H. Nagabhushana

Tumkur University, Tumkūr, Karnātaka, India

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Publications (128)200.41 Total impact

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    ABSTRACT: a b s t r a c t Eco-friendly, cost effective and bio template route was used for the preparation of cubic Gd 2 O 3 :Eu 3+ nanophosphors using Euphorbia tirucalli (E. tirucalli) plant latex as fuel. As – formed Gd 2 O 3 :Eu 3+ (7 mol%, 1–7 ml), calcined Gd 2 O 3 :Eu 3+ (7 mol%, 1–7 ml) and Gd 2 O 3 :Eu 3+ (1–11 mol%, 7 ml) samples were characterized using XRD, SEM and UV–Vis absorption spectrophotometer. With increase in latex concen-tration, the nanophosphor gets transformed from nano plates to rose – like nanoflowers with size varying from 20 to 30 nm. X-ray diffraction pattern of as – formed product shows hexagonal Gd (OH) 3 : Eu 3+ phase and it converts to pure cubic phase of Gd 2 O 3 :Eu 3+ on calcination at 600 °C for 3 h. Rietveld refinement of Gd 2 O 3 :Eu 3+ (7 mol%, 7 ml) revealed the presence of cations in the 8b (0.25, 0.25, 0. 25) and 24d positions (À0.0287, 0.00, 0. 25) and the anions in the 48e positions (0.39, 0.15, 0. 37) with space group Ia-3(206). The photoluminescence intensities of transitions between different J levels depend on the symmetry of the local environment of Eu 3+ ion activators and the high ratio of intensity of (5 D 0 ? 7 F 2) and (5 D 0 ? 7 F 1) provides the conclusion that Eu 3+ ion occupies sites with a low symmetry and without an inversion centre. The chromaticity and the CIE coordinates were very close to the standard red color region. The absorption observed in the excitation spectra shows the suitability of the nanophosphor obtained in this study for getting excited in UV, NUV and visible regions for variety of display applica-tions. Further, the Gd 2 O 3 :Eu 3+ (7 mol%, 1–7 ml) samples were experimented towards the photocatalytic behavior on Congo red (CR) and correlated with emission of PL intensity. The decolorization of dye was found to decreased from 83 to 54% with increase in the plant latex concentration. Ó 2014 Elsevier B.V. All rights reserved.
    09/2015;
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    ABSTRACT: ZrO2:Tb3+ nanophosphors were synthesized by low temperature combustion method.•The crystal structure changes from tetragonal to cubic symmetry.•CIE chromaticity coordinates gets tuned from pale green to warm white.•It may find potential applications in luminescence devices especially in WLED’s.•Superior photocatalytic activity was observed for ZrO2:Tb3+ (7 mol%) photocatalyst.
    Journal of Alloys and Compounds 02/2015; 622. · 2.73 Impact Factor
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    ABSTRACT: Stolzite polymorph of PbWO4 catalyst was prepared by the facile room temperature precipitation method. Structural parameters were refined by the Rietveld analysis using powder X-ray data. PbWO4 was crystallized in the scheelite-type tetragonal structure with space group I41/a (No. 88). Field emission scanning electron microscopy revealed leaf like morphology. Photoluminescence spectra exhibit broad blue emission (425 nm) under the excitation of 356 nm. The photocatalytic degradation of Methylene blue, Rhodamine B and Methyl orange dyes were measured under visible illumination. The 100% dye degradation was observed for MB and RhB dyes within 60 and 105 min. The rate constant was found to be in the decreasing order of MB > RhB > MO which followed the 1st order kinetic mechanism. Therefore, PbWO4 can be a potential candidate for blue component in white LEDs and also acts as a catalyst for the treatment of toxic and non-biodegradable organic pollutants in water.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 02/2015; 136:348-355. · 1.98 Impact Factor
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    ABSTRACT: The study involves preparation of samarium doped Y2SiO5 (YSO) nano powders by solution combustion method using urea as a fuel for the first time. Effect of different fluxes on the crystallization behavior, morphology and photoluminescence (PL) properties of YSO:Sm(3+) (1-9mol%) were investigated. The final product was characterized by Powder X-ray diffraction (PXRD), Scanning Electron Microscopy (SEM) and UV-Vis spectroscopy. The average crystallite size estimated by Debye-Scherer's and Williamson-Hall plots were found to be in the range of 10-50nm. Samples calcined at 1100°C show pure monoclinic X1 phase; whereas, samples calcined at 1200 and 1300°C show pure X2 phase of YSO. Photoluminescence (PL) studies of Sm(3+) (1-9mol%) doped YSO for near ultra violet (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 (∼560nm), (4)G5/2→(6)H7/2 (600-613nm), (4)G5/2→(6)H9/2 (∼650nm), (4)G5/2→(6)H11/2 (715nm) and (4)G5/2→(6)H13/2 (763nm) respectively. The emission intensity of the phosphor was found to be enhancing after addition of fluxes. Further, the emission at 600-613nm show strong orange-red emission and can be applied to the orange-red emission of phosphor for near ultra violet excitation. Copyright © 2014 Elsevier B.V. All rights reserved.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 02/2015; 136 Pt B:356-65. · 1.98 Impact Factor
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    ABSTRACT: Scheelite-type MWO4 (M = Ca, Sr, and Ba) nanophosphors were synthesized by the precipitation method. All compounds crystallized in the tetragonal structure with space group I41/a (No. 88). Scherrer’s and TEM results revealed that the average crystallite size varies from 32 to 55 nm. FE-SEM illustrate the spherical (CaWO4), bouquet (SrWO4), and fish (BaWO4) like morphologies. PL spectra indicate the broad emission peak maximum at 436 (CaWO4), 440 (SrWO4), and 433 nm (BaWO4) under UV excitation. The calculated CIE color coordinates of MWO4 nanophosphors are close to the commercial BAM and National Television System Committee blue phosphor. The photocatalytic activities of MWO4 were investigated for the degradation of methylene blue dye under UV illumination. At pH 3, BaWO4 nanocatalyst showed 100% dye degradation within 60 min. The photocatalytic activity was in the decreasing order of BaWO4 > CaWO4 > SrWO4 under both neutral and acidic conditions.
    Materials Research Bulletin 01/2015; 61:422-432. · 1.97 Impact Factor
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    ABSTRACT: A series of scheelite-type Eu3+-activated CaMoO4 phosphors were synthesized by the nitrate–citrate gel combustion method. All the compounds crystallized in the tetragonal structure with space group I4 1 /a (No. 88). FESEM results reveal the spherical-like morphology. The CaMoO4 phosphor exhibited broad emission centered at 500 nm under the excitation of 298 nm wavelength, while Eu3+-activated CaMoO4 shows an intense characteristic red emission peak at 615 nm at different excitation wavelengths, due to 5D0 → 7F2 transition of Eu3+ ions. The intensities of transitions between different J levels depend on the symmetry of the local environment of Eu3+ ions and were estimated using the Judd–Ofelt analysis. The high asymmetric ratio revealed that Eu3+ occupies sites with a low symmetry and without an inversion center. The CIE chromaticity co-ordinates (x, y) were calculated from emission spectra, and the values were close to the NTSC standard. Therefore, the present phosphor is highly useful for LEDs applications.
    Journal of Materials Science 01/2015; 50(1). · 2.31 Impact Factor
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    ABSTRACT: Graphical abstract PL Emission and CIE diagram of Mg2SiO4:Tb3+ nanophosphor.
    Journal of Alloys and Compounds 12/2014; 617:69–75. · 2.73 Impact Factor
  • Journal of Alloys and Compounds 12/2014; 616:284–292. · 2.73 Impact Factor
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    ABSTRACT: TiO2:Ag nanoparticles have been successfully prepared at 120 1C in one day using an ionic liquid assisted hydrothermal method with methoxyethyl methyl imidazolium methanesulfonate as the ionic liquid. The obtained product was characterized using various techniques. The XRD pattern indicated the formation of TiO2:Ag nanoparticles, the average crystallite size was found to be 40 nm. XPS confirmed the formation of TiO2:Ag nanoparticles. The UV-Vis spectrum indicated a maximum absorbance at 362 nm which is red shifted compared to nano-sized TiO2. The surface morphology was analyzed using SEM, which shows a leaf-like structure for the TiO2:Ag nanoparticles. TEM images showed almost elliptically (rice pellet) shaped nanoparticles with an average particle size of about 60 nm. The EDS spectrum revealed the presence of Ti, O and Ag with atomic percentages of 42.6, 43.7 and 2.3%, respectively. The TiO2:Ag nanoparticles generate 2230 mmol H2 per 1 g of photocatalyst in 2.5 h via the water splitting reaction. They also show good photocatalytic activity in the degradation of trypan blue.
    New Journal of Chemistry 11/2014; · 3.16 Impact Factor
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    ABSTRACT: Zinc oxide nanoparticles were synthesized by gel-combustion method using a novel bio-fuel tapioca starch pearls, derived from the tubers of Mannihot esculenta. The product is characterized using various techniques. X-Ray diffraction pattern correspond to a hexagonal zincite structure. Fourier transform infrared spectrum showed main absorption peaks at 394 and 508 cm-1 due to stretching vibration of Zn-O. Ultravoilet-Visible spectrum of zinc oxide nanoparticles showed absorption maximum at 373 nm whereas the maximum of the bulk zinc oxide was 377 nm. The morphology of the product was studied using scanning electron microscopy and transmission electron microscopy. The scanning electron microscopic images showed that the products are agglomerated and porous in nature. The transmission electron microscopic images revealed spherical particles of 40- 50 nm diameter. The photocatalytic degradation of methylene blue was examined using zinc oxide nanoparticles and found more efficient in sunlight than ultra-violet light due to reduced band gap. The antibacterial properties of zinc oxide nanoparticles was investigated against four bacterial strains Klebsiella aerogenes, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aereus, where Pseudomonas. aeruginosa and Staphylococcus. aereus exhibited significant antibacterial activity in agar well diffusion method when compared to positive control.
    Materials Characterization 11/2014; · 1.88 Impact Factor
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    ABSTRACT: A simple and low-cost solution combustion method was used to prepare Eu(3+) (1-11mol%) doped Zn2TiO4 nanophosphors at 500°C using zinc nitrates as precursors and oxalyl di-hydrazide (ODH) as fuel. The final product was calcined at 1100°C for 3h and then characterized by powder X-ray diffraction (PXRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-visible absorption (UV-Vis). The PXRD patterns of the sample calcined at 1100°C show pure cubic phase. The crystallite size was estimated using Scherrer's method and found to be in the range 20-25nm and the same was confirmed by TEM studies. Effects of Eu(3+) (1-11mol%) cations on the luminescence properties of Zn2TiO4 nanoparticles were studied. The samples exhibit intense red emission upon 395nm near ultra violet (NUV) excitation. The characteristic emission peaks recorded at ∼578, 592, 613 and 654nm may be attributed to the 4f-4f intra shell transitions ((5)D0→(7)Fj=0,1,2,3) of Eu(3+) cations. The CIE chromaticity co-ordinates and CCT were calculated from emission spectra and the values (x, y) were very close to NTSC standard values for red emission and CCT was close to Plankian locus. Therefore, the present phosphor may be highly useful for display applications. Copyright © 2014 Elsevier B.V. All rights reserved.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 11/2014; · 1.98 Impact Factor
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    ABSTRACT: PL emission spectra and CIE diagram of MgO:Dy3 + nanophosphor.
    Materials Characterization 11/2014; 97:27–36. · 1.88 Impact Factor
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    ABSTRACT: Cubic ZrO2: Fe3+ (0.5–4 mol%) nanoparticles (NPs) were synthesized via bio-inspired, inexpensive and simple route using Phyllanthus acidus as fuel. PXRD, SEM, TEM, FTIR, UV absorption and PL studies were performed to ascertain the formation of NPs. Rietveld analysis confirmed the formation of cubic structure. The influence of Fe3+ on the structure, morphology, UV absorption, PL emission and photocatalytic activity of NPs were investigated. The CIE chromaticity coordinates (0.36, 0.41) show that NPs could be a promising candidate for white LEDs. The influence of Fe3+ on ZrO2 matrix for photocatalytic degradation of AO7 was evaluated under UVA and Sunlight irradiation. The enhanced photocatalytic activity of spherical shaped ZrO2: Fe3+ (2 mol%) under UVA light was attributed to dopant concentration, crystallite size, narrow band gap, textural properties and capability for reducing the electron–hole pair recombination. The trend of inhibitory effect in the presence of different radical scavengers were followed the order SO42− > Cl− > C2H5OH > HCO3− > CO32−. The recycling catalytic ability of the ZrO2: Fe3+ (2 mol%) was also evaluated with a negligible decrease in the degradation efficiency even after the sixth successive run.
    Journal of Molecular Catalysis A Chemical 11/2014; · 3.19 Impact Factor
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    ABSTRACT: Rod like structures of hexagonal Y(OH)3:Ni2+ and cubic Y2O3:Ni2+ phosphors have been successfully synthesized by solvothermal method. X-ray diffraction studies of as-formed product shows hexagonal phase, whereas the product heat treated at 700 °C shows pure cubic phase. Scanning electron micrographs (SEM) of Y(OH)3:Ni2+ show hexagonal rods while Y2O3:Ni2+ rods were found to consist of many nanoparticles stacked together forming multi-particle-chains. EPR studies suggest that the site symmetry around Ni2+ ions is predominantly octahedral. PL spectra show emission in blue, green and red regions due to the 3T1(3P)→3A2(3F), 1T2(1D)→3A2(3F) and 1T2(1D)→3T2(3F) transitions of Ni2+ ions, respectively. TL studies were carried out for Y(OH)3:Ni2+ and Y2O3:Ni2+ phosphor upon γ-dose for 1–6 kGy. A single well resolved glow peaks at 195 and 230 °C were recorded for Y(OH)3:Ni2+ and Y2O3:Ni2+, respectively. The glow peak intensity increases linearly up to 4 kGy and 5 kGy for Y(OH)3:Ni2+ and Y2O3:Ni2+, respectively. The kinetic parameters such as activation energy (E), frequency factor (s) and order of kinetics (b) were estimated by different methods. The phosphor follows simple glow peak structure, linear response with gamma dose, low fading and simple trap distribution, suggesting that it is quite suitable for radiation dosimetry.
    Journal of Luminescence 11/2014; 155:125–134. · 2.14 Impact Factor
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    ABSTRACT: ZnAl2O4:Cr(3+) nanophosphors were synthesized for the first time by a simple and environment friendly route using Calotropis procera milk latex as fuel. The structural and surface morphological studies were carried out using powder X-ray diffraction (PXRD), scanning electron microscopy and transmission electron microscopy techniques. The photoluminescence (PL) properties of ZnAl2O4:Cr(3+) as a function of dopant concentration and calcination temperature was studied in detail. The PXRD patterns and Rietveld confinement confirmed the cubic crystal system with space group Fd-3m. The crystallite size estimated from Scherrer's and W-H plots was found to be in the range of 16-26nm. The PL spectrum shows an intense peak at ∼688 and ∼699nm assigned to spin - forbidden (2)Eg→(4)A2g transition of Cr(3+) ions. The PL measurements for two excitations (∼410 and 527nm) and with respect to calcination temperature indicated no significant change in the shape and position of emission peak except PL intensity. The CIE chromaticity coordinates lies well within the white region. Thermoluminescence (TL) studies revealed well resolved glow peak at ∼212°C with a small shoulder at 188 and 233°C. The glow peak intensity at ∼212°C increases linearly with γ-dose which suggest ZnAl2O4:Cr(3+) is suitable candidate for radiation dosimetric applications. The activation energy (E in eV), order of kinetics (b) and Frequency factor (s) were estimated using glow peak shape method. Copyright © 2014 Elsevier B.V. All rights reserved.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 10/2014; 136PB:1027-1037. · 1.98 Impact Factor
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    ABSTRACT: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
    09/2014; doi.
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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

Publication Stats

75 Citations
200.41 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