Defect Engineering in Trivalent Ions Doped Ceria through Vanadium Assisted Charge Compensation: Insight using Photoluminescence, Positron Annihilation and Electron Spin Resonance Spectroscopy

Pair matching charge compensation with trivalent and pentavalent dopants in ceria was found to be an attractive strategy in engineering defects with minimal distortions in the lattice and get enhanced catalytic properties. In the present study, the charge compensation with vanadium codopant in trivalent doped ceria is studied. The defect evolution in the trivalent doped ceria with vanadium codoping has been studied in CeO2:Eu3+, CeO2:La3+,Eu3+ and CeO2:Y3+,Eu3+ systems and the choices of dopant and co-dopant are triggered by ionic radius. Eu3+ photoluminescence (PL) is used as spectroscopic probe to monitor local structural changes around the dopants. Positron lifetime studies showed that oxygen vacancies formed due to trivalent ion doping are weakly associated when larger ions are doped and result in the formation vacancy aggregates. Positron lifetime studies along with XRD studies show that vanadium codoping effectively removes the vacancies but the distortions are significant when the size mismatch between the pair match used for charge compensation is higher. Photoluminescence demonstrated that the oxygen vacancies associated with Eu are more effectively removed in the case of Y codoped samples. Electron spin resonance (ESR) studies suggested vanadium in excess over stoichiometric concentration of the trivalent ion can lead to additional defects. These studies are expected to help in tuning the vacancy concentrations as well as controlling the lattice distortions for technological applications such as catalysis, ionic conductivity etc.