Observation of Direct Transitions in Silicon Nanocrystallites

Silicon nanocrystallites show intense violet and blue luminescence at room temperature. The luminescence band exhibits separated peaks at a wavelength range from 350 nm to 550 nm under N2 pulse laser excitation. Lifetimes of these emissions can be fitted by double-exponential equations. The two parts of the lifetime, τ1 and τ2, were determined as 100∼300 ps and 600∼800 ps, respectively. All the optical events were finished within 5 ns. This short lifetime is suggested to be caused by an enhancement effect on the oscillator strength of the confined levels in zero-dimensionally confined Si nanocrystallites.