Chemistry Reference
In-Depth Information
obtained under careful control of hydrolysis and condensation reactions. Maintenance of the
Si-F bond during gelling, heating and aging was likely to be achieved by treating the gels under
an argon atmosphere.
One of the most useful materials containing fluorine is fluorine-doped tin dioxide
(FTO). This is utilized as transparent conductive films in a variety of optoelectronic
devices. Various types of fluorinated tin complexes were developed to fabricate FTO
films and nanopowders by the sol-gel method [27-31]. The precursors including Sn-F
bonds (for example, see Figure 10.4) are highly useful in obtaining conductive FTO
because the amount of fluorine could remain well above the effective doping level.
F
R
2
OR
1
O
Sn
R
1
=
t
Am,
i
Pr, Et
R
2
=
Me,
t
Bu
O
O
O
R
2
R
2
R
2
Figure 10.4 Structure in solution of the fluorinated SnF(OR)(acac)
2
compounds, where R
stands for Et ¼C
2
H
5
,
i
Pr ¼CH(CH
3
)
2
and
t
Am¼C(CH
3
)
2
C
2
H
5
. Reproduced from reference 31
by permission of Elsevier
10.4 Control of Shapes and Microstructures
Optical properties of materials greatly depend on their microscopic as well as macroscopic
shapes, based on the interaction with light as shown in Figure 10.5. Transparency of
materials is determined by absorption and scattering of incident light. Reflection at inter-
face is also an important factor influencing optical performance. To make good use of the
excellent optical properties of metal fluorides, their morphology and microstructure should
be carefully controlled.
In the bulk form, heavy-metal fluoride glasses and CaF
2
single crystals are the most
important fluoride materials as main optical components. Some other single crystals of
complex fluorides such as LiYF
4
are also important as laser materials [32]. Recently,
LuLiF
4
:Tm,Ho has received considerable attention, although LuLiF
4
has some difficulty
with crystal growth. Jing et al. succeeded in growing high-quality LuLiF
4
:Tm,Ho crystals
by the Czochralski method [33]. As such, bulk fluoride materials are fabricated generally
by high-temperature processes.
In contrast, low-temperature processes have been successfully employed for creating
fluorine-containing nanomaterials. BaMgF
4
and SrAlF
5
powders and thin films were first
synthesized by the sol-gel method using TFA as the fluorine source [34]. Damien et al. and
Lepoutre et al. synthesized LiGdF
4
:Eu
3
þ
and LiYF
4
:Er
3
þ
crystallized powders by the sol-
gel method [35, 36]. They showed that the organic groups were removed after annealing
treatments at 550 CinF
2
atmosphere. Yi et al. prepared high-quality LiYF
4
,BaYF
5
and
