Limits...
Tunability Limit of Photoluminescence in Colloidal Silicon Nanocrystals.

Wen X, Zhang P, Smith TA, Anthony RJ, Kortshagen UR, Yu P, Feng Y, Shrestha S, Coniber G, Huang S - Sci Rep (2015)

Bottom Line: In the "large size" regime (d > ~3 nm), quantum confinement dominantly determines the PL wavelength and thus the PL peak blue shifts upon decreasing the Si NC size.In the "small size" regime (d < ~2 nm) the effect of the yellow band overwhelms the effect of quantum confinement with distinctly increased nonradiative trapping.As a consequence, the photoluminescence peak does not exhibit any additional blue shift and the quantum yield drops abruptly with further decreasing the size of the Si NCs.

View Article: PubMed Central - PubMed

Affiliation: Australian Centre for Advanced Photovoltaics, University of New South Wales, Sydney 2052, Australia.

ABSTRACT
Luminescent silicon nanocrystals (Si NCs) have attracted tremendous research interest. Their size dependent photoluminescence (PL) shows great promise in various optoelectronic and biomedical applications and devices. However, it remains unclear why the exciton emission is limited to energy below 2.1 eV, no matter how small the nanocrystal is. Here we interpret a nanosecond transient yellow emission band at 590 nm (2.1 eV) as a critical limit of the wavelength tunability in colloidal silicon nanocrystals. In the "large size" regime (d > ~3 nm), quantum confinement dominantly determines the PL wavelength and thus the PL peak blue shifts upon decreasing the Si NC size. In the "small size" regime (d < ~2 nm) the effect of the yellow band overwhelms the effect of quantum confinement with distinctly increased nonradiative trapping. As a consequence, the photoluminescence peak does not exhibit any additional blue shift and the quantum yield drops abruptly with further decreasing the size of the Si NCs. This finding confirms that the PL originating from the quantum confined core states can only exist in the red/near infrared with energy below 2.1 eV; while the blue/green PL originates from surface related states and exhibits nanosecond transition.

No MeSH data available.


Related in: MedlinePlus

PL spectra of Si NCs of 2.5, 3.8 and 6.2 nm diameter.
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f1: PL spectra of Si NCs of 2.5, 3.8 and 6.2 nm diameter.

Mentions: Figure 1 shows the steady state PL spectra of 2.5, 3.8 and 6.2 nm Si NCs with excitation at 405 nm. The PL peak exhibits a blue-shift with decreasing NC size due to enhanced quantum confinement, consistent with the other observations182324. It is worth noting that the PL spectra of each sample of Si NCs are essentially invariant as a function of excitation wavelengths between 400 and 500 nm. PL evolution was observed in the μs timescale for 2.5 and 3.8 nm sizes of Si NCs (Figure S4)25. The PL evolution typically exhibits a stretched exponential decay and the emission lifetimes evidently decrease with decreasing wavelength72627.


Tunability Limit of Photoluminescence in Colloidal Silicon Nanocrystals.

Wen X, Zhang P, Smith TA, Anthony RJ, Kortshagen UR, Yu P, Feng Y, Shrestha S, Coniber G, Huang S - Sci Rep (2015)

PL spectra of Si NCs of 2.5, 3.8 and 6.2 nm diameter.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4510486&req=5

f1: PL spectra of Si NCs of 2.5, 3.8 and 6.2 nm diameter.
Mentions: Figure 1 shows the steady state PL spectra of 2.5, 3.8 and 6.2 nm Si NCs with excitation at 405 nm. The PL peak exhibits a blue-shift with decreasing NC size due to enhanced quantum confinement, consistent with the other observations182324. It is worth noting that the PL spectra of each sample of Si NCs are essentially invariant as a function of excitation wavelengths between 400 and 500 nm. PL evolution was observed in the μs timescale for 2.5 and 3.8 nm sizes of Si NCs (Figure S4)25. The PL evolution typically exhibits a stretched exponential decay and the emission lifetimes evidently decrease with decreasing wavelength72627.

Bottom Line: In the "large size" regime (d > ~3 nm), quantum confinement dominantly determines the PL wavelength and thus the PL peak blue shifts upon decreasing the Si NC size.In the "small size" regime (d < ~2 nm) the effect of the yellow band overwhelms the effect of quantum confinement with distinctly increased nonradiative trapping.As a consequence, the photoluminescence peak does not exhibit any additional blue shift and the quantum yield drops abruptly with further decreasing the size of the Si NCs.

View Article: PubMed Central - PubMed

Affiliation: Australian Centre for Advanced Photovoltaics, University of New South Wales, Sydney 2052, Australia.

ABSTRACT
Luminescent silicon nanocrystals (Si NCs) have attracted tremendous research interest. Their size dependent photoluminescence (PL) shows great promise in various optoelectronic and biomedical applications and devices. However, it remains unclear why the exciton emission is limited to energy below 2.1 eV, no matter how small the nanocrystal is. Here we interpret a nanosecond transient yellow emission band at 590 nm (2.1 eV) as a critical limit of the wavelength tunability in colloidal silicon nanocrystals. In the "large size" regime (d > ~3 nm), quantum confinement dominantly determines the PL wavelength and thus the PL peak blue shifts upon decreasing the Si NC size. In the "small size" regime (d < ~2 nm) the effect of the yellow band overwhelms the effect of quantum confinement with distinctly increased nonradiative trapping. As a consequence, the photoluminescence peak does not exhibit any additional blue shift and the quantum yield drops abruptly with further decreasing the size of the Si NCs. This finding confirms that the PL originating from the quantum confined core states can only exist in the red/near infrared with energy below 2.1 eV; while the blue/green PL originates from surface related states and exhibits nanosecond transition.

No MeSH data available.


Related in: MedlinePlus