Fast Spectroscopy @ Sheffield

Time-resolved spectroscopy of carbon-based materials

We use femtosecond pulses of light to study carbon based materials such as biological pigment-protein complexes and organic semiconductors.

Past highlights include demonstrating biexciton emission, the wave behaviour of electrons in organic solar cells, observation of one of the fastest conformational changes, a giant broadband non-linear response in dispersed graphene sheets and ultrafast all-optical switching in plastic optical fibre amplifiers.

Our current focus is on understanding the physics of singlet fission and triplet-triplet annihilation for photon harvesting.

Photophysics of pigment-proteins

Carotenoids are ubiquitous in photosynthetic and photoprotective systems such as the eye, skin, leaves and bacteria.

We have demonstrated that absorption of light in carotenoids in the presence of nearby pigments leads to the ultrafast (sub-100fs) creation of two distinct low-energy excited states or 'excitons'. In photosynthetic complexes this multi-exciton generation may enhance carotenoid-to-bacteriochlorophyll energy transfer.

We are currently exploring the physics of caroteno-proteins and other pigment-protein complexes, including fluorescent proteins.

Strong light-matter coupling: polaritons

Confining light in a microcavity with organic semiconductors enables the formation of new quasi-particles which are half photon and half exciton. These new quasi-particles are called polaritons.

We have recently demonstrated that the yield of light from bimolecular triplet-triplet annihilation (TTA) is increased due to polariton formation. We are now applying this phenomenon to improve TTA based upconversion, which can be applied directly to solar cells to improve their efficiencies.

We continue to explore the fundamental physics of strong light-matter coupling in organic microcavities.

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