| Through combining electron transition process anddipole moment evolution as well as electron-phonon coupling, molecular dynamics calculations show that the radiative decay of singlet excitons in a conjugated polymer, such as a PLED, is largely determined by the evolution of the dipole moment. Without an electric field, the decay life of a singlet exciton is about 1 ns. Once an electric field is applied and exceeds a critical value, with electron-phonon coupling, the original lattice structure evolves into to two new localized lattice distortions, consistent with the experimental results. Owing to the new lattice structure and self-trapping, the dipole moment rapidly decreases to zero within 5 fs, eliminating the radiative decay of the singlet exciton.Laser emission based on polymer fibers generally undergoes two unconventional processes-microscopic lattice/electron evolution and macroscopic localization of light emission.After an external laser pulse/beam is used to pump a conjugated polymer composed of random parallel polymer fibers, such as poly-thiophene,the external excitation immediately destroys the periodic structure of the polymer chain, with self-inducing of the localized lattice distortion along the polymer fiber chain. Along with the continuous optical pumping, the electron populations of the exciton in a single polymer fiber are reversed. The external gain, combined with multiple light scattering in a bunch of fibers, counteracts the leakage due to non-coherent light emission, with finally localizing the light in the middle of the bunch. Concurrent with the localization of the polymeric fiber laser, the multiple scattering, instead of phase tuning in the traditional resonator,causes the laser cavity to be composed only by all randomly-distributed polymer fibers, and thus to be "invisible.'... |
