ESR Detection of H Centre Generation by Photodestruction of U₂ Centres in KCl

Abstract

Understanding the mechanism of the generation of interstitial atoms is important for the study of radiation damage processes. Interstitial halogen atoms o r hole centres in ionic crystals a r e usually produced by ionizing radiation at low temperatures. Disadvantageous for the study of the production mechanism is the fact that several types of hole and electron centres a r e produced simultaneously. There seems to exist, however, a process to create one type of hole centres by UV irradiation of alkali halide crystals containing U centres (neutral hydrogen stoms in interstitial lattice positions, H . ) . It was reported by Kurz (1, 2) that by irradiation into the UV absorption band of U2 centres in KC1 at 4.5 OK it i s possible to destroy the U band and to create two absorption bands, which a r e identical with those of Subsequently the crystal was irradiated in the U2 band (peak 5.27 eV) with filtered light (filter W-R-250, Schott) for 14 h , resulting in a 30% bleaching of the U2 centres. The obtained optical absorption spectrum corresponds to the observations made by Kurz (1, 2). The decay of U2 centres and the creation of H centres could .be observed in the ESR spectrum (Fig. 1). The two outer line groups a r e due to U centres (3, 4). The other lines a r e due to H centres.

Generation of dichroic h centres in KCl by polarized optical bleaching of interstitial atomic hydrogen

“…Since H and HP centres are paramagnetic, the bleaching process can be studied also with ESR [9]. This difference in the spin-lattice relaxation time T, could indicate a perturbation of the measured H centres.…”

“…This process was studied with optical measurenients [7, 81, and it was established by ESR that indeed H centres and not another type of hole centres is created [9]. The advantage of this way of producing H centres is that the electronic state from which the H centre evolves is excited directly and not a t the end of a long chain of processes following the X-ray or electron-beam irradiation.…”