抄録
Decay behaviors of Self-Trapped Exciton (STE) luminescence categorized into type I in seven alkali halides, i.e., the σ bands in NaCl, KBr, RbBr, KI and RbI, and the π bands in NaBr and NaI, are studied by using synchrotron radiation pulses from UVSOR under single-bunch operation. Counting photons over four orders of magnitude reveals that every σ band involves a phosphorescent component with a lifetime longer than 100 ns, in addition to the main fluorescent component. This evidences that the σ band originates from the lowest orbital state of the STE. Simultaneous detection through two different time windows discloses a split in the peak energy of the fluorescent and phosphorescent components. From this result, a slight difference in the location of the minima is suggested in the adiabatic energy surfaces for a nearly degenerate singlet-triplet STE pair with the on-center configuration.
