Photoluminescence from C60-coupled porous structures formed on Fe+-implanted silicon.

111-oriented p-type Si wafer with a resistivity of 1-5 Omega cm was implanted with Fe+ and then annealed at 1100 degrees C in N2 for 60 min, followed by anodization in a solution of HF to form porous structure with beta-FeSi2 nanocrystallites. Photoluminescence (PL) spectral measurements show that a strong PL peak appears in the range of 610-670 nm. The position of the PL peak remains unchanged, but its intensity increases with the storage time in air until about three months and then saturates. C60 molecules were chemically coupled on the porous structure through a kind of silane coupling agent to form a nanocomposite. It is revealed that the stable PL peak monotonically shifts to a pinning wavelength at 570 nm. Experimental results from PL, PL excitation, Raman scattering, and x-ray diffraction measurements clearly show that the pinned PL originates from optical transition in C60-related defect states, whereas the photoexcited carriers occur in the beta-FeSi2 nanocrystallites formed during anodization. This work opens a new way to tailor nanometer environment for seeking optimal luminescent properties.