In targeting reduced valent lanthanide chalcogenides, we report the first nanoparticle synthesis of the mixedvalent ferromagnets Eu 3 S 4 and EuSm 2 S 4 . 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 . 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. The UV/Vis, Raman and X-ray photoelectron spectroscopies for each phase were compared. 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. Interestingly, at lower temperatures EuI 2 initially forms EuS, and converts over time to Eu 3 S 4 .

In targeting reduced valent lanthanide chalcogenides, we report the first nanoparticle synthesis of the mixedvalent ferromagnets Eu 3 S 4 and EuSm 2 S 4 . 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 . 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. The UV/Vis, Raman and X-ray photoelectron spectroscopies for each phase were compared. 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. Interestingly, at lower temperatures EuI 2 initially forms EuS, and converts over time to Eu 3 S 4 .

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The luminescence properties of two divalent europium complexes of the type Eu­[N­(SPPh2)2]2(THF)2 (1) and Eu­[N­(SePPh2)2]2(THF)2 (2) were investigated. The first complex, Eu­[N­(SPPh2)2]2(THF)2 (1), was found to be isomorphous with the reported structure of complex 2 and exhibited room temperature luminescence with thermochromic emission upon cooling. We found the complex Eu­[N­(SePPh2)2]2(THF)2 (2) was also thermochromic but the emission intensity was sensitive to temperature. Both room temperature and low temperature (100 K) single crystal X-ray structural investigation of 1 and 2 indicate geometric distortions of the metal coordination, which may be important for understanding the thermochromic behavior of these complexes. The trivalent europium complex Eu­[N­(SPPh2)2]3 (3) with the same ligand as 1 was also structurally characterized as a function of temperature and exhibited temperature-dependent luminescence intensity, with no observable emission at room temperature but intense luminescence at 77 K. Variable temperature Raman spectroscopy was used to determine the onset temperature of luminescence of Eu­[N­(SPPh2)2]3 (3), where the 615 nm (5D0 → 7F2 transition) peak was quenched above 130 K. The UV–visible diffuse reflectance of 3 provides evidence of an LMCT band, supporting a mechanism of thermally activated LMCT quenching of Eu­(III) emitting states. A series of ten isomorphous, trivalent lanthanide complexes of type Ln­[N­(SPPh2)2]3 (Ln = Eu (3) Pr (4), Nd (5), Sm (6), Gd (7), Tb (8)) and Ln­[N­(SePPh2)2]3 (Ln = Pr (9), Nd (10, structure was previously reported), Sm (11), and Gd (12) for Q = Se) were also synthesized and structurally characterized. These complexes for Ln = Pr, Nd, Sm, and Tb exhibited room temperature luminescence. This study provides examples of temperature-dependent luminescence of both Eu2+ and Eu3+, and the use of soft-atom donor ligands to sensitize lanthanide luminescence in a range of trivalent lanthanides, spanning near IR and visible emitters.