Erbium Environment in ZnO:Er Polycrystalline Fibers Produced by Electrospinning
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1035-L11-24
Erbium Environment in ZnO:Er Polycrystalline Fibers Produced by Electrospinning Danilo Mustafa1, Ji Wu2, Jeffery L. Coffer2, and Leandro R. Tessler1 1 IFGW, Unicamp, C. P. 6165, Campinas, SP, 13083-970, Brazil 2 Department of Chemistry, Texas Christian University, College of Science and Engineering, Box 298860, Fort Worth, TX, 76129 ABSTRACT Erbium-doped polycrystalline ZnO fibers were prepared by electrospinning. Organometallic Zn and Er (0.5, 1.0 and 2.0 % Er/Zn ratio) precursors dissolved in methanol, DI water and acetic acid were forced through a syringe needle. An electric field of 20 kV over 16 cm was used to promote the growth of fibers from the needle to a rotating drum. The resulting material consisted of entangled fibers with 0.5 to 1 m typical diameter. The as-prepared samples present faint Er3+ luminescence at 1.5 m when excited by the 488 nm line of an Ar+ laser. This luminescence intensity increases up to 25 times when the samples are annealed for 30 min at 500 °C in air. The effect of annealing over the Er environment was determined by EXAFS measurements at the Er L3 edge. In all as-prepared samples Er is coordinated to 8.0 ± 0.5 oxygen atoms at up to 2.33 ± 0.02 Å interatomic separation. After annealing the coordination is reduced to 5.9 ± 0.5 and the atomic separation becomes 2.29 ± 0.02 Å. This is comparable to Er2O3 where the coordination is 6 and the first neighbor distance is 2.26 ± 0.02 Å. The overcoordination in the as-prepared samples is consistent with the Er L3 edge at 8361.7 ± 0.5 eV compared to 8360.4 ± 0.5 eV in the annealed samples and 8359.9 ± 0.5 eV in Er2O3. In conclusion, the annealing of electrospun ZnO:Er fibers makes the Er environment more similar to that of Er2O3 increasing the luminescence efficiency.
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INTRODUCTION Elctrospinning is a very versatile technique which has been used to prepare a variety of one-dimensional structures of several materials, including oxides [1]. Zinc oxide nanofibers have been successfully obtained by this technique [2]. One of the advantages of the process is the possibility of doping by adding suitable organo-metallic precursors to the starting template. In this work we report the preparation of Er-doped ZnO fibers that present Er3+ luminescence at 1.54 µm after annealing at 500°C in air. This material is a good candidate for efficient pumping of the Er3+ ions through the ZnO defect band. EXAFS is an element sensitive technique which allows the determination of the details of the chemical environment as the coordination, interatomic separation and average radial disorder. These parameters are very important in determining the probability transition for the 4 I13/2 4I15/2 intra-4f transition that results in the characteristic 1.54 µm emission of the Er3+ ions.
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EXPERIMENT Erbium-doped zinc-oxide nanofibers (0.5, 1 and 2 Er/Zn at. %) were prepared by electrospinning. Briefly, 0.5 g zinc acetate was dissolved in 1.0 mL methanol and 0.7 mL deionized water. This solution was mixed with another containing the appropriate amount of
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