Relaxation Process of Excitons in KI

It has been observed that the intensity of the π emission at 3.31 eV in KI increases sharply within an exciting pulse duration and temporarily further with a time constant (τ H ) of ∼1 µs, then decreases with a conventional decay time (τ S ) of about 1.8 µs after the excitation by a pulsed N 2 laser above ∼70 K. The height of the absorption band at 1.2 eV due to the transition from the 3 ∑ u + state to a higher excited state of the relaxed excitons behaves also in the same way. Such temporal increases suggest temporal increase of the population of the self trapped excitons at the 3 ∑ u + state. From the temperature dependence of τ H , τ S and of the intensity of the emission, a higher excited state of the self trapped excitons, from which excitons re-relax further into the 3 ∑ u + state, is discussed.