Anisotropy of Color Centers in Calcite

In calcite colored by 3-Mev electrons (10⁵ to 10⁶ rads) at -190^∘{}C, two absorption bands at 350 and 290 m{μ} have been observed. Samples cut parallel to the c axis colored and measured with polarized light (E_⊥c and EIIc) showed that the band at 350 m{μ} is isotropic while that at 290 m{μ} is anisotropic. The former is correlated to trapped electrons and the latter to trapped holes. Both bands are stable at -190^∘{}C but decay simultaneously at room temperature, accompanied by strong luminescence with a peak at 590 m{μ}.