RELAXATION JUMPS AND HOT LUMINESCENCE OF EXCITONS IN RARE-GAS CRYSTALS

A nonperturbative theory of anharmonic multiphonon decay of strong loc al vibrations in crystals is presented. The theory predicts a slow-dow n of the decay at large amplitudes, and its jump-libe acceleration nea r the critical amplitudes of approximate to 0.3 Angstrom. Local vibrat ion with such or larger amplitude is created e.g. on exciting quasi-mo lecules (localised excitons) Xe-2 in solid Xe. The time evolution of this vibration manifests itself in the hot luminescence of Xe crystal. A comparison between the calculated and the observed spectra allows o ne to conclude that the relaxation rate of Xe-2 in solid the has inde ed a strong maximum at the amplitude of approximate to 0.3 Angstrom.