Upadhyayula V Varadaraju

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.

Na0.5Gd0.5-xRExTiO3 (RE=Eu and Dy) phases with orthorhombic perovskite structure were synthesized by high temperature solid state reaction and the photoluminescence properties were investigated. The phase purity was confirmed by Rietveld refinement of the powder XRD patterns in Pnma space group. The band gap of the host was found to be 3.41 eV from UV/Vis diffuse reflectance spectrum. In the Eu3+ doped phases, the 5D0→7F2 electric dipole (ED) transition is predominant in the emission spectrum of Eu3+, under 397 nm excitation, and is in agreement with the non-centrosymmetric Cs point group of the EuO8 polyhedron. The critical concentration of the Eu3+ was found to be x=0.075 above which, concentration quenching occurs. Dy3+ doping resulted in intense white light emission under 389 nm excitation.

Eu3 photoluminescence is studied in La5Si 2BO13 with apatite related structure. La 5-xEuxSi2BO13 [x=0.05, 0.1, 0.3, 0.5, 0.7, 1.0, 2.0] compositions are synthesized. The emission results shows that Eu3 ions occupy two different cationic sites viz., La(1) and La(2). The increase in the intensity of 5D07F0 line with increasing Eu3 content shows the preferential occupancy of Eu3 in La(2) site due to the existence of short La(2)O(4) (free oxide ion) bond. The observation of antiferromagnetic interactions in Gd and Dy analogues supports the structural features elucidates from photoluminescence studies. © 2010 Published by Elsevier Inc.

A comparative study of Eu 3+ photoluminescence in the Scheelite-type oxides LiGd(WO 4 ) 2 and LiGd(MoO 4 ) 2 is made. From the emission results, it is observed that the 5 D 0 → 7 F 2 electric dipole transition at 615 nm is predominant in both cases. The critical concentration of Eu 3+ is found to be x=0.3 in both LiGd 1-x Eu x (WO 4 ) 2 as well as LiGd 1-x Eu x (MoO 4 ) 2 . The emission intensity of Eu 3+ is higher in the tungstate host lattice vis a vis the molybdate. In addition, the emission intensity of Eu 3+ in LiGd 0.7 Eu 0.3 (WO 4 ) 2 is 3.3 times higher compared to that of Y 2 O 3 :0.05Eu 3+ commercial red phosphor.

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.

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.