Photoluminescence responses of Si nanocrystal to differing pumping conditions

Under a CW Ar+ laser beam excitation with wavelength of 496 nm, the relationship of photoluminescence (PL) intensity versus pumping power density was investigated for both multilayered Si nanocrystal doped SiO2/SiO2 sample (or Si-nc:SiO2/SiO2) and single-layered Si-nc: SiO2 one. The threshold of pump power density for the transition from linear to superlinear relation of PL intensity versus pump power was similar to 86 W cm(-2) for the multilayered sample, while such a transition was not found for the single-layered one that possessed the same excess Si content within the power density range of this work. Using a pulsed Ti:sapphire laser (wavelength = 400 nm), a net optical gain coefficient was measured by means of variable slit length for the multilayered sample, which was 114 cm(-1) at the pump fluence of 200 mJ cm(-2), but only optical absorption was found for the single-layered sample. We attributed our results to the relatively high PL efficiency of the multilayered Si-nc:SiO2/SiO2. (C) 2011 American Institute of Physics. [doi:10.1063/1.3601350]