Observation of a NewGd3+ESR Center in Irradiated CaF2

A new type of ${\mathrm{Gd}}^{3+}$ ESR center has been observed in the Ca${\mathrm{F}}_2$ Lattice. This new ${\mathrm{Gd}}^{3+}$ center is produced as a result of x-ray irradiation of Ca${\mathrm{F}}_2$ crystals originally containing the tetragonal ${\mathrm{Gd}}^{3+}$ center charge compensated by an ${\mathrm{F}}^{-}$ ion. The crystal-field splitting associated with this new center is trigonally symmetric along the [111] axis of the Ca${\mathrm{F}}_2$ lattice and is characterized principally by ${b_2}^0\approx 2899\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$.