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

Abstract

Reported here are measurements aimed at development of high temperature luminescence-based fibre optic thermometry for temperatures up to at least 1700 °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 4I15/2–6H15/2 (456 nm) transition in the YAG:Dy,Er host ranged from 856 ns at 1600 °C to 401 ns at 1700 °C. Signals taken at 10 °C intervals were clearly resolvable. Decay times appeared constant at 800 °C and below with average values of 863 µs for YAG:Dy and 734 µs 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 µJ. 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 °C and 0.9% at 1700 °C. Dy emission was also detected at 405, 400 and 389 nm at 1575 °C and 1700 °C and showed the expected temperature dependence.