Abstract
The luminescence Br - -ions in NaCl single crystals was studied for concentrations of 10 -2 to 10 -1 mole fraction of NaBr at liquid nitrogen temperature. With ultraviolet excitation, two emission bands were observed at 4.0 eV and at 5.15 eV. These emission bands are known to be of Br - -monomer (4.0 eV) and of Br - -dimers (5.15 eV). By an analysis of the excitation spectra for the 5.15 eV luminescence, an absorption band of Br - -trimers was identified in the low energy side of the Br - -dimer absorption band. Excitation in this trimer band causes the only emission band at 5.15 eV which is known to arise from excitation in the Br - -dimer band. Therefore, the relaxed state of localized excitons at Br - -trimers is supposed to be identical with that of localized excitons at Br - -dimers.
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