Rare-Earth Sulfide Nanocrystals from Wet Colloidal Synthesis: Tunable Compositions, Size-Dependent Light Absorption,...

We report the synthesis of colloidal EuS, La₂S₃, and LaS₂ nanocrystals between 150 and 255 °C using rare-earth iodides in oleylamine. The sulfur source dictates phase selection between La₂S₃ and LaS₂, which are stabilized for the first time as colloidal nanocrystals. The indirect bandgap absorption of LaS₂ shifts from 635 nm for nanoellipsoids to 365 nm for square-based nanoplates. Er³⁺ photoluminescence in La₂S₃:Er³⁺ (10%) is sensitized by the semiconducting host in the 390-450 nm range. The synthetic route yields tunable compositions of rare-earth sulfide nanocrystals. Interaction of light with these novel semiconducting nanostructures hosting rare-earth emitters should be attractive for applications that require broadband sensitization of RE emitters.