Page 586 - Book Hosokawa Nanoparticle Technology Handbook

APPLICATIONS 33 DEVELOPMENT OF BRIGHT PHOSPHORS USING GLASSES
Finally, the mechanism of this phenomenon that the [6] W.C.W. Chan, S.M. Nie: Science, 281, 2016 (1998).
fluorescence intensity increases with irradiation with [7] X. Michalet, F. Pinaud, T.D. Lacoste, M. Dahan,
excitation light has not yet been fully clarified. By M.P. Bruchez, A.P. Alivisatos and S. Weiss: Single
explaining this mechanism, it is expected not only Mol., 2, 261 (2001).
that it will be possible to control more accurately the [8] A.P. Alivisatos: Nat. Biotechnol., 22, 47 (2003).
fluorescence intensity, but also that it can be extended [9] D.Y. Godovsky: Adv. Polym. Sci., 153, 163 (2000).
to nanoparticles of other materials.
[10] A.Y. Nazzal, L. Qu, X. Peng and M. Xiao: Nano Lett.,
3, 819 (2003).
References
[11] N. Eiha, S. Maenosono, K. Hanaki, K. Yamamoto
[1] C.B. Murray, D.J. Norris and M.G. Bawendi: J. Am. and Y. Yamaguchi: Jpn. J. Appl. Phys., 42, L310
Chem. Soc., 115, 8706 (1993). (2003).
[2] L. Qu, X.G. Peng: J. Am. Chem. Soc., 124, 2049 (2002). [12] S. Maenosono, E. Ozaki, K. Yoshie and Y. Yamaguchi:
[3] S.A. Empedocles, M.G. Bawendi: Science, 278, 2114 J. Appl. Phys., 40, L638 (2001).
(1997). [13] J. Kimura, S. Maenosono and Y. Yamaguchi:
[4] W.C.W. Chan, S.M. Nie: Science, 281, 2016 (1998). Nanotechnology, 14, 69 (2003).
[5] B.R. Fisher, H.J. Eisler, N.E. Scott and M.G. Bawendi: [14] T. Uematsu, J. Kimura and Y. Yamaguchi:
J. Chem. Phys., 108, 143 (2004). Nanotechnology, 15, 822 (2004).

APPLICATION 33

33 DEVELOPMENT OF BRIGHT PHOSPHORS USING GLASSES INCORPORATING
SEMICONDUCTOR NANOPARTICLES

Recently, a demand for bright phosphors is increasing showing various fluorescent colors with improved
because displays and lightings with high luminance, long-term stability by incorporating semiconductor
ultrafine resolution and low-energy consumption are nanoparticles. This study was supported in part by
required. In this field ceramics phosphors doped with the Nanotechnology Glass Project (2001–2006)
rare earth ions and transition metal ions have been related to the Nanomaterial Process Technology of
mainly researched and developed so far, because the Nanotechnology Program, sponsored by the New
those ceramics phosphors are highly stable. However, Energy and Industrial Technology Development
short-wavelength light is required for excitation, and Organization (NEDO), Japan [1, 2].
the control of the emission wavelength is not easy. In Semiconductor nanoparticles also find applications
addition, the photoluminescence (PL) of such ceram- to fluorescent markers for biological tissues and mate-
ics phosphors has long decay time (ca. 1 ms) because rials from a living body [3]. The position and the
the transition has a forbidden character. This causes movement of virus and various materials bound to the
the saturation of PL brightness when the excitation semiconductor nanoparticles can be monitored by
light intensity is increased. luminescence. So far organic fluorescent dyes have
Under such a situation, much attention is directed been widely used in this field. However, the wave-
to nanoparticles of group II–VI semiconductors such length difference between the excitation light and
as CdTe and ZnSe because they emit bright PL emission light is not very large, and therefore differ-
whose wavelength depends on the particle size. ent excitation wavelengths are needed for obtaining
These semiconductor nanoparticles have a direct PL from different dyes. Another disadvantage of
transition bandgap and short PL decay time of ca. 10 organic fluorescent dyes is their low stability that
ns that is shorter than those of rare earth ions and causes deterioration and luminescence quenching in a
transition metal ions by ca. 5 orders of magnitude. short time of irradiation. On the other hand, semicon-
The fast PL decay leads to high brightness that does ductor nanoparticles have much slower deterioration
not saturate easily when the excitation light intensity rate compared with organic dyes, and the long-term
is increased. Another feature of these semiconductor stability can be further improved by incorporating
nanoparticles is that the emission wavelength and them into glass matrices. Furthermore, two or more
emission efficiency are almost independent of exci- kinds of semiconductor nanoparticles with different
tation wavelengths. The authors have carried out emission wavelengths can be used at the same time,
research and development of glass phosphors using a single-excitation light wavelength.

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