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Bharat, L Krishna,Dugasani, Sreekantha Reddy,Seeta Rama Raju, G,Yu, Jae Su IOP 2017 Nanotechnology Vol.28 No.37
<P>Eu<SUP>3+</SUP> ions activated Ca<SUB>2</SUB>La<SUB>8</SUB>(SiO<SUB>4</SUB>)<SUB>6</SUB>O<SUB>2</SUB> (CLSO):Eu<SUP>3+</SUP> nanophosphor samples were synthesized by a mixed solvothermal and hydrothermal method. The samples were carefully studied using various characterization techniques. The XRD patterns of CLSO:Eu<SUP>3+</SUP> and CLSO confirmed that the samples were crystallized in hexagonal phase with a space group of P6<SUB>3</SUB>/m (176). The morphology of the nanoparticles was studied by varying the reaction parameters such as growth, temperature and time. The photoluminescence (PL) excitation and PL emission spectra exhibited the typical Eu<SUP>3+</SUP> bands in the wavelength range of 200–550 nm and 400–750 nm, respectively. The intensity of the <img ALIGN='MIDDLE' ALT='${}^{5}{\rm{D}}_{0}\to {}^{7}{\rm{F}}_{2}$' SRC='http://ej.iop.org/images/0957-4484/28/37/375601/nanoaa7dadieqn1.gif'/> electric dipole (ED) transition peak was strong in the PL emission spectrum which imparts the red color when observed under ultraviolet light. The ED transition peak intensity increased when the sample was calcined at an elevated temperature of 700 °C, indicating improved asymmetry ratio and good chromaticity coordinates. The electrical properties of the prepared materials were studied by spin-coating the powder dispersed solutions on the silica substrate. The output current values were also measured for the CLSO nanoparticles prepared under different growth conditions. These results showed the advantages of CLSO nanoparticles for their application in optics and feasibility in nanoelectronic and energy harvesting devices.</P>
Pavitra, E.,Seeta Rama Raju, G.,Krishna Bharat, L.,Park, Jin Young,Kwak, Cheol Hwan,Chung, Jong Won,Han, Young-Kyu,Huh, Yun Suk The Royal Society of Chemistry 2018 Journal of Materials Chemistry C Vol.6 No.46
<P>Since the commercialization of white light-emitting diodes (WLEDs) in 1996, they are rapidly replacing conventional lighting sources and have become an essential commodity for day-to-day human life. At present, most of the WLEDs existing in the market are rare-earth based, which are very limited, expensive and often not available due to monopolistic supply conditions. Hence, there is a serious demand for novel rare-earth free phosphors to achieve cost-effective and energy-efficient WLEDs with excellent luminous efficacy for general illumination. Herein we report on highly efficient rare-earth free Cs(1−x)RbxVO3phosphors as a single emitting compound for near UV-based WLEDs manufactured by the citrate sol-gel method for the first time. Rietveld refinement is performed for the X-ray diffraction patterns of the CsVO3host and CsVO3:0.25Rb phosphors to reveal their orthorhombic pyroxene structure. The difference in the ionic radii of Rb<SUP>+</SUP>and Cs<SUP>+</SUP>ions led to a more distorted VO4<SUP>3−</SUP>tetrahedron with a broken<I>T</I>dsymmetry, which allows spin forbidden transitions for CsVO3:0.25Rb phosphors, resulting in enhanced internal and external quantum efficiencies of 94.7% and 84.5% along with superior luminescence properties compared to the CsVO3host. When varying the input current from 20 to 200 mA, the fabricated WLED exhibited a good color rendering index of 69.7-81.5 and an extremely high luminous efficacy of 94.8-58.7 lm W<SUP>−1</SUP>, which are among the highest values for the same host lattice. These rare-earth free CsVO3:0.25Rb phosphors with a single emitting center may emerge as a new class of advanced inorganic phosphors for near UV-based WLEDs in the lighting industries.</P>
Raju, G. Seeta Rama,Pavitra, E.,Bharat, L. Krishna,Rao, Gattupalli Manikya,Jeon, Tae-Joon,Huh, Yun Suk,Han, Young-Kyu Elsevier 2018 CERAMICS INTERNATIONAL Vol.44 No.12
<P><B>Abstract</B></P> <P>Upconversion Sr<SUB>2</SUB>(Gd<SUB>.98-<I>x</I> </SUB>Er<SUB>.02</SUB>Yb<SUB> <I>x</I> </SUB>)<SUB>8</SUB>Si<SUB>6</SUB>O<SUB>26</SUB> (SGSO:2Er<SUP>3+</SUP>/<I>x</I>Yb<SUP>3+</SUP>) phosphor materials were synthesized using a citrate sol-gel process. X-ray diffraction patterns confirmed their hexagonal structure. Field emission scanning electron microscopy images of SGSO:2Er<SUP>3+</SUP>/<I>x</I>Yb<SUP>3+</SUP> phosphors depicted submicron particles. The enhanced upconversion luminescence properties of SGSO:2Er<SUP>3+</SUP>/<I>x</I>Yb<SUP>3+</SUP> phosphors were analysed as a function of Yb<SUP>3+</SUP> ion concentration and laser power. The energy transfer induced enhanced emission of the Er<SUP>3+</SUP>/ Yb<SUP>3+</SUP> ions co-doped SGSO phosphors was ascribed to multi-phonon relaxation. The calculated chromaticity coordinates of the SGSO:2Er<SUP>3+</SUP>/<I>x</I>Yb<SUP>3+</SUP> phosphors showed emissions could be tuned by changing Yb<SUP>3+</SUP> ion concentration. Optimized sample exhibited the chromaticity coordinate values near to the ultra-high definition television standard green emission coordinates.</P>
( Rahul Ghosh ),( A. Venugopal ),( Pradeep P I ),( L. Rama Krishna ),( P. Ramesh Narayanan ),( Bhanu Pant ),( Roy M Cherian ) 한국부식방식학회(구 한국부식학회) 2018 Corrosion Science and Technology Vol.17 No.3
AA7010 is an Al-Zn-Mg-Cu alloy containing Zr, developed as an alternate to traditional AA7075 alloy owing to their high strength combined with better fracture toughness. It is necessary to improve the corrosion resistance and surface properties of the alloy by incorporating plasma electrolytic oxidation (PEO) method. AA7010-T7452 aluminum alloy has been processed through the forging route with multi-stage working operations, and was coated with 10μm thick Al<sub>2</sub>O<sub>3</sub> ceramic aluminina coating using the plasma electrolytic oxidation (PEO) method. The corrosion, stress corrosion cracking (SCC) and nano-mechanical behaviours were examined by means of potentiodynamic polarization, slow strain rate test (SSRT) and nano-indentation tests. The results indicated that the additional thermomechanical treatment during the forging process caused a fully recrystallized microstructure, which lead to the poor environmental cracking resistance of the alloy in 3.5% NaCl solution, despite the overaging treatment. Although the fabricated PEO coating improved general corrosion resistance, the brittle nature of the coating did not provide any improvement in SCC resistance of the alloy. However, the hardness and elastic modulus of the coating were significantly higher than the base alloy.
Nagaraju, Goli,Sekhar, S. Chandra,Rama Raju, G. Seeta,Bharat, L. Krishna,Yu, Jae Su The Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.30
<▼1><P>Yolk–shell structured Mn3O4 nanospheres and biomass-derived activated carbon materials were prepared for use in high energy storage asymmetric supercapacitors.</P></▼1><▼2><P>Recently, yolk–shell structured electrode materials have attracted increasing interest in supercapacitors (SCs) due to their high surface area, good electrochemical activity and excellent mechanical stability towards superior energy storage performance. However, the synthesis strategies to prepare such yolk–shell structured materials without using chemical surfactants/solid templates are still inferior. Herein, a facile and cost-effective strategy to design yolk–shell structured trimanganese tetraoxide nanospheres (Mn3O4 NSs) with a distinctive core–void–shell configuration to use as an efficient positive electrode material in asymmetric SCs is demonstrated. Specifically, the yolk–shell structured Mn3O4 NSs were prepared by the inclusion of water droplets to the manganese precursor–isopropyl alcohol system, which facilitates the inside-out Ostwald ripening process to construct a yolk–shell-like configuration with porous properties. In aqueous electrolyte solution, the corresponding material exhibited a high specific capacitance (211.36 F g<SUP>−1</SUP> at a current density of 0.5 A g<SUP>−1</SUP>), a good rate capability (79.4% at 10 A g<SUP>−1</SUP>) and an excellent cycling stability (92% after 2000 cycles) compared to its solid counterparts. Meanwhile, a low-cost material based on biomass-derived activated carbon with a honeycomb-like structure is also prepared using waste corrugated boxes, which exhibits a reliable electrochemical performance for use as a negative electrode material. Moreover, the fabricated asymmetric SC using both electrode materials offers a maximum potential window of 2 V with higher energy density (19.47 W h kg<SUP>−1</SUP>) and power density (2263.89 W kg<SUP>−1</SUP>) values, which can effectively power up commercial light-emitting diodes for practical applications.</P></▼2>
Nagaraju, Goli,Sekhar, S. Chandra,Ramulu, Bhimanaboina,Bharat, L. Krishna,Raju, G. Seeta Rama,Han, Young-Kyu,Yu, Jae Su Elsevier 2018 Nano energy Vol.50 No.-
<P><B>Abstract</B></P> <P>An essential key to enhance the redox chemistry of battery-type materials is to construct rational design of nanoarchitectures with high electrochemical activity. Herein, we reported a hierarchical composite consisting of bilayered nickel hydroxide carbonate nanoplates-decorated nanoflowers on nickel foam (NHC NPs@NFs/Ni foam) <I>via</I> a facile homogeneous precipitation method for use as an effective cathode in hybrid supercapacitors (HSCs). Under controlled growth time (4 h), the bilayered NHC NPs@NFs with hierarchical alignment were spontaneously crystallized on Ni foam. The as-preapared hybrid structure greatly enhanced the electroactive surface area and enabled the rapid redox chemistry in alkaline electrolyte. Notably, the hybrid NHC NPs@NFs/Ni foam delivered a maximum areal capacity of 727.4 μAh/cm<SUP>2</SUP> at 2 mA/cm<SUP>2</SUP> and it is relatively higher than its oxide form (76.6 μAh/cm<SUP>2</SUP>) in a three-electrode system. Also, a pouch-type HSC with bilayered NHC NPs@NFs/Ni foam and porous carbon electrodes was fabricated, which demonstrated superior energy storage performance in terms of capacitance (1445.8 mF/cm<SUP>2</SUP>), energy density (0.506 mWh/cm<SUP>2</SUP>), power density (35.675 mW/cm<SUP>2</SUP>) and cycling stability (89.4%). Furthermore, the self-charging power station consisting of a solar cell for energy conversion and the HSCs for energy storage was also assembled to operate the portable electronic displays and wall clock effectively for long time. This facile approach for the cost-effective fabrication of hierarchically designed nanomaterials paves a path for the development of high-performance hybrid supercapacitors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hierarchical and bilayered NHC NPs@NFs/Ni foam-based cathode is facilely prepared. </LI> <LI> The bilayered hybrid composite effectively enables the redox chemistry to improve the capacity. </LI> <LI> A pouch-type hybrid supercapacitor is assembled to achieve the high energy storage performance. </LI> <LI> A self-charging power station model is designed for portable electronics. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>A hierarchically designed nickel hydroxide carbonate nanoplates-decorated nanoflowers on nickel foam are fabricated for high-performance hybrid supercapacitor. The solar charged hybrid supercapacitor provides a step forward for the development of self-powered portable electronic devices.</P> <P>[DISPLAY OMISSION]</P>