Luminescence of YAG:Dy and YAG:Dy,Er crystals to 1700 °C

Reported here are measurements aimed at development of high temperature luminescence-based fibre optic thermometry for temperatures up to at least 1700 degrees C. Cylindrical crystal samples of YAG:Dy(1%) and YAG:Dy(1.5%),Er(0.5%) were fabricated by the co-precipitation method. The optical system was comprised of Nd:YAG 355 nm laser light injected into one leg of flexible bifurcated optical fibre connected to a sapphire light pipe. The input end is water cooled and the sensing end is inside a furnace in proximity to the crystal. The emission originates from the Dy3+ dopant. Decay times for the I-4(15/2)-H-6(15/2) (456 nm) transition in the YAG:Dy,Er host ranged from 856 ns at 1600 degrees C to 401 ns at 1700 degrees C. Signals taken at 10 degrees C intervals were clearly resolvable. Decay times appeared constant at 800 degrees C and below with average values of 863 mu s for YAG:Dy and 734 mu s for YAG:Dy,Er. Decay times from these two materials appear to converge to the same value at high temperatures. These results were achieved with laser excitation of 100 to 150 mu J. The results were compared to physical models both of which yielded reasonable empirical agreement for the limited amount of data. Thermal sensitivity determined from a multiphonon model shows that decay times change by 1% per degree at 1400 degrees C and 0.9% at 1700 degrees C. Dy emission was also detected at 405, 400 and 389 nm at 1575 degrees C and 1700 degrees C and showed the expected temperature dependence.