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Singh, Vijay,Sivaramaiah, G.,Singh, N.,Pathak, M.S.,Srivastava, Anoop K.,Rao, J.L.,Natarajan, V. Elsevier 2018 OPTIK -STUTTGART- Vol.171 No.-
<P><B>Abstract</B></P> <P>Al<SUB>2</SUB>O<SUB>3</SUB>:Gd<SUP>3+</SUP> phosphor was prepared using single step urea combustion method. The prepared phosphor was characterized by X-ray diffraction (XRD), photoluminescence (PL) and electron paramagnetic resonance (EPR) techniques. The formation of the combustion products was confirmed by the XRD analysis. PL studies showed that the Al<SUB>2</SUB>O<SUB>3</SUB>:Gd<SUP>3+</SUP> phosphor could be excited at 273/276 nm, while an ultraviolet (UV) emission centered at ∼ 314/317 nm was exhibited. The EPR spectrum of sample exhibited resonance signals due to Gd<SUP>3+</SUP> ion at low symmetry sites in the host lattice. Both PL as well as EPR studies of the sample confirmed the presence of Gd<SUP>3+</SUP> in the Al<SUB>2</SUB>O<SUB>3</SUB> matrix.</P>
Singh, N.,Sivaramaiah, G.,Rao, J.L.,Watanabe, S.,Rao, T.K. Gundu,Patel, R.V.,Singh, Vijay Elsevier 2017 Journal of luminescence Vol.188 No.-
<P><B>Abstract</B></P> <P>Gadolinium activated UV-emitting ZrO<SUB>2</SUB> phosphor has been prepared by combustion synthesis. The prepared phosphor was characterized using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray techniques. The optical absorption spectrum in the 200−500nm region and excitation spectrum corresponding to the emission at 314nm for ZrO<SUB>2</SUB>:Gd<SUP>3+</SUP> phosphor has been recorded. Gd<SUP>3+</SUP> doped ZrO<SUB>2</SUB> displays electron spin resonance signals with effective g values at <I>g</I>≈1.9, 2.4 and 4.1. Low field signals are attributed to Gd<SUP>3+</SUP> ion located in distorted surroundings experiencing a relatively strong crystal field due to the proximity of charge compensator oxygen vacancies.</P>
Singh, Vijay,Sivaramaiah, G.,Rao, J.L.,Kim, S.H. Elsevier 2015 Journal of luminescence Vol.157 No.-
<P><B>Abstract</B></P> <P>The UV-emitting Y<SUB>4</SUB>Zr<SUB>3</SUB>O<SUB>12</SUB>:Gd phosphor has been prepared via a solution combustion method. This phosphor sample has been characterized by X-ray diffraction, scanning electron microscopy, diffuse reflectance, photoluminescence and electron spin resonance (EPR) spectroscopic techniques. Phase analysis indicates that the obtained product has a rhombohedral structure. Platelet like structures are obtained with non-uniform distribution. The emission spectrum, upon 274nm excitation exhibits a well-defined sharp and intense peak centered at 313nm emitting UV light. The EPR spectrum exhibits several resonance signals with the effective <I>g</I> values at <I>g</I> ≈5.58, 4.33, 3.51, 2.73 and 1.98. From EPR and optical studies, it is observed that gadolinium ions are present in trivalent state in the Y<SUB>4</SUB>Zr<SUB>3</SUB>O<SUB>12</SUB> matrix.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The rhombohedral phase of Y<SUB>4</SUB>Zr<SUB>3</SUB>O<SUB>12</SUB> could be obtained via the facile combustion method. </LI> <LI> The narrow-band ultraviolet B emission due to Gd<SUP>3+</SUP> ions were observed. </LI> <LI> EPR studies have confirmed the presence of Gd<SUP>3+</SUP> ions in the sample. </LI> </UL> </P>
Singh, V.,Sivaramaiah, G.,Rao, J. L.,Singh, N.,Srivastava, A. K.,Singh, P. K.,Pawar, S. U.,Gao, H.,Mardina, P. Springer Science + Business Media 2016 Journal of materials science Materials in electron Vol.27 No.5
<P>Fe doped CeO2 powder was prepared using solution combustion method. Powder X-ray diffraction and scanning electron microscopy methods are used to characterize the combustion derived powder. The optical absorption spectrum exhibits three bands due to Fe3+ and Fe2+ ions. Electron paramagnetic resonance (EPR) spectrum of this sample exhibits number of resonance signals due to Fe3+ ions. The number of spins (N) participating in resonance and its paramagnetic susceptibility (chi) has been evaluated. From EPR and optical studies it is observed that iron ions are present in trivalent state.</P>
EPR and optical investigations of LaMgAl<sub>11</sub>O<sub>19</sub>:Cr<sup>3+</sup> phosphor
Singh, V.,Sivaramaiah, G.,Rao, J.L.,Kim, S.H. Pergamon Press 2014 Materials research bulletin Vol.60 No.-
The LaMgAl<SUB>11</SUB>O<SUB>19</SUB>:Cr<SUP>3+</SUP> phosphor has been prepared by a low-temperature combustion synthesis method. As-prepared combustion synthesized powder was characterized using powder X-ray diffraction (XRD), diffuse reflectance (DRS), electron paramagnetic resonance (EPR) and photoluminescence (PL) studies. The X-ray diffraction pattern reveals crystalline hexagonal phases. The UV-vis diffuse reflectance spectrum exhibits three broad bands characteristic of Cr<SUP>3+</SUP> ions in octahedral symmetry. The EPR spectrum exhibits several resonance signals. The signals with the effective g values at g=4.84, 3.64 and 2.26 have been attributed to the isolated Cr<SUP>3+</SUP> ions. The signal with the effective g value at g=1.94 has been attributed to exchange coupled Cr<SUP>3+</SUP>-Cr<SUP>3+</SUP> ion pairs. The PL studies exhibit several bands characteristic of Cr<SUP>3+</SUP> ions in octahedral symmetry.
Singh, V.,Sivaramaiah, G.,Rao, J. L.,Singh, N.,Mohapatra, M.,Singh, P. K.,Pathak, M. S.,Dhoble, S. J. Minerals, Metals & Materials Society and the Insti 2017 Journal of Electronic Materials Vol. No.
<P>LiAl5O8 doped with Fe was synthesized by a propellant combustion route at furnace temperature of 773 K. The phosphor was characterized using powder x-ray diffraction, optical absorption, electron paramagnetic resonance (EPR) and photoluminescence spectroscopic techniques. The optical absorption spectrum exhibits a broad band at 242 nm characteristic of charge transfer between Fe3+-O2-. On excitation with 293 nm, emission band for the Fe3+ ion was observed at 687 nm. The CIE (International Commission on Illumination or Commission Internationale de l'Elcairage) coordinates for the system were evaluated adopting standard procedure which suggested that the system can be effective as a deep red emitting phosphor. The EPR spectrum of this phosphor exhibits a number of resonance signals characteristic of Fe3+ ions. The resonance signals at g = 3.16, 2.27 are attributed to Fe3+ present at tetrahedral site with an axial symmetry. The resonance signals at g = 1.98 and 1.43 are attributed to Fe3+ ions in octahedral site with an axial symmetry. Various EPR parameters such as the number of spins, Gibbs free energy, magnetic susceptibility, Curie constant and effective magnetic moment values are calculated and compared at room temperature and 110 K.</P>
Investigation of ultraviolet emitting Gd doped Sr<sub>2</sub>MgSi<sub>2</sub>O<sub>7</sub> phosphors
Singh, Vijay,Sivaramaiah, G.,Singh, N.,Pathak, M.S.,Rao, J.L.,Jirimali, H.D.,Natarajan, V. Elsevier 2018 Optik Vol.169 No.-
<P><B>Abstract</B></P> <P>This article deals with the ultraviolet (UV)-emitting gadolinium (Gd)-doped strontium magnesium disilicate (Sr<SUB>2</SUB>MgSi<SUB>2</SUB>O<SUB>7</SUB>) phosphors. A series of the Gd-doped Sr<SUB>2</SUB>MgSi<SUB>2</SUB>O<SUB>7</SUB> phosphors were prepared using a sol-gel method. The powders were well characterized using the X-ray powder diffraction (XRPD) and scanning electron microscope (SEM) techniques. The emission measurements upon a specific UV-light excitation (273 nm) showed the emission characteristics of the Gd<SUP>3+</SUP> that are due to the <SUP>6</SUP>P<SUB>J/2</SUB> → <SUP>8</SUP>S<SUB>7/2</SUB> transition. EPR spectra of the prepared samples indicated the presence of Gd<SUP>3+</SUP> ions in low symmetry sites in this sample.</P>
Singh, Vijay,Sivaramaiah, G.,Rao, J. L.,Kumaran, R. Senthil,Dhoble, S. J. American Scientific Publishers 2016 Journal of nanoscience and nanotechnology Vol.16 No.1
<P>By adopting a facile solution combustion synthesis, crystallized europium doped blue phosphors were successfully prepared. These phosphors were characterized by X-ray diffraction (XRD), Fourier transform infrared absorption (FT-IR), energy dispersive analysis of X-ray, Electron Paramagnetic Resonance (EPR) and Photoluminescence (PL) experimental methods. The photoluminescence spectrum indicates Eu2+ and Eu3+ ions in these phosphors. The band at around 442 nm is attributed to the spin-allowed 4f(6)5d(1) (D-2) -> (4)f(7)(S-6(7/2)) transition of Eu2+ ions. The sharp bands at 591 (D-5(0) -> F-7(1)) and 616 (D-5(0) -> F-7(2)) nm are attributed to the spin-forbidden transitions of Eu3+ ions. The EPR spectra of as-prepared and post-treated LaAl11O18:Eu phosphors exhibit signals characteristic of La2+ and Eu2+ ions. The number of spins, Gibbs energy, magnetic susceptibility, Curie constant and effective magnetic moment values were calculated and compared at 296 and 110 K.</P>