When single-crystal yttria-stabilized zirconia samples are exposed to ultraviolet photons with an energy higher than 4.0 eV, three paramagnetic centers are observed at g = 2.006, 1.97-1.95, and 1.91-1.86. With irradiation by ultraviolet photons, an absorption band and a photoluminescence (PL) band are also induced, showing respective peak energies at around 3.3 and 2.8 eV. The onset of the PL-excitation spectrum occurs around 4.0 eV. The induced absorption band and paramagnetic centers disappear with thermal annealing. By doing a numerical analysis on the experimentally obtained angular dependence of the signal at g = 1.91-1.86, it is determined that signals at g = 2.006 and 1.91-1.86 are due to the F+ center and the T center, respectively, and that the signal at g = 1.97-1.95 has some origin other than the two ESR centers. Since two ESR signals at g = 2.006 and 1.97-1.95, the 3.3-eV absorption, and the 2.8-eV PL have the same onset energy at around 4.0eV, the reactions that induce them are triggered by electrons excited into the conduction band tail.
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