Chemistry Reference
In-Depth Information
chemical vapor deposition (CVD) and magnetic sputtering. These
dry methods commonly require rigorous conditions such as high
reaction temperature and extreme conditions, hence may not be
perceived as favorable [29].
Conventional bulk YAG:RE phosphors are synthesized based
on the solid-state reaction method. However, in order to achieve
phosphors with large degree of homogeneity and smaller particle
size, wet methods synthetic routes have been adopted [30]. The
wet methods generally involve solution-based processes, where
various parameters may be varied, and thus phase purity, chemical
homogeneity, particle size, and morphology can be controlled. In
contrast to the dry methods, the wet methods are usually carried
out under milder reaction conditions and are more energy efficient
and economical. Rare earth doped nanophosphors are mainly
synthesized based on wet chemical methods.
In the following sections, solid-state synthesis for bulk
phosphors will be discussed first. Other synthesis techniques such
as coprecipitation [31-34], sol gel [35-39], and hydrothermal/
solvothermal methods [40-43] will also be discussed. These
techniques are applied for synthesis of both rare earth nanosize
phosphors as well as phosphors of smaller size as compared to bulk
phosphors, hence more superior in luminescence properties. For
more discussion on rare earth nanomaterials synthesis, please refer
to Chapter 1.
6.3.1
Solid-State Synthesis of Bulk YAG:Ce Phosphors
The solid-state synthesis method conventionally involves high
temperatures where the starting materials are first mixed thoroughly
with fluxes. Fluxes are substances added to raw material to help
crystal grow. After that, the mixture is calcined in a crucible at
high temperature and under reduced temperature for a few hours.
For example, starting materials for YAG:Ce phosphor synthesis
under this method are Y
, weighed according
to stoichiometric ratio of the chemical formula (Y
O
, CeO
, and Al
O
2
3
2
2
3
.
These starting materials are mixed thoroughly with fluxes such
as H
Ce
)Al
O
2.95
0.05
5
12
or alkali fluorides. Then, the mixture is calcined
under a reductive atmosphere (95% N
BO
, BaF
3
3
2
/5% H
), at 1500°C for 6 h
2
2
3+
3+
[44, 45]. Shao
doped
YAG:Ce phosphor, which used the same starting material as above
with the addition of La
et al
. reported the synthesis of Gd
and La
O
and Gd
O
. The calcinating temperature
2
3
2
3
