where 𝛷 #$% , 𝛷 &'" , 𝛷 ()( , 𝛷 ((# , and 𝛷 *+, are the quantum yields of photon absorption by sensitizer, intersystem crossing in the sensitizer, triplet energy transfer (TET) from the sensitizer to the emitter, TTA between two triplet emitters, and fluorescence of the emitter, respectively. Also, 𝑓, which is often called spin-statistical factor, is the probability to yield the radiative first-excited singlet (S1 emi ) from the nine spin-sublevels of singlet, triplet and quintet triplet-pairs. 𝛷 ((# is represented as follows , using the rate constant of TTA, 𝑘 ((# , and the lifetime of triplet excited state of the emitter molecule (triplet-exciton), 𝜏 ( :