Abstract
Broad Gaussian luminescence bands with large Stokes shift from free exciton absorption bands have been observed at 11.7 kcm -1 and 11.1 kcm -1 in mercurous halide single crystals of Hg 2 I 2 and Hg 2 Br 2 , respectively at 4.2 K. The excitation spectra and the temperature dependences of the peak energy, the intensity and the decay time have been studied in the above two luminescence bands. A model of self-trapped triplet excitons having two excited states separated by 70 cm -1 is proposed in order to explain the experimental results of the luminescence. The importance of interactions of a mercury diatomic molecule with ten neighboring halogen atoms is suggested from the unpolarized nature of the luminescence.
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