Influence of CeO₂ nanocrystals size on the vacancies formation processes determined by spectroscopic techniques

Abstract

In the paper influence of the size on the processes of oxygen vacancies formation in CeO₂ nanocrystals has been investigated. Changes in concentration of oxygen vacancies were determined by two independent indicators: intensity of 5d → 4f luminescence of Ce³⁺ ions and ratio between ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ luminescence bands of Eu³⁺ ions incorporated into ceria nanocrystals as structural probes. It was shown that for CeO₂ nanocrystals decrease of the size (from 75 nm to 20 nm) manifests itself in 1.5 times increase of the band intensity associated with vacancy-stabilized Ce³⁺ ions, while for CeO₂:Eu³⁺ nanocrystals it leads to lowering of symmetry for Eu³⁺ centre and correspondent decrease of ⁵D₀ → ⁷F₁/⁵D₀ → ⁷F₂ intensity ratio. It was shown that decrease of the size stimulates formation of the oxygen vacancies in ceria nanoparticles.