Origin of the Photoluminescence Quantum Yields Enhanced by Alkane-Termination of Freestanding Silicon Nanocrystals: Temperature-Dependence of Optical Properties

Abstract

On the basis of the systematic study on temperature dependence of photoluminescence (PL) properties along with relaxation dynamics we revise a long-accepted mechanism for enhancing absolute PL quantum yields (QYs) of freestanding silicon nanocrystals (ncSi). A hydrogen-terminated ncSi (ncSi:H) of 2.1 nm was prepared by thermal disproportination of (HSiO1.5)n, followed by hydrofluoric etching. Room-temperature PL QY of the ncSi:H increased twentyfold only by hydrosilylation of 1-octadecene (ncSi-OD). A combination of PL spectroscopic measurement from cryogenic to room temperature with structural characterization allows us to link the enhanced PL QYs with the notable difference in surface structure between the ncSi:H and the ncSi-OD. The hydride-terminated surface suffers from the presence of a large amount of nonradiative relaxation channels whereas the passivation with alkyl monolayers suppresses the creation of the nonradiative relaxation channels to yield the high PL QY.

Tracking the Fate of Porous Silicon Nanoparticles Delivering a Peptide Payload by Intrinsic Photoluminescence Lifetime

“…In addition to the ability of the intrinsic PL signal to directly report the location of the nanocarrier, the PL emission energy and the excited state lifetime both depend on the size of the nanostructure, so these spectral features can provide information on the extent of degradation of the material. It is already well established that as a silicon nanostructure dissolves in an aqueous medium, it displays a spectral blueshift and a decrease in lifetime of the excited state . Also, prior work has reported correlations between these spectral properties and payload release from PSiNPs in vitro, which has been described as a “self‐reporting” characteristic .…”

Manipulating the Optical Properties of Carbon Dots by Fine‐Tuning their Structural Features

“…[50,51] Continuouswave EPR spectroscopy was used to obtain an estimate of the relative radical concentrations (by comparing normalized peak intensities) as well as af irst indication of their chemical environment (basedo nt he characteristic g values), as shown in Figure 3b. [50,51] Continuouswave EPR spectroscopy was used to obtain an estimate of the relative radical concentrations (by comparing normalized peak intensities) as well as af irst indication of their chemical environment (basedo nt he characteristic g values), as shown in Figure 3b.…”

“…[52,53] The g values therefore suggest that o-CD radicals are more substituted with oxygen-containing groups than r-CD radicals owing to the milder conditions (H 2 O 2 and NH 4 OH are both weakly reactive chemicals). [51,56] Deeperi nsighti nto the chemical structure of these radicals was provided by pulse EPR experiments that measure the hyperfine coupling between electron and nuclear spins. [55] The F o /F r ratio is similar to the intensity ratio of r-CDs versus o-CDs, which offers ag ood indication of the effect of free radicals on the PL.…”

All-Inorganic Red-Light Emitting Diodes Based on Silicon Quantum Dots

“…The hydrogen-silicon surface bonds were replaced by carbon-silicon bonds through thermal hydrosilylation of 1-decene. We observed the enhanced photoluminescence quantum yields (PL QYs) from 0.2% (for hydrogen-termination) to 18% (for decane-termination) as a result of preventing the formation of nonradiative recombination channels in the surface of the QDs [22]. We call this role of the alkyl monolayer on enhanced PL QY the "anchor effect" [23].…”