Bright silicon quantum dot synthesis and LED design: insights into size–ligand–property relationships from slow- and fast-band engineering

Abstract

Multicolor, bright silicon quantum dots (SiQDs)—SiQDs with photoluminescence in a range of colors and quantum yields (PLQYs) of >90%—are promising heavy-metal-free light sources for full-color displays, lighting, and biomedical imaging. Colloidal SiQDs can be used to manufacture devices via printing and roll-to-roll processing. Furthermore, the in vivo use of biodegradable SiQDs and Si nanomaterials, for imaging cancer cells and as drug delivery systems, has been demonstrated. However, a large body of research demonstrates that the photoluminescence (PL) wavelength and PLQY of colloidal SiQDs are dependent not only on the SiQD particle size but also on the methods and/or procedures and chemical reagents used to synthesize them. This is because SiQDs are quite sensitive to both the intrinsic properties of Si and external factors. These intrinsic and external factors can be respectively linked to different PL mechanisms: the quantum confinement effect, which produces a slow-decaying “S”-band PL signal, and surface ligand effects, corresponding to fast-decaying “F”-band PL. This review focuses on mechanistic insights into the relationships linking the structures, ligands, and optical properties of SiQDs. Synthesis methods and the application performance of bright multicolor colloidal SiQDs, based on excellent state-of-the-art experimental and theoretical studies, are also reviewed.

1D, 2D, and 3D Mapping of Plasmon and Mie Resonances: A Review of Field Enhancement Imaging Based on Electron or Photon Spectromicroscopy

“…2D and/or 3D maps of PL, fluorescence, and Raman spectra can be obtained, and this data can be compared with AFM and/or SEM measurements and FDTD simulations corresponding to the same positions within the sample. This method can be applied to samples of noble metals with nano or submicrometer structural features, ,, semiconductors with submicrometer structural features, − ,, semiconducting organic materials, − and colloidal quantum dot materials. − ,− , To the best of our knowledge, only a few reports of the 2D and/or 3D mapping of electromagnetic field enhancement owing to the Mie resonances of semiconductors have been published. − …”

Ligand Stabilities and Reactivities of Green Photoluminescent Silicon Quantum Dots: Positive Aging in Solution

“…The properties of the photoluminescence (PL) of colloidal SiQDs have been characterized based on the quantum confinement effect (S-band) and surface ligand effect (Fband). 2,14 S-band PL is orange-red and has a slow (μs) decay time, and the PLQY can be as much as 70 38,40 or 80%. 12,13 In contrast, F-band PL is associated with surface ligand states and is blue-yellow with a fast (ns) decay time.…”

“…This is because the luminescence wavelength of bulk Si is in the invisible NIR region (λ = 1100 nm), and its photoluminescence quantum yield (PLQY) is typically ∼0.01% owing to the indirect nature of its interband transition. − However, Si quantum dots (SiQDs) exhibit luminescence across the entire visible spectral region. − In addition, for colloidal SiQDs, PLQYs of up to 80% have been reported, ,, and colloidal SiQD dispersions can be used to manufacture devices via printing and roll-to-roll processing. Thus, colloidal SiQDs have enormous potential as environmentally benign, heavy-metal-free materials for displays, light-emitting diodes (LEDs), lighting, and biomedical imaging . Moreover, SiQDs have been used as nanomedical agents, in applications including disease diagnosis/therapeutics, bioanalyte sensing, and tissue engineering .…”

“…The properties of the photoluminescence (PL) of colloidal SiQDs have been characterized based on the quantum confinement effect (S-band) and surface ligand effect (F-band). , S-band PL is orange-red and has a slow (μs) decay time, and the PLQY can be as much as 70 , or 80%. , In contrast, F-band PL is associated with surface ligand states and is blue-yellow with a fast (ns) decay time. PLQYs of up to 90% have been observed for the yellow PL of amine-terminated Si nanoparticles, , and replacing the hydrogens in hydride SiQDs with Cl, I, and Br ligands and then performing an alkyl termination reaction have been shown to produce blue, yellow, and red PL, respectively .…”

Why do Si quantum dots with stronger fast emission have lower external photoluminescence quantum yield?

“…Silicon quantum dots (SiQDs) are a class of materials with a wide range of prospective applications stemming from their appealing properties, such as material abundance and favorable toxicity profile, 1–5 in connection with their ability to relatively efficiently emit light with highly variable properties. 6 The most intensely studied photoluminescence (PL) channel in these nanoparticles is the size tunable red to infrared PL emission with decay lifetimes in the range of hundreds of microseconds, 7–10 sometimes referred to as the S band. However, in addition to this long-lived PL channel, also much faster PL emission spectrally often located in the visible blue region has been observed.…”