Time-Resolved Spectroscopic Study of Excitonic Luminescence Centers in RbI Crystals

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Abstract
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 π 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, π and σ bands. The optical absorption originating from the initial states for the 3.07-eV and π 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 π 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 π luminescence.