Volume Change due to Self-Trapped Exciton and Frenkel Pair in KBr

Transient volume change induced by irradiation of KBr with an electron pulse and a subsequent laser pulse at 6 K has been measured by means of the photoelastic technique. Close correlation is found between the decay curves of the volume and optical absorption changes induced by an electron pulse and between those induced by a laser pulse subsequent to an electron pulse irradiation. By comparing the decay curves of the volume and optical absorption changes quantitatively, the volume change per transient F - H pair relative to that per self-trapped exciton is obtained to be 1.4±0.3. The result indicates that lattice relaxation around a close Frenkel pair is nearly of the same magnitude as that around a self-trapped exciton.