A MECHANISM OF FAST FRENKEL-PAIR FORMATION BY ELECTRONIC EXCITATION IN ALKALI-HALIDES

We analyse the results of femtosecond pump-probe spectroscopy which de monstrate that Frenkel defect pairs are formed in KBr prior to the hol es relaxation into their most stable V-K centre state. The ab initio H artree-Fock calculations which account for lattice polarisation have r evealed that the fast process of the F-H pair formation in KBr prior t o the hole self-trapping is driven by instability of the one-centre ho le state towards formation of the two-centre state and by the interact ion of the relaxing holes with electrons. (C) 1998 Elsevier Science B. V. All rights reserved.