Browsing by Author "Gaballah, Soha"

Now showing 1 - 4 of 4
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    Embedded Ceria Nanoparticles in Crosslinked PVA Electrospun Nanofibers as Optical Sensors for Radicals
    Shehata, Nader; Samir, Effat; Gaballah, Soha; Hamed, Aya; Elrasheedy, Asmaa (MDPI, 2016-08-26)
    This work presents a new nanocomposite of cerium oxide (ceria) nanoparticles embedded in electrospun PVA nanofibers for optical sensing of radicals in solutions. Our ceria nanoparticles are synthesized to have O-vacancies which are the receptors for the radicals extracted from peroxide in water solution. Ceria nanoparticles are embedded insitu in PVA solution and then formed as nanofibers using an electrospinning technique. The formed nanocomposite emits visible fluorescent emissions under 430 nm excitation, due to the active ceria nanoparticles with fluorescent Ce3+ ionization states. When the formed nanocomposite is in contact with peroxide solution, the fluorescence emission intensity peak has been found to be reduced with increasing concentration of peroxide or the corresponding radicals through a fluorescence quenching mechanism. The fluorescence intensity peak is found to be reduced to more than 30% of its original value at a peroxide weight concentration up to 27%. This work could be helpful in further applications of radicals sensing using a solid mat through biomedical and environmental monitoring applications.
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    Enhanced Erbium-Doped Ceria Nanostructure Coating to Improve Solar Cell Performance
    Shehata, Nader; Clavel, Michael B.; Meehan, Kathleen; Samir, Effat; Gaballah, Soha; Salah, Mohamed (MDPI, 2015-11-12)
    This paper discusses the effect of adding reduced erbium-doped ceria nanoparticles (REDC NPs) as a coating on silicon solar cells. Reduced ceria nanoparticles doped with erbium have the advantages of both improving conductivity and optical conversion of solar cells. Oxygen vacancies in ceria nanoparticles reduce Ce4+ to Ce3+ which follow the rule of improving conductivity of solar cells through the hopping mechanism. The existence of Ce3+ helps in the down-conversion from 430 nm excitation to 530 nm emission. The erbium dopant forms energy levels inside the low-phonon ceria host to up-convert the 780 nm excitations into green and red emissions. When coating reduced erbium-doped ceria nanoparticles on the back side of a solar cell, a promising improvement in the solar cell efficiency has been observed from 15% to 16.5% due to the mutual impact of improved electric conductivity and multi-optical conversions. Finally, the impact of the added coater on the electric field distribution inside the solar cell has been studied.
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    Fluorescent Nanocomposite of Embedded Ceria Nanoparticles in Crosslinked PVA Electrospun Nanofibers
    Shehata, Nader; Gaballah, Soha; Samir, Effat; Hamed, Aya; Saad, Marwa (MDPI, 2016-06-01)
    This paper introduces a new fluorescent nanocomposite of electrospun biodegradable nanofibers embedded with optical nanoparticles. In detail, this work introduces the fluorescence properties of PVA nanofibers generated by the electrospinning technique with embedded cerium oxide (ceria) nanoparticles. Under near-ultra violet excitation, the synthesized nanocomposite generates a visible fluorescent emission at 520 nm, varying its intensity peak according to the concentration of in situ embedded ceria nanoparticles. This is due to the fact that the embedded ceria nanoparticles have optical tri-valiant cerium ions, associated with formed oxygen vacancies, with a direct allowed bandgap around 3.5 eV. In addition, the impact of chemical crosslinking of the PVA on the fluorescence emission is studied in both cases of adding ceria nanoparticles in situ or of a post-synthesis addition via a spin-coating mechanism. Other optical and structural characteristics such as absorbance dispersion, direct bandgap, FTIR spectroscopy, and SEM analysis are presented. The synthesized optical nanocomposite could be helpful in different applications such as environmental monitoring and bioimaging.
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    Study of Optical and Structural Characteristics of Ceria Nanoparticles Doped with Negative and Positive Association Lanthanide Elements
    Shehata, Nader; Meehan, Kathleen; Hudait, Mantu K.; Jain, Nikhil; Gaballah, Soha (Hindawi, 2014-11-30)
    This paper studies the effect of adding lanthanides with negative association energy, such as holmium and erbium, to ceria nanoparticles doped with positive association energy lanthanides, such as neodymium and samarium. That is what we called mixed doped ceria nanoparticles (MDC NPs). In MDC NPs of grain size range around 6 nm, it is proved qualitatively that the conversion rate from Ce4+ to Ce3+ is reduced, compared to ceria doped only with positive association energy lanthanides. There are many pieces of evidence which confirm the obtained conclusion. These indications are an increase in the allowed direct band gap which is calculated from the absorbance dispersion measurements, a decrease in the emitted fluorescence intensity, and an increase in the size of nanoparticles, which is measured using both techniques: transmission electron microscope (TEM) and X-ray diffractometer (XRD). That gives a novel conclusion that there are some trivalent dopants, such as holmium and erbium, which can suppress Ce3+ ionization states in ceria and consequently act as scavengers for active O-vacancies in MDC. This promising concept can develop applications which depend on the defects in ceria such as biomedicine, electronic devices, and gas sensors.