Femtosecond photoluminescence spectroscopy of silicon nanocrystals

Abstract

Abstract We report on the ultrafast photoluminescence dynamics in silicon nanocrystals measured by femtosecond up‐conversion technique. The samples were prepared by embedding porous silicon grains in a sol‐gel derived SiO 2 matrix. Efficient initial relaxation of the excess energy of photoexcited carriers with the effective rate ≥4 eV/ps was observed. The ultrafast photoluminescence decay (about 400 fs) was interpreted in terms of quenching the interior exciton radiative recombination by fast carrier trapping on the nanocrystal surface. We also present the observation of the photoluminescence excited by two‐photon absorption at 830 nm and open aperture Z‐scan measurements to demonstrate a strong optical nonlinearity in silicon nanocrystals. We have found the value of two‐photon absorption coefficient β = 1.7 m/GW which corresponds to the imaginary part of the third‐order nonlinear susceptibility Im χ (3) = – 1 × 10 –10 esu. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)