LnMOFVA nanofiber: energy transfer and multicolor light-emitting devices

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2013-10, Vol.1 (45), p.7574-7581
• Main Authors: Feijo de Melo, Etelino, Santana, Naiana da C, Bezerra Alves, Kleber G, de Sa, Gilberto F, Pinto de Melo, Celso, Rodrigues, Marcelo O, Junior, Severino A
• Format: Article
• Language: English
• Subjects: Devices; Distortion; Emission; Energy transfer; Nanostructure; Polyvinyl alcohols; Pyridines; Symmetry
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/c3tc31282h

In this paper, we report the use of electrospinning methods for the preparation of polymeric nanofibers containing Lanthanide-Organic Frameworks (LnMOFs) and present a detailed investigation of their spectroscopic properties. The nanocomposites were based in polyvinyl alcohol (PVA) and two isotypical 2D LnMOFs ([Ln(DPA)(HDPA)], where H sub(2)DPA is pyridine 2,6-dicarboxylic acid and Ln = Tb super(3+) and Eu super(3+) ions, which we have designated as EuMOFVA and TbMOFVA, respectively. Additionally, we prepared three tunable visible light-emitting devices based on nanofibers containing different [Tb(DPA)(HDPA)]/[Eu(DPA)(HDPA)] relative concentrations (95-5 wt%, 80-20 wt% and 50-50 wt%, designated as Tb sub(0.95)Eu sub(0.05)MOFVA, Tb sub(0.8)Eu sub(0.2)MOFVA, and Tb sub(0.5)Eu sub(0.5)MOFVA, respectively), and investigated the energy transfer among the optical centers. The emission spectrum of EuMOFVA presents typical narrow bands of the Eu super(3+ 5)D sub(0) arrow right super(7)F sub()Jtransitions centered in a non-centrosymmetric site, and its profile indicates that in EuMOFVA the point group of the Eu super(3+) ion is distorted from the local C sub(1) symmetry observed in as-prepared material. Horrocks' rule applied to EuMOFVA leads to n sub(w) = 0.40, in an indication that the encapsulation of LnMOF materials in PVA does not necessarily imply the coordination of water molecules in the inner-sphere of the lanthanide ion; thus, the distortion of the symmetry around of metal center can be solely associated to the steric effect of the PVA chains. The super(5)D sub(4) arrow right super(7)F sub(5) transition centered at ca.543 nm is the strongest in the emission spectrum of TbMOFVA, corresponding to ca.52% of the integrated emission spectrum. The emission spectra of Tb sub(0.95)Eu sub(0.05)MOFVA, Tb sub(0.8)Eu sub(0.2)MOFVA, and Tb sub(0.5)Eu sub(0.5)MOFVA show lines typical of the Eu super(3+) and Tb super(3+) ions. The colors emitted by Tb sub(0.95)Eu sub(0.05)MOFVA, Tb sub(0.8)Eu sub(0.2)MOFVA and Tb sub(0.5)Eu sub(0.5)MOFVA are in the green-yellow (0.4083, 0.4803), yellow (0.4364, 0.4616) and orange (0.5042, 0.4212) portions of the chromaticity chart, respectively. The Tb super(3+) arrow right Eu super(3+) and do not vary with the increasing of the acceptor (Eu super(3+)) concentration, since the donor-acceptor interaction strength is a function of distance.