Page 32 - Book Hosokawa Nanoparticle Technology Handbook

1.1 SIZE EFFECT AND PROPERTIES OF NANOPARTICLES FUNDAMENTALS
(4) Optical properties Fig. 1.1.6 shows the plasmon absorption of silver
As the size of particles becomes in the several nanoparticles, where the spectral absorption intensity
nanometers range, they absorb the light with a specific differs depending upon the particle size which is deter-
wavelength as the plasmon absorption [12] caused by mined by the concentration of the surfactant used for
the plasma oscillation of the electrons and the their preparation [14]. In case of gold nanoparticles, it
transmitted light with different color depending upon is reported that the maximum light absorption wave-
the kind of metal and particle size is obtained [13]. length is 525nm for the particles of 15nm but it is
enlarged by about 50nm for 45nm particles. In this
way, these gold and silver nanoparticles show the
color phenomena with splendid tinting strength, color
saturation and transparency compared with the con-
ventional pigments for the paint in the submicron size
and the tinting strength per unit volume of silver
nanoparticles becomes about 100 times higher than
that of organic pigments. Furthermore, since the
nanoparticles are smaller than the wavelength of visi-
ble light and the light scattering by the particles
becomes negligible, higher transparency can be
obtained with the nanoparticles than the conventional
pigment.
On the other hand, concerning the light emitting
performance, the indirect transition type substances
like silicon and germanium, which do not emit the
light as bulk material, give high light emitting effi-
ciency as the direct transition type substances as a
result of quantum effect, when the particle size is
reduced down to several nanometers.

(5) Mechanical properties
It is known that the hardness of the crystalline materi-
als generally increases with the decreasing crystalline
size, and that the mechanical strength of the materials
considerably increases by micronizing the structure of
Figure 1.1.5 the metal and ceramic material or composing them in
Change of Curie point PbTiO with its particle size. the nano range [15, 16]. Furthermore, with the ceramic
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Figure 1.1.6
Effect of concentration of nonionic surfactants C on the plasmon absorption of silver nanoparticles. C (a) 0.05, (b) 0.1,
s
s
(c) 0.2, (d) 0.4 mol/kg.
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