Unexpected green-light emission and correlating room-temperature diluted magnetism in pristine non-magnetic closed-shell 4d ⁰ yttria nanowires

We report the fabrication of pristine yttria (Y₂O₃) polycrystalline nanowires (NWs) using an electrospinning method. An intense green photoluminescence (GPL) emission at 544 nm was observed from the Y₂O₃ nanograins with a statistical average crystallite size of 14.3 nm. Interestingly, the full-shell d-electron Y₂O₃ NWs are found to be weakly antiferromagnetic, and the effective magnetic moment was estimated to be ∼1.62 × 10^-4μ_B per O at 10 K. The volume fraction of oxygen anion vacancies ([V_O]⁺) was estimated to be ∼1.62% in the anion-defective electrospun Y₂O₃ NWs. A symmetric electron paramagnetic resonance signal at g ∼ 2.0415 revealed the presence of an unpaired electron trapped in the Y₂O₃ NWs. Finally, a [V_O]⁺ electron-trapped state, i.e. F-center mechanism, is proposed to explain the PL and correlating weak magnetism, which provides new insight into the origin of 4d⁰ diluted magnetism in nonmagnetic closed-shell Y₂O₃ NWs (spin from Y₂O₃) with GPL.