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Apart from the temperature, four parameters were investigated for their impact on the phosphorescence characteristics of Mg 4 FGeO 6 :Mn with regards to phosphor thermometry: the dopant concentration, the laser pulse energy, gas compositional and pressure effects as well as irreversible changes due to heat treatments. Five specially produced phosphors with different dopant concentrations as well as commercially available Mg 4 FGeO 6 :Mn were investigated in the form of coatings and pure powder. The phosphorescence was excited by the third harmonic of a pulsed Nd:YAG laser (355 nm). The lifetime decay as well as the emission spectra of the subsequently emitted phosphorescence were determined. Generally, the decay time decreased with increasing dopant concentration, with increasing laser pulse energy and for coatings also with increasing maximum temperature and duration of heat treatments, whereas the impact of the laser power was minimized by a modified evaluation routine of the decay time. Gas compositional and pressure effects did not have a significant influence on the decay time of Mg 4 FGeO 6 :Mn. Neither the variation of the dopant concentration nor the exposure to heat treatments influenced the shape of the emission spectra in any way.

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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 lead 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. Y2O2: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. Decay time constants for Y2O2S:Sm are very short (3 µs at 1400 K), 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.