O2 atmospheric annealing-tunable defects in ionic oxide MgO nanoribbons

Abstract

An isotropic lattice shrinkage (lattice volume ratio ∼−0.462%) structure was reported in cubic magnesium oxide (MgO) nanocrystals, favoring the enhanced electron correlation. Upon postannealing in an O2 atmosphere, significant changes in photoluminescence spectra were detected in pristine MgO nanoribbons (NRs): a substantial reduction in F+-type centers (Fc) and an increase in a previously unknown peak at 358 nm (3.46 eV) which we attribute to a small polaron (SP) complex as a deep acceptor. A reduced diluted magnetism was found in the O2-annealed MgO NRs. A room temperature electron paramagnetic resonance signal at g ∼ 2.0959 revealed the presence of an unpaired electron trapped in the MgO NRs and a weak broad signal shift at g ∼ 2.0888, suggesting a reduced anisotropic spin–orbit coupling in the O2-annealed MgO NRs. Finally, a view on competition between Fc and SP was proposed: the Fc defect favors FM, and the SP complex leads to reduced FM in MgO NRs. The findings provide new insight into the origin and defect engineering of d0 diluted magnetism in MgO (spin from MgO), and this physical mechanism would be generally applied to other ionic oxide family materials in the field.