Relaxation Jumps and Hot Luminescence of Excitons in Rare Gas Crystals

A nonperturbative theory of anharmonic multiphonon decay of strong local vibrations in crystals is presented. The theory predicts a slow–down of the decay at large amplitudes, and its jump–like acceleration near the critical amplitudes of 0.3 Å. Local vibration with such or larger amplitude is created e.g. on exciting quasi–molecules (localised excitons) 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 one to conclude that the relaxation rate of in solid Xe has indeed a strong maximum at the amplitude of 0.3 Å.