High temperature thermographic phosphors YAG:Tm;Li and YAG:Dy in reduced oxygen environments

Abstract

Phosphor thermometry for surface temperature measurements has become an established remote thermometry technique. However, measuring at temperatures above 1700 K is still challenging because of the weak phosphorescence and intense background from black-body radiation, leading to low signal-to-noise ratios. Therefore, lifetime-based phosphor thermometry with YAG:Tm;Li and YAG:Dy for high-temperature applications were investigated in this study with the aim of improving the precision of high-temperature measurements. The phosphors were coated on an alumina-oxide disc, which was placed in a temperature-controlled oven that exposed the phosphors to temperatures of up to 1930 K. The emission spectra and temporal decay of the luminescence were recorded for the investigated phosphors including their sensitivity to oxygen concentration in the gas environment. Knowledge of oxygen environment sensitivities for measurements of reduced oxygen concentrations at high temperatures, such as in combustion, is of great importance to increase confidence in the measurement. The results suggest that performing a mono-exponential decay time fit in a region of the decay curve that is dominated by a single lifetime component reduces the sensitivity to changes in the gas oxygen concentration for YAG:Tm;Li. Moreover, YAG:Tm;Li performs better than YAG:Dy in terms of signal-to-noise ratio (SNR), with a peak signal value and SNR almost an order of magnitude higher. With an appropriate decay curve fitting procedure, the effects of oxygen quenching can be minimized, such that the measurement error due to oxygen quenching is within the measurement precision for both phosphors.