Abstract
The effect of dilatational stress on the relaxation of excitons in NaI is investigated by means of photoluminescence and decay time measurements. When the lattice spacing is expanded, a new luminescence band, which is ascribed to the self-trapped exciton in off-center configuration, appears around 3.05 eV in addition to the π band at 4.15 eV. The decay profile of the π band, consisting of 1.2-ns and 110-ns decay components, is not affected by the lattice expansion. The 3.05 eV band exhibits two decay components of 6.0 ns and 1.5 µs. These lifetimes are significantly longer than the corresponding values of the π band, indicating that the electron-hole overlap is smaller for the 3.05 eV-luminescent state. The relaxation processes of a free exciton into the self-trapped state in alkali halides are discussed with the help of the present and previous results.
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