It was noted that direct quantitative correlations had been observed between the T-center electron paramagnetic resonance signal, and an optical absorption band at 370nm, in X-irradiated yttria-stabilized material. It had been suggested that the color center and the paramagnetic center might be identical. In order to check this, theoretical models were analyzed. It was shown that the known electronic structure of the T-center was compatible with an optical transition that had an oscillator strength of the correct magnitude.

C.B.Azzoni, L.Bolis, P.Camagni, G.C.Campagnoli, M.De Simone: Radiation Effects and Defects in Solids, 1995, 134, 485-8