Light emission from dark excitons in light emitting devices

Applying the first order perturbation theory and a new time-dependent spin-orbit-photon interaction operator the rate of spontaneous emission from triplet (dark) excitons calculated in organic molecular solids, conjugated polymers and quan-tum dots is reviewed. The rates are found to be in good agreement with the experimental results in materials where the concept of Wannier-Mott type excitons is applicable, for example, in inorganic amorphous solids, conjugated polymers and quantum dots. In organic molecular solids or molecules, where Frenkel type excitons are formed, the calculated rates do not compare well with experiments. Application of the current theory is critically examined and discussed in light of the traditional approach of the second-order perturbation the-ory used for the triplet radiative recombination. � 2009 WILEY-VCH Verlag GmbH & Co, KGaA.