Silicon Nanocrystals: Photosensitizers for Oxygen Molecules


  • We thank the many colleagues and co-workers who have contributed ideas, theoretical and experimental work, and are not formally authors of this review. In particular, Egon Gross, Joachim Diener, Nicolai Künzner, and Viktor Timoshenko deserve mention here. A part of this work was supported by the Industrial Technology Research Grant Program from the New Energy and Industrial Technology Development Organization (NEDO), Japan and by Commission of the European Communities, 6th Framework Program (STRP 013875).


Molecular oxygen plays an important role in many of the chemical reactions involved in the synthesis of biological life. In this review, we explore the interaction between O2 and silicon nanocrystals, which can be employed in the photosynthesis of singlet oxygen. We demonstrate that nanoscale Si has entirely new properties owing to morphological and quantum size effects, i.e., large accessible surface areas and excitons of variable energies and with well-defined spin structures. These features result in new emerging functionality for nanoscale silicon: it is a very efficient spin-flip activator of O2, and therefore, a chemically and biologically active material. This whole effect is based on energy transfer from long-lived electronic excitations confined in Si nanocrystals to surrounding O2 via the exchange of single electrons of opposite spin, thus enabling the spin-flip activation of O2. Further, we discuss the implications of these findings for physics, chemistry, biology, and medicine.