflection, photoluminescence excitation and emission spectra) suitable for UV converted white LEDs, were produced by high temperature solid-state reaction method. The produced materials exhibited intense broad absorption bands at 220–500nm and a broad emission band centered at ca. 530nm, attributed to 4f–5d transitions of Eu2+. The emission intensity of Eu2+ ions was greatly enhanced by introducing Mn2+ ions into SrSi2O2N2:Eu2+ due to the energy transfer from Mn2+ to Eu2+. The energy transfer probability from Mn2+ to Eu2+ depends strongly on the Mn2+ concentration, which is maximized at a Mn2+ concentration of 3mol%. It drastically decreases for higher concentrations. The results indicated that SrSi2O2N2:Eu2+, Mn2+ is a promising green-emitting phosphor for white-light emitting diodes with near-UV LED chips. [Copyright &y& Elsevier]

Abstract: Divalent europium-activated strontium orthosilicate Sr2SiO4:Eu2+ and Mg0.1Sr1.9SiO4:Eu2+ phosphors were synthesized through the solid-state reaction technique. Their luminescent properties under ultraviolet excitation were investigated. The X-ray diffraction (XRD) results show that these phosphors are of α′-Sr2SiO4 phase with a trace of β-Sr2SiO4. Doping of Eu2+ ion into the crystal lattice results in the lattice constant being expended, while Mg2+ makes the lattice constant shrinking. A solid solution with the same crystal structure is formed when Eu2+ or Mg2+ substitutes part of Sr2+ ions and occupies the same lattice sites. The Sr2SiO4:Eu2+ phosphors show two emission spectra peaked at 535 and 473nm originated from the 5d–4f transition of Eu2+ ion doped in two different Sr2+ sites in the host lattice. By substitution of 0.1mol of Sr2+ with Mg2+, these two emission bands are tuned to be in the blue and yellow region (459 and 564nm for Mg0.1Sr1.88SiO4:Eu0.02), respectively. The tuning effect is discussed. With a combination of the blue and yellow emission bands the phosphors show white color, indicating that these phosphors may become promising phosphor candidates for white light-emitting diodes (LEDs). [Copyright &y& Elsevier]

Abstract: Tb-doped SrSi2O2N2 phosphors with promising luminescent properties were synthesized by the conventional solid-state reaction method, characterized by powder X-ray diffraction and studied by photoluminescence excitation and emission spectra. The synthesized materials exhibited a weak blue emission and a strong green emission in the region of 400–470nm and 480–650nm, which are attributed to 5D3→7F j (j=5, 4, 3) and 5D4→7Fj (j=6, 5, 4, 3) transitions of Tb3+, respectively. The green emission from 5D4→7F5 at 543nm showed the highest intensity under the optimized concentration of 0.1mol, after which the quenching concentration became relevant. The quenching behavior of the emission of Tb3+ was explained by the cross-relaxation of its excited state. [Copyright &y& Elsevier]

Herein, Ce3+ and Ce3+/Dy3+ co-doped Ca 3 Al 2 O 6 phosphors have been designed and synthesized via a facile citrate-based sol-gel technique, and their structural, photoluminescence properties and energy transfer phenomenon were investigated comprehensively. The XRD analysis indicated that pure Ca 3 Al 2 O 6 phase can be synthesized at low temperature (1000 °C) for merely 2 h. The photoluminescence spectra showed the dominant emission of Ce3+ singly doped phosphors is located in the blue region even at low Ce3+ doping level, which indeed favors the energy transfer from Ce3+ to other luminescent centers. When Dy3+ is co-doped into Ca 3 Al 2 O 6 :Ce3+ phosphors, the remarkable sensitizing effect of Ce3+ on Dy3+ is validated by comparatively analyzing the excitation, emission spectra and average lifetimes of the series of samples. Through the concentration quenching theory, the critical distance between Ce3+ and Dy3+ is calculated to be 13.50 Å. Furthermore, the energy transfer mechanism between them is most likely ascribed to electric dipole-dipole interaction. In virtue of the variation of the emission intensities of Ce3+ and Dy3+, the emitting colors of Ca 3 Al 2 O 6 :Ce3+, Dy3+ phosphors can realize tunable luminescence from deep blue to bluish-white region through controlling the Dy3+ content. Based on these analysis, Ca 3 Al 2 O 6 :Ce3+, Dy3+ phosphors could potentially be applied as a single-phase color-tunable phosphors pumped by near-ultraviolet (n-UV) radiation. • Developed a facile sol-gel method to prepare successfully Ca 3 Al 2 O 6 compound. • The blue emission of as-prepared Ca 3 Al 2 O 6 :Ce3+ phosphors dominates, which favors the energy transfer process. • The possible mechanism for the dominance of blue emission was discussed. • The energy transfer phenomenon in Ca 3 Al 2 O 6 :Ce3+, Dy3+ phosphors was investigated in detailed. • Ca 3 Al 2 O 6 :Ce3+, Dy3+ can serve as a single-phase color-tunable phosphors excited by near-ultraviolet radiation. [ABSTRACT FROM AUTHOR]

Abstract: The crystal structure and photoluminescence properties of Eu2+ doped Li2Ca0.7Sr0.3SiO4 phosphors were investigated. The Li2Ca0.7Sr0.3SiO4 is not an alloy between the tetragonal Li2CaSiO4 and hexagonal Li2SrSiO4 but crystallizes in orthorhombic structure similar to Li2(CaSr)SiO4. Photoluminescence properties of the Li2Ca0.7Sr0.3SiO4:Eu2+ phosphors, summarized in effective excitation in the UV region, strong emission in the blue light range (with a peak at 427nm) and the CIE chromaticity coordinate (0.154, 0.038), indicate this phosphor has great potential in UV-chip pumped white LEDs. White light output by mixing the Li2Ca0.7Sr0.3SiO4:Eu2+ blue and Li2SrSiO4:Eu2+ yellow phosphor was attempted. With proper molar ratio of these two compound phosphors, warm white light with CIE chromaticity coordinate close to that of the nature white light (0.33, 0.33) and color temperature about 5000K was obtained. The results indicated that the Li2Ca0.7Sr0.3SiO4:Eu2+ may become an important phosphor candidate for ultra-violet chip pumped and multi-phosphors converted white LEDs. [Copyright &y& Elsevier]