F-aggregate centers in uranium doped and undoped BaF2by neutron irradiation at low temperature

The aggregate centers in uranium doped (0.06 mol %) and undoped BaF2 are investigated by reactor irradiation at 20 K. The new bands at 778, 858 and 890 nm appear in undoped BaF2 at doses above 5 × 1016 n/cm2. From the thermal optical properties and the correlation 778 and 858 nm bands, it is proposed that the 778 and 858 nm bands are attributed to F2 and F+ 2 centers in BaF2, respectively. These aggregate centers behave as similar as that of the F2 and F+ 2 centers in SrF2.