Colour centre recovery in yttria-stabilised zirconia: photo-induced versus thermal processes

Abstract : The photo-annealing of colour centres in yttria-stabilized zirconia (YSZ) was studied by electron paramagnetic resonance spectroscopy upon UV-ray or laser light illumination, and compared to thermal annealing. Stable hole centres (HCs) were produced in as-grown YSZ single crystals by UV-ray irradiation at room temperature. The numbers of HCs decays to non-zero asymptotic values when UV light is set off. The HCs produced by 200-MeV Au ion irradiation are partially bleached by UV light, whereas the F$^+$-type centres (involving oxygen vacancies) were left unchanged. In contrast, a significant photo-annealing of the latter point defects was achieved in 1.4-MeV electron-irradiated YSZ by 553-nm laser light irradiation, inside the absorption band of F$^+$-type centres centred at a wavelength $\sim$550 nm. Thermal annealing of F$^+$-type centres was also followed by UV-visible absorption spectroscopy. Almost complete photo-bleaching by laser irradiation was achieved like for thermal bleaching at $\sim$500K. Kinetic rate models of colour-centre evolution are proposed for the photo-induced processes and correlated to the thermally-activated ones.