Quantum efficiencies, absolute intensities and signal‐to‐blackbody ratios of high‐temperature laser‐induced thermographic phosphors

Abstract

There are a number of issues related to high-temperature phosphor thermometry, which include measurement of faster decays, decreasing emission intensity and rising levels of blackbody radiation, that will impose limits on the maximum delectable temperature. This paper provides absolute intensity measurements, quantum efficiencies and signal-to-blackbody radiation ratios at peak emission wavelengths, at various temperatures (20-1400°C), for Y(2)O(3):Eu, YAG:Tb and YAG:Tm thermographic phosphors under 266 and 355 nm excitation from a Q-switched Nd:YAG laser. These terms are beneficial in a number of ways for engineers wanting to use a phosphor thermometry solution at high temperatures. They may also provide additional insight to the physical luminescence processes of phosphors at high temperatures. The phosphor signal:blackbody radiation ratio is useful because it combines the effects of blackbody radiation and phosphor emission intensities at various temperatures, providing a valuable quantitative evaluation that can be used as a design aid for phosphor selection. A figure of merit is the temperature when the blackbody radiation equals the phosphor emission (ratio = 1); this is the cross-over temperature at which the blackbody radiation rapidly starts to overtake and mask out phosphor emissions. To the best of our knowledge no such work exists previously. The results presented show a variation in phosphor intensity with increasing temperature, and although the intensity and quantum efficiencies for Y(2)O(3):Eu and YAG:Tb were much greater than YAG:Tm at low temperatures, YAG:Tm was found to be the most efficient phosphor investigated at higher temperatures (>900°C). With a peak emission wavelength of 458 nm, YAG:Tm experienced the lowest proportion of blackbody radiation therefore its advantage at higher temperatures was further amplified and was found to offer an advantage of approximately +350°C and +250°C increased upper temperature capability compared to Y(2)O(3):Eu and YAG:Tb phosphors, respectively.