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

Abstract

Capping ligands play an important role in the chemistry of nanoparticles synthesized with organic surfactants. This is relevant to a number of device applications where heating may cause major modifications of crystalline nanoparticles including amorphization, surface rearrangements or sintering. Ultrathin monodisperse Ln 2 O 2 S x oxysulfide nanoparticles (Ln = lanthanide) obtained in a mixture of oleylamine, oleic acid and 1-octadecene show promising luminescence and light absorption properties. In view of applications, one open question concerns the thermal behavior and the role of the ligands on the thermal reactivity of the nanoparticles. In this report, we show that the thermal stability of Gd 2 O 2 S x nanocrystals is limited because of their non-stoichiometric composition and strongly depends on the annealing atmosphere. The sintering temperature of the nanoparticles is lower in air than in inert atmosphere because of a rapid degradation of the ligands. Annealing the nanoparticles in air enables removing the ligands without altering the nanocrystals structure. The decomposition of the Gd 2 O 2 S x nanocrystals in inert atmosphere exhibits a complex multistep behavior that was precisely modeled. This work gives a comprehensive description of the stability conditions of lanthanide oxysulfide nanoparticles. It establishes the conditions for their practical use and opens the way to major improvements of the surface activity of Ln 2 O 2 S nanoparticles and related nanocrystals.

Unraveling the Role of Alkali Cations in the Growth Mechanism of Gd2O2S Nanoparticles

“…The reaction yields were all calculated assuming that the Ln 2 O 2 S phase is formed and that 30 % of the final powder is composed of oleates, as suggested by a previous thermogravimetric analysis combined with mass spectrometry. 7 For the reactions with Gd(acac) 3 and Er(acac) 3 , both Li and Na complexes yielded a significant amount of powder (η ≈ 55 % for Er and η = 60 -90 % for Gd). Interestingly, in the case of Er, a first difference was noticed in the color of the final reaction medium, which usually is orange for Gd with Na(oleate) and pinkish with Li(acac).…”

Band Gap Engineering from Cation Balance: The Case of Lanthanide Oxysulfide Nanoparticles

“…19 We also showed that the ligands around Gd 2 O 2 S nanoparticles are oleates in bridging and chelating coordination modes. 21 Here, cerium loading is defined as y = n Ce / (n Ce + n Gd ) where n refers to the initial metallic precursor quantity in mol. The Gd/Ce ratios of the precursors introduced at the beginning of the reaction and measured by energy dispersive X-ray spectroscopy (EDX) on the isolated product were consistent (Table S1 and Figure S0), meaning that the ratio in the final powder is similar to the introduced one.…”

An Overview of Gadolinium-Based Oxide and Oxysulfide Particles: Synthesis, Properties, and Biomedical Applications

“…However, it is also important to note that some of these methods produce compounds with low crystallinity and generate organic by-products that are difficult to remove. Eventually, these undesired products affect the particles' biological interaction and optical properties, limiting their application [123,124].…”