Bright and multicolor luminescent colloidal Si nanocrystals prepared by pulsed laser irradiation in liquid

Abstract

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.

Facile Formation of Stable Water‐Dispersed Luminescent Silicon Nanocrystals by Laser Processing in Liquid: Toward Fluorescent Labeling for Bio‐Imaging

“…Previously, we revealed that PL spectral features of A‐F: Si‐nc depend on that of original PSi target . Moreover, the size of the Si‐nc estimated from the PL peak energy is confirmed to be similar to that of PSi.…”

“…To investigate the surface chemistry of the colloidal Si‐nc, FTIR measurements were performed as shown in Figure (a). For the comparison purpose, FTIR spectrum of hydrophobic colloidal Si‐nc sample prepared by the similar laser irradiation process of PSi in 1‐decene was also measured [Figure (b)]. The hydrophobic Si‐nc shows absorption peaks of the stretching vibrational modes of Si−CH 3 at 850, 1270, and 1420 cm −1 , indicating that the sample prepared in 1‐decene is alkyl functionalized Si‐ncs (A‐F: Si‐nc).…”

“…Both spectra are peaked at ∼1.85 eV and have almost the same spectral width. In our previous work, it was found that the PL emission of the Si‐nc prepared by UV‐laser irradiation of PSi in 1‐decene was mainly attributed to the size dependent band‐to‐band transitions of the electron‐hole pairs in quantum confined Si‐nc cores. Thus, the same spectral features may indicate that the size distribution of UA‐F: Si‐nc is similar to that of A‐F: Si‐nc.…”

“…Photoluminescence (PL) band of Si‐nc synthesized by laser irradiation process usually appears in a blue to green region, and, organically capped ones have a high stability against chemical oxidation and relatively higher PL quantum efficiency due to the smaller number of surface defects . Previously, we prepared red‐emitting Si‐nc by pulsed UV laser irradiation of PSi target in unsaturated hydrocarbon solvent . However, due to its surface ligand (i. e., hydrocarbons), the Si‐nc samples are disperse only in non‐polar solvent.…”

“…[33] Previously, we prepared red-emitting Si-nc by pulsed UV laser irradiation of PSi target in unsaturated hydrocarbon solvent. [38,39] However, due to its surface ligand (i. e., hydrocarbons), the Si-nc samples are disperse only in non-polar solvent. Thus, in the view of bioapplications of Si-nc, it is expected to form water-soluble colloidal Si-nc exhibiting PL emission in the optical window of biomaterials (i. e., a red to near infrared spectral range) by using a one-step laser process in liquid.…”