Electron tunneling in processes of F-centre decay

Ideas about the tunneling mechanism of the recombination of donor acceptor pairs in crystals seem to be first used in ref. 51 to explain the low-temperature of photo-bleaching (i.e. decay on illumination) of F-centres in single crystals of KBr. F-centres are electrons located in anion vacancies and are generated simultaneously with hole centres (centres of the Br3 type which are called H-centres) via radiolysis of alkali halide crystals. 

2 TUNNELING RECOMBINATION LUMINESCENCE OF DONOR-ACCEPTOR PAIRS 

Numerous data about the processes of the tunneling recombination of radiation defects have been obtained in studies on tunneling recombination luminescence. The recombination luminescence of y-irradiated alkali halide crystals was discovered in the mid-1960s [58, 59] in studying the transfer of electrons from Ag and T1 atoms (electron donors) to Cl2 particles (electron acceptor). The Ag and T1 atoms are formed as a result of the action of irradiation on alkali halide crystals which contain Ag+ or Tl+ additives in amounts of about 10 3M. The electrons generated by the irradiation reduce the Ag4 or TU ions to Ag° or Tl° while the hole centres are stabilized in the form of the Cl2 ion occupying two anion positions in the lattice. The hole centres of this kind, whose structure is depicted schematically in Fig. 16, are referred to as Vk-centres. 

The processes resulting in the formation of neutral atoms and Vk-centres can be written as 

Thus the set of tunneling recombination processes leading to the luminescence of y-irradiated alkali halide crystals can be written in the form 

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