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Singh V.,Konkuk University | Sivaramaiah G.,Government College for Men Autonomous | Rao J.L.,Sri Venkateswara University | Kim S.H.,Konkuk University
Materials Research Bulletin | Year: 2014

The LaMgAl11O19:Cr3+phosphor has been prepared by a low-temperature combustion synthesis method. As-prepared combustion synthesized powder was characterized using powder X-ray diffraction (XRD), diffuse reflectance (DRS), electron paramagnetic resonance (EPR) and photoluminescence (PL) studies. The X-ray diffraction pattern reveals crystalline hexagonal phases. The UV-vis diffuse reflectance spectrum exhibits three broad bands characteristic of Cr3+ions in octahedral symmetry. The EPR spectrum exhibits several resonance signals. The signals with the effective g values at g = 4.84, 3.64 and 2.26 have been attributed to the isolated Cr3+ions. The signal with the effective g value at g = 1.94 has been attributed to exchange coupled Cr3+-Cr3+ion pairs. The PL studies exhibit several bands characteristic of Cr3+ions in octahedral symmetry. © 2014 Elsevier Ltd. All rights reserved.


Singh V.,Konkuk University | Sivaramaiah G.,Government College for Men Autonomous | Rao J.L.,Sri Venkateswara University | Singh N.,Konkuk University | And 6 more authors.
Journal of Electronic Materials | Year: 2016

Gallium garnets of lanthanides are multifunctional materials especially known for their complicated structure and magnetic properties. In addition, with a suitable transition metal dopant ion, these matrices have been proved to be excellent materials for lasers. In particular, gallium garnet of ytterbium (Yb3Ga5O12) is known to possess excellent properties with regards to these applications. In this connection, Yb3Ga5O12 doped with Cr3+ nanophosphors were synthesized by a solution combustion route. The synthesized material was characterized by powder x-ray diffraction and scanning electron microscopy for phase purity and homogenous morphology. In order to ascertain the oxidation state of the doped ion, diffuse reflectance (DRF), photoluminescence (PL) and electron paramagnetic resonance (EPR) experiments were performed on the sample. The DRF and PL data suggested the stabilisation of the trivalent Cr ion in the matrix. The EPR spectra exhibited two resonance signals with effective g values at g ≈ 7.6 and 4. The EPR data corroborated the DRF and PL results, suggesting the stabilisation of Cr3+ in the matrix at octahedral-type geometries. © 2016 The Minerals, Metals & Materials Society


Bhakshu L.M.,Government College for Men Autonomous | Venkata Ratnam K.,Rayalaseema University | Venkata Raju R.R.,Sri Krishnadevaraya University
Indian Journal of Natural Products and Resources | Year: 2016

The ethno-medico-botanical studies in Eastern Ghats provided an evidence for the tribal claims on the usage of medicinal plants for various human infectious diseases. The present investigation focused on the anticandidal activity of certain medicinal plants used for infectious diseases. The plant samples were extracted with solvents initially with petroleum ether followed by ethyl acetate and ethyl alcohol and the extracts were tested for anticandidal activity. The results indicated that, the extracts of twenty three medicinal plants significantly inhibited the growth of the test pathogen. The details of anticandidal activity, Minimum Inhibition Concentration (MIC) of active extracts and their phytochemical analysis with respect to alkaloids, flavonoids, glycosides, terpenes, saponins and essential oils were provided. The plants namely Andrographis nallamalayana Ellis, Boswellia ovalifoliolata Bal. et Henry, Crotalaria madurensis var. kurnoolica Ellis et Swaminathan, Hedychium coronarium Koeing, Pterocarpus santalinus L.f., Shorea tumbuggaia Roxb., Tylophora fasciculata Buch.-Ham. ex Wight were endemic and their extracts exhibited significant anticandidal activity. © 2016, National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved.


Singh V.,Konkuk University | Mohapatra M.,Bhabha Atomic Research Center | Sivaramaiah G.,Government College for Men Autonomous | Rao J.L.,Sri Venkateswara University | And 9 more authors.
Journal of Materials Science: Materials in Electronics | Year: 2015

Manganese doped BaMgAl10O17 nano-phosphors were synthesized by a low-temperature initiated, gas producing solution combustion process. Phase purity of the prepared phosphors was determined using X-ray diffraction technique. Dynamic light scattering technique was used to estimate the average particle size of the synthesized products. Scanning electron microscopy technique was used to study the morphology of the prepared samples. Fourier transform infrared spectroscopy was used to ascertain the formation of the aluminate host. UV–visible absorption spectroscopy showed band maxima at around 260 nm and intense band maxima at around 216 nm. Electron paramagnetic resonance experiments for the system were carried out to understand the site occupancy of the Mn ions. The photoluminescence excitation and emission spectra suggested the stabilisation of Mn ions in Td geometry. From the colour characterisation of the system it was found out that the system can be effective as a green phosphor material with wide range of applications. © 2015 Springer Science+Business Media New York


Singh V.,Konkuk University | Sivaramaiah G.,Government College for Men Autonomous | Rao J.L.,Sri Venkateswara University | Senthil Kumaran R.,Konkuk University | And 3 more authors.
Journal of Materials Science: Materials in Electronics | Year: 2015

The Gd3+ doped La2Zr2O7 phosphor has been prepared by solution combustion method and characterized using powder X-ray diffraction, scanning electron microscopy, electron paramagnetic resonance (EPR) and photoluminescence spectroscopy. The EPR spectrum of Gd3+ doped La2Zr2O7 exhibits resonance signals having effective g values at g ≈ 1.84, 1.93, 2.0, 3.00, 3.85 and 6.12. Upon UV light excitation (274 nm), the phosphor exhibits a strong and sharp UV emission at 312.5 nm, which is ascribed to 6P7/2 → 8S7/2 transition of Gd3+ ions. EPR and optical investigations of the sample confirm the presence of Gd3+ in the La2Zr2O7 matrix. © 2015, Springer Science+Business Media New York.

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