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Thermalization of the triplet excitons and quenching of the phosphorescence in NaNO2 crystal

Triplet absorption and phosphorescence spectra of NaNO2 crystal have been studied in the temperature range of 1.8 approximately 40 K by means of high resolution spectroscopy. Profiles of the absorption and phosphorescence phonon sidebands of the 0 - 0 line show that the triplet excitons are not in thermal equilibrium at 2 K but approach to the equilibrium above approximately 10 K. The intensity and decay time of the phosphorescence were found to decrease drastically in the temperature range of 3 approximately 6 K. The quenching of the phosphorescence is discussed in terms of spin-lattice relaxation caused by two-phonon processes. The relation between the thermalization of excitons and quenching of the phosphorescence are also discussed.