Chemistry Reference
In-Depth Information
Figure 6.7
(a) PL emission spectra and (b) PL excitation spectra of YAG:Ce
and Pr co-doped YAG:Ce samples. (c) Energy transfer processes
of Ce
3+
and
Pr
3+
[21].
In terms of color rendering index, the highest R
(CRI) of 83 could
be obtained from Pr co-doped YAG:Ce phosphor when used in white
LED. This was because the red spectral component by Pr co-doping
contributed to the improved R
a
. However, the luminescence efficiency
decreased by about 25% due to the energy transfer process. Pr co-
doped Ga substituted YAG:Ce showed a similar R
a
value to YAG:Ce
based white LED and had very low efficiency, hence is not a good
candidate.
(c) Temperature quenching of YAG:Ce phosphors
As the market for high power LEDs is rapidly developing [61, 62], the
temperature of the phosphors can reach up to 450 K for commercially
available products. In Tamura
a
.'s work [63], it was found that
with increasing temperatures, there was a decrease in emission
intensity of blue light from the LED and a red shift in emission
et al
