Two decay components (slow and fast) of the luminescence of O vacancy centers were observed in alkaline-earth fluoride and barium fluorohalide crystals at 17 to 300K. Very slow components were observed in all of the crystals, except for type-II O centers in BaFBr. At temperatures above 100 to 150K, the integrated intensity of very slow components decreased in parallel with the decay time, with a thermal energy of 0.1 to 0.2eV. The integrated intensity of the slow component did not decrease between 17 and 300K, while the decay time decreased from several hundred microseconds to several microseconds. This behavior was explained in terms of thermal interaction between 3 closed excited levels with differing radiative lifetimes. It was tentatively proposed that these 3 levels belonged to different O vacancy center configurations in the lowest excited state.

E.Radzhabov: Journal of Physics - Condensed Matter, 1994, 6[45], 9807-15