Chemistry Reference
In-Depth Information
6.4.3.1.1
Luminescence characteristics of silicates
(a) Effect of dopants on luminescence properties
Divalent europium is an important activator in many luminescent
materials. Most green phosphors are activated using Eu
to give
an emission band in the green region. The absorption and emission
of Eu
2+
2+
ions are characterized as many efficient broadband when
used in many different hosts as the 4f-5d transition in Eu
2+
ions are
electric-dipole allowed [90].
Zhang
et
al
. synthesized SrBaSiO
:Eu
2+
[89], which was the
4
intermediate phase of Sr
by a solid-state reaction
method. When excited by 430 nm light, the PLE spectra showed
a broad absorption band peaking at 430 nm, attributed to the
4f
SiO
and Ba
SiO
2
4
2
4
7
6
1
2+
4f
5d
transition of the Eu
ion. No red characteristic emission
lines due to Eu
3+
were observed, indicating that all the Eu
3+
in the
2+
crystalline matrix has been reduced into Eu
ions. The PL spectra
showed a wide green emission band, which centers at 512 nm. Under
395 nm excitation, the emission intensity was lowered, but emission
profile remained largely similar. The SrBaSiO
2+
phosphor was
tested in a white LED with a 395 nm emitting InGan chip. Figure
6.8 shows the PLE and PL spectra of the observed results. Under a
high forward bias current, it was found that SrBaSiO
:Eu
4
2+
has high
current tolerability, which renders it useful for LED applications.
:Eu
4
l
em
l
Figure 6.8
PLE (
= 512 nm) and PL(
= 395 nm, 430 nm) spectra of
ex
SrBaSiO
4
:0.02Eu
2+
[89].
