Influence of the Matrix on the Red Emission in Europium Self-Activated Orthoceramics

Abstract

Different oxide host matrices of ABO 4 with A 3+ (Eu) and B 5+ (Nb, Ta, and Sb) were prepared to investigate the solid state luminescence behavior of Eu 3+ 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 (4f n-1 5d → 4f n ) and charge transfer bands (X 5+ -O 2-) were observed, besides split Stark levels indicating low local symmetry. The influence of host matrices on the optical behavior of ortocompounds was noticed by changes in the energy of the typical Eu 3+ transitions. In this case, the larger blue-shifted peaks were observed for EuSbO 4 while the larger red-shifted positions for EuNbO 4 , with respect to emission spectra of orthocompounds studied here.These results were correlated to the respective 5 th ionization energies and covalent fraction as well as to the crystal structures exhibited by the different host matrices (I2/a: Nb, Ta; P2 1 /c: Sb). The presence of more than one component for the 5 D 0 → 7 F 0 transition in each compound was observed at low temperature and it could be justified by nonstoichiometric defects like the oxygen vacancy and Eu 2+ . 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 5 D 0 state and chromaticity diagrams confirmed our orthoceramics as good optical emitters in the redend region.

Bioinspired Mineralization of Type I Collagen Fibrils with Apatite in Presence of Citrate and Europium Ions

“…The broad band between 200 and 300 nm, centered at 240 nm, corresponds to charge transfer (called charge transfer band; CTB), which occurs by electron delocalization from the filled 2p shell of O 2to the partially filled 4f shell of Eu 3+ . Also, this band can partly be attributed to the charge transfer transition X 5+ -O 2- [46,47]. The weaker bands centered at 321, 364, 385 and 395 nm correspond to the excitation of the Eu 3+ ; 7 F 0 → 5 H 6 , 7 F 0 → 5 D 4 , 7 F 0 → 5 L 7 and 7 F 0 → 5 L 6 transitions [48].…”

Clustering in complex ionic liquids in two dimensions

“…In particular, this hindered charge order produces local clustering of the charged segments, which, in turn, produces a scattering pre-peak in the structure factors. These effects are well documented for realistic RTIL in 3D [8,9,10,11,12,13,14]. For the 2D case, it would be interesting to know how this screening of the charge order, induced by the presence of neutral sites, is affected, when we expect lesser possibilities of molecular conformations?…”

X‐ray photoelectron spectroscopy study of neodymium niobate and tantalate precursors and thin films

“…Neodymium niobate NdNbO 4 (NNO) and tantalate NdTaO 4 (NTO) ceramics and films possess mixed types of conduction processes, including protonic, ionic, and electronic conduction which is determined by fabrication conditions, and these materials are promising for sensors, solid fuel cell electrolytes, and high-temperature proton conductors. [1][2][3][4][5] One of the most detailed structural studies on LnMO 4 (Ln = rare earths; M = Nd, Ta), which covers lanthanide ions, were implemented by Siqueira et al [6][7][8][9] For these materials, several polymorph modifications are known. At room temperature, these compounds crystallize in the monoclinic M-and M′-fergusonite structures and transformed to the tetragonal T scheelite-type structure 3 depending on sol-gel synthesis conditions.…”