These quantum dots have unique properties arising from their indirect band gap, including long-lived luminescent excited-states and large Stokes shifts.
[5][6] The unique properties of silicon quantum dots lend themselves to an array of potential applications: biological imaging, luminescent solar concentrators, light emitting diodes, sensors, and lithium-ion battery anodes.
[9][10] Recognizing the vast potential of their unique optical properties, many researchers explored, and developed methods to synthesize silicon quantum dots.
Long-lived luminescence excited states (S-band, slow decay rate) are typically associated with size-dependent photoluminescence ranging from yellow/orange to the near-infrared.
Short-lived luminescent excited states (F-band, fast decay rate) are typically associated with size-independent blue photoluminescence and in some cases nitrogen impurities have been implicated in these processes.
[5][6] Defining the size of silicon quantum dots is essential because it influences their optical properties (especially S-band luminescence).
Hydride-terminated SiQDs require post synthesis modification because they tend to oxidize under ambient conditions and exhibit limited solution processability.
These surfaces are often passivated with organic molecules (e.g., alkyl chains) to render SiQDs resistant to oxidation and compatible with common solvents.
Hydrosilylation, which involves the formal addition of a Si-H bond across a C-C double or triple bond, is commonly used to introduce alkenes and alkynes to silicon quantum dot surfaces and also provides access to useful terminal functional groups (e.g., carboxylic acid, ester, silanes) that can define solvent compatibility and provide locations for further derivatization.
Owing to these (and other) properties, the potential applications of SiQDs are diverse, spanning medical, sensing, defense, and energy related fields.
The biocompatibility of silicon quantum dots along with their long luminescent lifetimes and near-infrared emission makes them well-suited for fluorescence imaging in biological systems.
[39][40] Luminescent solar concentrators take advantage of the large Stokes shift of the silicon quantum dots to convert light into electricity.
[41] By designing the LSC carefully, the silicon quantum dots can be prepared as a transparent film over the glass limiting losses due to scattering, while making them suitable as replacements for windows in buildings.
Photochemical sensors take advantage of the silicon quantum dot photoluminescence by quenching photon emission in the presence of the analyte.
Photochemical sensors based on silicon quantum dots have been used to sense a wide variety of analytes, including pesticides,[49] antibiotics,[50] nerve agents,[51] heavy metals,[52] ethanol,[53] and pH,[54] often employing either electron transfer or fluorescence resonance energy transfer (FRET) as the method of quenching.
[55] Hazardous high energy materials, such as nitroaromatic compounds (i.e., TNT and DNT), can be detected at nanogram levels via electron transfer.
By functionalizing the quantum dots with enzymes, various biologically relevant materials can be sensed due to the formation of metabolites.