Details of Grant 

EPSRC Reference:	EP/I004424/1
Title:	Elucidating the photochemistry of inorganic nanostructures
Principal Investigator:	Zwijnenburg, Professor MA
Other Investigators:
Researcher Co-Investigators:
Project Partners:	Universite Pierre et Marie Curie University of Barcelona
Department:	Chemistry
Organisation:	UCL
Scheme:	Career Acceleration Fellowship
Starts:	13 December 2010	Ends:	30 April 2016	Value (£):	927,473
EPSRC Research Topic Classifications:	Condensed Matter Physics
EPSRC Industrial Sector Classifications:	No relevance to Underpinning Sectors
Related Grants:
Panel History:	Panel Date Panel Name Outcome 02 Jun 2010 EPSRC Fellowships 2010 Interview Panel E Announced
Summary on Grant Application Form
Nanostructures are systems with one or more dimensions (particle-size, rod diameter, film thickness, pore-size) ranging from 1E-10 metres, the scale of atomic bonds, to 1E-7, the size of a typical biological virus. Most of the time such nanostructures are in their low energy ground state, but when they absorb light some electrons from the ground state can be excited to form a so-called excited state, which lies higher in energy. Excited states, however, are not stable and typically in 1E-15 to 1E-6 seconds the excited electrons will fall back to the ground state, filling the holes that they left upon excitation.The relaxation of an excited state can follow different paths: Firstly, the nanostructure can reemit light in a process called photoluminescence (PL). Secondly, the nanostructure can undergo a chemical reaction which results in a permanent rearrangement of its atoms. Thirdly, the excited electrons and/or holes can be transferred to a molecule adsorbed on the nanostructure and fourthly the nanostructure can heat up. These different relaxation paths have major practical implications. PL in inorganic nanostructures is successfully exploited in applications such as lasers and energy efficient solid state lighting. The transfer of excited electrons or holes to an adsorbed molecule is a critical step in both heterogeneous photocatalysis and in dye-sensitised solar cells. Finally, the structural changes induced by light impose a limit to the service life of solar cells and other devices that are routinely exposed to direct intense sunlight. Now, in spite of the enormous practical importance of the applications discussed above, fundamental knowledge of the different excited state relaxation paths is limited. For example the final structure of the excited state is often unknown. This knowledge gap arises because the inherent disorder of nanostructures and the short lifetimes of excited states make it difficult to characterise the relevant processes in experiment. As a result progress in photoactive materials development for these applications has been mostly through trial and error. The aim of my fellowship is to close the knowledge gap by using theoretical methods to generate microscopic insight into the photophysics and photochemistry of inorganic nanostructures. This will allow me to answer important practical questions such as on which part of the nanostructures the excited electrons are likely to get trapped, which material properties determine what relaxation path is dominant and how these could be successfully tuned experimentally, thus replacing serendipity by insight.In practice this means I will employ a theoretical method named time-dependent density functional theory (TD-DFT) to probe the geometry and chemical nature of the relaxed excited state in different nanostructures. This method, when properly validated, gives accurate results whilst at the same time being computationally cheap enough to efficiently study the systems of interest. Furthermore, where possible I will compare the obtained results, for example predicted PL spectra, to those obtained by my experimental collaborators. In a first step, I will study stoichiometric nanostructures for a range of sizes, shapes and compositions. Building on this work, I will then switch my attention to the fate of excited states in nanostructures that miss some atoms, are doped with foreign atoms or have molecules adsorbed on their surface. Study of these latter systems is especially important for understanding photocatalysis, an application that has to date not been studied with theoretical methods such as TD-DFT. Finally, as a latter part of the proposed work, I will apply the developed theoretical approach to realistic photocatalytic systems studied by my collaborators in the laboratory. Pooling our experimental and theoretical results will allow us to find, for example, new and improved water splitting catalysts for renewable hydrogen production.
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