Fracture‐induced luminescence in Alkali Halides

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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.