OPTICALLY DETECTED MAGNETIC-RESONANCE OF THE SELF-TRAPPED EXCITON IN NABR

The optically detected electron paramagnetic resonance spectrum of the self-trapped exciton in NaBr is measured using x-ray excitation of th e triplet luminescence. The zero-field splitting parameter was found t o be D = (23 +/- 2.5) mT, an order of magnitude smaller than that of K Br and RbBr. The self-trapped exciton in NaBr is believed to be of typ e I, i.e. the electron and hole occupying an on-centre geometry in con trast to the off-centre configuration of type III, found in most alkal i halides. For an explanation of the small D value measured one has to assume, however, that also in NaBr the electron and hole are split as in a primitive F-H pair, with the distance between them of about 1.5- 3 Angstrom.