Schematic representations of recombination pathways
Radiative processes, corresponding to absorption or emission of light;
Non-radiative processes.
a: Fluorescence
b: Intersystem crossing (ISC)
c: Photoinduced triplet-triplet    absorption
d: Phosphorescence
Excitons are bound “electron-hole” pairs which includes structural relaxation of a single polymer chain (i.e., electron-phonon coupling)
Decay pathways for singlet and triplet decay
S0 is the ground (singlet) state; S1 is the first excited singlet; T1 the first excited triplet; and Ti and Tn are higher lying triplet states.