Evaluation of Cr-doped yttrium aluminum garnet crystals for hybrid fiber-optic thermometer application

Rare-earth aluminate crystals have chemical and thermal stability, which are advantage for the sensor materials of a fiber-optic fluorescence thermometer. Among many rare-earth aluminate crystals, rare-earth garnet, Y3Al5O12, doped with Cr2O3 (Cr-doped YAG), is found to be useful as the sensor materials for fluorescence thermometer. Fluorescence lifetime of Cr-doped YAG crystal decreases from 2 ms to 0.1 ms as the temperature increases from 273 K to 900 K. Moreover, thermal radiation from Cr-doped YAG crystal can be observed from 800 K using Si photo-detector. The fiber-optic thermometer with extremely wide temperature range is considered to be produced by the combination of the temperature dependence of the fluorescence lifetime and the thermal radiation from Cr-doped YAG crystal.