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Unveiling the correlation between structural order-disorder character and photoluminescence emissions of NaNbO3

Abstract

NaNbO3 samples were synthesized via the microwave-assisted hydrothermal method under different processing times (ranging from 30-90 minutes) at 180°C using NaOH as mineralizer. XRD and Rietveld refinement data confirmed the obtention of NaNbO3 with orthorhombic (Pbma) crystallographic structure devoid of secondary phases. The Raman scattering spectra revealed that the symmetry of NaNbO3 space group has vibrational modes associated with librations and internal vibrational modes of NbO6 octahedron.The NaNbO3 particles grow as polyhedral shape highly agglomerated way, assuming plate-like manner, however, as time increases the particles become less agglomerated assuming parallelepiped-like shapes. With increase in the processing time, the optical band gap (3.24 eV (30 min); 3.32 eV (60 min) and 3.34 eV (90min)) showed presents a slight difference in the density of intermediary energy levels within the band gap which affects the electronic transitions. The broad band PL emission (350-800 nm) obtained at room temperature, with a PL sub-band at ~ 455 nm (blue component) dominant, displays that the changes in the electronic density are related to the defects of oxygen vacancies (at bulk and surface) due to the strucutural disorder degree at medium-range, i.e., distortions of the NbO6 octahedron as result of the changes in the Nb-O bond lengths and O-Nb-O bond angles, causing a decline in the PL intensity as synthesis time increases. This structural disorder at medium-range is able to transform the NaNbO3 ordered strucuture, which is constituted of [NbO6]x clusters, into ordered-disordered NaNbO3 structure, formed by [NbO5.VOx], [NbO5.VO] and [NbO5.VO(••)] complex clusters.

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Publication details

The article was received on 30 Jan 2017, accepted on 25 May 2017 and first published on 25 May 2017


Article type: Paper
DOI: 10.1039/C7CE00218A
Citation: CrystEngComm, 2017, Accepted Manuscript
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    Unveiling the correlation between structural order-disorder character and photoluminescence emissions of NaNbO3

    G. F. Teixeira, E. Silva Junior, A. Z. Simoes, E. Longo and M. A. Zaghete, CrystEngComm, 2017, Accepted Manuscript , DOI: 10.1039/C7CE00218A

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