| Abstract: | Crack propagation in dielectric solids is connected with many structural and electronic excitation processes. In order to obtain some information on the elementary excitation mechanism, crack velocity and fracture-induced luminescence in LiF and NaF (as received; doped; X-irradiated) under high vacuum conditions were correlated. Time-resolved crack velocity measurements revealed the usually discontinuous manner of crack propagation; maximum crack velccities of 3800 m/s (LiF) and 3000 m/s (NaF) were observed. Luminescence excitation in the X-irradiated samples occured at slow crack motion i.e. for increased plastic processes in the crack tip zone. The luminescence was explained by the recombination of stabilized radiation defects (F-centres and interstitial halogen atoms) involving a radiative exciton decay. The recombination is triggered by the crack via mobilization of the recombination partners by dislocations or lattice deformation processes. |
