Nanofiber Based Er(III) Metal Pyrochlore Oxides : Synthesis and Characterization
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1023-JJ05-07
Nanofiber Based Er(III) Metal Pyrochlore Oxides : Synthesis and Characterization Ruofeng Wang1, Edward T. Bender2,3, Mohannad T. Aljarrah1, Edward A. Evans1, and Rex D. Ramsier2,3 1 Department of Chemical and Biomolecular Engineering, The University of Akron, Whitby Hall Room 211, The University of Akron, Akron, OH, 44325-3906 2 Department of Physics, The University of Akron, Leigh Hall Room 412, The University of Akron, Akron, OH, 44325 3 Department of Chemistry, The University of Akron, Akron, OH, 44325 ABSTRACT Erbium(III) doped TiO2 nanofibers (Er2Ti2O7) have been synthesized by electrospinning mixtures of polymers, metal-containing materials, and erbium acetate. These electrospun nanofibers were subsequently annealed at temperatures of 550, 750, 950, and 1150 oC to remove the organics and leave behind the metal oxides. The crystal structure and optical properties of the nanofiber pyrochlores were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transformation IR (FTIR) spectroscopy. Different crystal structures were formed by controlling the annealing conditions. XRD data are compared with near-IR spectra to better understand the effects of annealing temperature on the Er (III) thermally-excited selective optical emission process. INTRODUCTION Erbium(III) doped materials have been investigated over the last decade to develop structures for optical communication and optoelectronics[1-3]. In this work erbium doped titania nanofibers are being developed for thermophotovoltaic (TPV) devices. TPV devices produce electrical energy directly from infrared (IR) light radiated by heated elements[4-8]. Erbiaís 4I13/2 4I15/2 transition takes place at 1.53 µm which is compatible with the band gap of the GaSb and InGaAs photovoltaic cell in TPV devices[9]. In very recent years, the electronspinning technique has been used to make ceramic, hybrid polymer, and metal oxide nanofibres with high surface area and large aspect ratio (length/diameter)[10-13]. If the nanofiber based emitter device is efficient then a broad group of new applications for TPV energy conversion devices may become feasible. The goal of this work is to demonstrate the synthesis and characterization of hightemperature nanoscale materials with optical properties suitable for TPV applications. We investigate the amorphous to pyrochlore phase transformation of Er3+ doped TiO2 nanofibers annealed at different temperatures (from 550 ∞C up to 1150 ∞C), and the effect of the crystal structure on the near-IR emission band from the intra-4f transition of erbium ions at 1.53 µm. EXPERIMENT The TiO2 nanofibers doped with 50 mol% erbium ions were fabricated from a mixture of organic alkoxy titanate (Tyzor TPT; Dupont TyzorÆ), polyvinylpyrrolidone (PVP; Aldrich, Mw = 1,300,000 a.m.u.) and erbium (III) acetate hydrate (Aldrich, 99.9%). In order to obtain the polymer solution for electrospinning, 3g PVP powder was mixed with 50 ml ethanol and set at
room temperature for 24 hours to allow for polymerization. An
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