ABSTRACT
Light-emitting diodes (LEDs) based on luminescent small organic molecules (OLEDs) and polymers (PLEDs) have become one of the major areas in the science of organic materials. The principle of operation of all LEDs is based on radiative decay of excited states (excitons) created in the molecule (polymer, inorganic material) by injecting electrons and holes in the lowest unoccupied molecular orbital and highest occupied molecular orbital, respectively. As these electrons and holes are generally injected with random spins, their recombination would give both symmetric (triplet) and antisymmetric (singlet) states. This chapter gives a brief description of the photo-physics beyond the operation of electrophosphorescent devices, followed by examples of the materials, devices, and processes experimentally studied in the field till the beginning of 2013.
