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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.
H. A. Deore,J. Mishra,A. G. Rao,B. D. Bhanushali,V. D. Hiwarkar 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.1
Ti–6Al–4V/B4C surface composite, having uniform dispersion of reinforcement, was successfully fabricated via additive friction stir processing (AFSP) technique. The chemical reaction between B4C particles and Ti matrix resulted in the formationof intermetallics like TiBX and TiC. Optical microscopy, scanning electron microscopy, electron backscattered difractionand X-ray difraction were carried out to investigate the infuence of FSP, B4C reinforcement and post-FSP heat treatment onmicrostructure evolution. Microhardness, Charpy impact and pin on disc wear tests were performed to examine mechanicaland wear properties. Fully β transformed microstructure composed of basket-weave lamellar α/β together with the needle-likeultrafne martensite α′ was observed in FSPed stir zone. B4C particles brought about additional microstructure refnementby pinning prior β grain boundaries (Zener pinning) and enhancing the nucleation rate (particle stimulated nucleation). Surface composites fabricated via AFSP exhibited higher hardness, wear-resistance and impact toughness compared to thebase metal Ti–6Al–4V and FSPed Ti–6Al–4V.
Cr3+-Doped Yb3Ga5O12 Nanophosphor: Synthesis, Optical, EPR, Studies
Singh, V.,Sivaramaiah, G.,Rao, J. L.,Singh, N.,Pathak, M. S.,Jirimali, H. D.,Singh, P. K.,Srivastava, A. K.,Dhoble, S. J.,Mohapatra, M. Springer Science + Business Media 2016 Journal of electronic materials Vol.45 No.8
<P>Gallium garnets of lanthanides are multifunctional materials especially known for their complicated structure and magnetic properties. In addition, with a suitable transition metal dopant ion, these matrices have been proved to be excellent materials for lasers. In particular, gallium garnet of ytterbium (Yb3Ga5O12) is known to possess excellent properties with regards to these applications. In this connection, Yb3Ga5O12 doped with Cr3+ nanophosphors were synthesized by a solution combustion route. The synthesized material was characterized by powder x-ray diffraction and scanning electron microscopy for phase purity and homogenous morphology. In order to ascertain the oxidation state of the doped ion, diffuse reflectance (DRF), photoluminescence (PL) and electron paramagnetic resonance (EPR) experiments were performed on the sample. The DRF and PL data suggested the stabilisation of the trivalent Cr ion in the matrix. The EPR spectra exhibited two resonance signals with effective g values at g approximate to 7.6 and 4. The EPR data corroborated the DRF and PL results, suggesting the stabilisation of Cr3+ in the matrix at octahedral-type geometries.</P>
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>
Eu2+ and Mn2+ Co-doped BaMgAl10O17 Blue- and Green-Emitting Phosphor: A Luminescence and EPR Study
Singh, V.,Sivaramaiah, G.,Rao, J. L.,Singh, N.,Srivastava, A. K.,Jirimali, H. D.,Li, J.,Gao, H.,Kumaran, R. S.,Singh, P. K. Springer Science + Business Media 2016 Journal of electronic materials Vol.45 No.6
<P>Eu2+ and Mn2+ co-doped BaMgAl10O17 phosphor has been prepared by a solution combustion method. The structural, morphological and compositional analysis of the BaMgAl10O17:Eu2+ and Mn2+ powders have been studied by x-ray diffraction, scanning electron microscopy and energy dispersive x-ray spectroscopy. The electron paramagnetic resonance (EPR) spectrum exhibited resonance signals with the effective g values of g a parts per thousand 4.88 and g a parts per thousand 1.98. The resonance signal with the effective g value of g a parts per thousand 4.88 is characteristic of Eu2+ ions whereas g a parts per thousand 1.98 is due to Mn2+ ions. The number of spins participating in resonance, Gibbs free energy, magnetic susceptibility, Curie constant, effective magnetic moment, zero-field splitting parameter and hyperfine splitting constant have been evaluated. From optical and EPR correlation, it is inferred that Eu2+ and Mn2+ are present in the BaMgAl10O17 matrix.</P>
Hussain, Sk.K.,Rao, G.M.,Raju, G.S.R.,Krishna Bharat, L.,Subba Rao, P.S.V.,Yu, J.S. Elsevier [etc.] 2016 Journal of luminescence Vol.178 No.-
<P>Trivalent terbium (Tb3+) or samarium (Sm3+) ions individually activated green and orange emitting Sr2Gd8Si6O26 (SGSO) phosphors were synthesized by a citrate sol-gel method. The X-ray diffraction patterns of SGSO:Tb3+ and SGSO:Sm3+ phosphors exhibited the characteristic diffraction peaks of oxyapatite in a hexagonal lattice structure. The photoluminescence (PL) properties at ultraviolet (UV) or near-UV excitation wavelengths were measured for Tb3+ or Sm3+ ions doped SGSO phosphors as a function of its respective concentration. The PL spectra of SGSO:Tb3+ phosphors revealed the characteristic emission peaks of both Gd3+ and Tb3+ ions which are associated with 4f-4f transitions under 274 nm of excitation wavelength. When the concentration of Tb3+ ions increased over 0.05 mol (5 mol%), the emission intensities of D-5(3) transitions decreased due to the well-known cross-relaxation process. However, based on the intensities of D-5(4) transitions, the optimum concentration of Tb3+ ions was found to be 0.05 mol. Under 404 nm of excitation wavelength, the SGSO:Sm3+ phosphors exhibited the characteristic orange emission at 600 nm due to the (4)G(5/2) -> H-6(7/2) electronic transition. The optimum concentration of SGSO:Sm3+ phosphors was found to be 0.02 mol. The decay curves of the optimized SGSO:Tb3+ and SGSO:Sm3+ phosphors were well fitted to single exponential functions and their lifetimes were calculated. Furthermore, the optimized phosphor samples showed good thermal stability. Likewise, cathodoluminescence properties were also studied for the optimized samples as a function of filament current and accelerating voltage. The Commission International de I-Eclairage chromaticity coordinates were calculated for the SGSO:Tb3+ and SGSO:Sm3+ phosphors. (C) 2016 Elsevier B.V. All rights reserved.</P>
V. S. MUTHUKUMAR,J. K. KIRAN,JASON REPPERT,R. SATYAJIT,VAMSI KRISHNA,G. NAGESHWAR RAO,S. SIVA RAMA KRISHNAN,S. SIVA SANKARA SAI,K. VENKATARAMANIAH,A. M. RAO 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2008 NANO Vol.3 No.3
Saturable absorbers and optical limiters have contrary optical transmission properties. We report observations of simultaneous occurrence of both these effects in a nickel sulphide nanoparticle (average dia. ~5 nm) solution and a simultaneous quantitative measurement of both. Intensity dependent nonlinear transmission studies carried out using a 7 ns Nd:YAG laser at 532 nm by the Z-scan method, revealed efficient optical limiting in nickel sulphide nanoparticle suspensions. Induced nonlinear optical scattering was identified to be the mechanism of optical limiting, and absorption at 532 nm was found to saturate. A modification of the conventional Z-scan implementation led to the retrieval of the saturation intensity which is otherwise overshadowed by very strong nonlinear scattering.
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>
Dhand, V.,Venkateswer Rao, M.,Mittal, G.,Rhee, K.Y.,Park, S.J. Elsevier 2015 CURRENT APPLIED PHYSICS Vol.15 No.3
An in-situ approach to synthesize lithium-graphite nanotubes (LGN) is demonstrated using chemical vapour deposition (CVD). Lithium acetate was used as precursor and as a self-intercalating agent in the presence of copper. Methane was selected as the secondary carbon source. To synthesize lithium-graphite nanotubes (LGN), CVD reactor was set to 500 <SUP>o</SUP>C in the presence of argon (200 sccm), hydrogen (40 sccm) and methane (75 sccm) gas under atmospheric conditions. X-ray diffraction shows that the samples are highly crystalline with the c-axis oriented toward the (002) and (111) planes of the graphitic carbon. High resolution transmission and scanning electron microscopic analyses of the samples shows that lithium has been doped into the layers of graphitic carbon matrix. They also show the formation of an alloy phase with distinctive lattice boundaries and stacked graphitic carbon with a small number of nanorods (lithium carbide). HR-Raman analysis shows the characteristic D and G bands of SP<SUP>2</SUP> carbon with a narrow G band and broad D band indicating defects produced through doping. X-ray photoelectron spectroscopy results show the presence of predominant lithium and carbon peaks. Thermal analysis shows that the sample is stable up to 300 <SUP>o</SUP>C in air.