Temperature variation of phosphorescence decay in NaNO2 crystals: Spin-lattice relaxation of the triplet state in NO2-

Temporal behavior of the phosphorescence in NaNO2 has been studied in the temperature range of 1.8 similar to 40 K, Intensities and decay times of the phosphorescence show steep decrease as temperature rises from 2.5 to 6 K. Below 2 K, the decay curves of the E//b and E//c polarizations consist of three exponential decay components with tau(s) similar or equal to 660, tau(m), similar or equal to 110 and tau(f) similar or equal to 20 mu sec. Above 8 K, the three components merge into a single one with tau similar or equal to 30 mu sec. These results are discussed using simple rate equations for the populations of the three sublevels of the lowest triplet state in the NO2- molecule, by taking account of spin-lattice relaxation among the sublevels. Excitonic features in the phosphorescence decay are also discussed qualitatively.