Photoluminescence and the thermal stability of color centers in γ-irradiated LiF and LiF(Mg)

Pure and magnesium doped (2000 ppm) LiF crystals have been irradiated with γ rays from Am241 and Co60 sources and the thermal stability of the resulting defects has been studied using photoluminescence (PL) and optical absorption (OA). The composite nature of the M band at 440 nm is highlighted by PL data which reveal emission attributed to F3+ defects otherwise hidden in OA measurements. The following bands appear in excitation spectra; Z3 (222 nm), Z2 (285 nm), R1 (329 nm), R2 (375 nm), F3+ (440 nm), and F2 (440 nm). Notable differences are observed between pure and doped samples during thermal annealing relating to the F2 and F3+ bands in particular. Results support the idea of Z centers as being F and F− centers trapped at impurity ions in the crystal.