Photophysical Processes in the Vapor of Carbazole

The characteristics of the rapid and retarded fluorescence of the vapor of carbazole excited by the radiation of a nitrogen laser are studied. The dependences of the intensity and rate of decay of the retarded fluorescence on the exciting-radiation intensity, the temperature, and the pressure of the vapor and foreign gases are used to determine the predominant mechanisms of relaxation of triplet molecules. It is shown that the decay of the retarded luminescence is governed by the competition between the processes of triplet-triplet annihilation that lead to the emission of annihilation retarded fluorescence and intercombination conversion of the triplet molecules to the ground electronic state. The characteristic times of these processes and the lifetimes of the triplet state in the vapor _T are evaluated; the temperature dependence of _T is analyzed in a wide interval of temperatures (77–573 K). It is inferred that in all aggregative states, the reduction in _T with increase in the temperature has a common nature and reflects an increase in the rate of intercombination transition T ₁ — S ₀ with increase in the content of vibrational energy.