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

1995 ◽  
Vol 392 ◽  
Author(s):  
S. R. Forrest ◽  
E. I. Haskal ◽  
P. E. Burrows
Keyword(s):  
Multiple Quantum Well ◽  
Organic Films ◽  
Small Radius ◽  
Multiple Quantum ◽  
Molecular Beam Deposition ◽  
Spatially Extended ◽  
Franck Condon ◽  
Low Temperature Fluorescence Spectra ◽  
Beam Deposition ◽  
Rule Out

AbstractWe 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.

Characterization and Griwth of Oicanic Multiple Qanm Well Structures

1990 ◽  
Vol 198 ◽  
Author(s):  
F.F. So ◽  
S.R. Forrest ◽  
Y.Q. Shi ◽  
W.H. Steier
Keyword(s):  
Quantum Well ◽  
Layer Thickness ◽  
Organic Semiconductors ◽  
Multiple Quantum Well ◽  
Energy Shift ◽  
Blue Shift ◽  
Multiple Quantum ◽  
Quantum Well Structures ◽  
Singlet Exciton ◽  
Molecular Beam Deposition

ABSTRACTMultiple quantum well structures consisting of alternating layers of two crystalline organic semiconductors, namely, 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA) and 3,4,7,8 naphthalenetetracarboxylic dianhydride (NTCDA), have been grown by organic molecular beam deposition. The layer thickness was varied from 10 to 200 Å. Birefringence measurements indicate that there is a strong structural ordering in all PrCDA layers, although the PrCDA and NTCDA crystal structures are incommensurate. From optical absorption measurements, it is found there is a blue shift in the lowest energy PICDA singlet exciton line with decreasing layer thickness. A model based on exciton quantum confinement is proposed to explain the energy shift. We have measured the low temperature photoluminescence spectra of organic quantum well structures, and found a slight red shift in the spectra with decreasing well width. These results are also discussed.

Optical Properties of Oriented Crystalline Oligothiophene Thin Films

1995 ◽  
Vol 413 ◽  
Author(s):  
K. Suzuki ◽  
N. Shimizu ◽  
Y. Shiraishi ◽  
M. Kuroda ◽  
Y. Kanemitsu
Keyword(s):  
Thin Films ◽  
Optical Properties ◽  
Fused Silica ◽  
Organic Films ◽  
Luminescence Spectra ◽  
Silica Glasses ◽  
Molecular Beam Deposition ◽  
Crystalline Films ◽  
Average Size ◽  
Beam Deposition

ABSTRACTWe have studied optical properties of oriented crystalline oligothiophene (T4-T6) thin films to analyze the correlation between optical properties and microstructures in organic films. By using conventional vacuum deposition and organic molecular beam deposition techniques, we fabricated oriented crystalline oligothiophene thin films on fused silica glasses. Luminescence spectrum and dynamic. depend on the thickness of the crystalline films. X-ray and scanning electron microscope analyses show that with an increase of film thickness, the average size of microcrystals increases and then saturates to a constant (∼300 nm). The anisotropy of absorption and luminescence spectra show the orientation of molecules in thick films.

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