  Thermally activated delayed fluorescence has been reported in a number of
OLED emitter materials engineered to have low singlet-triplet energy gaps. Here
we derive closed solutions for steady state and transient behaviors, and apply
these results to obtain the singlet and triplet relaxation, forward and reverse
crossing rates and the gap energy and reverse crossing prefactor from delayed
and prompt relaxation rates measured over a series of temperatures. The primary
rates are then used to calculate the fluorescent/phosphorescent ratio and the
singlet/triplet population ratio. The method avoids the need for gated yield
measurements. Good fits are obtained using previously published data for 4CzIPN
and m-MTDATA:t-Bu-PBD and the results appear to be consistent with reported
quantities were available, and with reported behaviors of OLEDS that use these
materials.
