Annealing temperature and oxygen-vacancy-dependent variation of lattice strain, band gap and luminescence properties of CeO2 nanoparticles

CeO2 nanoparticles are annealed in vacuum at 200 degrees C and in air at 200 degrees C, 600 degrees C and 1000 degrees C, respectively. Vacuum-annealed CeO2 contains high concentration of oxygen vacancies and exhibits very high lattice strain, whereas the corresponding values decrease on air annealing. Oxygen-deficient CeO2 has redshift in band gap with high Urbach energy. The magnitude of this energy decreases as CeO2 is annealed in air at 600 degrees C. At 1000 degrees C, thermal disorder increases the Urbach energy. Photoluminescence property of the samples depends on the presence of radiative and non-radiative oxygen vacancy centres. Vacuum-annealed ceria have large numbers of non-radiative oxygen vacancies that act as emission quencher. CeO2 annealed at 600 degrees C contains requisite amount of oxygen vacancies to show better luminescence property.