Electronic structure, charge transfer, and intrinsic luminescence of gadolinium oxide nanoparticles: Experiment and theory

摘要

Highlights•Gd2O3-nanoparticles in cubic and monoclinic phases were synthesized and studied by SEM.•Visible amount of oxygen-defects were detected by XPS and VB spectroscopy.•Significant changes of electronic structure on the surface were confirmed by DFT calculations.•New energy levels caused by surface states and defects is the source of photoluminescence.AbstractThe cubic (c) and monoclinic (m) polymorphs of Gd2O3were studied using the combined analysis of several materials science techniques – X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. Density functional theory (DFT) based calculations for the samples under study were performed as well. The cubic phase of gadolinium oxide (c-Gd2O3) synthesized using a precipitation method exhibits spheroidal-like nanoclusters with well-defined edges assembled from primary nanoparticles with an average size of 50 nm, whereas the monoclinic phase of gadolinium oxide (m-Gd2O3) deposited using explosive pyrolysis has a denser structure compared with natural gadolinia. This phase also has a structure composed of three-dimensional complex agglomerates without clear-edged boundaries that are ∼21 nm in size plus a cubic phase admixture of only 2 at.% composed of primary edge-boundary nanoparticles ∼15 nm in size. These atomic features appear in the electronic structure as different defects ([Gd…OOH] and [Gd…OO]) and have dissimilar contributions to the charge-transferprocesses among the appropriate electronic states with ambiguous contributions in the Gd 5р – O 2s core-like levels in the valence band structures. The origin of [Gd…OOH] defects found by XPS was well-supported by PL analysis. The electronic and atomic structures of the synthesized gadolinias calculated using DFT were compared and discussed on the basis of the well-known joint OKT–van der Laan model, and good agreement was established.