Size-dependent absolute quantum yields for size-separated colloidally-stable silicon nanocrystals

Area of Science:

• Materials Science
• Nanotechnology
• Optoelectronics

Background:

• Silicon nanocrystals (Si-NCs) offer potential for "green" optoelectronic devices.
• Understanding the relationship between Si-NC size and optical properties is crucial for device development.
• Heavy metal chalcogenides dominate current light-emitting diode (LED) technology, posing environmental concerns.

Purpose of the Study:

• To synthesize and size-selectively precipitate allylbenzene-capped silicon nanocrystals (Si-NCs).
• To investigate the size-dependent photoluminescence (PL) properties, including absolute quantum yield (AQY) and lifetime.
• To evaluate the potential of Si-NCs for developing environmentally friendly, color-tunable LEDs.

Main Methods:

• Size-selective precipitation was employed to obtain monodisperse Si-NC fractions.
• Photoluminescence quantum yield (PLQY) and lifetime measurements were performed across a size range of 1-5 nm.
• Characterization focused on correlating Si-NC size with optical emission characteristics.

Main Results:

• Monodisperse Si-NC fractions emitting in the visible spectrum were successfully isolated.
• Both AQY and PL lifetime monotonically decreased with decreasing Si-NC size.
• High visible emission AQY (up to 43%) was achieved, indicating efficient light emission.

Conclusions:

• Nonradiative processes (vibrational and surface defects) dominate over quantum confinement effects in smaller Si-NCs.
• The observed high AQY supports the feasibility of "green" silicon nanocrystal color-tunable light-emitting diodes.
• Si-NCs present a promising, non-toxic alternative to heavy metal-based light-emitting technologies.