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Research on Photo-Induced Exciton Formation and Electric Field-Tuned Polymer Amplified Spontaneous E

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Tutor: LiSheng
School: Zhejiang Normal University
Course: Theoretical Physics
Keywords: Exciton,Conjugated Polymer,Localization,Relaxation,AmplifiedSpontaneous Emission
CLC: TM914.4
Type: Master's thesis
Year:  2013
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Abstract:
This paper employs molecule dynamics to uncover the time profile of exciton formation, which can be divided into two stages:the localization of electron-hole pairs and the relaxation process. Under photoexcitation, the electron transition rapidly forms the electron-hole pair which also leads to its localization, which triggers the total energy to shift violently and oscillate. The oscillation during the first40fs induces the excitation to step into the second stage, i.e., relaxation. After the relaxation process of about850fs, the total energy, lattice energy and electron energy reach certain values while the lattice configuration and electron remain localized, and indicating the formation of a singlet exciton. After an external laser pulse/beam is used to pump a conjugated polymer, such as poly(phenylene vinylene)(PPV),the continuous optical pumping reverses the electron populations in a polymer light-emitting diode, leading to amplified spontaneous emission(ASE). This is accompanied by localized lattice distortion along the polymer chain due to the excitation of a singlet exciton. With the application of an electric field along the polymer, the inversion of electron population is weakened. Once the strength of the applied electric field exceeds a certain threshold, it leads to the aberrance of the localization contributed by the excitation of exciton, which not only forbids the electron transition, but quenches the ASE.
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