A study was made of the early stages of F-center aggregation into colloids in the pure halide under the influence of irradiation. The crystals were irradiated at a dose rate of 2Mrad/h, to doses of up to 1500Mrad, and were studied by means of optical absorption spectroscopy. The F, M and colloid bands were analyzed qualitatively and quantitatively. A relationship was detected, between the concentrations of F- and M-centers, which changed from quadratic to linear. The colloid band appeared to peak at 2 distinct wavelengths; thus indicating that 2 types of colloid were formed during the nucleation stage. The defect concentrations were determined as a function of dose and irradiation temperature, and were explained in terms of models which described the kinetics of defect formation.

J.Seinen, J.C.Groote, J.R.W.Weerkamp, H.W.Den Hartog: Physical Review B, 1994, 50[14], 9787-92