Energy Transfer and Relaxation Mechanism among Exciton States in Layered Crystal BiI3. I. Energy Transfer by Triplet Excitons

Abstract

Energy transfer from the triplet state of the bulk exciton to the exciton states localized at a stacking fault interface (stacking fault exciton; SFE) in BiI 3 crystals is investigated by observing the temporal behavior and space-resolved spectra of their resonant luminescence. The recombination luminescence with decay time constant of 1.5 nsec from the triplet exciton appears in the sample having the SFE transition, by taking the SFE states as intermediate states. For the excitation at the indirect exciton region, one of the SFE luminescence shows a slow decay with the same time constant as that of the triplet state in addition to an intrinsic fast decay component with the time constant of 40 psec. The space-resolved luminescence spectra indicate that the triplet excitons transport their energy far from the exciting light spot and transfer it to the SFE states efficiently.