BO₂-F⁺ Centers in the Radiation-damaged YCOB Crystals

An intense paramagnetic EPR signal generated from x-ray-irradiated, powdered YCOB crystals was observed at the liquid nitrogen temperature for the first time. Five peaks, located at the positions where the effective g factor equals to 1.992, 1.986, 1.980, 1.974 and 1.965, labeled as A, B, C, D and E respectively, were observed. It is believed that the peaks A, B, C and D generated from the BO₂-F⁺ center which is a single electron trapped in an oxygen vacancy which was originally occupied by an O^2- ion bonded to a (BO₃)^3- anion group. The peak E is thought of coming from Y²⁺ ions that are formed by the Y³⁺ ions trapping electrons. The mechanism for the formation of the radiation-induced defects in the YCOB crystals is suggested.