TIME-RESOLVED SPECTROSCOPIC STUDY OF EXCITONIC LUMINESCENCE-CENTERS IN RBI CRYSTALS

Luminescence and optical absorption associated with relaxed excitons in pure RbI have been studied by means of time-resolved spectroscopy. It is found that the emission band near 3.0 eV consists of an intrinsic component and an extrinsic component arising from Br- impurities. The intrinsic component, characterized by the same decay time as that of the pi-luminescence, exhibits an emission band peaking at 3.07 eV. The results indicate the presence of three intrinsic emission bands in RbI, the 3.07 eV, pi and sigma bands. The optical absorption originating from the initial states for the 3.07-eV and pi-luminescence is compared with the corresponding absorption in other alkali halides by means of the Mollwo-Ivey relation. It is shown that the absorption bands from the initial state of the pi-luminescence in alkali halides, except NaBr and NaI, can be categorized into two groups: one includes that for the 3.07-eV luminescence and the other that for the pi-luminescence.