Direct measurement of spin-lattice relaxation rates between triplet spin sublevels using optical detection of magnetic resonance

A method is described for the direct measurement of spin-lattice relaxation rates between the triplet spin sublevels of phosphorescent molecules. The method also yields the correct values (in the presence of spin-lattice relaxation) for the total sublevel decay rates and can be used in conjunction with standard optically detected magnetic resonance experiments to find correct values for relative populating rate constants, radiative rate constants and steady state populations of the triplet sublevels. The technique is applied herein to the study of indole and tryptophan molecules in several environments.