| 1. |
- Granlund, Thomas, et al.
(författare)
-
A polythiophene microcavity laser
- 1998
-
Ingår i: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 288:5-6, s. 879-884
-
Tidskriftsartikel (refereegranskat)abstract
- We report photopumped lasing in a microcavity device with a polythiophene layer as the emitter. These microcavity devices are built by joining two polymer coated dielectric mirrors at elevated temperature. When photopumping the film, a lasing threshold is observed at 120 nJ/cm(2). Comparative studies with fast pump-probe spectroscopy of thin polythiophene films and the same polymer in photopumped lasing studies, indicate that the gain coefficient is 80 +/- 20 cm(-1), and that the exciton concentration is 2 X 10(17) cm(-3) at the lasing transition, well below the exciton-exciton recombination level. (C) 1998 Elsevier Science B.V. All rights reserved.
|
|
| 2. |
- Granlund, Thomas, et al.
(författare)
-
Lasing in substituted polythiophene between dielectric mirrors
- 1999
-
Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 102:1-3, s. 1038-1041
-
Tidskriftsartikel (refereegranskat)abstract
- We report photopumped lasing in a microcavity device with a polythiophene layer as emitter. The microcavity is made of a polymer film between two dielectric Bragg reflecting mirrors (DBR). The:microcavity devices is built by joining two polymer coated DBR mirrors at elevated temperature. When photopumping the film,a lasing threshold is observed at 120 nJ/cm(2). Comparative studies with fast pump-probe spectroscopy of thin polythiophene films, and the same polymer in photopumped lasing studies, indicate that the gain coefficient is 80 +/- 20 cm(2) and that the exciton concentration is 2X10(17) cm(2) at the lasing transition, well below the exciton-exciton recombination level.
|
|
| 3. |
- Ruseckas, Arvydas, et al.
(författare)
-
Luminescence quenching by inter-chain aggregates in substituted polythiophenes
- 2001
-
Ingår i: Journal of Photochemistry and Photobiology, A: Chemistry. - 1873-2666 .- 1010-6030. ; 144:1, s. 3-12
-
Tidskriftsartikel (refereegranskat)abstract
- Time-resolved photo luminescence spectra measured in solid films of two polythiophene derivatives with different chain packing allow to distinguish emission of intra-chain excitations from the luminescence of inter-chain aggregates. Aggregate luminescence is red shifted by about 0.1 eV relative to intra-chain emission and shows vibronic coupling to the C=C bond stretch with the Huang-Phys factor of S approximate to 1.5, which is twice bigger than that of the intra-chain emission. Combining time resolved luminescence data with femtosecond transient absorption, we show that the dynamic quenching of the luminescence in films with dense chain packing is mainly due to excitation energy transfer to aggregates. The radiative lifetime of the lowest excited state of the aggregate with the optical gap of 1.84-1.9 eV is estimated to be about 20 ns. The aggregate contribution to the total luminescence in the polythiophene films with dense chain packing is about 50% and does not change significantly with temperature. (C) 2001 Elsevier Science B.V. All rights reserved.
|
|
| 4. |
- Theander, Mathias
(författare)
-
Photoluminescence in Conjugated Polymers : Experimental Investigations of Excited State Events
- 2000
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- After an extensive scientific effort spent on the understanding of conjugated polymers and molecules, these material are on the border of commercialisation. Even though highly efficient devices can be made with conjugated polymers the underlying physics is far from being fully understood. In this thesis, photoluminescence is used for studying excited state events inconjugated polymers. The work is relevant for a number of applications, such as photodiodes, lasers and light emitting devices.A close co-operation with chemists which have synthesised a number of phenyl substituted polythiophenes has made it possible to find correlation's between the chemical structure and the resulting photoluminescence of these polythiophenes. The yield of photoluminescence is set by intrachain properties influencing the geometry of the single chain and interchain properties. By comparing the photoluminescence of the polymers in solution and thin film one can assign the intrachain properties, which are dominant in solution and the interchain properties which act in the thin film. We have found that polymers with planar backbones give the most luminescent polymers in solution. Using interchain interaction to increase the planarity has been shown to increase the PL yield even further. In thin films the interchain interaction between different chains can give both intrachain emitting species, and an increase of exciton transport, which increase the possibility of finding PL quenching sites in the polymer film, thus reducing the PL yield in the thin film.With a strong electron acceptor, the exciton on the polymer chain can split into its constituents, forming an electron and a hole. A quenching of the photoluminescence occurs. This has been used to determine the exciton quenching range in a polythiophene, close to a strong donor-acceptor interface. A short distance was found (5 nm) which is strongly limiting the efficiency of photovoltaic devices.
|
|
