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.

Synthesis, crystal structure and optical properties of AgY 0.95Eu 0.05(WO 4) 2-x(MoO 4) x and AgY 1-xEu x(MoO 4) 2 phases with scheelite related structures are described. The 5D 0- 7F 2 electric dipole transition at 615 nm is predominant in the photoluminescence (PL) emission spectra, under 465 nm excitation. The critical concentration of Eu 3+ is x 0.5 in AgY 1-x(MoO 4) 2, beyond which concentration quenching is observed. In AgY 0.95Eu 0.05(WO 4) 2-x(MoO 4) x phases, the 5D 0- 7F 2 emission intensity of Eu 3+ is increased with the increase of Mo content. © 2011 The Electrochemical Society.

Electrochemical lithium insertion studies on WNb12O33 synthesized by solid state reaction (SSR) are carried out in the voltage range 1.0-3.2 V. During first discharge 15.6 Li are inserted with a specific capacity of 221 mAh/g. WNb12O33 is also synthesized by sol-gel (SG) technique with a view to enhance the rate capability and cycling properties. The SSR and SG samples are characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and galvanostatic cycling. Electrochemical cycling performance of SG samples is superior to that of the SSR sample at high 'C' rates. The sample synthesized by SG method exhibits high specific capacity of 142 mAh/g after 20 cycles at 20C rate. © 2010 Elsevier Inc. All rights reserved.

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.

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.

The exchange of lithium for univalent copper in CuNbO3 has been investigated. A new form of LiNbO3 with a lamellar structure has been synthesized from the topotactic reaction between CuNbO3 and a molten salt corresponding to the eutectic "LiCl/LiNO3". This compound crystallizes in the P21/a space group with a = 9.433 Å, b = 8.226 Å, c = 6.213 Å, and β = 90.2°. This new phase intercalates one lithium on the first discharge and shows reversibility of 0.7 lithium through a first-order transformation leading to a capacity of 120 mAh/g at a potential of 1.65 V vs Li+/Li. © 2011 American Chemical Society.

In the present work, we have synthesized maleevite mineral phase BaB 2Si2O8 for the first time, which is isostructural with the pekovite mineral SrB2Si2O 8. In these europium doped host lattices, we observed the partial reduction of Eu3 to Eu2 at high temperature during the synthesis in air. Tb3 co-doping in MB2Si2O 8:0.01(Eu3/Eu2) [M=Sr, Ba] improves the emission properties towards white light. The emission color varies from bluish white to greenish white under UV lamp excitation when the host cation changes from Sr to Ba. © 2010 Elsevier Inc. All rights reserved.

Molybdenophosphates Na 2Y 1-xEu x(MoO 4)(PO 4) and Na 2Y 1-xTb x(MoO 4)(PO 4), were shown to exhibit photoluminescence (PL) properties for a broad substitution range. Under near-UV excitation, Na 2Y(MoO 4)(PO 4):Eu 3+ and Na 2Y(MoO 4)(PO 4):Tb 3+ phosphors show emission lines corresponding to 5D 0→ 7F J (J = 0-4, red) and 5D 4→ 7F J (J = 4-6, green), respectively. The critical concentrations of Eu 3+ and Tb 3+ are 0.5 and 0.7, respectively beyond which concentration quenching occurs. This behavior is explained on the basis of Eu 3+-Eu 3+ and Tb 3+-Tb 3+ distances. For x = 1, Na 2Tb(MoO 4)(PO 4), emission from the 5D 4 level of Tb 3+ that appears yellow in color is observed. © 2012 The Electrochemical Society.

A new series of gallozincates LnBaZn3GaO7 (Ln=La, Nd, Sm, Eu, Gd, Dy, Y) and new aluminozincates LnBaZn3AlO7 (Ln=Y, Eu, Dy) have been synthesized. Their structure refinements show that these phases belong to the "114" series, with hexagonal P63mc space group previously described for SmBaZn3AlO7. The photoluminescence study of these oxides shows that the Eu3+ activated LnBaZn3MO7 oxides with Ln=Y, La, Gd; and M=Al, Ga exhibit strong magnetic and electric dipole transitions (multiband emission) which is of interest for white light production. These results also confirm that the site occupied by Eu3+ is not strictly centrosymmetric. The electric dipole transition intensity is the highest in GdBaZn3MO7 [M=Al, Ga]: 0.05Eu3+ as compared with other Eu3+ activated compositions. This is due to the layer distortion around GdO6 octahedra when compared with YO6 and LaO6 octahedra. © 2009 Elsevier Inc. All rights reserved.

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.