Ultrafast photogeneration mechanisms of triplet states in<i>para</i>-hexaphenyl

Zenz, Christian; Cerullo, Giulio; Lanzani, Guglielmo; Graupner, W.; Meghdadi, F.; Leising, G.; Silvestri, S. De

doi:10.1103/physrevb.59.14336

Cited by 43 publications

(50 citation statements)

References 27 publications

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“…The PA limiting the gain bandwidth at low energies in p-6P has been attributed to the disorder-induced formation of polarons and triplet excitons. [26] Such a conclusion supports the speculation that the much larger extent of gain bandwidth at low energies observed in our epitaxial samples on mica is due to the minimization of structural disorder, leading to the inhibition of polaron and triplet-state creation through extrinsic processes. Intrinsic mechanisms for polaron formation can be possibly activated by increasing the photon excess energy DE g , which would explain the blue shift observed in the (low-energy) isosbestic point shown in the inset of Figure 1b.…”

supporting

confidence: 80%

“…On the other hand, E ga , and thus the effective gain bandwidth C g , is strongly dependent on the interaction with the substrate. Films deposited on more conventional substrates, like quartz plates, have a smaller gain bandwidth (C g ∼ 0.5 eV), [25,26] which is half the one observed in heteroepitaxial films grown on mica. Neargap PA is observed at longer delays.…”

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confidence: 97%

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Optical Gain Performance of Epitaxially Grown para‐Sexiphenyl Films

et al. 2007

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The great progress in the growth of ordered thin films of small linear molecules achieved in the past decade has made control of supramolecular arrangement and its effect on the physical properties frontline challenges for materials science. During film growth, multiple nucleation results in small, randomly oriented crystal domains. It has been recently shown that dipole-assisted, heteroepitaxial techniques allow deposition of thin films with unusual long-range order, consisting of crystalline aggregates that self-assemble to form nanofibers with sub-micrometer cross section, lengths of up to millimeters, orientational alignment extending to the centimeter size range, and controllable interaggregate distance. [1][2][3] These nanofibers have shown remarkable optical functionalities: photo-and electroluminescence, [2,4] optical waveguiding, [5,6]

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confidence: 80%

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confidence: 97%

Optical Gain Performance of Epitaxially Grown para‐Sexiphenyl Films

et al. 2007

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“…26,28,[54][55][56] In contrast, the assumption of a fixed k ISC would lead to a nearly complete depletion of the triplet state under stimulated emission.…”

Section: Organic Semiconductor Laser Modelmentioning

confidence: 99%

Plasmonic Sinks for the Selective Removal of Long-Lived States

et al. 2011

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The use of plasmonic nanostructures for the removal of unwanted long-lived states is investigated. We show that the total decay rate of such a state can be increased by up to four orders of magnitude, as compared to its intrinsic radiative decay rate, while leaving other neighboring optical transitions unaffected. For the specific case of molecular triplet excited states, we show that the use of a "plasmonic sink" has the potential to reduce photobleaching and ground state depletion by at least two orders of magnitude. We consider, in addition, the impact of such structures on the performance of organic semiconductor lasers and show that, under realistic device conditions, plasmonic sinks have the capacity to increase the achievable laser repetition rate by a factor equal to the triplet decay rate enhancement. We conclude by studying the effect of exciton diffusion on the triplet density in the presence of metallic nanoparticles. KeywordsPlasmons, Sinks, Nanoshells, Purcell Effect, Quenching, Triplets, Organic Lasers, Photobleaching, Non-radiative decay Plasmonic nanoparticles and antennas have demonstrated significant potential for enhancing the luminescence of adjacent emitters. [1][2][3][4][5][6] The mechanisms for enhancement, however, can be varied and the origin of the increased brightness difficult to unravel. For example, the nanostructure can serve to increase the local electric field at the excitation wavelength resulting in an increased excitation rate, 7-9 or equivalently, absorption efficiency of the emitter. In addition, the scattering cross-section of the particle or radiation pattern of the antenna can lead to a higher collection or out-coupling efficiency for the emitted light. 2, 10 Finally, and most importantly for this work, the increased photonic density of states at the emission wavelength can result, via the Purcell effect, in an increased radiative decay rate, Γ R , for the emitter. [1][2][8][9][10] This effect, however, is typically concomitant with an unwanted and stronger increase in the non-radiative decay rate, Γ NR , due to Joule heating of the metal. [9][10] In the usual case where Γ NR >> Γ R , increases in quantum yield, φ F , are only possible for emitters with very low intrinsic yields 0 R NR φ < Γ Γ . 11 In this work, we show that instead of being detrimental, the high non-radiative decay rate typical of emitters in close proximity to plasmonic structures can be exploited to selectively remove unwanted excited states in a number of physical systems.In molecular systems, for example, the build-up of large triplet state populations prevents the efficient excitation of organic molecules with high repetition rates or continuous sources, 12-13 and can be a significant source of photobleaching. 14-17 Indeed,Hale et al. first proposed and demonstrated the possibility of using plasmonic nanoparticles to increase the photostability of organic thin films. 18 In a later section weshow that in that case, the effect fits into the "diffusive regime", which has several advantages, bu...

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“…Owing to the ultrafast injection of singlet excitons in the active medium, lasing threshold with femtosecond-pulsed excitation is indeed expected to be determined predominantly by feedback losses and other linear optical losses such as ground-state absorption, while only weakly affected by excited-state lifetime shortening and photoinduced absorption of secondary excitations. [25] In fact, photoinduced absorption of primary singlet and triplet excitons overlaps with gain only at low energies, [12,26] while near-gap photoinduced absorption is fully effective only upon activation of charge-transfer excitons (tens to hundreds of picoseconds after photoexcitation). [12,18] To translate monomolecular lasing into a significant milestone, one has however to demonstrate how lasing performance scales with increasing duration of excitation pulses, as useful devices would require pulses not shorter than a few nanoseconds, favoring accumulation of long-lived charge-transfer excitons.…”

Section: à2mentioning

confidence: 99%