Quantum Confined High Entropy Lanthanide Oxysulfide Colloidal Nanocrystals

We have synthesized the first reported example of quantum confined high entropy (HE) nanoparticles, using the lanthanide oxysulfide, Ln2SO2, system as the host phase for a equimolar mixture of Pr, Nd, Gd, Dy and Er. A uniform HE phase was achieved via the simultaneous thermolysis of a mixture of lanthanide dithiocarbamate precursors in solution. This was confirmed by powder X-ray diffraction and high-resolution scanning transmission electron microscopy, with energy dispersive X-ray spectroscopic mapping confirming the uniform distribution of the lanthanides throughout the particles. The nanoparticle dispersion displayed a significant blue shift in the absorption and photoluminescence spectra relative to our previously reported bulk sample with the same composition, with an absorption edge at 330 nm and a λmax at 410 nm compared to the absorption edge at 500 nm and a λmax at 450 nm in the bulk, which is indicative of quantum confinement. We support this postulate with experimental and theoretical analysis of the band gap energy as a function of strain and surface effects (ligand binding) and calculation of the Bohr exciton radius for the end member compounds.