Now showing 1 - 5 of 5
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    Host-sensitized emission of LiInW2O8 wolframites: From red-Eu3 to white-Dy3 phosphors
    (01-09-2011)
    Asiri Naidu, S.
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    Boudin, S.
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    Raveau, B.
    The LiInW2O8:Eu3, LiInW2O 8:Dy3 and LiInW2O8:Eu 3/Dy3 phosphors were synthesized by solid-state reaction and their photoluminescence properties were studied. Under UV excitation, the LiInW2O8:Eu3 phosphor exhibits an intense red emission whereas the LiInW2O8:Dy3 and LiInW2O8:Dy3/Eu3 phosphors show a white emission. The WO6 octahedra play a major role in the luminescence of the host lattice, characterized by a blue emission under UV excitation. The emission of activator ion results from an efficient energy transfer from the LiInW2O8 host lattice to the Eu 3 and Dy3 ions. The LiIn0.97Dy30.03W2O8 and LiIn0.965 Dy 30.03Eu30.005W2O 8 samples, optimized for white emission, are interesting candidates for solid-state lighting applications. © 2011 Elsevier Inc.
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    Enhanced luminescence of Sr2SiO4:Dy3+ by sensitization (Ce3+/Eu2+) and fabrication of white light-emitting-diodes
    (15-02-2014)
    Pardha Saradhi, M.
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    Lakshminarasimhan, N.
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    Boudin, S.
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    Vijay Kumar Gupta, K.
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    Raveau, B.
    The role of sensitization by co-doping Ce3+/Eu2+ in the Sr2SiO4:Dy3+ phosphor system is studied with a view of improving the emission properties and chromaticity coordinates. The concentration dependence of the emission intensity of Dy3+ in Sr2-2xDyxLixSiO4: (x=0.01-0.05 in steps of 0.01) is studied, and the critical concentration is found to be 3 mol% Dy3+ per formula unit. Partial energy transfer from Ce3+ to Dy3+ is observed, and the luminescence intensity of Dy 3+ is enhanced. It is also found that Eu2+, Ce 3+ containing compositions show better white emission than the corresponding Sr2SiO4:Dy3+. LEDs fabricated by coating the ultraviolet (UV) emitting chips with the synthesized phosphor compositions show bright white emission with reasonable chromaticity coordinates. © 2013 Elsevier B.V.
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    Li3Gd3Te2O12:Eu3+- an intense red phosphor for solid state lighting applications
    (01-02-2017)
    Tiwari, Hansnath
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    Asiri Naidu, S.
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    Li3Gd3−3xEu3xTe2O12 (x=0.05−1.0) phases with garnet structure were synthesized by high temperature solid state reaction and the photoluminescence properties were investigated. The appearance of bands due to intra 4 f transitions of Gd3+ in the excitation spectra recorded by monitoring the 612 nm emission line of the activator indicates Gd3+→Eu3+ energy transfer in this host lattice. Under 395 nm excitation, the electric dipole transition is predominant in the emission spectrum of Eu3+ and is in agreement with the C2 point group (noncentrosymmetric) of the EuO8 polyhedron. The critical concentration of the Eu3+ activator in this series was found to be 0.6 (x=0.2) above which, concentration quenching occurs. The emission intensity of the phosphor composition, Li3Gd2.4Eu0.6Te2O12 is ~4 times that of the commercial sample of Y2O3:Eu3+ phosphor.
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    Influence of structural distortions upon photoluminescence properties of Eu 3 and Tb 3 activated Na 3Ln(BO 3) 2 (Ln=Y, Gd) borates
    (01-06-2012)
    Asiri Naidu, S.
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    Boudin, S.
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    Raveau, B.
    The comparative study of the structure and photoluminescence (PL) properties of the Eu 3 and Tb 3 activated Na 3Ln(BO 3) 2, with Ln=Y, Gd, showed the important role of the host lattice structure upon PL. Higher emission intensities of Eu 3 and Tb 3 are observed for Na 3Gd(BO 3) 2 than for Na 3Y(BO 3) 2, through direct Eu 3 excitation at 395 nm for Eu 3 doped borates, and through Gd 3 excitation around 280 nm for Tb 3 doped borates. This higher performance for Na 3Gd(BO 3) 2 is due to the less regular environment of Eu 3 (Tb 3) in the Gd sites than in the Y sites and to energy transfer from Gd 3 to Eu 3(Tb 3). The smaller critical concentration in Na 3Ln 1-xTb x(BO 3) 2 observed for Ln=Gd, x=0.5, compared to x=0.6 for Ln=Y, is explained by shorter Ln-Ln distances (4.11 Å for Gd-Gd vs. 4.59 Å for Y-Y). Both Na 3Y 0.4Tb 0.6(BO 3) 2 and Na 3Gd 0.5Tb 0.5(BO 3) 2 show intense green emission under UV excitation. © 2012 Elsevier Inc.
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    Photoluminescence properties of rare earths (Eu 3, Tb 3, Dy 3 and Tm 3) activated NaInW 2O 8 wolframite host lattice
    (01-01-2012)
    Asiri Naidu, S.
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    Boudin, S.
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    Raveau, B.
    The photoluminescence (PL) studies on NaIn 1-xRE xW 2O 8, with RE=Eu 3, Tb 3, Dy 3 and Tm 3 phases have shown that the relative contribution of the host lattice and of the intra-ff emission of the activators to the PL varies with the nature of the rare earth cation. In the case of Dy 3 and Tm 3 activators, with yellow and blue emission, respectively, the energy transfer from host to the activator plays a major role. In contrast for Eu 3, with intense red emission, the host absorption is less pronounced and the intra-ff transitions of the Eu 3 ions play a major role, whereas for Tb 3 intra-ff transitions are only observed, giving rise to green emission. © 2011 Elsevier Inc. All rights reserved.