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Umesh B.,PVP Polytechnic | Nagabhushana H.,Tumkur University | Sharma S.C.,BMS College of Engineering | Eraiah B.,Bangalore University | And 4 more authors.
Journal of Alloys and Compounds | Year: 2014

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 Nd 2O3 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. © 2013 Elsevier B.V. All rights reserved. Source


Umesh B.,PVP Polytechnic | Umesh B.,Bangalore University | Eraiah B.,Bangalore University | Nagabhushana H.,Tumkur University | And 5 more authors.
Journal of Alloys and Compounds | Year: 2011

Spherical and rod like nanocrystalline Nd2O3 phosphors have been prepared by solution combustion and hydrothermal methods respectively. The Powder X-ray diffraction (PXRD) results confirm that hexagonal A-type Nd2O3 has been obtained with calcination at 900 °C for 3 h and the lattice parameters have been evaluated by Rietveld refinement. Surface morphology of Nd2O3 phosphors show the formation of nanorods in hydrothermal synthesis whereas spherical particles in combustion method. TEM results also confirm the same. Raman studies show major peaks, which are assigned, to Fg and combination of Ag + Eg modes. The PL spectrum shows a series of emission bands at ∼326-373 nm (UV), 421-485 nm (blue), 529-542 nm (green) and 622 nm (red). The UV, blue, green and red emission in the PL spectrum indicates that Nd 2O3 nanocrystals are promising for high performance materials and white light emitting diodes (LEDs). © 2010 Elsevier B.V. All rights reserved. Source


Nagabhushana H.,Government Science College | Nagabhushana B.M.,M.S. Ramaiah Institute of Technology | Umesh B.,PVP Polytechnic | Premkumar H.B.,Bangalore University | And 3 more authors.
Philosophical Magazine | Year: 2010

Enstatite (MgSiO3) ceramic powders were synthesised by a low-temperature initiated self-propagating, gas-producing solution combustion process. The prepared powders were characterised by powder X-ray diffraction, scanning electron microscopy and Brunauer-Emmer-Teller specific surface area measurements. Defect centres induced by radiation were studied using the techniques of thermoluminescence (TL) and electron spin resonance (ESR). A well-resolved glow with peak at 178°C and a shouldered peak at 120°C were observed. Two defect centres were identified by ESR measurements, which were carried out at room temperature, and these were assigned to an O- ion and F+ centre. The O- ion (hole centre) appears to correlate with the main TL peak at 178°C. Source


Umesh B.,PVP Polytechnic | Umesh B.,Bangalore University | Eraiah B.,Bangalore University | Nagabhushana H.,Tumkur University | And 5 more authors.
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2012

Nanocrystalline Nd 2O 3:Cu 2+ (2 mol %) phosphors have been prepared by a low temperature solution combustion technique. Powder X-ray diffraction (PXRD) results confirm that hexagonal A-type Nd 2O 3 (900°C, 3 h) and the lattice parameters have been evaluated by Rietveld refinement. Surface morphology of as-formed and Cu 2+ doped Nd 2O 3 phosphors show that the particles are irregular in shape and porous in nature. TEM results also confirm the nature and size of the particles. The EPR spectrum exhibits two resonance signals with effective g values at g≈ 2.12 and g ⊥ ≈ 2.04. The g values indicate that the site symmetry of Cu 2+ ions is octahedral symmetry with elongated tetragonal distortion. Raman studies show major peaks, which are assigned, to F g and combination of A g + E g modes. It is observed that the Raman peaks and intensity have been reduced in Cu 2+ doped samples. UV-Visible absorption spectra exhibit a strong and broad absorption band at ∼240 nm. Further, the absorption peak shifts to ∼14 nm in Cu 2+ doped samples. The optical band gap is estimated to be 5.28 eV for Cu doped Nd 2O 3 nanoparticles which are higher than the bulk Nd 2O 3 (4.7 eV). This can be attributed to the quantum confinement effect of the nanoparticles. © 2012 Elsevier B.V. All rights reserved. Source


Umesh B.,PVP Polytechnic | Umesh B.,Bangalore University | Eraiah B.,Bangalore University | Nagabhushana H.,Tumkur University | And 6 more authors.
Materials Research Bulletin | Year: 2013

Nd2O3:Co2+ (1-4 mol%) nanophosphors (15-25 nm) have been prepared via low temperature solution combustion method. Scanning electron micrograph (SEM) shows that the product is highly porous in nature. The stokes line in the Raman spectrum at ∼2000 cm-1 is assigned to Fg mode and the anti-stokes lines are assigned to a combination of Ag + Eg modes. With increase of Co2+ concentration, the intensity of Fg mode decreases, whereas the combination of Ag + Fg modes completely disappears. Electron paramagnetic resonance (EPR) spectrum exhibits two resonance signals with effective g values at g = 2.25 and g = 2.03. Thermoluminescence (TL) response of Nd2O3:Co2+ nanopowders with γ dose 0.23-2.05 kGy was studied. The activation energy (E) and frequency factor (s) are estimated using Chen's glow peak shape method and obtained to be in the range 0.45-1.67 eV and 1.8 × 104 to 4.0 × 1012 s-1, respectively. It is observed that the TL glow peak intensity at 430 K increases linearly with γ dose which is suitable for radiation dosimetry. © 2012 Elsevier Ltd. Source

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