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Magnetic field dependence of singlet oxygen generation by nanoporous silicon.

Amonkosolpan J, Aliev GN, Wolverson D, Snow PA, Davies JJ - Nanoscale Res Lett (2014)

Bottom Line: Energy transfer from photoexcited excitons localized in silicon nanoparticles to adsorbed oxygen molecules excites them to the reactive singlet spin state.This process has been studied experimentally as a function of nanoparticle size and applied external magnetic field as a test of the accepted understanding of this process in terms of the exchange coupling between the nano-Si exciton and the adsorbed O2 molecules.

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Affiliation: Department of Physics, University of Bath, Claverton Down, BA2 7AY Bath, UK.

ABSTRACT
Energy transfer from photoexcited excitons localized in silicon nanoparticles to adsorbed oxygen molecules excites them to the reactive singlet spin state. This process has been studied experimentally as a function of nanoparticle size and applied external magnetic field as a test of the accepted understanding of this process in terms of the exchange coupling between the nano-Si exciton and the adsorbed O2 molecules.

No MeSH data available.


Schematic overview of energy transfer from photoexcited excitons in siliconnanoparticles to absorbed oxygen molecules. Optical excitation (greenarrows, ‘pump’) generates excitons confined in silicon nanoparticlesthat can recombine to emit photoluminescence (red arrows, ‘PL’) or cantransfer energy to those absorbed oxygen molecules that are in the triplet groundstate (black arrow, ‘energy transfer’). Excited oxygen molecules inthe singlet state can return to their ground state (blue arrows,‘relaxation’) via emission of luminescence and/or non-radiativerelaxation processes.
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Figure 3: Schematic overview of energy transfer from photoexcited excitons in siliconnanoparticles to absorbed oxygen molecules. Optical excitation (greenarrows, ‘pump’) generates excitons confined in silicon nanoparticlesthat can recombine to emit photoluminescence (red arrows, ‘PL’) or cantransfer energy to those absorbed oxygen molecules that are in the triplet groundstate (black arrow, ‘energy transfer’). Excited oxygen molecules inthe singlet state can return to their ground state (blue arrows,‘relaxation’) via emission of luminescence and/or non-radiativerelaxation processes.

Mentions: The differences between Figures 1 and 2point to an interplay between the rates for the physical processes (light absorption,radiative recombination, spin relaxation, and energy transfer) that control the shape ofthe PL spectrum. These processes are indicated schematically in Figure 3, which serves as a guide to the rate equation model we develop below.Figure 3 summarises the situation of NPs with oxygen present, forwhich there are four possible states (represented by the four boxes): the oxygenmolecule can be in either a singlet or a triplet state, and the NP may or may notcontain an exciton. Optical pumping creates excitons, whilst PL emission and energytransfer processes annihilate them. Only energy transfer generates singlet oxygen,whilst spin relaxation (or infrared PL) processes return the oxygen to the tripletground state. In the rate equation model for these processes, the photoexcitedpopulations of the separate spin states of the excitons and the oxygen molecules aretreated explicitly, taking into account the spin dependence of the energy transfer toO2, the radiative exciton recombination rate, the processes of thermalexcitation and spin-lattice relaxation that lead to population redistribution betweenthe spin states for a given silicon NP, and the rates of relaxation from singlet totriplet oxygen states.


Magnetic field dependence of singlet oxygen generation by nanoporous silicon.

Amonkosolpan J, Aliev GN, Wolverson D, Snow PA, Davies JJ - Nanoscale Res Lett (2014)

Schematic overview of energy transfer from photoexcited excitons in siliconnanoparticles to absorbed oxygen molecules. Optical excitation (greenarrows, ‘pump’) generates excitons confined in silicon nanoparticlesthat can recombine to emit photoluminescence (red arrows, ‘PL’) or cantransfer energy to those absorbed oxygen molecules that are in the triplet groundstate (black arrow, ‘energy transfer’). Excited oxygen molecules inthe singlet state can return to their ground state (blue arrows,‘relaxation’) via emission of luminescence and/or non-radiativerelaxation processes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4115642&req=5

Figure 3: Schematic overview of energy transfer from photoexcited excitons in siliconnanoparticles to absorbed oxygen molecules. Optical excitation (greenarrows, ‘pump’) generates excitons confined in silicon nanoparticlesthat can recombine to emit photoluminescence (red arrows, ‘PL’) or cantransfer energy to those absorbed oxygen molecules that are in the triplet groundstate (black arrow, ‘energy transfer’). Excited oxygen molecules inthe singlet state can return to their ground state (blue arrows,‘relaxation’) via emission of luminescence and/or non-radiativerelaxation processes.
Mentions: The differences between Figures 1 and 2point to an interplay between the rates for the physical processes (light absorption,radiative recombination, spin relaxation, and energy transfer) that control the shape ofthe PL spectrum. These processes are indicated schematically in Figure 3, which serves as a guide to the rate equation model we develop below.Figure 3 summarises the situation of NPs with oxygen present, forwhich there are four possible states (represented by the four boxes): the oxygenmolecule can be in either a singlet or a triplet state, and the NP may or may notcontain an exciton. Optical pumping creates excitons, whilst PL emission and energytransfer processes annihilate them. Only energy transfer generates singlet oxygen,whilst spin relaxation (or infrared PL) processes return the oxygen to the tripletground state. In the rate equation model for these processes, the photoexcitedpopulations of the separate spin states of the excitons and the oxygen molecules aretreated explicitly, taking into account the spin dependence of the energy transfer toO2, the radiative exciton recombination rate, the processes of thermalexcitation and spin-lattice relaxation that lead to population redistribution betweenthe spin states for a given silicon NP, and the rates of relaxation from singlet totriplet oxygen states.

Bottom Line: Energy transfer from photoexcited excitons localized in silicon nanoparticles to adsorbed oxygen molecules excites them to the reactive singlet spin state.This process has been studied experimentally as a function of nanoparticle size and applied external magnetic field as a test of the accepted understanding of this process in terms of the exchange coupling between the nano-Si exciton and the adsorbed O2 molecules.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, University of Bath, Claverton Down, BA2 7AY Bath, UK.

ABSTRACT
Energy transfer from photoexcited excitons localized in silicon nanoparticles to adsorbed oxygen molecules excites them to the reactive singlet spin state. This process has been studied experimentally as a function of nanoparticle size and applied external magnetic field as a test of the accepted understanding of this process in terms of the exchange coupling between the nano-Si exciton and the adsorbed O2 molecules.

No MeSH data available.