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Exciton Confinement in Ultrathin Crystalline Organic Films Grown by Organic Molecular Beam Deposition

Published online by Cambridge University Press:  21 February 2011

S. R. Forrest ,
E. I. Haskal  and
P. E. Burrows
S. R. Forrest
Affiliation:
Department of Electrical Engineering, Advanced Technology Center for Photonics and Optoelectronic Materials, Princeton University, Princeton, NJ, 08544
E. I. Haskal
Affiliation:
Current Address: IBM, Zurich, Switzerland
P. E. Burrows
Affiliation:
Department of Electrical Engineering, Advanced Technology Center for Photonics and Optoelectronic Materials, Princeton University, Princeton, NJ, 08544
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Abstract

We use the low temperature fluorescence spectra of organic multiple quantum well samples consisting of the archetype materials, 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA); 3,4,7,8 naphthalenetetracarboxylic dianhydride (NTCDA), and 3,4,9,10 perylenetetracarboxylic-bis-benzimidazole (PTCBI), to study the effects of quantum confinement on the lowest energy excited and ground electronic states of these molecular crystals. Both the Franck-Condon and the dominant ground state vibronic mode energies are observed to undergo significant shifts with decreasing PTCDA layer thicknesses (ranging from 500Å to 10Å) in PTCDA/NTCDA MQWs, while no such effects are observed for PTCBI/NTCDA MQWs. These results are interpreted in the context of confinement of spatially extended excitons in ultra thin PTCDA layers, whereas the considerably smaller radius PTCBI excitons are not affected over the range of layer thicknesses investigated. These results unambiguously rule out previous hypotheses suggesting that binding of small radius excitons to interfaces results in the blue shifts previously observed in the absorption spectra of PTCDA-based MQWs.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 392: Symposium U – Thin Films for Integrated Optics Applications , 1995 , 77
Copyright
Copyright © Materials Research Society 1995

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