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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.


Photoluminescence of porous silicon containing a low concentration of molecularoxygen. Photoluminescence (PL) spectra of a porous silicon sample exposedto a small quantity of oxygen gas are shown for magnetic fields of 0 to 6 T. Thesample was held in superfluid helium at 1.5 K, and the PL was excited with 450-nm(2.76 eV) continuous wave excitation. The vertical dashed line indicates thethreshold energy, above which photoexcited excitons in the silicon nanoparticleshave sufficient energy to excite the adsorbed oxygen from its triplet3Σ to its singlet 1Σ state.
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Figure 1: Photoluminescence of porous silicon containing a low concentration of molecularoxygen. Photoluminescence (PL) spectra of a porous silicon sample exposedto a small quantity of oxygen gas are shown for magnetic fields of 0 to 6 T. Thesample was held in superfluid helium at 1.5 K, and the PL was excited with 450-nm(2.76 eV) continuous wave excitation. The vertical dashed line indicates thethreshold energy, above which photoexcited excitons in the silicon nanoparticleshave sufficient energy to excite the adsorbed oxygen from its triplet3Σ to its singlet 1Σ state.

Mentions: Four typical PL spectra at 1.5 K for a porous silicon sample exposed to a low oxygenconcentration are shown in Figure 1 (spectra were recorded at0.5-T intervals, but for clarity, we omit the spectra at intermediate fields). The broadluminescence band corresponding to a wide distribution of silicon nanoparticle (NP)sizes is observed [8-10]; this band is similar in shape to that obtained in the absence of oxygen butis lower in intensity. The overall intensity of the PL band increases by about 20% asthe applied magnetic field is increased to around 4 T and then ceases to increasefurther. This behaviour differs quite markedly from the first reported experiments usinga magnetic field, where the oxygen concentration was high enough that PL above thethreshold energy of 1.63 eV for singlet oxygen production was still completelysuppressed even at fields as high as 10 T and the field-induced recovery of the PLintensity was only observed below 1.63 eV [2].Figure 2 shows the PL spectra obtained at higher oxygenconcentrations (Figure 2) in a second piece of the porous siliconsample used to obtain the results of Figure 1. It is not possibleto measure quantitatively the oxygen concentration adsorbed on the silicon NPs, but themuch stronger quenching of the PL gives a clear indication that the concentration ishigher than in the case of Figure 1.


Magnetic field dependence of singlet oxygen generation by nanoporous silicon.

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

Photoluminescence of porous silicon containing a low concentration of molecularoxygen. Photoluminescence (PL) spectra of a porous silicon sample exposedto a small quantity of oxygen gas are shown for magnetic fields of 0 to 6 T. Thesample was held in superfluid helium at 1.5 K, and the PL was excited with 450-nm(2.76 eV) continuous wave excitation. The vertical dashed line indicates thethreshold energy, above which photoexcited excitons in the silicon nanoparticleshave sufficient energy to excite the adsorbed oxygen from its triplet3Σ to its singlet 1Σ state.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: Photoluminescence of porous silicon containing a low concentration of molecularoxygen. Photoluminescence (PL) spectra of a porous silicon sample exposedto a small quantity of oxygen gas are shown for magnetic fields of 0 to 6 T. Thesample was held in superfluid helium at 1.5 K, and the PL was excited with 450-nm(2.76 eV) continuous wave excitation. The vertical dashed line indicates thethreshold energy, above which photoexcited excitons in the silicon nanoparticleshave sufficient energy to excite the adsorbed oxygen from its triplet3Σ to its singlet 1Σ state.
Mentions: Four typical PL spectra at 1.5 K for a porous silicon sample exposed to a low oxygenconcentration are shown in Figure 1 (spectra were recorded at0.5-T intervals, but for clarity, we omit the spectra at intermediate fields). The broadluminescence band corresponding to a wide distribution of silicon nanoparticle (NP)sizes is observed [8-10]; this band is similar in shape to that obtained in the absence of oxygen butis lower in intensity. The overall intensity of the PL band increases by about 20% asthe applied magnetic field is increased to around 4 T and then ceases to increasefurther. This behaviour differs quite markedly from the first reported experiments usinga magnetic field, where the oxygen concentration was high enough that PL above thethreshold energy of 1.63 eV for singlet oxygen production was still completelysuppressed even at fields as high as 10 T and the field-induced recovery of the PLintensity was only observed below 1.63 eV [2].Figure 2 shows the PL spectra obtained at higher oxygenconcentrations (Figure 2) in a second piece of the porous siliconsample used to obtain the results of Figure 1. It is not possibleto measure quantitatively the oxygen concentration adsorbed on the silicon NPs, but themuch stronger quenching of the PL gives a clear indication that the concentration ishigher than in the case of Figure 1.

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.