Ultrathin Y₂O₃:Eu³⁺nanodiscs: spectroscopic investigations and evidence for reduced concentration quenching

Here, we report the synthesis and spectral properties of ultrathin nanodiscs (NDs) of Y₂O₃:Eu³⁺. It was found that the NDs of Y₂O₃:Eu³⁺ with a thickness of about 1 nm can be fabricated in a reproducible, facile and self-assembling process, which does not depend on the Eu³⁺ concentration. The thickness and morphology of these NDs were determined with small angle x-ray scattering and transmission electron microscopy. We found that the crystal field in these nanoparticles deviates from both the cubic and monoclinic characteristics, albeit the shape of the ⁵D₀ → ⁷F _J (J = 0, 1, 2) transitions shows some similarity with the transitions in the monoclinic material. The Raman spectra of the non-annealed NDs manifest various vibration modes of the oleic acid molecules, which are used to stabilise the NDs. The annealed NDs show two very weak Raman lines, which may be assigned to vibrational modes of Y₂O₃ NDs. The concentration quenching of the Eu³⁺ luminescence of the NDs before annealing is largely suppressed and might be explained in terms of a reduction of the phonon density of states.