Phosphor thermometry using rare-earth doped materials

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.