Radiative recombination and lifetime of a triplet excitation mediated by spin-orbit coupling in amorphous semiconductors

A charge carrier spin-photon interaction time-dependent transition operator is derived and used for calculating the rate of spontaneous emission of a photon from the radiative recombination of a triplet excited electron in atoms and molecules and triplet excitons in amorphous semiconductors. The derived results are then applied to the hydrogenated amorphous silicon (a-Si:H) to calculate the rate of spontaneous emission and radiative lifetime of triplet excitons. The temperature dependence of the rate of emission is also studied. The calculated radiative lifetimes are compared with the recent experimental results and good agreement was found. The theory is general and can be applied to any amorphous materials, including organic solids.