63 research outputs found
Recent advances in solid-state organic lasers
Organic solid-state lasers are reviewed, with a special emphasis on works
published during the last decade. Referring originally to dyes in solid-state
polymeric matrices, organic lasers also include the rich family of organic
semiconductors, paced by the rapid development of organic light emitting
diodes. Organic lasers are broadly tunable coherent sources are potentially
compact, convenient and manufactured at low-costs. In this review, we describe
the basic photophysics of the materials used as gain media in organic lasers
with a specific look at the distinctive feature of dyes and semiconductors. We
also outline the laser architectures used in state-of-the-art organic lasers
and the performances of these devices with regard to output power, lifetime,
and beam quality. A survey of the recent trends in the field is given,
highlighting the latest developments in terms of wavelength coverage,
wavelength agility, efficiency and compactness, or towards integrated low-cost
sources, with a special focus on the great challenges remaining for achieving
direct electrical pumping. Finally, we discuss the very recent demonstration of
new kinds of organic lasers based on polaritons or surface plasmons, which open
new and very promising routes in the field of organic nanophotonics
Low thresholds for a nonconventional polymer blend-Amplified spontaneous emission and lasing in F8<sub>1-</sub> <sub>x</sub>:SY<sub>x</sub> system
The nature of singlet exciton fission in carotenoid aggregates.
Singlet exciton fission allows the fast and efficient generation of two spin triplet states from one photoexcited singlet. It has the potential to improve organic photovoltaics, enabling efficient coupling to the blue to ultraviolet region of the solar spectrum to capture the energy generally lost as waste heat. However, many questions remain about the underlying fission mechanism. The relation between intermolecular geometry and singlet fission rate and yield is poorly understood and remains one of the most significant barriers to the design of new singlet fission sensitizers. Here we explore the structure-property relationship and examine the mechanism of singlet fission in aggregates of astaxanthin, a small polyene. We isolate five distinct supramolecular structures of astaxanthin generated through self-assembly in solution. Each is capable of undergoing intermolecular singlet fission, with rates of triplet generation and annihilation that can be correlated with intermolecular coupling strength. In contrast with the conventional model of singlet fission in linear molecules, we demonstrate that no intermediate states are involved in the triplet formation: instead, singlet fission occurs directly from the initial 1B(u) photoexcited state on ultrafast time scales. This result demands a re-evaluation of current theories of polyene photophysics and highlights the robustness of carotenoid singlet fission.This work was supported by the EPSRC (UK) (EP/G060738/
1), the European Community (LASERLAB-EUROPE, grant
agreement no. 284464, EC’s Seventh Framework Programme;
and Marie-Curie ITN-SUPERIOR, PITN-GA-2009-238177),
and the Winton Programme for the Physics of Sustainability.
G.C. acknowledges support by the European Research Council
Advanced Grant STRATUS (ERC-2011-AdG No. 291198).
J.C. acknowledges support by the Royal Society Dorothy
Hodgkin Fellowship and The University of Sheffield’s Vice-
Chancellor’s Fellowship scheme.This is the final published version. It was first made available by ACS at http://pubs.acs.org/doi/abs/10.1021/jacs.5b01130
Manipulating molecules with strong coupling: harvesting triplet excitons in organic exciton microcavities
Exciton-polaritons are quasiparticles with mixed photon and exciton character that demonstrate rich quantum phenomena, novel optoelectronic devices and the potential to modify chemical properties of materials. Organic semiconductors are of current interest for their room-temperature polariton formation. However, within organic optoelectronic devices, it is often the 'dark' spin-1 triplet excitons that dominate operation. These triplets have been largely ignored in treatments of polariton physics. Here we demonstrate polariton population from the triplet manifold via triplet-triplet annihilation, leading to polariton emission that is longer-lived (>microseconds) even than exciton emission in bare films. This enhancement arises from spin-2 triplet-pair states, formed by singlet fission or triplet-triplet annihilation, feeding the polariton. This is possible due to state mixing, which -in the strong coupling regime- leads to sharing of photonic character with states that are formally non-emissive. Such 'photonic sharing' offers the enticing possibility of harvesting or manipulating even states that are formally dark
High-efficiency perovskite–polymer bulk heterostructure light-emitting diodes
Perovskite-based optoelectronic devices have gained significant attention due
to their remarkable performance and low processing cost, particularly for solar
cells. However, for perovskite light-emitting diodes (LEDs), non-radiative
charge carrier recombination has limited electroluminescence (EL) efficiency.
Here we demonstrate perovskite-polymer bulk heterostructure LEDs exhibiting
record-high external quantum efficiencies (EQEs) exceeding 20%, and an EL
half-life of 46 hours under continuous operation. This performance is achieved
with an emissive layer comprising quasi-2D and 3D perovskites and an insulating
polymer. Transient optical spectroscopy reveals that photogenerated excitations
at the quasi-2D perovskite component migrate to lower-energy sites within 1 ps.
The dominant component of the photoluminescence (PL) is primarily bimolecular
and is characteristic of the 3D regions. From PL quantum efficiency and
transient kinetics of the emissive layer with/without charge-transport
contacts, we find non-radiative recombination pathways to be effectively
eliminated. Light outcoupling from planar LEDs, as used in OLED displays,
generally limits EQE to 20-30%, and we model our reported EL efficiency of over
20% in the forward direction to indicate the internal quantum efficiency (IQE)
to be close to 100%. Together with the low drive voltages needed to achieve
useful photon fluxes (2-3 V for 0.1-1 mA/cm2), these results establish that
perovskite-based LEDs have significant potential for light-emission
applications
Conjugated zwitterionic polyelectrolyte as the charge injection layer for high-performance polymer light-emitting diodes
Contains fulltext :
91658.pdf (publisher's version ) (Open Access
Simple Fabrication of an Organic Laser by Microcontact Molding of a Distributed Feedback Grating
Lasing from an organic polymer is demonstrated in a device utilizing a distributed feedback (DFB) grating, manufactured by microcontact molding of CdSe nanocrystals (NCs) directly on top of the emitter layer. Besides the simpler fabrication in comparison with a reference device based on a photolithographically prepared DFB grating in a bottom dielectric layer, a much higher DFB strength for NC-gratings is observed, resulting in reduced lasing threshold and a fourfold differential lasing efficiency
Spectroscopic observation of triplet exciton dynamics during operation in polymer light emitting diodes
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