Page 583 - Book Hosokawa Nanoparticle Technology Handbook

32 DEVELOPMENT OF OPTICAL MEMORY APPLICATIONS
APPLICATION 32

32 DEVELOPMENT OF OPTICAL MEMORY USING SEMICONDUCTOR
NANOPARTICLES

While nanotechnology has been drawing a lot of an organic phosphorus compound at a high temper-
attention in recent years, the “quantum size effect” is ature.
one of the properties unique to “nanosizes” that do The features of these CdSe nanoparticles are, as is
not appear in either the bulk form or in the atomic and shown in Fig. 32.1a, that the light emission wave-
molecular levels. In this phenomenon when the size of length can be controlled easily in the visible range,
a material becomes smaller than the effective Bohr and that a high quantum efficiency of 85% can be
radius (about 10 nm or less), the band levels become realized [2]. In order to establish this method of syn-
discrete and the band gap becomes larger. In other thesis, research on CdSe nanoparticles was carried
words, since it is possible to control the band gap of out widely, and a large number of characteristics
the material by controlling the size, it is possible to peculiar to nanoparticles were reported [3–5].
expect applications as a material with characteristics
not present conventionally.
Although all materials such as metals, magnetic 1. Fluorescence characteristics of semiconductor
materials, and semiconductors are researched as nanoparticles
types of nanoparticles, here, we consider CdSe,
which is a II–VI compound semiconductor. Large These nanoparticles are modified on the particle
volume synthesis of CdSe nanoparticles became surface with an organic material in order to prevent
easy after the 1990s when a method of synthesis aggregation (Fig. 32.1b). Further, it is also possible to
called the “hot soap method” was developed [1, 2] synthesize core-shell type of nanoparticles
in which organic metal compounds are injected into (Fig. 32.1c) in which a different type of semiconductor

(a)
(b)

Surface modifier

Core part
(c)

Shell part

Particle diameter Small Medium Large

Figure 32.1
(a) Fluorescence of solutions of CdSe nanoparticles with different particle diameters. (b) Core-type nanoparticle.
(c) Core-shell-type nanoparticle.

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