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Y. Kobayashi and H. Kobayashi
9.1 Photoluminescence From Si Nanostructures
9.1.1 Introduction
Si is a nonpoisonous material, and thus, its photoluminescence (PL) phenomenon is
applicable to biology [1]. PL from Si nanoparticles is attributed to (i) intrinsic bandto-band transition [2, 3] and (ii) extrinsic transition involving states such as defect
states in an oxide layer [3, 4]. For case (i), the PL energy depends on the size of Si
nanoparticles because the band-gap energy strongly depends on the size due to the
quantum confinement effect [5, 6]. For example, the energy shift of the PL peaks
by oxidation of Si nanoparticles results from case (i) because oxidation decreases
the size of Si nanoparticles by the formation of SiO 2 [2, 3]. For case (ii), on the
other hand, the PL energies are less dependent or independent of the nanoparticle
size [3, 4].
Trave et al. [6] fabricated Si nanoparticles by the laser pyrolysis method and
found that the PL intensity of as-deposited nanoparticles was weak, but it increased
after thermal oxidation at temperatures between 700 and 1000 ◦ C accompanied by
blue shift to the wavelength region between 800 and 900 nm. Kang et al. [2] showed
that using the oxidation method which could control the size of Si nanoparticles, the
PL emission color could be varied in the wide wavelength range between red and
blue. For Si nanoparticles produced using the pulsed laser ablation method in liquid,
a PL peak was observed at ∼500 nm [7] or 450 and 600 nm [8]. Si nanoparticles
which exhibited PL were also formed by the use of the laser ablation method in
helium gas [9]. Si nanoparticles of ∼3 nm size were fabricated by implantation of
Si + ions onto SiO 2 , and the PL peak was observed in the 750∼950 nm wavelength
region [10]. Si nanoparticles embedded in silicon oxide were formed by the rf cosputtering method, and their PL spectra were greatly changed by heat treatment up
to 1100 ◦ C [8]. Using ball-milling of graphite and SiO 2 powder, Si nanoparticles
with PL emission in the broad wavelength region between 650 and 900 nm were
fabricated [11]. For Si nanoparticles fabricated using ball milling of graphite and
SiO 2 powder, broad PL spectra were observed in the wavelength region between
650 and 900 nm [12].
Several researchers investigated effects of adsorbates on Si nanoparticles on PL
behavior. Ryabechikov et al. [13] showed that adsorption of alkyl groups caused
blue shift of the PL peak accompanied with broadening of the peak and attributed the
phenomenon to prevention of energy transfer from small to large Si nanoparticles
by adsorption. For phenyl-passivated Si nanoparticles in hexane, Imamura et al.
[14] reported three-peaked PL spectra (∼3.52, ∼3.68, and ∼3.85 eV) which did
not depend on excitation photon energies. Fang et al. [15] observed enhancement of
PL from adsorbed porphyrin on Ag nanoparticle-covered Si surfaces and attributed
the enhancement to the resonant excitation by local surface plasmons and to the
increased radiative decay rate. We observed peaked structure in the PL spectra
for Si nanopowder in hexane and attributed it to 9,10-dimethylanthracene (DMA)
adsorbed on the surface by which the PL intensity was greatly enhanced [16, 17].
Y. Kobayashi and H. Kobayashi
9.1 Photoluminescence From Si Nanostructures
9.1.1 Introduction
Si is a nonpoisonous material, and thus, its photoluminescence (PL) phenomenon is
applicable to biology [1]. PL from Si nanoparticles is attributed to (i) intrinsic bandto-band transition [2, 3] and (ii) extrinsic transition involving states such as defect
states in an oxide layer [3, 4]. For case (i), the PL energy depends on the size of Si
nanoparticles because the band-gap energy strongly depends on the size due to the
quantum confinement effect [5, 6]. For example, the energy shift of the PL peaks
by oxidation of Si nanoparticles results from case (i) because oxidation decreases
the size of Si nanoparticles by the formation of SiO 2 [2, 3]. For case (ii), on the
other hand, the PL energies are less dependent or independent of the nanoparticle
size [3, 4].
Trave et al. [6] fabricated Si nanoparticles by the laser pyrolysis method and
found that the PL intensity of as-deposited nanoparticles was weak, but it increased
after thermal oxidation at temperatures between 700 and 1000 ◦ C accompanied by
blue shift to the wavelength region between 800 and 900 nm. Kang et al. [2] showed
that using the oxidation method which could control the size of Si nanoparticles, the
PL emission color could be varied in the wide wavelength range between red and
blue. For Si nanoparticles produced using the pulsed laser ablation method in liquid,
a PL peak was observed at ∼500 nm [7] or 450 and 600 nm [8]. Si nanoparticles
which exhibited PL were also formed by the use of the laser ablation method in
helium gas [9]. Si nanoparticles of ∼3 nm size were fabricated by implantation of
Si + ions onto SiO 2 , and the PL peak was observed in the 750∼950 nm wavelength
region [10]. Si nanoparticles embedded in silicon oxide were formed by the rf cosputtering method, and their PL spectra were greatly changed by heat treatment up
to 1100 ◦ C [8]. Using ball-milling of graphite and SiO 2 powder, Si nanoparticles
with PL emission in the broad wavelength region between 650 and 900 nm were
fabricated [11]. For Si nanoparticles fabricated using ball milling of graphite and
SiO 2 powder, broad PL spectra were observed in the wavelength region between
650 and 900 nm [12].
Several researchers investigated effects of adsorbates on Si nanoparticles on PL
behavior. Ryabechikov et al. [13] showed that adsorption of alkyl groups caused
blue shift of the PL peak accompanied with broadening of the peak and attributed the
phenomenon to prevention of energy transfer from small to large Si nanoparticles
by adsorption. For phenyl-passivated Si nanoparticles in hexane, Imamura et al.
[14] reported three-peaked PL spectra (∼3.52, ∼3.68, and ∼3.85 eV) which did
not depend on excitation photon energies. Fang et al. [15] observed enhancement of
PL from adsorbed porphyrin on Ag nanoparticle-covered Si surfaces and attributed
the enhancement to the resonant excitation by local surface plasmons and to the
increased radiative decay rate. We observed peaked structure in the PL spectra
for Si nanopowder in hexane and attributed it to 9,10-dimethylanthracene (DMA)
adsorbed on the surface by which the PL intensity was greatly enhanced [16, 17].