Chemistry Reference
In-Depth Information
pumped white LED showed excellent bright white light and had
especially higher R
at 82. Near-UV-LED pumped white LED also
showed white light with stable color coordinates [70].
Similarly, He
a
et
al
. achieved promising results in their studies on
3+
phosphors, which demonstrated a good yellow
light source for white LED applications. Further studies were also
performed on Ce
Eu
doped Li
SrSiO
2
4
3+
3+
, Eu
co-doped Li
SrSiO
phosphor
to investigate
2
4
the luminescence properties and Ce
3+
-Eu
3+
energy transfer in the
3+
3+
phosphor. The PL spectra of Li
phosphor showed
two emission peaks in the blue (420 nm) and yellow regime (570
nm), respectively, due to Ce
SrSiO
: Ce
, Eu
2
4
3+
3+
, respectively. The energy
transfer process was confirmed by PL excitation, UV-vis absorption
and PL decay measurements, which showed that there is a spectral
overlap between the emission of Ce
and Eu
3+
3+
and absorption of Eu
. With
3+
Ce
co-doping, the absorption of the phosphor with n-UV pumped
LED is greatly enhanced [71].
6.4.2
Red-Emitting Phosphors
Red-emitting phosphors are usually combined with green- and/
or blue-emitting phosphors for white LED applications, irradiated
under UV light or blue light LED. Research on potential red-emitting
phosphors has focused on Eu
2+
doped materials and sulfides [72,
73]. This is due to the f-f electrons in Eu
2+
, which corresponds to
2+
red-emission wavelength. However, Eu
doped sulfides and oxides
are not favorable due to the low absorption in the blue light range
of oxides and low chemical stability of sulfides [18, 74]. Therefore,
many recent studies have shown silicon-based nitrides as potentially
good host lattices for red luminescence phosphors. Furthermore,
many new host materials have been discovered as potential red
phosphors for white LED applications and some will be discussed in
the following sections.
6.4.2.1
Nitride-based phosphors
Nitridoaluminosilicate and its doped derivatives have received much
attention due to their red luminescence properties. (Sr, Ca, Eu)AlSiN
3
have been reported [74, 75]. Li
et al
. reported [76] another popular
2+
nitride-based phosphor Eu
(M = Ca, Sr, Ba), where
aluminum was not used. Similar to the nitridoaluminosilicate-based
-doped M
Si
N
2
5
8
