The characterization of Y2O2S:Sm powder as a thermographic phosphor for high temperature applications

Thermographic phosphors may be used to measure surface temperatures in hostile and high temperature environments and have applications in gas turbine combustors and high temperature regions of the turbine. Most phosphors are excited by UV light and exhibit a temperature sensitive exponential decay in emission once excitation has ceased. This can be characterized using a photomultiplier enabling temperatures to be measured at discrete points on the surface. However, one phosphor, YAG:Dy, is known to exhibit temperature sensitivity in the relative intensity of specific lines in its emission spectrum. Emission intensity can be recorded as an image using a CCD camera and hence this type of response can lend to the measurement of surface temperature distributions. In the paper the energy level characteristics of Dy leading to the intensity ratio response are discussed. Another lanthanide, Sm, is shown to exhibit similar characteristics and has been experimentally investigated using Y2O2S:Sm powder. Y2O2S:Sm has been shown to exhibit intensity ratio sensitivity over a temperature range from room temperature to 1100 K and to be suitable for temperature measurement by this means with an uncertainty of approximately +/-1%. It has also been shown to exhibit lifetime decay sensitivity over the temperature range from 900 to 1425 K and to be suitable for temperature measurement by this means with an uncertainty of approximately +/-1%. In both cases the upper temperature limit is a function of the instrumentation used and the dynamic response may extend further. Decoy time constants for Y2O2S:Sm are very short (3 mu s at 1400K), compared to those for YAG:Dy, making it suitable for use on moving surfaces by either response mode. This material, or other Sm doped phosphors, may therefore be useful for surface temperature measurement on rotating turbine blades.