Chemistry Reference
In-Depth Information
potassium sulphate dodecahydrate, KAl(SO
)
·6H
O,
cerium
4
2
2
nitrate, Ce(NO
O. The aluminum source may be replaced by
aluminum nitrate, Al(NO
)
·6H
3
3
2
)
·9H
O [30, 35]. A chelating agent like
3
3
2
citric acid, (C
O), and polymerization agent like ethylene
glycol (EG) were required. The general steps were as follows:
Y(NO
H
O
·H
6
8
7
2
O aqueous solution was added drop-wise to a beaker
containing the aluminum aqueous solution. The mixture was added
into Ce(NO
)
·6H
3
3
2
O aqueous solution. The whole solution was
stirred at room temperature for 20 min. The above solution was
then added dropwise to a beaker containing citric acid dissolved in
EG with constant magnetic stirring until a transparent mixture was
obtained. This stirring step was done in a water bath of 60-80°C.
The solution was then heated to around 120 or 180°C in an electric
oven for 24 h. The result was a brown gel substance, which under
further heating at 400°C or 600°C for 2 h transformed into dark solid
mass, an amorphous gel. After cooling to room temperature, the
solid was grounded into a fine powder. The powder then underwent
calcination at 700-1200°C for 5 h in air to give the final products.
)
·6H
3
3
2
6.3.4
Hydrothermal/Solvothermal Synthesis of LED
Rare Earth Phosphors
The hydrothermal/solvothermal synthesis has relatively simple
steps. The reaction is typically done in autoclaves, which results
in superheated solvents and high pressures such that the
microenvironment of the experiment is distinctly different from other
common synthetic systems. When chelating agents are employed, the
final products usually have few defects with high crystallinity and
fine homogeneity. Typically, the starting materials were mixed and
then heated in autoclave for a few hours at a particular temperature.
After the reaction was complete, the precipitate was collected and
washed with de-ionized water and ethanol for a few times. Finally,
the precipitate was dried to obtain the final products [40-43].
Xiao
et
al
. reported the hydrothermal synthesis of Sm
3+
doped
CaWO
red-emitting phosphor with good luminescence properties
promising for white LED applications. Ca(NO
4
)
·4H
O (0.2 M) and
3
2
2
Sm(NO
(0.2 M) solution and stirred
for 30 min. After which, the mixture was poured into an autoclave,
sealed, and heated at 150°C for 6 h. After the reaction, the precipitate
was left to cool naturally and then collected, washed, and dried at
)
were mixed with Na
WO
3
3
2
4
