Development of inorganic fluorescent coatings for high temperature aerospace applications

For many years, phosphor thermometry has been used for non-contact measurements in hostile high temperature environments, including large blackbody radiation backgrounds, vibration, rotation, fire/flame, pressure, or noise. Often these environments restrict the use of more common thermocouples or infrared thermometric techniques. In particular, temperature measurements inside jet turbines, rocket engines, or similar devices are especially amenable to fluorescence techniques. Often the fluorescent materials are used as powders, either suspended in binders and applied like paint or applied as high temperature sprays. These coatings will quickly assume the same temperature as the surface to which they are applied. The temperature dependence of fluorescent materials is a function of the base matrix atoms and a small quantity of added activator or "dopant" ions. Often for high temperature applications, the selected materials are refractory and include rare earth ions. Phosphors like Y ₃Al ₅O ₁₂ (YAG) doped with Eu, Dy, or Tm, Y ₂O ₃ doped with Eu, or similar rare earth compounds, will survive high temperatures and can be configured to emit light that changes rapidly in lifetime and intensity. For example, fluorescence from YAG:Dy was recently observed at 1,600°C at the Oak Ridge National Laboratory (ORNL) National Transportation Research Center (NTRC) in Tennessee. This paper will give research results applicable to the use of phosphors for thermometry purposes.