The stable formation of color centers was investigated in single crystals which were irradiated with 5MeV electrons, at room temperature and 213K, to doses ranging from 1019 to 1023eV/cm3. It was found that the temperature during irradiation affected the production of aggregate defects. This was particularly true of the ratio of F3+ to F2 laser-active centers and the number of parasitic complex defects. Study of optical absorption and photoluminescence spectra permitted the clarification of the role played by various aggregate defects in the emission properties of F3+ and F2 centers at concentrations of up to 1018/cm3.

High Concentrations of Aggregate Color Centers in Heavily Irradiated LiF Crystals. G.Baldacchini, F.Bonfigli, F.Menchini, R.M.Montereali: Nuclear Instruments and Methods in Physics Research B, 2002, 191[1-4], 216-20