Effects of ion irradiation and annealing on optical and structural properties of CeO2 films on sapphire

(0 0 l) CeO2 films deposited on r-cut sapphire were irradiated by N+ ions at fluences of 1x1016, 5x1016 and 1x1017 ion/cm2 at room temperature and then annealed at 200-900 deg. C in O2 ambient. X-ray diffraction results showed that there was no change for the orientation and crystallinity of CeO2 film after irradiation. However, the diffraction peaks became sharper after annealing at 900 deg. C. Atomic force microscope measurements revealed isolated voids after ion irradiation. The optical transmittance spectra indicated a blueshift of band gap due to the valence transition of Ce3+→Ce4+ induced by thermal annealing. As-deposited films exhibited three photoluminescence bands at 300-390, 380-550, and 460-550 nm. A new emission band peaked at 670 nm appeared while the emission band at 460-550 nm disappeared after annealing. The CeO2 films show good thermal stability and irradiation resistance except some isolated voids in this work