H. Nagabhushana

Tumkur University, Tumkūr, Karnātaka, India

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Publications (115)162.59 Total impact

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    ABSTRACT: Pure zirconia (ZrO 2) nano powders were prepared by hydrothermal method using three different precursors namely zirconium nitrate, zirconyl nitrate and zirconium oxy-chloride. The products were characterized by Powder X-Ray Diffraction (PXRD), Fourier Transform Infrared spectroscopy (FTIR), scanning electron microscopy (SEM), UV-Visible spectroscopy. Photoluminescence behavior is studied with respect to different precursors while keeping other reaction parameters constant. The PXRD studies show the formation of monoclinic ZrO 2 nanopowders irrespective of precursor used. The average crystallite size calculated from X-ray line broadening ranges from 20 -30 nm. Upon excitation at 380 nm, the PL emission spectra of all the three compounds consists of intense bands centered at 416, 438, 467 nm along with less intense peaks at 518 and 624 nm. All these bands can be ascribed to the defects in the crystal (F + centers) and oxygen vacancy defects. The difference in the intensity of PL spectra with precursors is attributed to difference in the number of defect centers.
    Journal of chemical engineering and Reserch. 09/2014; 2(1):105-111.
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    ABSTRACT: A series of Dy3+ (0.5–9 mol%) and Li+ (0.5–3 mol%) co-doped strontium cerate (Sr2CeO4) nanopowders are synthesized by low temperature solution combustion synthesis. The effects of Li+ doping on the crystal structure, chemical composition, surface morphology and photoluminescence properties are investigated. The X-ray diffraction results confirm that all the samples calcined at 900 °C show the pure orthorhombic (Pbam) phase. Scanning electron microscopy analysis reveals that the particles adopt irregular morphology and the porous nature of the product. Room temperature photoluminescence results indicate that the phosphor can be effectively excited by near UV radiation (290 to 390 nm) which results in the blue (484 nm) and yellow (575 nm) emission. Furthermore, PL emission intensity and wavelength are highly dependent on the concentration of Li+ doping. The emission intensity is enhanced by 3 fold with Li+ doping. White light is achieved by merely varying dopant concentration. The colour purity of the phosphor is confirmed by CIE co-ordinates (x = 0.298, y = 0.360). The study demonstrates a simple and efficient method for the synthesis of novel nanophosphors with enhanced white emission.
    RSC Advances 08/2014; 4(73). · 3.71 Impact Factor
  • Article: ww
    07/2014;
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    ABSTRACT: The investigation aims at the synthesis of Copper oxide nanoparticles (CuO Nps) using Gloriosa superba L. plant extract as fuel by solution combustion synthesis, their characterization and studies on antibacterial activities against selected pathogenic bacteria. X-ray diffraction studies showed that the particles are monoclinic in nature. The UV–visible absorption spectrum of CuO Nps indicates the blue shift with increase of concentration of plant extract. SEM images reveal that the particles are spherical in nature. TEM image indicates that as-formed CuO Nps are spherical in shape, and the size is found to be in the range 5-10 nm. Further, as-formed CuO Nps exhibit significant antibacterial activity against pathogenic bacterial strains namely Gram -ve Klebsiella aerogenes, Pseudomonas desmolyticum, and Escherichia coli, Gram + ve bacteria Staphylococcus aureus. The current study demonstrates convenient utilization of Gloriosa superba L. extract as a fuel for the efficient synthesis of CuO nanoparticles through a green synthesis method to obtain significantly active antibacterial material.
    Journal of Taibah University for Science. 07/2014;
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    ABSTRACT: Novel crystalline tetragonal ZrO2: Eu(3+) phosphors were prepared by a facile and efficient low temperature solution combustion method at 400±10°C using oxalyl dihydrazide (ODH) as fuel. The powder X-ray diffraction patterns and Rietveld confinement of as formed ZrO2: Eu(3+) (1-11mol%) confirmed the presence of body centered tetragonal phase. The crystallite size estimated from Scherrer's and W-H plots was found to be in the range of 7-17nm. These results were in good agreement with transmission electron microscopy studies. The calculated microstrain in most of the planes indicated the presence of tensile stress along various planes of the particles. The observed space group (P42/nmc) revealed the presence of cations in the 2b positions (0.75, 0.25, 0.25) and the anions in the 4d positions (0.25, 0.25, 0.45). The optical band gap energies estimated from Wood and Tauc's relation was found to be in the range 4.3-4.7eV. Photoluminescence (PL) emission was recorded under 394 and 464nm excitation shows an intense emission peak at 605nm along with other emission peaks at 537, 592, 605 and 713nm. These emission peaks were attributed to the transition of (5)D0→(7)FJ (J=0, 1, 2, 3) of Eu(3+) ions. The high ratio of Intensity of ((5)D0→(7)F2) and ((5)D0→(7)F1) infers that Eu(3+) occupies sites with a low symmetry and without an inversion center. CIE color coordinates indicated the red regions which could meet the needs of illumination devices.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 07/2014; 135C:241-251. · 1.98 Impact Factor
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    ABSTRACT: For the first time, different morphologies of zinc oxide (ZnO) superstructures are synthesized by a simple and environmental friendly route using Nerium oleander leaf extract as fuel. Powder X-ray diffraction, scanning electron microscopy, UV−visible spectroscopy, and photoluminescence studies are performed to ascertain the formation and characterization of ZnO. X-ray diffraction confirmed the crystalline nature of the compound with hexagonal Wurtzite structure. When the concentration of the leaf extract is varied, different morphologies are formed. ZnO are tested for antifungal using soybean seed-borne fungi by food-poison method and antibacterial activity against bacterial human pathogens by a broth microplate dilution method using 96-well plates. Among the screened soybean seed-borne fungi, Fusarium equisiti was found to be more susceptible, which was followed by Macrophomina phaseolina for ZnO nanoparticles (NPs) prepared using 0.2188 mol/dm3 N. oleander leaf extract. It was observed that NPs exhibited pronounced antifungal activity in a dose-dependent manner with a relatively high percentage of mycelial inhibition. ZnO obtained with the concentration of 0.2188 mol/dm3 leaf extract showed both minimum inhibitory concentration and minimum bactericidal concentration effectiveness compared to other synthesized compounds. It is observed that the samples with small crystallite size show greater antibacterial activity than those of larger crystallite size. Further, we found that crystallite size and morphology significantly affects the antibacterial activity of ZnO. Prepared compounds showed significant inhibition against Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Pseudomonas aeurginosa. Among the tested bacteria, P. aeurginosa is more susceptible and E. coli is the least effective against bacterial pathogens. The antibacterial activities of the as-formed ZnO are preliminarily studied against Gram-positive (B. subtilis and S. aureus) and Gram-negative (E. coli and P. aeruginosa) bacteria and are found to be dependent on the shape of the nanostructures.
    Crystal Growth & Design 06/2014; 14,:4068−4079. · 4.69 Impact Factor
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    ABSTRACT: Dosimetric studies on single crystals of YAlO3:Mn co-doped with transition (Co, Cu, Fe) and rare earth (Yb, Ce) metal ions using UV radiation exposure for the duration 5–30 min have been studied. A single well resolved thermoluminescence glow peak was observed at 183 °C in Co and Cu co-doped single crystals. In Fe co-doped single crystals, two well resolved glow peaks at 196 °C and 238 °C were observed. A well resolved glow peak at 215 °C in Yb and 176 °C in Ce co-doped single crystals was observed. Variations of thermoluminescent (TL) glow peaks intensity in all the co-doped crystals with different UV-exposures were studied. TL glow peak intensity increases sublinearly in Co, Cu co-doped crystals, whereas in Fe co-doped crystals glow peaks at 196 °C and 238 °C increase linearly. Fading effect was studied at different intervals up to 30 d for all co-doped crystals exposed to UV source for 10 min. Strong fading was observed initially and stabilized after 15 d. Fe co-doped YAlO3:Mn2+ records 40% fading, whereas other samples of YAlO3:Mn2+ co-doped with Cu, Co, Yb and Ce show 60% fading. The kinetic parameters (E, b, s) were estimated using glow peak shape method for UV irradiated samples and results are discussed in detail.
    Materials Research Express. 06/2014; 1(2):025710.
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    ABSTRACT: GdAlO3, GdAlO3:Eu(3+) and GdAlO3:Eu(3+):Bi(3+) nanophosphors were synthesised by solution combustion technique. Pure orthorhombic phase was obtained from powder X-ray diffraction (PXRD) studies. Scanning electron microscopy (SEM) micrographs showed the porous, agglomerated and irregular shaped particles. The particle size obtained by transmission electron microscopy (TEM) measurement was in good agreement with the values obtained by Debye Scherrer's and W-H plots. The selected area electron diffraction (SAED) pattern show single crystalline nature of the sample. Photoluminescence (PL) measurements were carried out for GdAlO3:Eu(3+) and GdAlO3:Eu(3+):Bi(3+) phosphors excited at a wavelength of 274nm. The characteristic emission peaks of Eu(3+) ions were recorded at 590, 614, 655 and 695nm corresponding to (5)D0→(7)FJ (J=1, 2, 3, 4) transitions respectively. However, with addition of Bi(3+) ions in GdAlO3:Eu(3+), PL intensity drastically enhanced. Orange red color was tuned to deep red color with the addition of Bi(3+) ions in GdAlO3:Eu(3+) phosphor. Therefore, the phosphor was highly useful as red component in WLEDs. A single well resoled glow peak at 225°C was recorded in GdAlO3 and GdAlO3:Eu(3+). Further, with addition of Bi(3+) ions, an additional peak at 300°C was recorded. TL glow curves of different UV-exposed GdAlO3:Eu(3+):Bi(3+) show two TL peaks at 207 and 300°C respectively. The 207°C peak show simple glow peak structure and its intensity increases linearly up to 25min and after that it decrease.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 06/2014; 133C:550-558. · 1.98 Impact Factor
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    ABSTRACT: In the present work, Zinc Oxide nanoparticles (ZnO Nps) have been prepared by a simple solution combustion method using Zinc nitrate as a precursor and grape juice as a fuel. The structure and morphology of the synthesized ZnO Nps were analyzed using X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), UV-Vis spectroscopy, Photoluminescence (PL) spectroscopy, Scanning Electron Microscopy (SEM). XRD pattern indicates that the prepared product belongs to hexagonal wurtzite structure. The FT-IR spectrum of ZnO Nps shows significant spectroscopic band at 416 cm-1 associated with the characteristic vibrational mode of Zn–O bonding. The UV-Vis spectrum shows a maximum absorbance at 371 nm. The band at 502 nm in the in the yellow region is due to the intrinsic defects of oxygen vacancies. SEM images showed that the prepared particles were agglomerated to form loofa like structure. ZnO NPs shows good photocatalytic activity for the degradation of methylene blue (MB) dye, as well as significant antibacterial activities against four pathogenic bacterial strains.
    IJLTEMAS. 06/2014; Volume III,(Issue VI,):ISSN 2278 - 2540, IF: 1.356.
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    ABSTRACT: A series of red light emission phosphors of Sr2SiO4:Eu3+ (1–5 mol%) and Sr2SiO4:Eu3+:M+ (M+ = Na+, K+ and Li+) were prepared through simple low temperature solution combustion method and their luminescence properties were studied. The powder X-ray diffraction (XRD) results revealed the formation of highly crystalline Sr2SiO4:Eu3+ nanophosphor having an average particle size 45–60 nm and strain was measured to be (2.4–3.1) � 103. The SEM pictures of Sr2SiO4:Eu3+ and Sr2SiO4:Eu3+: M+ showed porous in nature and irregular shaped particles. The phosphors can be effectively excited by the light of 395 nm and show the characteristic emission peaks assigned to transitions of 5D0?4FJ (J =0, 1, 2, 3, 4). The excitation and emission spectra indicate that the phosphors can be effectively excited by UV (�395 nm) light which emits an intense red light peaked at �614 nm. The Eu3+ concentration quenching mechanism was verified to be multipole–multipole interaction and critical energy transfer distance (RC) was 16.43 nm. The effects of different concentration of Eu3+ and charge compensations on luminescence properties were discussed. The highest PL intensity was recorded for 4 mol% Eu3+ ions. Further, Li+ (0.03) has the best charge compensation effect followed by Na+ and K+ respectively. The c-induced studies showed three glow peaks at 211, 163 and 243 (shouldered peaks) respectively at a warming rate of 5 �C s�1. The glow peak intensity at 163 �C increases linearly up to 3 kGy and after that it decreases. Up to 3 kGy, the phosphor was quite useful for radiation dosimetry.
    Journal of Alloys and Compounds 595 (2014) 192–199. 05/2014; 595:192-199.
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    ABSTRACT: Cobalt copper ferrite nanopowders with composition Co1-xCuxFe2O4 (0.0⩽x⩽0.5) was synthesized by solution combustion method. The powder X-ray diffraction studies reveal the formation of single ferrite phase with particle size of ∼11-35nm. Due to increase in electron density with in a material, X-ray density increase with increase of Cu(2+) ions concentration. As Cu(2+) ions concentration increases, saturation magnetization decreases from 38.5 to 26.7emug(-1). Further, the squareness ratio was found to be ∼0.31-0.46 which was well below the typical value 1, which indicates the existence of single domain isolated ferrimagnetic samples. The dielectric and electrical modulus was studied over a frequency range of 1Hz to 1MHz at room temperature using the complex impedance spectroscopy technique. Impedance plots showed only one semi-circle which corresponds to the contributions of grain boundaries. The lower values of dielectric loss at higher frequency region may be quite useful for high frequency applications such as microwave devices.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 05/2014; 132C:256-262. · 1.98 Impact Factor
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    ABSTRACT: Porous and irregular shaped nanoparticles of Sr2SiO4:Eu3+ and Sr2SiO4:Eu3+:M+ (M: Na, K, Li) are prepared by low temperature combustion synthesis of an aqueous solution of metal nitrates and oxalyl dihydrazide as the fuel (muffle furnace, 500 °C, 5 min) followed by grinding and heating of the resulting powder (900 °C, 2 h).
    ChemInform 05/2014; 45(18).
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    ABSTRACT: ZnO:Eu (0.1mol%) nanopowders have been synthesized by auto ignition based low temperature solution combustion method. Powder X-ray diffraction (PXRD) patterns confirm the nanosized particles which exhibit hexagonal wurtzite structure. The crystallite size estimated from Scherrer's formula was found to be in the range 35-39nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies reveal particles are agglomerated with quasi-hexagonal morphology. A blue shift of absorption edge with increase in band gap is observed for Eu doped ZnO samples. Upon 254nm excitation, ZnO:Eu nanopowders show peaks in regions blue (420-484nm), green (528nm) and red (600nm) which corresponds to both Eu(2+) and Eu(3+) ions. The electron paramagnetic resonance (EPR) spectrum exhibits a broad resonance signal at g=4.195 which is attributed to Eu(2+) ions. Further, EPR and thermoluminescence (TL) studies reveal presence of native defects in this phosphor. Using TL glow peaks the trap parameters have been evaluated and discussed.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 05/2014; 132C:305-312. · 1.98 Impact Factor
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    ABSTRACT: Despite extensive efforts to design a white light generating phosphor, single component phosphors which exhibit multi-color emissions are very limited. In this work we report synthesis of novel single component color tuneable strontium cerate (Sr2-xSmxCeO4) phosphor using facile low temperature solution combustion synthesis. A single-composition, color tuneable phosphor is produced by doping with different concentrations of Sm3+ into the Sr2CeO4 matrix. Chromaticity of Sr2-xSmxCeO4 depends sensitively on the Sm3+ concentration. This is because of energy transfer from Sr2CeO4 to Sm3+ determines the emission colors of the phosphors. At low concentration of Sm3+ Commission Internationale d'Eclairage (CIE) coordinates that are very close to white light emission (0.317, 0.303) is observed. However, at higher dopant concentration (x=0.11of Sm3+) the compound exhibits red emission (0.407, 0.343). Hence, a single host multi-color emitting phosphor is realized by doping and energy transfer. Thermoluminescence studies are carried out for Sr2CeO4: Sm3+ phosphor using γ-irradiation for the dose range of 1-6 KGy. The kinetic parameters namely activation energy (E), frequency factor (s) and order of kinetics (b) were estimated by Chen's glow peak shape method and are discussed in detail for their possible usage in dosimetry.
    Chemical Engineering Journal 05/2014; · 3.47 Impact Factor
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    ABSTRACT: Naocrystalline ferrites Mn1-xZnxFe2O4 (x = 0.00, 0.25, 0.50, 0.75 and 1.00) were prepared by combustion method. The samples were characterized by XRD technique. The dielectric measurements were carried out in the frequency range 40 Hz to 100 MHz at room temperature. All the measurements were performed before and after gamma 60Co irradiation. The X-ray diffraction patterns revealed the formation of nanocrystalline and single-phase spinel structure. The lattice parameter decrease with zinc ion concentration and increased after the irradiation due to ferric ions of smaller radius converted to ferrous ions of larger radius. The dielectric behavior is attributed to the Maxwell-Wagner type interfacial polarization. The dielctric contant, dielectric loss and AC conductivity enhanced after the irradiation.
    03/2014; 1591(1).
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    ABSTRACT: CaTiO3:Sm(3+) (1-11mol%) nanophosphors were successfully synthesized by a low temperature solution combustion method [LCS]. The structural and morphological properties of the phosphors were studied by using Powder X-ray diffractometer (PXRD), Fourier transform infrared (FTIR), X-ray photo electron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscopy (TEM). TEM studies indicate that the size of the phosphor is ∼20-35nm. Photoluminescence (PL) properties of Sm(3+) (1-11mol%) doped CaTiO3 for NUV excitation (407nm) was studied in order to investigate the possibility of its use in White light emitting diode (WLED) applications. The emission spectra consists of intra 4f transitions of Sm(3+), such as (4)G5/2→(6)H5/2 (561nm), (4)G5/2→(6)H7/2 (601-611nm), (4)G5/2→(6)H9/2 (648nm) and (4)G5/2→(6)H11/2 (703nm) respectively. Further, the emission at 601-611nm show strong orange-red emission and can be applied to the orange-red emission of phosphor for the application for near ultra violet (NUV) excitation. Thermoluminescence (TL) of the samples irradiated with gamma source in the dose range 100-500Gy was recorded at a heating rate of 5°Cs(-1). Two well resolved glow peaks at 164°C and 214°C along with shouldered peak at 186°C were recorded. TL intensity increases up to 300Gy and thereafter, it decreases with further increase of dose. The kinetic parameters namely activation energy (E), frequency factor (s) and order of kinetics were estimated and results were discussed in detail.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 03/2014; 128C:891-901. · 1.98 Impact Factor
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    ABSTRACT: Gd1.96-xYxEu0.04O3 (x=0.0, 0.49, 0.98, 1.47, 1.96mol%) nanophosphors were synthesized by propellant combustion method at low temperature (400°C). The powder X-ray diffraction patterns of as formed Gd1.96Eu0.04O3 showed monoclinic phase, however with the addition of yttria it transforms from monoclinic to pure cubic phase. The porous nature increases with increase of yttria content. The particle size was estimated from Scherrer's and W-H plots which was found to be in the range 30-40nm. These results were in well agreement with transmission electron microscopy studies. The optical band gap energies estimated were found to be in the range 5.32-5.49eV. PL emission was recorded under 305nm excitation show an intense emission peak at 611 nm along with other emission peaks at 582, 641nm. These emission peaks were attributed to the transition of (5)D0→(7)FJ (J=0, 1, 2, 3) of Eu(3+) ions. It was observed that PL intensity increases with increase of Y content up to x=0.98 and thereafter intensity decreases. CIE color co-ordinates indicates that at x=1.47 an intense red bright color can be achieved, which could find a promising application in flat panel displays. The cubic and monoclinic phases show different thermoluminescence glow peak values measured under identical conditions. The response of the cubic phase to the applied dose showed good linearity, negligible fading, and simple glow curve structure than monoclinic phase indicating that suitability of this phosphor in dosimetric applications.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 03/2014; 128C:730-739. · 1.98 Impact Factor
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    ABSTRACT: Y2SiO5 nanopowders are prepared by solution combustion method using DFH, sugar and urea as fuels. The final product was well characterized by powder X-ray diffraction, Scanning Electron Microscopy and UV-Vis spectroscopy. The average crystallite size was estimated using Debye-Scherer's formula and Williamson-Hall plots and are found to be in the range 34-40nm for DFH, 45-50nm for urea and 35-42nm for sugar respectively. X1-X2 type YSO phase was obtained for all the samples calcined from 1200 to 1400°C. The optical energy band gaps (Eg) of the samples were estimated from Tauc relation and varies from 5.58 to 5.60eV. SEM micrographs of sugar and urea used Y2SiO5 show agglomerated particles with porous morphology. However, for the sample prepared using DFH fuel observed to be almost spherical in shape. Thermoluminescence (TL) properties of γ-irradiated (1-5kGy) and UV irradiated (1-30min) Y2SiO5 nanopowder at a heating rate of 2.5°Cs(-1) was studied. The samples prepared by using urea and sugar fuels show a broad TL glow peak at 189°C. However, DFH used Y2SiO5 show a well resolved peak at 196°C with shouldered peak at 189°C. Among the fuels, DFH used Y2SiO5 show simple glow peak structure which perhaps useful in radiation dosimetry. This may be due to fuel and particle size effect. The kinetic parameters such as activation energy (E), frequency factor (s) and order of kinetics are estimated by Chens glow peak shape method.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 01/2014; 127:177–184. · 1.98 Impact Factor
  • Materials Research Bulletin. 01/2014; 55:237–245.
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    ABSTRACT: Zinc oxide nanoparticles (ZnO Nps) were successfully synthesized by solution combustion method (SCM) using pigeon pea as a fuel for the first time. X-Ray diffraction pattern reveals that the product belongs to hexagonal system. FTIR spectrum of ZnO Nps shows the band at 420 cm�1 associated with the characteristic vibration of Zn–O. TEM images show that the nanoparticles are found to be �40–80 nm. Furthermore, the as-prepared ZnO Nps exhibits good photocatalytic activity for the photodegradation of methylene blue (MB), indicating that they are indeed a promising photocatalytic semiconductor. The antibacterial properties of ZnO nanopowders were investigated by their bactericidal activity against four bacterial strains.
    Materials Research Bulletin 01/2014; 57:325-334. · 1.97 Impact Factor

Publication Stats

52 Citations
162.59 Total Impact Points

Institutions

  • 2010–2014
    • Tumkur University
      Tumkūr, Karnātaka, India
  • 2013
    • Bharathiar University
      Koyambattūr, Tamil Nādu, India
  • 2012
    • BMS Institute of Technology
      Bengalūru, Karnātaka, India
    • Dr. Ambedkar Institute of Technology
      Bengalūru, Karnātaka, India
  • 2011
    • M.S. Ramaiah Institute of Technology
      • Department of Physics
      Bengalore, State of Karnataka, India
  • 2003–2011
    • Bangalore University
      • Department of Physics
      Bengalore, State of Karnataka, India