On-line optical absorption of electron-irradiated yttria-stabilized zirconia

The kinetics of color-center formation and decay in electron-irradiated cubic yttria-stabilized zirconia (ZrO2: Y3+) has been followed by on-line UV/Vis absorption spectroscopy. The growth and decay with time of absorption spectra have been measured upon electron irradiation and subsequent beam shut-off for energies of 0.8, 1.0, 1.75, and 2.5 MeV. Spectra have been fitted with two broad absorption bands centered at about 3.0 eV and 3.8 eV for high beam current intensity. These bands are assigned to so-called T-centers, i.e. Zr3+ ions in trigonal point symmetry, which are produced by ionization processes induced by either photon irradiation or charged particle irradiation. A red-shift of the absorption spectra is observed for lower current intensities irrespective of electron energy: these spectra have been fitted with two broad absorption bands centered at about 3.0 eV and 3.3 eV. This modification is attributed to a change in the local environment of Zr3+ ions due to the formation of neighboring oxygen vacancies by elastic collisions, which depends on the electron energy and flux. A common behavior of an increase in differential absorbance to similar saturation values after accumulation of the irradiation dose and decays with time to similar non-zero asymptotic values has been observed, irrespective of the electron energy and flux. However, the rise time and lifetime deduced from the growth and decay curves of the absorbance are dependent on the electron energy. The increase and saturation of the T-center growth rate with electron energy can be attributed to competitive channels of hole trapping at the oxygen and zirconium vacancies induced by elastic collisions. The present on-line experiments reveal the complex process of point-defect generation resulting from the interplay of displacement damage and electronic excitation.