Phosphor thermometry using rare-earth doped materials
Hansel, Rachael Ann
:
2010-08-17
Abstract
The goal of this work was to determine the luminescent lifetime of these phosphor
materials as a function of temperature. Cerium-doped yttrium aluminum garnet and
europium-doped pyrochlores were synthesized using combustion synthesis. The
phosphors were characterized using X-ray diffraction, transmission electron microscopy,
and photoluminescence spectroscopy. Lifetime measurements were taken over a range of
temperatures. The garnet materials exhibited thermal quenching between 30-125 ◦ C . In
contrast, the pyrochlore materials did not exhibit thermal quenching until well past 300 ◦ C
. The results presented in this work have shown that high energy states, such as the charge
transfer state or the d -orbitals, play a key role in the thermal quenching properties of
materials. For Ce-doped materials, our results indicate that materials which cause the
splitting of the d -orbitals to increase will cause the emission from the d1
→ 4 f transition
to thermally quench at higher temperatures. The lifetime of the 5 D0
→ 4 f emission line of
Eu3+ is dependent on the location of the charge transfer state. We suggest that the reason
higher quenching temperature are observed in materials such as YBO3 : Eu and the other
pyrochlores is because these materials have high-energy charge transfer states. Tuning
Eu3+ materials to maximize the energy of the charge transfer state may improve thermal
quenching properties of thermographic phosphors.