INTRABAND ENERGY RELAXATION OF HOT-EXCITONS LOCALIZED AT A STACKING DISORDER PLANE IN BII3

We study the intraband energy-relaxation of excitons localized at a st acking fault interface in a layered crystal BiJ(3) observing the tempo ral behavior of the luminescence. The relaxation processes in this sys tem are investigated by analyzing the time-resolved luminescence of a phonon sideband which directly reflects the exciton distribution in th e band. When the exciton is resonantly excited by a picosecond laser p ulse, the exciton population reveals a 'hot' distribution at an early stage, The effective temperature decreases immediately according to th e intraband energy-relaxation via the interaction with phonons, and af ter similar to 40 psec, the distribution almost reaches the thermal eq uilibrium with the lattice. We obtain the consistent population relaxa tion time (T-1) from the three-beam degenerate four-wave mixing signal s.