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Babu, P.,Jang, K.H.,Kim, E.S.,Vijaya, R.,Jayasankar, C.K.,Lavin, V.,Seo, H.J. North-Holland 2011 Journal of non-crystalline solids Vol.357 No.10
A fluorometaphosphate laser glass doped with Eu<SUP>3+</SUP> ions has been synthesized and studied by broad band optical spectroscopy and time-resolved fluorescence line narrowing techniques in order to explore the local field dependent fluorescence properties of the lanthanide ions in this host. From the Raman and the vibronic spectra, various structural phosphate groups coupled to the Eu<SUP>3+</SUP> ions have been identified. Local field dependent <SUP>5</SUP>D<SUB>0</SUB>→<SUP>7</SUP>F<SUB>J</SUB> (J=0-6) emission spectra and the lifetimes of the <SUP>5</SUP>D<SUB>0</SUB> level have been measured under resonant excitation of the Eu<SUP>3+</SUP> ions at different wavelengths within the <SUP>7</SUP>F<SUB>0</SUB>→<SUP>5</SUP>D<SUB>0</SUB> band at 16K. From these data and using the Stark level positions of the <SUP>7</SUP>F<SUB>1</SUB> and <SUP>7</SUP>F<SUB>2</SUB> multiplets, a crystal-field analysis has been carried out assuming a C<SUB>2v</SUB> orthorhombic local symmetry. The radiative Judd-Ofelt parameters have been calculated for the different local fields found in the glass and their relative variation has been discussed. The results obtained suggest the existence of a relatively narrow distribution of local fields generated by successive distortions of a unique kind of site for all the Eu<SUP>3+</SUP> ions in this fluorometaphosphate glass.
Babu, P.,Jang, Kyoung Hyuk,Kim, Eun Sik,Shi, Liang,Vijaya, R.,Laví,n, V.,Jayasankar, C.K.,Seo, Hyo Jin Elsevier 2010 Journal of non-crystalline solids Vol.356 No.4
<P><B>Abstract</B></P><P>Dysprosium-doped oxyfluoride glasses and nanocrystalline glass–ceramics have been synthesized and studied by X-ray diffraction, transmission electron microscope, optical spectroscopy and time-resolved decay curves measurements. From the absorption spectra, Judd–Ofelt intensity parameters have been obtained and are used to predict radiative properties for the excited states of Dy<SUP>3+</SUP> ions. From the visible emission spectra, yellow to blue intensity ratios have been calculated and their relative variations have been discussed based on the concentration of Dy<SUP>3+</SUP> ions and the heat treatment conditions used to prepare the glass–ceramics. Luminescence decay curves of the <SUP>4</SUP>F<SUB>9/2</SUB> emitting level are found to be single exponential for 0.01mol% Dy<SUP>3+</SUP>-doped glass and non-exponential for the remaining samples. The nature of energy transfer processes between Dy<SUP>3+</SUP> ions, responsible for the non-exponential behavior of the decay curves, has been analyzed in the frame work of the Inokuti–Hirayama model. Lifetimes of the <SUP>4</SUP>F<SUB>9/2</SUB> level are found to decrease with the concentration of Dy<SUP>3+</SUP> ions as well as with the time of heat treatment.</P>
K. Krishna Prasad,S. Venkata Mohan,Y. Vijaya Bhaskar,S. V. Ramanaiah,V. Lalit Babu,B. R. Pati,P. N. Sarma 한국미생물학회 2005 The journal of microbiology Vol.43 No.3
The feasibility of laccase production by immobilization of Pleurotus ostreatus 1804 on polyurethane foam (PUF) cubes with respect to media composition was studied in both batch and reactor systems. Enhanced laccase yield was evidenced due to immobilization. A relatively high maximum laccase activity of 312.6 U was observed with immobilized mycelia in shake flasks compared to the maximum laccase activity of free mycelia (272.2 U). It is evident from this study that the culture conditions studied, i.e. biomass level, pH, substrate concentration, yeast extract concentration, Cu2+ concentration, and alcohol nature, showed significant influence on the laccase yield. Gel electrophoretic analysis showed the molecular weight of the laccase produced by immobilized P. ostreatus to be 66 kDa. The laccase yield was significantly higher and more rapid in the packed bed reactor than in the shake flask experiments. A maximum laccase yield of 392.9 U was observed within 144 h of the fermentation period with complete glucose depletion.
Prasad K. Krishna,Mohan S. Venkata,Bhaskar Y. Vijaya,Ramanaiah S. V.,Babu V. Lalit,Pati B. R.,Sarma P. N. The Microbiological Society of Korea 2005 The journal of microbiology Vol.43 No.3
The feasibility of laccase production by immobilization of Pleurotus ostreatus 1804 on polyurethane foam (PUF) cubes with respect to media composition was studied in both batch and reactor systems. Enhanced laccase yield was evidenced due to immobilization. A relatively high maximum laccase activity of 312.6 U was observed with immobilized mycelia in shake flasks compared to the maximum laccase activity of free mycelia (272.2 U). It is evident from this study that the culture conditions studied, i.e. biomass level, pH, substrate concentration, yeast extract concentration, $Cu^{2+}$ concentration, and alcohol nature, showed significant influence on the laccase yield. Gel electrophoretic analysis showed the molecular weight of the laccase produced by immobilized P. ostreatus to be 66 kDa. The laccase yield was significantly higher and more rapid in the packed bed reactor than in the shake flask experiments. A maximum laccase yield of 392.9 U was observed within 144 h of the fermentation period with complete glucose depletion.
G. Satyanarayana,G. Nageswara Rao,K. Vijaya Babu,G. V. Santosh Kumar,G. Dinesh Reddy 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.74 No.7
In this work, Ni$_{0.7}$Zn$_{0.2}$Cu$_{0.1}$Fe$_{2-x}$Cr$_x$O$_4$ ($x$ = 0.02, 0.04, 0.06, 0.08 and 0.1) ferrites were synthesized by using the solid state reaction method and how relevant properties of the samples were modified accordingly. The structural, morphological, magnetic and electrical features of the ferrites were evaluated by using X-ray diffraction, scanning electron microscopy, Fourier transmission infrared (FTIR) spectra, vibrating sample magnetometry, electron spin resonance and network analyser. The lattice constant decreases with increasing chromium concentration and the decrease in the lattice constant is attributed to the ionic radius of chromium being smaller than that of iron. The distribution of metal cations in the spinel structure was estimated from the X-ray diffraction data and showed that along with Ni$^{2+}$ ions, most of the Zn$^{2+}$ and the Cu$^{2+}$ ions additionally occupied the octahedral [B] sites. The FTIR spectra revealed two prominent frequency bands in the wave number range 400--600 cm$^{-1}$ which confirm the cubic spinel structure. The magnetic properties, such as the initial permeability, saturation magnetization and coercivity, were investigated at room temperature. The frequency-dependent dielectric constant was observed to decrease with increasing chromium concentration. This behavior was using Koop’s phenomenological theory.
Taddesse Paulos,Gebrekiros Haftu,Veeraiah V.,Babu K. Vijaya,Babu K. Ephraim,Rao M. Koteswara 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.10
Conventional high-temperature (800 °C) synthesis of fluoride-substituted samples from LiF has been found to encounter the volatilization of fluorine and to limit the fluorine content, as reported in our earlier paper. In the present study, a fluoride-substituted spinel LiMn2O4 material was synthesized by using a solid-state reaction method with (NH4)HF2 as the fluorine source. The structure and the electrochemical properties of the synthesized samples were characterized by using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), surface area analysis, Fourier transform infrared (FT-IR) spectroscopy, cyclic voltammetry (CV) and charge-discharge tests. As indicated by XRD, all samples showed a spinel cubic structure with space group Fd\={3}m. In comparison with the pure LiMn2O4, fluoride substitution leads to an increase in the lattice parameter, as well as the crystal size, and a decrease in the oxidation state of manganese. From N2-sorption, LiMn2O3.85F0.15 was found to have the smallest specific surface area and the largest pore diameter compared to the LiMn2O4 and the LiMn2O3.95F0.05 samples. Additionally, the majority of the pores in all samples were found to be located in the region of mesopores. The results of the electrochemical study showed that a fluoride substitution into LiMn2O4 improved the initial discharge capacity of the materials. Among the synthesized samples, LiMn2O3.85F0.15 can be used as a starting material for producing better performing spinel-type cathode materials.