Spectral investigation of colour centres in gamma irradiated lithium fluoride thin films

The stable formation of several colour centres has been investigated in four lithium fluoride polycrystalline thin films irradiated in air by gamma rays with doses from 103 up to 106 Gy. Careful spectrophotometric measurements allowed estimating the concentrations of primary F defects and aggregate F3+ and F2 laser-active centres only at the two highest doses. These visible-emitting electronic defects were identified through laser-induced photoluminescence spectra even at the lowest doses. For both the F2 and F3+ light-emitting centres, the luminescence signal increases sub-linearly with the irradiation doses.