Investigation of aerosol phosphor thermometry (APT) measurement biases for Eu:BAM

Abstract

Aerosol phosphor thermometry (APT) utilizes the luminescence intensity ratio (LIR) of emission from two wavelength bands to infer temperature. This work characterizes the impacts of phosphor seeding concentration and laser fluence on the measured emission spectrum and resulting LIR vs. temperature calibration for the phosphor Eu:BAM in both a heated air jet and a tube furnace. Increasing seeding density led to spectral broadening, but this effect had a minimal impact on the LIR over the range investigated. Increasing laser fluence from 5 to 60 mJ/cm² resulted in a blue shift in the emission spectrum, corresponding to an increase in the particle temperature of approximately 50 K inferred from the LIR, as previously observed in the literature. Heated jet measurements found that the temperature sensitivity of the LIR for Eu:BAM was not significantly affected by increasing laser fluence for the conditions studied. In contrast, the temperature sensitivity of the LIR measured in the tube furnace was significantly lower than in the jet, likely due to the high phosphor particle concentration present in the aggregate powder environment. These measurements highlight the importance of performing LIR calibrations at representative conditions to achieve unbiased APT measurements when relying on the spectral temperature-dependence of thermographic phosphors.