Synthesis of Ce₂O₂S and Gd_2(1–y)Ce_2yO₂S Nanoparticles and Reactivity from in Situ X-ray Absorption Spectroscopy and X-ray Photoelectron Spectroscopy

Abstract

Lanthanide oxysulfide nanoparticles have recently attracted interest in view of their potential applications, such as lighting devices and MRI contrast agents, which requires a good stability in air and a controlled surface. In order to address these issues, in this work, air-sensitive CeOS nanoparticles of hexagonal shape were successfully prepared and characterized under inert conditions. Bimetallic GdCeOS nanoparticles of similar shape and size were also synthesized for the whole composition range (y from 0 to 1). X-ray diffraction structural data are found to follow Vegard's law up to y = 0.4, which is attributed to the loss of stability in air of Ce-rich nanocrystals beyond this threshold. This picture is supported by X-ray absorption spectra taken at the S K-edge and Ce L-edge that show the partial oxidation of sulfide species and of Ce to Ce in the presence of air or water. A complementary near-ambient-pressure X-ray photoelectron spectroscopy study shows that at least two types of oxidized sulfur species form on the nanoparticle surface. Even in GdOS nanoparticles that are generally considered to be air-stable, we found that sulfide ions are partially oxidized to sulfate in air. These results unveil the physicochemical mechanisms responsible for the surface reactivity of lanthanide oxysulfides nanoparticles in air.

Designing Nanoparticles and Nanoalloys with Controlled Surface and Reactivity

“…Because of the higher attenuation of the incoming beam, operating under vacuum is required. Like for TEM, gas cells and liquid cells were thus developed, using thin membranes such as Si 3 N 4 to separate the sample from the vacuum (Figure right). The nanoparticles are deposited on a substrate and exposed to a chosen gas mixture at a pressure of 1 bar or less.…”

Thermal Stability of Oleate‐Stabilized Gd2O2S Nanoplates in Inert and Oxidizing Atmospheres

“…Gd 2 O 2 S nanoparticles were synthesized following an optimized protocol described in the experimental section and previously reported by our group . Briefly, Gd(acac) 3 ⋅ x H 2 O (0.5 mmol) was mixed with elemental sulfur (0.5 equiv.…”

“…Oleylamine helps dissolving the elemental sulfur and forming reactive sulfide species . With the help of an alkaline source, Ln 2 O 2 S nanoplates surrounded by organic ligands are obtained …”

“…Typical feature are the non‐stoichiometry, the presence of alkyl‐chains at the surface and the capability of self‐assembling into wires . For example, gadolinium oxysulfide easily form small non‐stoichiometric Gd 2 O 2 S x nanoplates (8 nm×1.5 nm) with x =0.4–0.6, which self‐assemble in solution into nanowires ,…”

Photo/cathodoluminescence and stability of Gd2O2S:Tb,Pr green phosphor hexagons calcined from layered hydroxide sulfate

“…For example, ~3‐10 μm sized particles were reported to provide an optimal packing condition and match the required scintillator features in planar X‐ray applications . The synthesis of RE 2 O 2 S with high purity is, first of all, rather challenging, since RE has a much lower affinity toward S than O according to the hard and soft acid and base (HSAB) theory . Consequently, oxide impurities are frequently observed in the products.…”