| 1. |
- Gubaydullin, A. R., et al.
(author)
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Control of spontaneous emission rate in Tamm plasmon structures
- 2018
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In: 2018 INTERNATIONAL CONFERENCE LASER OPTICS (ICLO 2018). - : IEEE. - 9781538636121 ; , s. 131-131
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Conference paper (peer-reviewed)abstract
- We have studied experimentally and theoretically spontaneous emission rate modification in Tamm plasmon structures with semiconductor( InAs/GaAs quantum dots) and organic (CBP) emitters. Time-resolved spectroscopy demonstrates that spontaneous emission rate is increased by one order in magnitude. Experimentally measured spontaneous emission pattern coincides with calculated dependence of modal Purcel factor on frequency and angle of emission.
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| 2. |
- Morozov, Konstantin M., et al.
(author)
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Efficient UV Luminescence from Organic-Based Tamm Plasmon Structures Emitting in the Strong-Coupling Regime
- 2020
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In: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:39, s. 21656-21663
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Journal article (peer-reviewed)abstract
- Excitons in organic semiconductors possessing a large oscillator strength demonstrate strong coupling with cavity modes at room temperature. A large Stokes shift in some organic semiconductors enriches and complicates the picture of the emission in strongly coupled systems of organic excitons and light. Here, we demonstrate strong coupling of excitons in 4,4-bis(N-carbazolyl)-1,1-biphenyl (CBP) and Tamm plasmons in the ultraviolet (UV) band, accompanied by a bright emission from the structure. Reflection measurements demonstrate the pronounced formation of the lower and upper polariton modes with Rabi splitting of the magnitude of 0.3 eV, and the emission peak experiences a substantial red shift with respect to the lower polariton mode. Both radiative and nonradiative decay rates in the Tamm plasmon CBP structure are increased with respect to a bare CBP. Such peculiar behavior is attributed to the simultaneous manifestation of strong coupling and weak coupling of the CBP molecule emitters to the Tamm plasmons.
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| 3. |
- Morozov, Konstantin M., et al.
(author)
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Opposite Sign of Polarization Splitting in Ultrastrongly Coupled Organic Tamm Plasmon Structures
- 2021
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In: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 125:15, s. 8376-8381
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Journal article (peer-reviewed)abstract
- The properties of the ultrastrongly coupled Tamm plasmon cavity filled with a high-oscillator-strength organic material DPAVBi (4,4-bis[4-(di-p-tolylamino)styryl]biphenyl) are studied using theoretical and experimental methods. An analytical model predicts the opposite sign of polarization splitting for the lower and upper polariton cases and a giant absolute value of the splitting. A set of organic Tamm plasmon cavities with different detuning parameters are fabricated. We demonstrate that all structures are operating in the ultrastrong coupling regime: the values of the Rabi splitting are close to a 20% fraction of the exciton energy. The measured angle-dependent reflectivity spectra structure for both transverse electric (TE) and transverse magnetic (TM) polarizations confirm the predicted theoretical model. We obtained a giant value of the polarization splitting of up to 180 meV for both polariton branches. We believe that it is the first demonstration of such peculiar polarization splitting behavior of polaritons in the ultrastrong coupling regime.
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| 4. |
- Greczynski, G., et al.
(author)
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Electronic structure of pristine and sodium doped poly(p-pyridine)
- 2001
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 114:9, s. 4243-4252
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Journal article (peer-reviewed)abstract
- Ultraviolet spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS) were used to study the valence electronic structures of pristine and sodium doped poly (p-pyridine) (PPY). The UPS spectra were analyzed by studying the density-of-valence-states (DOVS) derived from quantum chemical calculations. The electronic band structure of the PPY chains was also theoretically investigated using the valence effective Hamiltonian (VEH) method. The theoretical approach was found to be more accurate in describing the electronic structure of PPY.
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| 5. |
- Magnuson, Martin, 1965-, et al.
(author)
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Resonant inelastic soft X-ray scattering spectra at the nitrogen and carbon K-edges of poly(pyridine-2,5-diyl)
- 1999
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In: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 101-103, s. 573-578
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Journal article (peer-reviewed)abstract
- Resonant inelastic scattering measurements of the conjugated polymer, poly(pyridine-2,5-diyl) have been performed at the nitrogen and carbon K-edges using synchrotron radiation. For comparison, molecular orbital calculations of the spectra have been carried out with the repeat unit as a model molecule of the polymer chain. The resonant emission spectra show depletion of the π electron bands which is consistent with symmetry selection and momentum conservation rules. The depletion is most obvious in the resonant inelastic scattering spectra of carbon while the nitrogen spectra are dominated by lone pair n orbital emission of σ symmetry and are less excitation energy dependent. By comparing the measurements to calculations an isomeric dependence of the resonant spectra is found giving preference to two of the four possible isomers in the polymer.
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| 6. |
- Magnuson, Martin, 1965-, et al.
(author)
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The electronic structure of poly(pyridine-2,5-diyl) investigated by soft X-ray absorption and emission spectroscopies
- 1998
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In: Chemical Physics. - 0301-0104 .- 1873-4421. ; 237:3, s. 295-304
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Journal article (peer-reviewed)abstract
- The electronic structure of the poly-pyridine conjugated polymer has been investigated by resonant and non-resonant inelastic X-ray scattering and X-ray absorption spectroscopies using synchrotron radiation. The measurements were made for both the carbon and nitrogen contents of the polymer. The analysis of the spectra has been carried out in comparison with molecular orbital calculations taking the repeat-unit cell as a model molecule of the polymer chain. The simulations indicate no significant differences in the absorption and in the non-resonant X-ray scattering spectra for the different isomeric geometries, while some isomeric dependence of the resonant spectra is predicted. The resonant emission spectra show depletion of the electron bands in line with symmetry selection and momentum conservation rules. The effect is most visual for the carbon spectra; the nitrogen spectra are dominated by lone pair n orbital emission of symmetry and are less frequency dependent.
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| 7. |
- Magnuson, Martin, 1965-, et al.
(author)
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The electronic structure of polyaniline and doped phases studied by soft X-ray absorption and emission spectroscopies
- 1999
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 111:10, s. 4756-4761
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Journal article (peer-reviewed)abstract
- The electronic structure of the conjugated polymer, polyaniline, has been studied by resonant and nonresonant soft x-ray emission spectroscopy using synchrotron radiation for the excitation. The measurements were made on polyaniline and a few doped (protonated) phases for both the carbon and nitrogen contents. The resonant x-ray emission spectra show depletion of the π electron bands due to the selective excitation which enhances the effect of symmetry selection rules. The valence band structures in the x-ray emission spectra attributed to the π bands show unambiguous changes of the electronic structure upon protonation. By comparing to x-ray absorption measurements, the chemical bonding and electronic configuration is characterized.
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| 8. |
- Morozov, Konstantin M., et al.
(author)
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Revising of the Purcell effect in periodic metal-dielectric structures: the role of absorption
- 2019
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In: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 9
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Journal article (peer-reviewed)abstract
- Periodic metal-dielectric structures attract substantial interest since it was previously proposed that the spontaneous emission amplification rates (the Purcell factor) in such structures can reach enormous values up to 105. However, the role of absorption in real metals has not been thoroughly considered. We provide a theoretical analysis showing that absorption leads to diminishing values of Purcell factor. We also suggest that using emitting organic compounds such as CBP (4,4-Bis(N-carbazolyl)-1,1-biphenyl) can lead to a moderate increase of about an order of magnitude in the Purcell factor. Defining the experimentally measured Purcell factor as a ratio between the excited state lifetimes in bare CBP and in periodic structure, this increase in the fabricated periodic structure is demonstrated through a 4-8 times decrease in excited state radiative lifetime compared to a bare organic material in a wide emission spectrum.
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| 9. |
- Campoy-Quiles, M., et al.
(author)
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On the determination of anistropy in polymer thin films : A comparative study of optical techniques
- 2008
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In: Physica Status Solidi. C: Current Topics in Solid State Physics. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 1862-6351. ; 5:5, s. 1270-1273
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Journal article (peer-reviewed)abstract
- We have used seven different techniques to measure the anisotropic refractive index of poly(vinylcarbazole) films. These techniques are: two types of variable angle spectroscopic ellipsometry (VASE) with multiple sample analysis, Interference enhanced VASE, Transmittance combined with VASE, Polarised Reflectance, beta-scan VASE, and prism coupling. We have found the average ordinary and extraordinary indices at 633 nm to be no = nTE = 1.675 ± 0.008, and ne = nTM = 1.722 ± 0.018, respectively, consistent amongst methods and conclusive on the magnitude of Δn in polymer films.
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| 10. |
- Knaapila, Matti, et al.
(author)
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An effect of side chain length on the solution structure of poly(9,9-dialkylfluorene)s in toluene
- 2008
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In: Polymer. - : Elsevier BV. - 0032-3861. ; 49:8, s. 2033-2038
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Journal article (peer-reviewed)abstract
- The effect of side chain length of pi-conjugated poly(9,9-dialkylfluorene)s has been studied in semi-dilute (10 mg/mL) toluene solutions using small-angle neutron scattering (SANS) and H-1 and H-2 NMR spectroscopies. Under these conditions, SANS data indicate that poly(9,9-dinonylfluorene) and poly(9,9-dioctylfluorene) are dissolved down to the molecule level and appear as elongated one-dimensional chains (length >20-30 nm). In contrast, the shorter side chain polymers exhibit a self-association so that poly(9,9-diheptylfluorene) forms thin sheet-like (similar to 1 nm) and poly(9,9-dihexylfluorene) thin (similar to 1 nm) and thick sheet-like (>6 nm) aggregates. H-1 NMR data, together with the density functional theory (DFT) calculations, however, show that this occurs without changes in the conformation of the polymer backbone.
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| 11. |
- Knaapila, Matti, et al.
(author)
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Control over phase behavior and solution structure of hairy-rod polyfluorene by means of side-chain length and branching
- 2008
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In: Physical Review E (Statistical, Nonlinear, and Soft Matter Physics). - 1539-3755. ; 77:5
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Journal article (peer-reviewed)abstract
- We present guidelines on how the solution structure of pi-conjugated hairy-rod polyfluorenes is controlled by the side-chain length and branching. First, the semiquantitative mean-field theory is formulated to predict the phase behavior of the system as a function of side-chain beads (N). The phase transition at N=N* separates a lyotropic phase with solvent coexistence (N < N*) and a metastable membrane phase (N > N*). The membrane phase transforms into the isotropic phase of dissolved rodlike polymers at the temperature T-mem*(N), which decreases both with N and with the degree of side-chain branching. This picture is complemented by polymer demixing with the transition temperature T-IN*(N), which decreases with N. For N < N*, the lyotropic phase turns isotropic with increasing T at T-IN*. For N > N*, stable membranes are predicted for T-IN*< T < T-mem* and metastable membranes with nematic coexistence for T < T-IN*. Second, in experiment, samples of poly(9,9-dialkylfluorene) with N=6-10 were mixed in methylcyclohexane. For N=8 the side-chain branching was controlled by (9,9-dioctylfluorene)/(9,9-bis(2-ethylhexyl)fluorene) (F8/F2/6) random copolymers. The proportion of F8 to F2/6 repeat units was 100:0, 95:5, 90:10, 50:50, and 0:100. In accordance with the theory, lyotropic, membrane, and isotropic phases with the corresponding phase transitions were observed. For N < N*similar to 6 only the lyotropic phase is present for attainable temperatures. The membrane and isotropic phases are present for N > N*. T-mem*(N) decreases from 340 K to 280 K for N >= 8. For copolymers, the membrane phase is found when the fraction of F8 units is at least 90%, T-mem* decreasing with this fraction. The membrane phase contains three material types: loose sheets of two polymer layers, a better packed beta phase, and dissolved polymer. For N >= 7 and T < T-mem* the tendency for membrane formation becomes stronger with increasing temperature.
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| 12. |
- Knaapila, Matti, et al.
(author)
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Influence of side chain length on the self-assembly of hairy-rod poly(9,9-dialkylfluorene)s in the poor solvent methylcyclohexane
- 2007
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In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:26, s. 9398-9405
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Journal article (peer-reviewed)abstract
- We report on the phase behavior of poly(9,9-dihexylfluorene) (PF6), poly(9,9-diheptylfluorene) (PF7), poly(9,9-diocylfluorene) (PF8) poly(9,9-dinonylfluorene) (PF9), and poly(9,9-didecylfluorene) (PF10) in methylcyclohexane (MCH). After a heating-cooling cycle, in the 10-50 mg/mL. concentration range. PF6/ MCH. PF7/MCH. PF8/MCH, and PF9/MCH systems were found to be gel-like, while PF10/MCH appears less viscous. PF6/MCH, PF7/MCH, PF8/MCH, and PF9/MCH form large (10- 100 nm) sheetlike assemblies (thickness of 2-3 nm). The larger length scale Structures of these sheets show an odd-even dependence on the side chain (spacer) length: the PF6 and PF8 sheets are broader and thinner, whereas PF7 and PF9 sheets are thicker with a Putative double layer Structure. PF10 does not follow this sequence, and only part of the polymer is assembled into a sheetlike structure the rest remaining dissolved at the molecular level. PF8/MCH and PF9/MCH mixtures also have lower length scale crystalline structures with an internal period corresponding to the periodicity observed in the solid-state P phase of PF8. Vestiges of crystalline domains are found for PF6 and PF7 but not for PF10. PF7/MCH. PF8/MCH, and PF9/MCH systems contain the conformational isomer C, of those chains observed in the ss phase, while this is not observed with other polymer/MCH systems.
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| 13. |
- Knaapila, Matti, et al.
(author)
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Meridional orientation in biaxially aligned thin films of hairy-rod polyfluorene
- 2007
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In: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 7:9, s. 1706-1711
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Journal article (peer-reviewed)abstract
- The uniaxial chain alignment and equatorial patterning of poly [9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (M-n = 29 kg/mol, M-w = 68 kg/mol) thin films atop rubbed polyimide substrates have been studied by grazing incidence X-ray diffraction. This specific molecular weight yields among the highest observed levels of chain alignment and optical anisotropy and, after thermal annealing, the sample undergoes transformation to a highly textured crystalline hexagonal phase. The two dominant equatorial orientations (i.e., types I and II crystallites) are found to have almost identical meridional orientation distributions. The X-ray deduced orientation is in quantitative agreement with that obtained by optical absorption measurements. It is also shown that the equatorial ordering is paracrystalline in nature, and both type I and type II crystallites are similar in this respect. This equatorial scattering is superimposed on a background of a hexagonal phase polymer with a cylindrically isotropic orientation (type III).
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| 14. |
- Samuelsen, E.J., et al.
(author)
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The structure of polypyridine
- 2001
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In: Synthetic metals. - 0379-6779 .- 1879-3290. ; 124:2-3, s. 393-398
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Journal article (peer-reviewed)abstract
- X-ray diffraction on samples in the form of a deposited thin layer, a crushed powder and a flake were used to deduce models for the crystalline structure of polypyridine (-(C5H3N)n-), a conjugated polymer of great interest for applications. A monoclinic unit cell with lattice parameters a = 7.47 Å, b = 5.83 Å, c = 4.25 Å, ? = 108.7° containing two chains running along the c-axis and with the molecular plane normal to the a-axis gives a good fit with the observations. The interchain packing distance is about 3.6 Å, i.e. in the same range as intermolecular distances found in conductive charge transfer salts. The deposited layer is highly anisotropic, with the a-c-plane parallel to the substrate. © 2001 Elsevier Science B.V. All rights reserved.
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| 15. |
- Westerling, M., et al.
(author)
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Photoexcitation dynamics in an alternating polyfluorene copolymer
- 2007
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In: Phys. Rev. B: Condens. Matter Mater. Phys. FIELD Full Journal Title:Physical Review B: Condensed Matter and Materials Physics. ; 75:22
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Journal article (peer-reviewed)abstract
- The authors used transient photoinduced absorption on femtosecond to nanosecond time scales as well as delayed fluorescence up to microseconds to study the photogeneration and recombination of charges in thin films of the alternating polyfluorene copolymer poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]. The authors interpret the results using a coupled rate equation model and find that the authors can fit all exptl. results with a single set of parameters. The model includes prompt (
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