2 research outputs found
Size <i>vs</i> Surface: Tuning the Photoluminescence of Freestanding Silicon Nanocrystals Across the Visible Spectrum <i>via</i> Surface Groups
The syntheses of colloidal silicon nanocrystals (Si-NCs) with dimensions in the 3–4 nm size regime as well as effective methodologies for their functionalization with alkyl, amine, phosphine, and acetal functional groups are reported. Through rational variation in the surface moieties we demonstrate that the photoluminescence of Si-NCs can be effectively tuned across the entire visible spectral region without changing particle size. The surface-state dependent emission exhibited short-lived excited-states and higher relative photoluminescence quantum yields compared to Si-NCs of equivalent size exhibiting emission originating from the band gap transition. The Si-NCs were exhaustively characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transformed infrared spectroscopy (FTIR), and their optical properties were thoroughly investigated using fluorescence spectroscopy, excited-state lifetime measurements, photobleaching experiments, and solvatochromism studies
Evolution of the Ultrafast Photoluminescence of Colloidal Silicon Nanocrystals with Changing Surface Chemistry
The
role of surface species in the optical properties of silicon nanocrystals
(SiNCs) is the subject of intense debate. Changes in photoluminescence
(PL) energy following hydrosilylation of SiNCs with alkyl-terminated
surfaces are most often ascribed to enhanced quantum confinement in
the smaller cores of oxidized NCs or to oxygen-induced defect emission.
We have investigated the PL properties of alkyl-functionalized SiNCs
prepared using two related methods: thermal and photochemical hydrosilylation.
Photochemically functionalized SiNCs exhibit higher emission energies
than the thermally functionalized equivalent. While microsecond lifetime
emission attributed to carrier recombination within the NC core was
observed from all samples, much faster, size-independent nanosecond
lifetime components were only observed in samples prepared using photochemical
hydrosilylation that possessed substantial surface oxidation. In addition,
photochemically modified SiNCs exhibit higher absolute photoluminescent
quantum yields (AQY), consistent with radiative recombination processes
occurring at the oxygen-based defects. Correlating spectrally- and
time-resolved PL measurements and XPS-derived relative surface oxidation
for NCs prepared using different photoassisted hydrosilylation reaction
times provides evidence the PL blue-shift as well as the short-lived
PL emission observed for photochemically functionalized SiNCs are
related to the relative concentration of oxygen surface defects