Effect of phonon confinement on photoluminescence from colloidal silicon nanostructures

Room temperature time-resolved photoluminescence (TRPL) of colloidal silicon nanostructures prepared by repetitive oxidation-etching-oxidation of mechanically milled silicon, indicate towards phonon confinement in Si nanostructures. The Si nanocrystals have a well-defined Raman peak, which is asymmetrically broadened and red shifted, compared to bulk silicon. The PL intensities exhibit tri-exponential decay characteristics with decay times ranging between pico to nanosecond. For a fixed emission wavelength, the decay time is found to be strongly dependent on excitation wavelength. Steady state luminescence spectra reveal that PL peak positions and intensities are dependent of excitation energy. On the basis of these observations we show that phonon confinement plays a significant role in the non-radiative relaxation of excited carriers at the band edges of nanocrystalline Si core.