Gamma-ray induced color centers in Yb:YAG crystals grown by Czochralski method

20 at.% Yb:YAG single crystals have been grown by the CZ method and gamma-ray irradiation induced color centers and valence change of Fe3+ and Y b3+ ions in Yb:YAG have been studied. One significant 255 nm absorption band was observed in as-grown crystals and was attributed to Fe3+ ions. Two additional absorption (AA) bands located at 255 nm and 345 nm, respectively, were produced after gamma irradiation. The changes in the AA spectra after gamma irradiation and air annealing are mainly related to the charge exchange of the Fe3+, Fe2+, oxygen vacancies and F-type color centers. Analysis shows that the broad AA band is associated with Fe2+ ions and F-type color centers. The transition Y b3+→Y b2+ takes place as an effect of recharging of one of the Y b3+ ions from a pair in the process of gamma irradiation.