Photophysics of n-Butyl-Capped Silicon Nanoparticles

The photophysical properties are described of silicon nanoparticles protected with a shell of n-butyl chains, and with an asymmetric size distribution with a peak between 2 and 3 nm, and a tail extending up to 7 nm. The excited nanoparticles decay via multi-exponential luminescence on a time scale of a few nanoseconds. Longer-lived nonluminescent dark states were observed by nanosecond transient absorption spectroscopy. The average lifetime of the luminescent excited states increased somewhat with increasing wavelengths of excitation and emission. The nanosecond transient absorption spectra shifted to longer wavelengths with time. Probably, these observations are related to the size distribution of the particles: larger particles are excited at longer wavelength, emit at longer wavelength, and have longer-lived and red-shifted nanosecond transient absorption spectra. Two-photon excited luminescence showed broader emission spectra than one-photon excited luminescence at the same excitation energies. The two-photon cross-sections were found to be surprisingly small.