Lanthanide-lanthanide and lanthanide-defect interactions in co-doped ceria revealed by luminescence spectroscopy

Here, we present a first study on the local structure properties, lanthanide-lanthanide and lanthanide-defect interactions in lanthanide (Sm3+/Nd3+ and Sm3+/Eu3+) co-doped CeO2 nanoparticles by use of luminescence spectroscopy. By comparing the emission/excitation spectra and decays measured with the single doped and co-doped ceria, it is established that the local structure at Sm3+ sites is not affected by the presence of the Nd3+ or Eu3+ co-dopant irrespective of concentration. The results suggest that the excess of oxygen vacancies generated by the co-dopant is not associated with Sm3+, being more probably associated with the Nd3+/Eu3+ or/and Ce4+ cations. It is also observed that Sm3+ is not involved in significant non-radiative energy transfer to Nd3+ or Eu3+ while the relative strong shortening of Nd3+ luminescence decay with concentration is most probably related to cross-relaxation in Nd3+-Nd3+ pairs.