Bifunctional Ce_1−xEu_xO₂ (0 ≤ x ≤ 0.3) nanoparticles for photoluminescence and photocatalyst applications: an X-ray absorption spectroscopy study

Abstract

Ce1-xEuxO2 (0 ≤x≤ 0.3) nanoparticles (NPs) were synthesized by the chemical precipitation method. The microstructures and morphology were characterized by synchrotron X-ray diffraction and high resolution transmission electron microscopy. X-ray absorption near edge structure (XANES) spectra at the Eu M5,4-edge and atomic-multiplet calculations revealed that Eu(3+) was predominantly present in the CeO2 lattice and Eu(2+) was negligibly present within the entire doping range. The detailed analysis of the Ce M5,4-edge and the O K-edge has shown strong dependence of the Ce(3+)/Ce(4+) ratio and oxygen vacancy with Eu content. Extended X-ray absorption fine structure (EXAFS) spectra at the Ce K-edge, along with theoretical fitting, have shown systematic variation in the coordination number, bond length and Debye-Waller factor with Eu doping. A blue shift in the absorption edge was observed which implies a net increase in the charge transfer gap between the O 2p and Ce 4f bands due to the increased number of Ce(3+) ions in the Eu doped samples. The excitation and emission spectra of pure CeO2 NPs did not show any photoluminescence (PL) characteristic; however, Ce1-xEuxO2 (x = 0.1-0.3) NPs showed significant improvements in the 4f-4f, (5)D0-(7)F2 and (5)D0-(7)F1 transitions induced luminescence properties. Eu doping has two major effects on the electronic structure and optical properties of CeO2 NPs: the first, at an Eu content of 10 mol%, is the formation of Ce(4+)-O-Eu(3+) networks, i.e., Eu(3+) ions substitute the Ce(4+) ions and introduce oxygen vacancies and Ce(3+) ions in the host lattice, which favors the (5)D0-(7)F2 induced PL properties. The other, at an Eu doping over 10 mol%, is the formation of both Ce(4+)-O-Eu(3+) and Ce(3+)-O-Eu(3+), i.e., Eu(3+) ions not only take substitutional sites of Ce(4+) ions but also replace a fraction of Ce(3+) ions in the CeO2 lattice which favors (5)D0-(7)F1 induced PL properties. As an application of CeO2 NPs towards the degradation of water pollutants, we demonstrated that the Ce1-xEuxO2 (0 ≤x≤ 0.3) NPs can serve as effective photocatalyst materials towards the degradation of the methyl-orange aqueous pollutant dye under UV light irradiation.

Nanoceria Tween-assisted synthesis, characterization, photocatalytic efficiency and antimicrobial activity

“…The Nano sized CeO 2 samples produced in the presence of tween 20 show higher photocatalytic activity than CeO 2 NPs produced in the presence of tween 80 and this may be attributed to the smaller particle sizes which produced in case of using tween 20. The results show that the maximum degradation efficiency was obtained at a pH of 10.5 which coincides with earlier work [66] and that pH was used for further studies. presence of T1-T6 using initial concentration of 10 mg/L under the optimized conditions.…”

“…On the other hand, another reactive intermediate which is responsible for the degradation is hydroxyl radical (OH•), which can be generated from the water by the holes [66,67] . The powerful oxidizing agent hydroxyl radicals degrade most of MB by the following reactions; Fig.…”

Oxygen Uptake of Tb–CeO2: Analysis of Ce3+ and Oxygen Vacancies

“…These ratios are higher than that of CeO 2 and may be attributed to modification of the local environment surrounding the Ce cations due to the introduction of Tb. We attribute the increase in the Ce I M5 / I M4 ratio following Tb addition to an increase in the amount of Ce 3+ , as did Sharma et al 46 for CeO 2 doped with Eu. In their work, the addition of 10% Eu resulted in the generation of Ce 3+ from the reduction of Ce 4+ .…”

Investigation on cation distribution and luminescence in spinel phase γ-Ga3−δO4 : Sm nanostructures using X-ray absorption spectroscopy

“…In this regard, X-ray absorption spectroscopy (XAS), with its two branches of X-ray absorption near edge structure (XANES) and extended X-ray absorption ne structure (EXAFS), becomes the important elemental characterization technique and has been known to be highly sensitive to the local electronic/atomic structure properties and effectively overcomes the issue of sensitivity to the structure and electronic structure characterization of small sized, poorly crystalline or embedded nanostructures. [26][27][28] In the last few years, probing the local symmetry of the diluted doped elements, 29,30 quantication of the valence state changes of host metal ions upon foreign element doping, [31][32][33] changes in the orbital occupancy, 34,35 and variation in the crystal eld effects 36,37 have been studied for various compounds using the XANES. On the other side, EXAFS, due to the sensitivity to the local atomic structure, has become a powerful probing tool for determining the variation in the coordination number and bond lengths of the constituent elements of the probed material.…”

“…On the other side, EXAFS, due to the sensitivity to the local atomic structure, has become a powerful probing tool for determining the variation in the coordination number and bond lengths of the constituent elements of the probed material. [32][33][34][35][36][37][38][39][40] Besides providing detailed experimental and simulated results on the Ga 2 O 3 polymorphous compounds, the XANES-EXAFS analysis presented in this article addresses various aspects. Firstly, O K-edge XANES spectra were examined to specically look into the diversity in the oxygen environment of g-Ga 3Àd O 4 and b polymorphous phases and to assimilate the effect of Sm insertion on the metal 4s/4p and O 2p orbital hybridization.…”