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Ravikumar B.S.,Tumkur University | Nagabhushana H.,Tumkur University | Sharma S.C.,Chhattisgarh Swami Vivekananda Technical University | Vidya Y.S.,LBSGFGC | Anantharaju K.S.,East-West Center
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2015

ZnAl2O4:Cr3+ 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:Cr3+ 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 16-26 nm. The PL spectrum shows an intense peak at ∼688 and ∼699 nm assigned to spin - forbidden 2Eg → 4A2g transition of Cr3+ ions. The PL measurements for two excitations (∼410 and 527 nm) 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:Cr3+ 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. © 2014 Elsevier B.V. All rights reserved.


Vidya Y.S.,LBSGFGC | Anantharaju K.S.,East-West Center | Nagabhushana H.,Tumkur University | Sharma S.C.,Chhattisgarh Swami Vivekananda Technical University
Journal of Alloys and Compounds | Year: 2014

Eco-friendly, cost effective and bio template route was used for the preparation of cubic Gd2O3:Eu3+ nanophosphors using Euphorbia tirucalli (E. tirucalli) plant latex as fuel. As - formed Gd2O3:Eu3+ (7 mol%, 1-7 ml), calcined Gd2O3:Eu3+ (7 mol%, 1-7 ml) and Gd2O3:Eu3+ (1-11 mol%, 7 ml) samples were characterized using XRD, SEM and UV-Vis absorption spectrophotometer. With increase in latex concentration, 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: Eu3+ phase and it converts to pure cubic phase of Gd2O3:Eu3+ on calcination at 600 °C for 3 h. Rietveld refinement of Gd2O3:Eu3+ (7 mol%, 7 ml) revealed the presence of cations in the 8b (0.25, 0.25, 0. 25) and 24d positions (-0.0287, 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 Eu3+ ion activators and the high ratio of intensity of (5D0 → 7F2) and (5D0 → 7F1) provides the conclusion that Eu3+ 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 applications. Further, the Gd2O3:Eu3+ (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. © 2014 Elsevier B.V. All rights reserved.


Suresh D.,Tumkur University | Nethravathi P.C.,Tumkur University | Udayabhanu A.,Tumkur University | Nagabhushana H.,Tumkur University | And 2 more authors.
Ceramics International | Year: 2014

Spinach (Spinacia oleracea) leaves mediated efficient green reduction of graphene oxide (GO) was achieved to produce multifunctional reduced graphene oxide (rGO). GO was mixed with spinach juice and refluxed for 30 min at 100 °C. Powder XRD, TEM and UV-visible techniques demonstrate the formation of well-organized layered rGO. Industrially important carcinogenic Methylene blue (MB) and Malachite green (MG) dyes absorption experiments with rGO were performed under dark condition. Complete removal of MB and MG occurs in spans of 60 and 40 min respectively in the presence of 20 mg rGO. Potential antioxidant activity was exhibited by the rGO with 50% inhibitory concentration of 1590 μg/mL against the scavenging of 2, 2-diphenyl-1-picrylhydrazyl (DPPH) free radicals. Environment friendly, economical and facile reduction method is suggested for the efficient reduction of GO. © 2014 Elsevier Ltd and Techna Group S.r.l.


Monika D.L.,Tumkur University | Nagabhushana H.,Tumkur University | Krishna R.H.,M.S. Ramaiah Institute of Technology | Nagabhushana B.M.,M.S. Ramaiah Institute of Technology | And 2 more authors.
RSC Advances | Year: 2014

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. © the Partner Organisations 2014.


Suresh D.,Tumkur University | Shobharani R.M.,Tumkur University | Nethravathi P.C.,Tumkur University | Pavan Kumar M.A.,Tumkur University | And 3 more authors.
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2015

We report green synthesis of multifunctional ZnO nanoparticles (NPs) using Artocarpus gomezianus (AG) extract as fuel by solution combustion synthesis. The formation of NPs was confirmed by powder XRD, SEM, TEM and UV-Visible studies. The NPs were subjected for photoluminescence, photodegradative and antioxidant studies. XRD data reveals that the ZnO NPs possess wurtzite structure. UV-Visible spectrum shows absorbance maximum at 370 nm which corresponds to the energy band gap of 3.3 eV. Morphology studies indicate the highly porous nature of the NPs. PL spectra of NPs found to display very interesting blue, green and red emissions upon excitation at 325 nm. The NPs exhibit potential photocatalytic activity towards the degradation of methylene blue (MB) dye upon exposure to sun light and UV light. ZnO NPs found to have considerable antioxidant activity against DPPH (2,2-diphenyl-1-picrylhydrazyl) free radicals. The study successfully demonstrates a simple and eco-friendly method for the synthesis of efficient multifunctional ZnO nanoparticles using green synthetic approach. © 2015 Elsevier B.V. All rights reserved.


Vidya Y.S.,Lal Bahadur Shastry Government First Grade College | Anantharaju K.S.,East-West Center | Nagabhushana H.,Tumkur University | Sharma S.C.,Chhattisgarh Swami Vivekananda Technical University | And 4 more authors.
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2015

Novel crystalline tetragonal ZrO2: Eu3+ 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 ZrO 2: Eu3+ (1-11 mol%) 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 7-17 nm. 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 4.3-4.7 eV. Photoluminescence (PL) emission was recorded under 394 and 464 nm excitation shows an intense emission peak at 605 nm along with other emission peaks at 537, 592, 605 and 713 nm. These emission peaks were attributed to the transition of 5D0 → 7FJ (J = 0, 1, 2, 3) of Eu3+ ions. The high ratio of Intensity of (5D0 → 7F2) and (5D0 → 7F1) infers that Eu3+ 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. © 2014 Elsevier B.V. All rights reserved..


Ramakrishna G.,Tumkur University | Nagabhushana H.,Tumkur University | Prashantha S.C.,East-West Center | Sharma S.C.,Chhattisgarh Swami Vivekananda Technical University | Nagabhushana B.M.,M.S. Ramaiah Institute of Technology
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2015

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:Sm3+ (1-9 mol%) 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 10-50 nm. 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 Sm3+ (1-9 mol%) doped YSO for near ultra violet (NUV) excitation (407 nm) 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 Sm3+, such as 4G5/2 → 6H5/2 (∼560 nm), 4G5/2 → 6H7/2 (600-613 nm), 4G5/2 → 6H9/2 (∼650 nm), 4G5/2 → 6H11/2 (715 nm) and 4G5/2 → 6H13/2 (763 nm) respectively. The emission intensity of the phosphor was found to be enhancing after addition of fluxes. Further, the emission at 600-613 nm show strong orange-red emission and can be applied to the orange-red emission of phosphor for near ultra violet excitation. © 2014 Elsevier B.V. All rights reserved.


Malleshappa J.,Tumkur University | Nagabhushana H.,Tumkur University | Prashantha S.C.,East West Institute of Technology | Sharma S.C.,Chhattisgarh Swami Vivekananda Technical University | And 3 more authors.
Journal of Alloys and Compounds | Year: 2014

The investigation involves preparation and photoluminescence properties of CeO2:Eu3+ (1-11 mol%) nano phosphors by eco-friendly green combustion route using Euphorbia tirucalli plant latex as fuel. The final product was characterized by powder X-ray diffraction (PXRD), Scanning electron microcopy (SEM) and Transmission electron microscopy (TEM). The PXRD and SEM results reveals cubic fluorite phase with flaky structure. The crystallite size obtained from TEM was found to be ∼20-25 nm, which was comparable to W-H plots and Scherrer's method. Photoluminescence (PL) emission of all the Eu 3+ doped samples shows characteristic bands arising from the transitions of 5D0 → 5FJ (J = 0, 1, 2, 3, 4) manifolds under excitation at 373 and 467 nm excitation. The 5D0 → 7F2 (613 nm) transition often dominate the emission spectra, indicating that the Eu3+ cations occupy a site without inversion center. The highest PL intensity was recorded for 9 mol% Eu3+ ions with 5 ml latex. PL quenching was observed upon further increase in Eu3+ concentration. The international commission on illumination (CIE) chromaticity co-ordinates were calculated from emission spectra, the values (x, y) were very close to national television system committee (NTSC) standard values of pure red emission. The results demonstrate that the synthesized phosphor material could be very useful for display applications. Further, the phosphor material prepared by this method was found to be non toxic, environmental friendly and could be a potential alternative to economical routes. © 2014 Elsevier Inc. All rights reserved.


Suresh D.,Tumkur University | Udayabhanu,Tumkur University | Pavan Kumar M.A.,Tumkur University | Nagabhushana H.,Tumkur University | And 2 more authors.
Materials Letters | Year: 2015

Abstract A simple and efficient method of reduction for the preparation of reduced graphene oxide (rGO) from graphene oxide (GO) using Cinnamon (Cinnamomum zeylanicum) extract is reported. The reduction of GO was confirmed by XRD, TEM and UV-visible techniques. The rGO has shown to possess significantly high dye removal property of Malachite green (MG) and Methylene blue (MB) dyes in the absence of UV or Sun light. Further, it showed considerable antioxidant activity against scavenging of 1, 1-Diphenyl-2-picrylhydrazyl (DPPH) free radicals. The study illustrates an environment friendly green method for the efficient reduction of GO. © 2015 Elsevier B.V. All rights reserved.


Vidya Y.S.,Lal Bahadur Shastri Government First Grade College | Gurushantha K.,East-West Center | Nagabhushana H.,Tumkur University | Sharma S.C.,Chhattisgarh Swami Vivekananda Technical University | And 6 more authors.
Journal of Alloys and Compounds | Year: 2015

The current study involves synthesis of a series of Tb3+ doped ZrO2 nanophosphors by solution combustion method using oxalyl dihydrazide as fuel. The as-formed ZrO2:Tb3+ nanophosphors having different concentrations of Tb3+ (1-11 mol%) were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-Visible spectroscopic techniques and the materials were subjected to photoluminescence and photocatalytic dye decolorization studies. The PXRD analysis indicates the formation of tetragonal symmetry up to 5 mol% concentration of Tb3+. Further increase in Tb3+ concentration has lead to cubic phase formation and the same was confirmed by Rietveld refinement analysis. SEM images revealed that material was highly porous in nature comprising of large voids and cracks with irregular morphology. TEM and SAED images clearly confirm the formation of high quality tetragonal nanocrystals. The emissive properties of nanophosphors were found to be dependent on Tb3+ dopant concentration. The green emission of the material was turned to white emission with the increase of Tb3+ ion concentration. The photocatalytic activities of these nanophosphors were probed for the decolorization of Congo red under UV and Sunlight irradiation. All the photocatalysts showed enhanced activity under UV light compared to Sunlight. The photocatalyst with 7 mol% Tb3+ showed enhanced activity attributed to effective separation of charge carriers due to phase transformation from tetragonal to cubic. The influence of crystallite size and PL on charge carrier trapping-recombination dynamics was investigated. The study successfully demonstrates synthesis of tetragonal and cubic ZrO2:Tb3+ green nanophosphors with superior photoluminescence and photocatalytic activities. © 2014 Elsevier B.V. All rights reserved.

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