Characterization of excited state reactions in tris(8-hydroxyquinoline) aluminum (Alq3).
Item
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Title
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Characterization of excited state reactions in tris(8-hydroxyquinoline) aluminum (Alq3).
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Identifier
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AAI9820573
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identifier
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9820573
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Creator
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Priestly, Richard S.
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Contributor
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Adviser: Ardie D. Walser
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Date
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1998
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Electronics and Electrical
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Abstract
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Recently organic materials have sparked a great deal of interest for their potential use in electroluminescent (EL) displays and thin film light emmiting diodes (LED's). Light emitted from these organic materials is produced by the radiative decay of singlet excitons formed by way of charge carrier injection or photoexcitation. Any reactions which cause these excitons to decay nonradiatively will reduce the luminescence quantum efficiency of the material and hence, the optimum performance of electroluminescent devices. Therefore, an understanding of exciton interactions directly associated with luminescence quenching is vital before we can effectively exploit these devices for technological applications.;In this thesis we have examined the underlying mechanisms of various reactions which can produce a low luminescence quantum efficiency in tris(8-hydroxyquinoline) aluminum (Alq{dollar}\sb3),{dollar} a prominent material currently being used as the emitting layer of organic LED's.;Our experimental results are summarized as follows: (i) We have examined exciton-exciton interactions due to the formation of a high concentration of singlet excitons. Measurements show that such reactions reduce the photoluminescence (PL), radiative excited state lifetime and PL quantum efficiency in Alq{dollar}\sb3.{dollar} Calculations were obtained for the bimolecular recombination rate constant, singlet exciton diffusion coefficient and exciton diffusion length. (ii) We investigated the photooxidation reaction of singlet excitons with UV light and oxygen/water. Our measurements indicate that Alq{dollar}\sb3{dollar} light emission degrades as a result of exposure to UV light and water, or UV light and oxygen molecules. Products of photooxidation act as quenching centers for singlet excitons thereby decreasing the peak photoluminescence, radiative excited state lifetime and PL quantum efficiency in Alq{dollar}\sb3.{dollar} (iii) We studied the temperature dependence of the dynamics of singlet excited states in Alq{dollar}\sb3.{dollar} Our results revealed an increase in the peak PL, radiative excited state lifetime and PL quantum efficiency with decreasing temperature from 300K to 77K. At low temperature we observed a decrease in the bimolecular recombination rate, singlet exciton diffusion coefficient and diffusion length. These results are explained in terms of a singlet exciton trapping model.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
