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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: CaSi2O2N2 phosphors co-doped with Ce3+ and Eu2+ was synthesized via solid-state reaction method. The experiments aimed at optimizing the composition of those phosphors for achieving the highest luminescence intensity as well as at shedding light in the mechanism that governs their luminescence behavior. The overlap of the blue emission spectrum due to Ce3+ with the yellow excitation spectrum due to Eu2+ suggests resonance-type energy transfer mechanism from Ce3+ to Eu2+ taking place in the CaSi2O2N2 host lattice, where electric dipole–dipole interactions dominate. The properties of the produced phosphors qualify them for further consideration in the technology of white light-emitting diodes. [ABSTRACT FROM AUTHOR]

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]

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]