Singlet oxygen generation in porous silicon with fullerenes

Abstract

We have studied light‐induced processes in ultra‐thin porous silicon (por‐Si) impregnated with fullerene C60. After insertion of C60 molecules a photoluminescence (PL) is quenched for more than one order of magnitude. No additional EPR defects were detected under fullerene insertion as it was revealed in por‐Si powder. Under illumination in oxygen the PL intensity could be restored to nearly initial level or to yet more. Recovery degree was dependent on oxidation state of por‐Si before C60 insertion. As was observed by ellipsometry a PL recovery is accompanied with oxidation of porous layer. Observed phenomenon is related with known ability of C60 to produce singlet oxygen. We suppose that generation efficiency of fullerenes to produce singlet oxygen is enhanced by energy transfer from photoexcited nanocrystallites. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Singlet oxygen inhibits nonradiative defects in porous silicon

“…Above reasons may lead to an artifact. On the other hand, the present results are in accordance with our data on specific role of fullerene molecules in photostimulated phenomena in impregnated PSi [1]. In comparison with binding energies of the main bonds in a PSi (Si-Si: ~1.8 eV and Si-H: ~3.1 eV) the excess energy ≈1 eV of singlet 1 Δ g is not enough to break above bonds.…”

“…It should be stressed that remarkable similarity in recovery phenomenon was earlier observed by us on Si porous layers impregnated with fullerene molecules [1]. In that experiment a PL recovery after ozone adsorption was achieved by photoexcitation of immobilized fullerenes in air ambient -see Fig.…”

“…It occupies an intermediate position between above oxygen species having the excess energy near 1 eV. Earlier [1] we have observed that visible light exposure of PSi impregnated with fullerene molecules C 60 in oxygen ambient leads to gradual improvement of photoluminescence (PL) efficiency. It was assumed that fullerene as an effective photosensitizer generates singlet oxygen in PSi matrix passivating intrinsic defects.…”

Origin of visible photoluminescence from arrays of vertically arranged Si-nanopillars decorated with Si-nanocrystals

“…Since the discovery of efficient visible photoluminescence (PL) from porous Si by Canham and co-workers at the beginning of 1990 [1][2][3] the optical properties of nanostructured Si have been studied intensively [1][2][3][4][5][6][7]. Applications of silicon nanostructures, such as Si-nanocrystals (Si-NCs), Si-nanopillars and porous Si, include light emitting diodes (LED) and lasers [7][8][9], luminescent bio-labels and chemical sensors [9,10], photosensitizers [11], and bio-compatible scaffolds [12].…”

Porous silicon versus its composite with C60: testing in vitro

“…Previous works on singlet oxygen generation by the pristine PSi [2] and its composite with fullerene C 60 [3] and porphyrins [4] have cleared a way to use these materials as PDT drugs. To our knowledge, the only work [5] deals with biomedical effect of pristine PSi on cells.…”