Amplified spontaneous emission (ASE), as a microscopic dynamical process, significantly influences the quality of optically pumped conjugated polymeric lasers. Based on the continuous optical pumping that couples with the prominent self-trapping process of conjugated polymer, four localized phonon modes are distinguished in conjugated polymers, all of which greatly contribute to localization of the excited state as well as local distortion along alternating single and double bonds. Consequently, the ultrafast localized distortion of alternating bonds constructs “instantaneous” structuresan effective four-level electronic structure and population inversionfor ASE. It is shown that all the evolving localized vibrational modes possess even parity, which not only makes it highly possible to be probed through the infrared phonon spectrum, but also opens up an opportunity to improve the quantum efficiency of a polymer ASE/laser by modification of localized phonon modes.

Experiments have shown that intensive charge injections are able to greatly enhance the efficiency of polymer light emitting diodes (PLEDs). Yet, under strong external electric filed/high voltages, there is a certain degree of efficiency roll-off. For this paradox, this article reveals the following underlying mechanism: Under a low electric field, a charged polaron is driven to the potential well created by an exciton, where they fuse together to form a "charged exciton". The carrier fusion induces the triplet state to fluoresce, which greatly enhances the performance of the device (ideally, the internal quantum efficiency can exceed 95%). As long as the external field continues to increase and surpasses 4.5 × 10 4 V/cm, the above confinement is broken, and the polaron also steps out of the potential well, which leads to a major setback of the overall device efficiency. Then, when the electric field reaches as high as 0.8 MV/cm, the original exciton is dissociated. For achieving highly efficient fluorescent PLEDs, it is seen that the appropriate electric field magnitude ranges from 5 × 10 2 to 2 × 10 4 V/cm.

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