Two remarkable effects for the recently invented chromium-magnesium (Cr-Mg) co-doped yttria-alumino-silicate fiber are reported: (i) strong and spectrally peculiar darkening under the action of energetic (6 MeV) beta-electrons with dosage up to 1.0 x 10(15) cm(-2) and (ii) posterior optical bleaching of the darkening loss at exposure to low-power (of a mW-range) 633 nm light. Both phenomena are revealed to be conspecific to co-doping the fiber with Mg and to the presence of versatile valence forms of Cr ions. The reported results seem to be impactful for exploiting fiber of such type for dosimetry and in space technology
