Chemistry Reference
In-Depth Information
The decomposition reaction of the metal trifluoroacetates involves the generation of
gaseous phases such as (CF
3
CO)
2
O, CF
3
COF and COF
2
[19] in addition to the dehydration
and the vaporization of the organic components. It seems that F
can be supplied from
these organofluorine species because, in the presence of water, F
ions can be supplied by
hydrolysis of CF
3
COF and COF
2
. Thus the Eu
3
þ
!
Eu
2
þ
reduction process is regarded as
a solid-gas reaction in this case.
Eu-doped CaF
2
and MgF
2
films were synthesized by the sol-gel method using TFA [96].
It was found that the films of CaF
2
and MgF
2
doped with Eu resulted in luminescence of
Eu
2
þ
and Eu
3
þ
ions, respectively. Eu
2
þ
-activated CaF
2
and SrF
2
nanoparticles were also
prepared by the sol-gel method assisted with a thermal-carbon reducing atmosphere
(TCRA) treatment [97]. Photoluminescence with a peak at 425 and 416 nm due to Eu
2
þ
was observed for CaF
2
and SrF
2
, respectively.
Li et al. reported systematic manipulation of the morphologies and architectures of
-
NaYF
4
microcrystals using a simple and mild solution-growth method [98]. They inves-
tigated influences of fluoride sources (NaF and NH
4
F) and pH values on the shapes of
-
NaYF
4
microstructures developed during hydrothermal treatments. In addition, experi-
mental results indicated that optical properties of
-NaYF
4
:Tb
3
þ
phosphors with different
microarchitectures were strongly dependent on their morphologies and sizes. Nano-sizing
and microstructure engineering are now becoming key to the fabrication of novel lumi-
nescent materials both in oxides and non-oxides.
10.6 Concluding Remarks
This chapter reviewed recent advances in sol-gel technologies for the elaboration of novel,
structure-controlled and high-performance metal fluoride nanomaterials in the form of
nanocrystals, thin films, nanocomposites and oxyfluoride glass ceramics. Their excellent
optical properties, which can surpass those of metal oxides, mean that metal fluorides are
increasingly studied by chemists, physicists and materials scientists. The sol-gel method
described in this chapter includes the direct fluorination of oxide precursor gels, the
thermal decomposition of metal organofluorine materials and the building-up of metal
fluoride crystals from F
ions and metal cations in the solutions. Although the functions
mentioned in this chapter were limited to antireflective effects and luminescence, there is
no doubt that these fluoride nanomaterials have a great potential for use in optics,
photonics and optoelectronics. Energy and environmental materials are also emerging
from fluoride nanomaterials, which can also be fabricated by the sol-gel method.
References
[1] C.J. Brinker and G.W. Scherer, Sol-Gel Science, Academic Press, New York, 1990.
[2] A.C. Pierre, Introduction to Sol-Gel Processing, Kluwer, Boston, 1998.
[3] S. Sakka (ed.), Handbook of Sol-Gel Science and Technology; Processing, Characterization
and Applications, Kluwer, Boston, 2005.
[4] S. Fujihara, C. Sasaki and T. Kimura, Crystallization behavior and origin of c-axis orientation
in sol-gel-derived ZnO:Li thin films on glass substrates, Appl. Surf. Sci., 180, 341-350 (2001).
