Mechanism of Ligand-Controlled Emission in Silicon Nanoparticles

Abstract

Although bulk silicon (Si) is known to be a poor emitter, Si nanoparticles (NPs) exhibit size-dependent photoluminescence in the red or near-infrared due to quantum confinement. Recently, it has been shown that surface modification of Si NPs with nitrogen-capped ligands results in bluer emission wavelengths and quantum yields of up to 90%. However, the emission mechanism operating in these surface-modified Si NPs and the factors that determine their emission maxima are still unclear. Here, the emission in these species is shown to arise from a charge-transfer state between the Si surface and the ligand. The energy of this state is linearly correlated to the calculated ground-state dipole moment of the free ligand. This trend can be used in a predictive fashion for the design and synthesis of Si NPs with a broader range of emission wavelengths.

Bright Silicon Nanocrystals from a Liquid Precursor: Quasi-Direct Recombination with High Quantum Yield

“…At the same time, several recent studies have reported multimodal PL relaxation spanning a range of wavelengths and time scales, − where the faster modes have been attributed to both surface effects and quasi-direct recombination, − although the distinction between the two is becoming increasingly blurred. In studies directed at extending the range of visible SiNC luminescence to shorter wavelengths, recent focus has been on bright size-independent emission tuned through a variety of complex surface ligands, − with the primary role of the Si core being optical absorption, and where PL color is determined by the charge-transfer characteristics of the ligands as opposed to quantum confinement.…”

Cell-Tailored Silicon Nanoparticles with Ultrahigh Fluorescence and Photostability for Cellular Imaging

“…In particular, the unique hydrophilic and optical properties of ES-SiNPs were probably attributable to their massive naturally modifying proteins secreted from yeast. 34,44 Long-Term Cellular Imaging. As fluorescent probes, the cytotoxicity of ES-SiNPs is necessary to be evaluated.…”

“…The FTIR results are consistent with those of XPS, and it is therefore reasonably deduced that the above-mentioned yeast-derived proteins played a crucial role as reductants and stabilizers in the biomimetic synthesis of ES-SiNPs. In particular, the unique hydrophilic and optical properties of ES-SiNPs were probably attributable to their massive naturally modifying proteins secreted from yeast. , …”

Nanomaterials for Quantum Information Science and Engineering

“…Si NPs have been shown to have high quantum efficiency [539] . The mechanism for emission is a charge transfer state between the ligand and the Si NP surface [540] . This charge transfer emission has been shown to produce non-classical light, as photon antibunching measurements have shown g (2) (0) values as low as 0.05 with high dependence on the substrate and ligand [541] .…”