Influence of the matrix on the red emission in europium self-activated orthoceramics.
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2015
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Different oxide host matrices of ABO4 with A3+ (Eu) and B5+ (Nb, Ta,
and Sb) were prepared to investigate the solid state luminescence behavior of Eu3+ as
a self-activated emitter in orthoceramics. Crystal structures, phonon modes, metal
valence states, optical excitation, and emission luminescence properties including
emission decay curves, colorimetry, and nonstoichiometry defects were studied using
X-ray diffraction (XRD), Raman spectroscopy, photoluminescence (PL), X-ray
photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR).
Classical intraconfigurational (f−f transitions), interconfigurational (4fn−15d → 4fn),
and charge transfer bands (X5+−O2−) were observed, besides split Stark levels
indicating low local symmetry. The influence of host matrices on the optical behavior
of orthocompounds was noticed by changes in the energy of the typical Eu3+
transitions. In this case, the larger blue-shifted peaks were observed for EuSbO4 and
the larger red-shifted positions for EuNbO4, with respect to emission spectra of
orthocompounds studied here. These results were correlated to the respective fifth ionization energies and covalent fraction as
well as to the crystal structures exhibited by the different host matrices (I2/a: Nb, Ta; P21/c: Sb). The presence of more than one
component for the 5D0 → 7F0 transition in each compound was observed at low temperature, and it could be justified by
nonstoichiometric defects like the oxygen vacancy and Eu2+. These typical defects are observed in nonstoichiometric oxide
materials, and they were analyzed in the orthoceramics by EPR and XPS spectroscopy. Finally, the lifetime of the 5D0 state and
chromaticity diagrams confirmed our orthoceramics as good optical emitters in the red-end region.
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SIQUEIRA, K. P. F. et al. Influence of the matrix on the red emission in europium self-activated orthoceramics. The Journal of Physical Chemistry C, v. 119, p. 17825-17835, 2015. Disponível em: <http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.5b05473>. Acesso em: 05 ago. 2017.