Photoluminescence and cathodoluminescence properties of Sr₂Gd₈Si₆O₂₆:RE³⁺(RE³⁺=Tb³⁺or Sm³⁺) phosphors

Hussain, Sk.K.,Rao, G.M.,Raju, G.S.R.,Krishna Bharat, L.,Subba Rao, P.S.V.,Yu, J.S. Elsevier [etc.] 2016 Journal of luminescence Vol.178 No.-

<P>Trivalent terbium (Tb3+) or samarium (Sm3+) ions individually activated green and orange emitting Sr2Gd8Si6O26 (SGSO) phosphors were synthesized by a citrate sol-gel method. The X-ray diffraction patterns of SGSO:Tb3+ and SGSO:Sm3+ phosphors exhibited the characteristic diffraction peaks of oxyapatite in a hexagonal lattice structure. The photoluminescence (PL) properties at ultraviolet (UV) or near-UV excitation wavelengths were measured for Tb3+ or Sm3+ ions doped SGSO phosphors as a function of its respective concentration. The PL spectra of SGSO:Tb3+ phosphors revealed the characteristic emission peaks of both Gd3+ and Tb3+ ions which are associated with 4f-4f transitions under 274 nm of excitation wavelength. When the concentration of Tb3+ ions increased over 0.05 mol (5 mol%), the emission intensities of D-5(3) transitions decreased due to the well-known cross-relaxation process. However, based on the intensities of D-5(4) transitions, the optimum concentration of Tb3+ ions was found to be 0.05 mol. Under 404 nm of excitation wavelength, the SGSO:Sm3+ phosphors exhibited the characteristic orange emission at 600 nm due to the (4)G(5/2) -> H-6(7/2) electronic transition. The optimum concentration of SGSO:Sm3+ phosphors was found to be 0.02 mol. The decay curves of the optimized SGSO:Tb3+ and SGSO:Sm3+ phosphors were well fitted to single exponential functions and their lifetimes were calculated. Furthermore, the optimized phosphor samples showed good thermal stability. Likewise, cathodoluminescence properties were also studied for the optimized samples as a function of filament current and accelerating voltage. The Commission International de I-Eclairage chromaticity coordinates were calculated for the SGSO:Tb3+ and SGSO:Sm3+ phosphors. (C) 2016 Elsevier B.V. All rights reserved.</P>

Structural and Magnetic Characterizations of Ni—Zn—Co Ferrite Nanoparticles Synthesized by Sol—Gel Autocombustion Method

Ramesh, S.,Dhanalakshmi, B.,Sekhar, B. Chandra,Rao, P. S. V. Subba,Rao, B. Parvatheeswara,Kim, CheolGi American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.10

<P>Cobalt substituted Ni-Zn ferrite nanoparticles with the formula, Ni0.4Zn0.6-xCoxFe2O4, where x varies from 0.00 to 0.25 in steps of 0.05, were prepared by sol-gel autocombustion method and analyzed for their structural and magnetic properties. The synthesized nanoparticles were subjected to X-ray analysis, transmission electron microscopy, Fourier transform infrared spectroscopy, thermal analysis and magnetic measurements. The X-ray patterns confirm cubic spinel structures with the crystallite sizes in the range from 31.72 nm to 36.87 nm. The particle sizes estimated using electron micrographs are in good agreement with the crystallite sizes obtained from the X-ray data. Infrared data confirms the spinel structure by showing Fe-A-O and Fe-B-O stretching vibrations while the thermal data hints at a slight weight gain due to oxidation. The obtained magnetic data suggests a marginal increase in saturation magnetization with the Co substitution at x = 0.10 and 0.25. The results are analyzed in terms of the compositional and structural modifications, and it was found that the variation of magnetic moment was governed by a corresponding change in the oxygen positional parameter in these materials.</P>

Synthesis of Alginate Based Silver Nanocomposite Hydrogels for Biomedical Applications

P. Rama Subba Reddy,하창식,K. Madhusudana Rao,K. S. V. Krishna Rao,Yury Shchipunov 한국고분자학회 2014 Macromolecular Research Vol.22 No.8

Sodium alginate and poly(acrylamide-co-N-vinylcaprolactam-co-acrylamidoglycolic acid) based dualresponsive semi-IPN hydrogels (SA-PAVA) were successfully synthesized by free radical redox polymerization. N,N'-Methylene-bis-acrylamide was used as a crosslinker and 5-fluorouracil, an anti-cancer drug, was loaded ontothese semi-IPN hydrogels via equilibrium swelling method. The hydrogels were also used as templates for the productionof silver nanoparticles by using NaBH4 as reducing agent. In order to understand the polymer-drug interactions,pristine, as well as drug loaded, SA-PAVA hydrogels were characterized by Fourier transform infrared spectroscopyand differential scanning calorimetry. The formation of silver nanoparticles was confirmed by UV-visible spectroscopy,thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy(TEM). The swelling behavior of the hydrogel was investigated in distilled water under various pH and temperatureconditions. In vitro release of 5-fluorouracil from these SA-PAVA hydrogels was carried out in gastro-intestinal fluidsdifferent temperatures. The SA-PAVA hydrogel/silver nanocomposites showed excellent anti-bacterial activitytowards Escherichia coli and Bacilli.

Enhanced Ferromagnetic Order in Mn Doped BiFeO₃—Ni_0.5Zn_0.5Fe₂O₄ Multiferroic Composites

Dhanalakshmi, B.,Rao, P. S. V. Subba,Rao, B. Parvatheeswara,Kim, CheolGi American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.10

<P>Multiferroic composites of 0.5 BiFeO3-0.5Ni(0.5)Zn(0.5)Fe(2)O(4) and 0.5Bi(0.95)Mn(0.05)FeO(3)-0.5 Ni0.5Zn0.5Fe2O4 were prepared by combining sol-gel autocombustion and solid state methods. X-ray diffraction analysis of the composites reveals that the samples are formed as di-phase compounds while retaining the spinel phase for the Ni-Zn ferrite and perovskite phase for the Bi-ferrite. Fourier transform infrared spectroscopy measurements on the composites confirm their structures with the presence of Fe-O and Bi-O bonds. Dielectric measurements on the composites were used to discuss about the possible polarization/conduction mechanisms, phase transitions and magnetoelectric coupling. Room temperature ferroelectric and magnetic hysteresis loop studies on the samples ensure that the Mn doped composite exhibits enhanced remnant polarization as well as saturation magnetization compared to the undoped composite. Moreover, the Mn doping has further translated the composite into magnetically softened with coercivity almost close to zero. The obtained improvements in the dielectric and multiferroic properties of the composites are attributed to the corresponding structural modifications brought about by the Mn doping.</P>

Tunable emissions <i>via</i> the white region from Sr₂Gd₈(SiO₄)₆O₂:RE³⁺ (RE³⁺: Dy³⁺, Tm³⁺, Eu³⁺) phosphors

Rao, Gattupalli Manikya,Seeta Rama Raju, G.,Hussain, Sk. Khaja,Pavitra, E.,Rao, P. S. V. Subba,Yu, Jae Su The Royal Society of Chemistry 2016 NEW JOURNAL OF CHEMISTRY Vol.40 No.7

<P>Single, double and triple trivalent rare-earth (RE3+ = Dy3+, Tm3+, Tm3+/Dy3+ and Tm3+/Dy3+/Eu3+) ions activated Sr2Gd8(SiO4)(6)O-2 (SGSO) phosphors were synthesized by a sol-gel process. X-ray diffraction profiles confirmed their oxyapatite structure after annealing at 1450 degrees C for 12 h. Morphological studies were performed by taking scanning and transmission electron microscopy images, which displayed rod-like shapes. SGSO phosphors exhibited good photoluminescence (PL) properties in the respective regions when doped with Dy3+ and Tm3+ ions. Dy3+ co-activated SGSO: Tm3+ phosphors revealed tunable emissions from cool white light to warm white light towards the yellow region based on the co-activator concentration. However, Eu3+ ions co-doped SGSO: Tm3+/Dy3+ phosphors tuned the emissions towards the red region. The energy transfers from Tm3+ to Dy3+ ions and Tm3+/Dy3+ to Eu3+ ions were established based on the energy level diagram. The cathodoluminescence properties of these phosphors showed excellent emission behavior when the single, double or triple trivalent RE ions were doped into the SGSO host lattice. Unlike the case of the PL, the energy transfer process was observed to take place. The calculated Commission Internationale de l'Eclairage chromaticity coordinates of Tm3+ and Dy3+ individual ion doped SGSO phosphors confirmed the blue and white emissions, while the co-doped samples exhibited tunable emissions.</P>

Dual Responsive Pectin Hydrogels and Their Silver Nanocomposites: Swelling Studies, Controlled Drug Delivery and Antimicrobial Applications

P. Rama Subba Reddy,S. Eswaramma,K. S. V. Krishna Rao,이용일 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.8

Novel dual responsive pectin hydrogels composed from poly(acrylamidoglycolic acid-co-vinylcaprolactam)/ Pectin (PAV-PC) and also PAV-PC hydrogels are used as templates for the production of silver nanoparticles. 5-Fluorouracil is an anticancer drug and has been loaded in situ into PAV-PC hydrogels. Structure and morphology characterization of PAV-PC hydrogels were investigated by fourier transform infrared spectroscopy, differential scanning calorimetry, thermo gravimetric analysis, X-ray diffraction studies, scanning electron microscopy and transmission electron microscopy. The results revealed a molecular level dispersion of the drug in PAV-PC hydrogels. In vitro release of 5-fluorouracil from the PAV-PC hydrogels has been carried out in GIT fluids as well as in various temperatures. 5-Fluorouracil released from PAV-PC hydrogels was 50% at pH 1.2, and 85% at pH 7.4 within 24 h. The release profile was characterized with PAV-PC hydrogels and initial burst effect was significantly reduced in two buffer media (1.2 and 7.4), followed by a continuous and controlled release phase, the drug release mechanism from polymer was due to Fickian diffusion. In situ fabrication of silver nanoparticles inside the hydrogel network via the reduction of sodium borohydrate by PAV-PC chains led to hydrogel nanocomposites. The diameter of the nanocomposites was about 50-100 nm, suitable for uptake within the gastrointestinal tract due to their nanosize range and mucoadhesive properties. These nanocomposite PAV-PC hydrogels showed strong antimicrobial activity towards Bacillus subtilis (G+ve) and Escherichia coli (G-ve).

Study on low frequency energy harvesting system in laminated aluminum beam structures with delamination

Siva Subba Rao Patange,S. Raja,Vijayakumar M. P.,V. R. Ranganath 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.5

Piezoelectric material based energy harvesting system (EHS) has been designed and developed to study the influence of delamination on EHS in low frequency vibrating beam structures. The stiffness reduction due to the presence of delamination of specified size and its location is evaluated using the harvested energy in different vibrating elastic modes. Four aluminium beam specimens were fabricated, each having two layers of 1 mm thickness and a specified dimension of delamination was introduced by using a thin Teflon film. The beam without delamination is considered to be healthy and served as the reference structure. The PZT-5H patches were surface bonded on the beams to work as energy harvesting transducers. A suitable electronic circuit is developed to receive the energy from the vibrating beam. The experimental results in terms of energy generated by the four laminated beams have been compared with analytical results at resonant conditions and correlated to assess the effect of delamination on energy produced by low frequency vibration modes. The location of delamination has made a significant change in the harvested energy of second and third bendings; in particular, the delaminations at edge and root have displayed a clear trend. Resonant and off-resonant excitations have revealed that the edge delaminated beam produces lower energy output. The current work has demonstrated that energy harvesting from different elastic modes and with a variable frequency at constant force excitation can be a useful health monitoring technique, employing low frequency vibration, besides utilising the harvested energy itself.

Dual Responsive Pectin Hydrogels and Their Silver Nanocomposites: Swelling Studies, Controlled Drug Delivery and Antimicrobial Applications

Reddy, P. Rama Subba,Eswaramma, S.,Krishna Rao, K.S.V.,Lee, Yong Ill Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.8

Novel dual responsive pectin hydrogels composed from poly(acrylamidoglycolic acid-co-vinylcaprolactam)/Pectin (PAV-PC) and also PAV-PC hydrogels are used as templates for the production of silver nanoparticles. 5-Fluorouracil is an anticancer drug and has been loaded in situ into PAV-PC hydrogels. Structure and morphology characterization of PAV-PC hydrogels were investigated by fourier transform infrared spectroscopy, differential scanning calorimetry, thermo gravimetric analysis, X-ray diffraction studies, scanning electron microscopy and transmission electron microscopy. The results revealed a molecular level dispersion of the drug in PAV-PC hydrogels. In vitro release of 5-fluorouracil from the PAV-PC hydrogels has been carried out in GIT fluids as well as in various temperatures. 5-Fluorouracil released from PAV-PC hydrogels was 50% at pH 1.2, and 85% at pH 7.4 within 24 h. The release profile was characterized with PAV-PC hydrogels and initial burst effect was significantly reduced in two buffer media (1.2 and 7.4), followed by a continuous and controlled release phase, the drug release mechanism from polymer was due to Fickian diffusion. In situ fabrication of silver nanoparticles inside the hydrogel network via the reduction of sodium borohydrate by PAV-PC chains led to hydrogel nanocomposites. The diameter of the nanocomposites was about 50-100 nm, suitable for uptake within the gastrointestinal tract due to their nanosize range and mucoadhesive properties. These nanocomposite PAV-PC hydrogels showed strong antimicrobial activity towards Bacillus subtilis (G+ve) and Escherichia coli (G-ve).

Tritrophic Interactions of Cowpea [Vigna unguiculata subsp unguiculata(L.)], Aphids [Aphis craccivora (Koch)] and Coccinellids [Menochilus sexmaculatus (Fab.)] under eCO2 and eTemp

M. Srinivasa Rao,O. Shaila,P. Sreelakshmi,S. Vennila,M. Vanaja,A.V.M. Subba Rao,M. Maheswari,K. Sammi Reddy 한국응용곤충학회 2018 Journal of Asia-Pacific Entomology Vol.21 No.2

Experiments were conducted to understand the direct and indirect effects of temperature and elevated CO2 (eCO2), on tritrophic interactions of cowpea (Vigna unguiculata subsp. unguiculata L.), legume aphid Aphis craccivora Koch and coccinellid predator Menochilus sexmaculatus Fab. Reduction of the leaf nitrogen (6%), amino acid (6%) and protein (7%) of cowpea foliage with increased carbon (13%) and C:N ratio (21%) at eCO2 over aCO2 indicated the dilution of biochemical constituents at first trophic level. Shortened development time, DT and increment of reproductive rate, RR at eCO2 over ambient CO2(aCO2)was significant with increase in temperature from 20 to 35 °C. Reduction of the mean degree day, DD requirement of both nymphal (75.79 ± 15.163) and adult stages (157.15 ± 67.04) at eCO2 over aCO2 and same was reflected in the summation DD for both the stages at eCO2 (232.96 ± 80.32)and aCO2 (247.07 ± 64.77) across six temperatures. The ‘rm’ and ‘Ro’ increased gradually with increase in temperature followed the non-linear trend and reached maximum values at 27 °C with shortened ‘T’ across 20 to 35 °C temperatures at eCO2 indicating the significant variation of growth and development at the second trophic level. Decreased grub duration (23%) with increased predation capacity (19%) of M. sexmaculatus on A. craccivora at eCO2 over ambient was noted, indicating the incidence of A. craccivora is likely to be higher with increased predation in the future climate change scenario.

Development of Polymeric Blend Microspheres from Chitosan-Hydroxypropylmethyl Cellulose for Controlled Release of an Anti-Cancer Drug

Reddy, Lakshmi C. Narayana,Reddy, Rama Subba P.,Rao, Krishna K.S.V.,Subha, M.C.S.,Rao, Chowdoji K. Korean Chemical Society 2013 대한화학회지 Vol.57 No.4

Chitosan (CS) and hydroxypropylmethyl cellulose (HPMC) blend microspheres were prepared by water-in-oil emulsion technique and were loaded with an anti-cancer drug 5-fluorouracil (5-FU). CS-HPMC microspheres were characterized by Fourier transform infrared spectroscopy to confirm the cross-linking reaction. Scanning electron microscopy (SEM) was also used to assess the surface morphology of particles prepared. The quantity of release of 5-FU from the microspheres have been studied in terms of blend composition and amount of cross-linking agent. Differential scanning calorimetry and X-ray diffraction techniques indicated a uniform distribution of 5-FU particles in microspheres, whereas SEM suggested the spherical structure of the microspheres with slight rough surface. The in vitro drug release indicated that the particle size and release kinetics depend upon blend composition, amount of cross-linking agent used and amount of 5-FU present in the microspheres.