H. Nagabhushana

Tumkur University, Tumkūr, Karnātaka, India

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Publications (103)140.79 Total impact

  • Article: ww
    07/2014;
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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: 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 substituted cobalt ferrite powders {Co(1−x)ZnxFe2O4} (0.0 ⩽ x ⩽ 0.5) were prepared by the solution combustion method. The structural, morphological, magnetic and electrical properties of as synthesized samples were studied. Powder X-ray diffraction patterns reveals single phase, cubic spinel structure with space group No. Fd3¯m (2 2 7). As zinc concentration increases, the lattice constant increases and the crystallite size decreases. The minimum crystallite size of ∼12 nm was observed for x = 0.5 composition. The synthesized ferrite compounds show ferrimagnetic behavior, with coercivity value of 10779 Oe (Hard ferrite) at 20 K and 1298 Oe (soft ferrite) at room temperature (RT). The maximum saturation magnetization recorded for the Co0.5Zn0.5Fe2O4 composition was 99.78 emu g−1 and 63.83 emu g−1 at 20 K and RT respectively. The dielectric parameters such as dielectric constant, loss tangent and AC conductivity were determined as a function of frequency at RT. The magnetic and dielectric properties of the samples illustrates that the materials were quite useful for the fabrication of nanoelectronic devices.
    Journal of Alloys and Compounds 01/2014; 587:50–58. · 2.39 Impact Factor
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    ABSTRACT: Graphical abstract Variation of dielectric loss tangent (tan δ) with frequency for Co1−xCuxFe2O4 nanopowder.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 01/2014; 132:256–262. · 1.98 Impact Factor
  • Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 01/2014; 132:305–312. · 1.98 Impact Factor
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    ABSTRACT: Preparation of nanocrystalline Nd2O3:Gd3+ (2 mol%) phosphor was prepared by propellant combustion route at low temperature. Powder X-ray diffraction (PXRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques were used to study the structural and morphological features. A and C type hexagonal phase of Nd2O3 was obtained in as-formed and calcined product at 900 °C for 3 h. SEM images show the product was highly porous, agglomerated and irregular shaped particles. The average crystallite size estimated from Scherrer’s and W–H plots were found to be in the range ∼20–50 nm. Combination of Fg and (Fg + Eg) modes were observed from Raman studies. A single TL glow peak at 409 K was recorded at a warming rate 5 °C s−1. TL response as a function of γ-irradiation showed linear response up to 1.6 kGy and later it followed exponential growth. The phosphor show simple glow curve structure with less fading over a period of 30 days. Trap parameters were estimated from Chen’s peak shape method. The activation energy (E) and frequency factor (s) was found to in the range 1.377–2.934 eV and 2.01 × 1011–8.70 × 1022 Hz respectively.
    Journal of Alloys and Compounds 01/2014; 591:286–292. · 2.39 Impact Factor
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    ABSTRACT: This work explores the preparation of nanocrystalline Cr(3+) (1-5mol%) doped CaSiO3 phosphors by solution combustion process and study of its photoluminescence (PL) behavior. The nanopowders are well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra-red (FTIR) spectroscopy. PXRD results confirm monoclinic phase upon calcination at 950°C for 3h. SEM micrographs indicates that the powder is highly porous and agglomerated. The TEM images show the powder to consist of spherical shaped particles of size ∼30-60nm. Upon 323nm excitation, the emission profile of CaSiO3:Cr(3+) exhibits a narrow red emission peak at 641nm due to (2)E→(4)A2transition and broad band at 722nm due to (4)T2g→(4)A2g. It is observed that PL intensity increases with increase in Cr(3+) concentration and highest PL intensity is observed for 3mol% doped sample. The PL intensity decreases with further increase in Cr(3+) doping. This decrease in PL intensity beyond 3mol% is ascribed to concentration quenching. Racah parameters are calculated to describe the effects of electron-electron repulsion within the crystal lattice. The parameters show 21% reduction in the Racah parameter of free ion and the complex, indicating the moderate nephelauxetic effect in the lattice.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 01/2014; 128:403–407. · 1.98 Impact Factor
  • Chemical Engineering Journal. 01/2014; 253:155–164.
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    ABSTRACT: Undoped and Tb3+ (1–10 mol%) doped CeO2 nanophosphors were synthesized by low temperature solution combustion method. The combustion derived products were well studied by Powder X-ray diffraction (PXRD), Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and Ultraviolet visible (UV–Vis) characterizations. The thermoluminescence (TL) glow curves of CeO2:Tb3+ (1–10 mol%) nanophosphors exposed to γ source (60Co) for various doses were discussed for the first time. Two TL glow peaks recorded at 182 and 262 °C respectively. The TL intensity at 262 °C peak increases linearly in the dose range 0.5–7 kGy. Further, this peak was well defined, intense and glow peak structure does not change with γ-dose as a result, it was quite useful in TL dosimetry of ionizing radiations. The kinetic parameters associated with the glow peak were estimated using Chen’s half width method. The photoluminescence emission (PLE) spectra consists of characteristic peaks at 544 and 655 nm which were attributed to 5D4 → 7F5 and 5D4 → 7F2 transitions of Tb3+ ions. The optimal concentration of Tb3+ ions was found to be 7 mol%. The color co-ordinates of CeO2:Tb3+ (1–10 mol%) located in green region. Hence, this phosphor was quite useful for display applications.
    Journal of Alloys and Compounds 01/2014; 590:131–139. · 2.39 Impact Factor

Publication Stats

47 Citations
140.79 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