Ceria nanomaterials containing ytterbium: low and high concentration – luminescence analyzed in the near infrared region

Abstract

Lanthanide based ceria nanomaterials are important practical materials due to the redox properties that are useful in the avenues pertaining to technology and life sciences. Sub 10 nm spherical and highly monodisperse Ce_1−xYb_xO_2−y (0.04 ≤ x ≤ 0.22) nanoparticles were synthesized by thermal decomposition, annealed separately at 773 K and 1273 K for 2 hours and characterized. Elemental mapping for Yb³⁺ doped ceria nanoparticles shows homogeneous distribution of Yb³⁺ atoms in the ceria with low Yb³⁺ content annealed at 773 K and 1273 K for 2 hours. However, clusters are observed for 773 K annealed ceria samples with high concentration of Yb³⁺. These clusters are not detected in 1273 K annealed nanomaterials. Introducing small amounts of Yb³⁺ ions into the ceria lattice as spectroscopic probes can provide detailed information about the atomic structure and local environments allowing the monitoring of small structural changes, such as clustering. The emission spectra observed at room temperature and at 4 K have a manifold of bands that corresponds to the ²F_5/2 → ²F_7/2 transition of Yb³⁺ ions. Some small shifts are observed in the Stark splitting pattern depending on the sample and the annealing conditions. The deconvolution by PARAFAC analysis yielded luminescence decay kinetics as well as the associated luminescence spectra of three species for each of the low Yb³⁺ doped ceria samples annealed at 773 K and one species for the 1273 K annealed samples. However, the ceria samples with high concentration of Yb³⁺ annealed at the two temperatures showed only one species with lower decay times as compared to the low Yb³⁺ doped ceria samples.