Synthesis of Mixed-Valent Lanthanide Sulfide Nanoparticles.

Abstract

In targeting reduced valent lanthanide chalcogenides, we report the first nanoparticle synthesis of the mixed-valent ferromagnets Eu 3 S 4 and EuSm 2 S 4 .\xa0 Using divalent lanthanide halides with bis(trimethylsilyl)sulfide and oleylamine, we prepared nanoparticles of EuS, Eu 3 S 4 , EuSm 2 S 4 , SmS 1.9 , and Sm 3 S 4 .\xa0 All nanoparticle phases were identified using powder X-ray diffraction, transmission electron microscopy was used to confirm morphology and nanoparticle size, and magnetic susceptibility measurements for determining the ordering temperatures and valence.\xa0 The UV-visible, Raman spectroscopy, and X-ray photoelectron spectroscopies for each phase were compared.\xa0 Surprisingly, the phase is influenced by the halide and the reaction temperature, where EuCl 2 formed EuS while EuI 2 formed Eu 3 S 4 , highlighting the role of kinetics in phase stabilization.\xa0 Interestingly, at lower temperatures EuI 2 initially forms EuS, and converts over time to Eu 3 S 4 .