Abstract
Rapid quenching of KBr crystals doped with Se 2- gives isolated Se 2- ions which are strongly luminescent. Two emission spectra were observed, one with a maximum intensity at about 14100 cm -1 and the other with a maximum intensity at about 17200 cm -1. Only the red emission is observed by excitation into the lowest energy absorption band at 24600 cm -1, while between 10 K and about 150 K both red and yellow emissions are observed by excitation into the second absorption band at 26770 cm -1. Both are assigned to the isolated Se 2- center in different distorted charge transfer states. The yellow emission is observed below about 100 K, reaches maximum intensity at about 35 K and is absent below 10 K. There are complementary changes in the intensity of the red emission so that the sum of the two emission intensities is constant. The absorption spectra of the isolated Se 2- and the (Se 2--vacancy) pair have been identified as well as the spectrum of a cluster of two or more (Se 2--vacancy) pairs.
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