We reported the preparation of bright and multicolor luminescent colloidal Si nanocrystal (Si-nc) by pulsed UV laser irradiation to porous Si (PSi) in an organic solvent. The different-luminescence-color (different-sized) colloidal Si-nc was produced by the pulsed laser-induced fragmentation of different-sized porous nanostructures. The colloidal Si-nc samples were found to have higher photoluminescence quantum efficiencies (20%–23%) than the PSi samples (1%–3%). The brighter emission of the colloidal Si-nc was attributed to an enhanced radiative band-to-band transition rate due to the presence of a surface organic layer formed by UV laser-induced hydrosilylation.
We demonstrate the higher-yield (one order of magnitude) preparation of blue-emitting colloidal Si nanocrystals with a diameter range of 1-3 nm by selective laser ablation of porous Si powder in an organic solution, compared with the ablation of bulk Si powder. This increase in yield is the result of the lower thermal conductivity and the larger surface area of porous Si. The prepared colloidal Si nanocrystal exhibits size-dependent, higher-lying bandgap energies and large radiative decay rates as a result of the quantum confinement effect. Reversible luminescence color change from blue to yellow and vice versa in the colloidal Si nanocrystal film is also observed, and this is attributed to the non-radiative inter-crystal energy transfer.
We
report the highly improvement of colloidal Si nanocrystal (Si-nc)
formation by pulsed-UV-laser irradiation of porous silicon in a HF-contained
organic solvent. The Si-nc in such reactive organic solvent exhibits
higher photoluminescence quantum yield (∼50–70%) than
that in an ordinary organic solvent without HF (∼20%). This
enhancement of the quantum yield is caused by HF-induced removal of
the surface oxidation layer and subsequent hydrogen termination of
the Si surface. These reaction kinetics promote an efficient hydrosilylation
between the hydrogen-terminated surface and an organic solvent, resulting
in oxygen-free surface terminated by alkyl groups. Furthermore, the
preparation yield in the HF-contained solvent is higher and the size
distribution of Si-nc becomes more homogeneous than those in the ordinary
solvent. These results can be attributed to efficient pulsed-laser-induced
fragmentation by the removal of the oxidation layer on the porous
Si target surface.
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