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Tirupati, India

Pushpa Manjari V.,Acharya Nagarjuna University | Rama Krishna Ch.,Acharya Nagarjuna University | Rama Krishna Ch.,Koneru Lakshmaiah College of Engineering | Venkata Reddy Ch.,Acharya Nagarjuna University | And 4 more authors.
Journal of Luminescence | Year: 2014

Undoped and Fe(III) ions doped NaCaAlPO4F3 phosphor has been synthesized using solid state reaction method. The prepared phosphor material was characterized by powder X-ray diffraction (XRD), SEM with EDS, optical absorption, photoluminescence (PL), electron paramagnetic resonance (EPR) and FT-IR techniques. The average crystallite size was calculated from powder XRD data. SEM micrographs show the presence of several irregular shaped particles. Optical absorption spectrum exhibited the characteristic absorption bands of Fe(III) ions in distorted octahedral site symmetry. EPR spectrum exhibited two resonance signals at g=4.25 and g=2.00. PL spectrums of both undoped phosphor exhibits emission peaks at 407, 413 and 469 nm and Fe(III) ions doped phosphor gave the emission peaks at 373 and 450 nm under UV excitation. The Commission Internationale deI'Eclairage (CIE) chromaticity coordinates for undoped and Fe(III) ions doped NaCaAlPO4F3 phosphor material are calculated from the emission spectrum. Vibrational bands related to phosphate molecules, P-O-H and hydroxyl ions are observed in the FT-IR spectrum. © 2013 Elsevier B.V. All rights reserved. Source


Venkata Reddy Ch.,Acharya Nagarjuna University | Rama Krishna Ch.,Acharya Nagarjuna University | Raghavendra Rao T.,Acharya Nagarjuna University | Udayachandran Thampy U.S.,Acharya Nagarjuna University | And 3 more authors.
Journal of Molecular Structure | Year: 2012

Fe 3+ doped β-BaB 2O 4 nano crystallite powder is synthesized and characterized by spectroscopic techniques. From the Powder X-ray diffraction data, Fe 3+ doped β-BBO material is observed to be monoclinic. Its average crystallite size is evaluated about 75 nm. The particle-like morphology has been observed from SEM images. The EPR spectrum shows two resonance signals at g = 4.23 and g = 2.07, respectively which are indicative of Fe 3+ ions in tetragonally distorted octahedral site symmetry. Crystal field parameter (Dq) and Racah parameters (B and C) are evaluated. Fe 3+ doped β-BaB 2O 4 nano crystallite powder luminescence properties have been studied. The emission of β-BaB 2O 4:Fe 3+ sample is exhibited two main peaks at 419 and 443 nm. FT-IR spectrum shows the characteristic vibrations of host lattice. © 2012 Elsevier B.V. All rights reserved. Source


Rao T.R.,Acharya Nagarjuna University | Krishna C.R.,Acharya Nagarjuna University | Thampy U.S.U.,Acharya Nagarjuna University | Reddy C.V.,Acharya Nagarjuna University | And 3 more authors.
Applied Magnetic Resonance | Year: 2011

Physical and spectral studies on 20ZnO + xLi2O + (30-x)Na2O + 50B2O3 (5 ≤ x ≥ 25) doped with 0.1 mol% of paramagnetic CuO impurity are carried out. Powder X-ray diffraction patterns of the glass samples confirm the amorphous nature. The physical parameters of all the glasses were also evaluated with respect to the composition. The electron paramagnetic resonance spectra of all these glasses exhibit resonance signals that are characteristic of Cu2+ ions. The optical absorption spectra also confirm the Cu2+ ion in tetragonally elongated octahedral site. Various crystal field, spin-Hamiltonian and bonding parameters are evaluated. It is observed that the mixed alkali effect is significant. © 2011 Springer-Verlag. Source


Raghavendra Rao T.,Acharya Nagarjuna University | Rama Krishna C.,Acharya Nagarjuna University | Udayachandran Thampy U.S.,Acharya Nagarjuna University | Venkata Reddy C.,Acharya Nagarjuna University | And 3 more authors.
Physica B: Condensed Matter | Year: 2011

The effect of Li 2O content in vanadyl doped 20ZnOxLi 2O(30-x)Na 2O50B 2O 3 (5≤x≥25) glasses has been studied with respect to their physical and structural properties. The absence of sharp peaks in XRD spectra of these glass samples confirms the amorphous nature. The physical parameters like density, refractive index, ionic concentration and electronic polarizability vary non-linearly with x mol% depending on the diffusivities of alkali ions. EPR and optical absorption spectra reveal that the resonance signals are characteristics of VO 2 ions in tetragonally compressed octahedral site. Spin-Hamiltonian, crystal field, tetragonal field and bonding parameters are found to be in good agreement with the other reported glass systems. The tetragonal distortion (g ⊥g ∥) and Dt reveals that their values vary non-linearly with Li 2O content and reaches a minimum at x=10 mol%. An anomaly of character has been observed in all the properties of vanadyl doped glass systems, which gives a clear indication of mixed alkali effect. © 2011 Elsevier B.V. All rights reserved. Source


Rama Krishna C.H.,Acharya Nagarjuna University | Venkata Reddy C.H.,Acharya Nagarjuna University | Udayachandran Thampy U.S.,Acharya Nagarjuna University | Chandrasekhar A.V.,Physics Research Center | And 3 more authors.
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2012

Chlorocadmiumphosphate Cd(HPO 4)Cl·[H 3N(CH 2) 6NH 3] 0.5 crystals containing Cu(II) ions have been successfully synthesized at room temperature by using organic amine 1,6-diamino hexane as a template. The samples are characterized by X-ray powder diffraction, Thermal and spectroscopic studies. These are crystallizes in the monoclinic crystal system with cell dimensions: a = 1.7697, b = 0.6576, c = 1.9026 nm and β = 106.5°. FT-IR spectrum showed the absorption bands related to PO 4, NH 3 + ions and other organic molecule vibrations originated from the templated molecule. The prepared crystals are stable at room temperature and as well as up to around 300 °C which were confirmed by thermal analysis. Optical absorption and EPR studies suggest that Cu(II) ion enters in to the lattice as tetragonally distorted octahedral symmetry, for which crystal field and spin-Hamiltonian parameters are calculated. Bonding parameters are suggesting that there exists partial covalent nature between Cu(II) ions and ligands. © 2011 Elsevier B.V. All rights reserved. Source

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