1 American Institute of Aeronautics and Astronautics (AIAA) ADVANCES IN HIGH TEMPERATURE PHOSPHOR THERMOMETRY FOR AEROSPACE APPLICATIONS S.W. Allison, S.M. Goedeke, D.L. Beshears, and M.R. Cates Oak Ridge National Laboratory (ORNL), National Transportation Research Center (NTRC), 2360 Cherahala Blvd., MS-6472, Knoxville, Tennessee 37932 W.A. Hollerman, F.N. Womack, and N.P. Bergeron Department of Physics, University of Louisiana at Lafayette, P.O. Box 44210, Lafayette, Louisiana 70504 T.J. Bencic, and C.R. Mercer Optical Instrumentation Technology Branch, NASA John H. Glenn Research Center at Lewis Field, 21000 Brookpark Road, Mailstop 77-1, Cleveland, Ohio 4135-3191 J.I. Eldridge Environmental Durability Branch, NASA John H. Glenn Research Center at Lewis Field, 21000 Brookpark Road, Cleveland, Ohio 44135 ABSTRACT Phosphor thermometry has been used for many years for non-contact temperature measurements in hostile environments. Aerospace systems are particularly prone to adverse high temperature environments, including large blackbody background, vibration, rotation, fire/flame, pressure, or noise. These environments often restrict the use of more common thermocouples or infrared thermometric techniques. Temperature measurements inside jet turbines, rocket engines, or similar devices are especially amenable to fluorescence techniques. Often the phosphor powders are suspended in binders and applied like paint or applied as high temperature sprays. Thin coatings will quickly assume the same temperature as the surface to which they are applied. The temperature dependence of phosphors 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 3 Al 5 O 12 (YAG) doped with Eu, Dy, or Tm, Y 2 O 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. Recently, a YAG:Cr phosphor paint emitted fluorescence during short duration tests in a high Mach number hydrogen flame at 2,200 °C. One of the biggest challenges is to locate a binder material that can withstand tremendous variations in temperature in an adverse aerospace environment. This presentation will give research results applicable to the use of phosphors for aerospace thermometry. Emphasis will be placed on the selection of phosphor and binder combinations that can withstand high temperatures. INTRODUCTION Phosphors are fine powders that are doped with trace elements that emit visible light when suitably excited. Most of these materials are ceramics that can withstand high temperatures. Many of the fluorescence characteristics of these phosphors can be temperature dependent. Thus, a phosphor coating can indicate the temperature of the surface. There are a wide variety of ceramic phosphors that survive hazardous physical and chemical environments, are insoluble in water, durable, and easy to apply. Some phosphors have no trouble surviving and functioning in high temperatures such as those present during combustion. The basic principle of thermal phosphors is well established, and researchers at Oak Ridge National Laboratory (ORNL) have demonstrated several useful applications 1-7 . Phosphor thermometry typically relies on measuring the rate of decay of the fluorescent response of an inorganic phosphor as a function of temperature. Having calibrated the phosphor over the desired temperature range, a small surface deposit of phosphor is excited with a pulsed laser and the fluorescent decay is measured (typically in less than 1 ms) to calculate the temperature of the substrate. In many instances, like for a continuous steel galvanneal process, a simple puff of powder onto the surface provides an adequate fluorescent signal. Often temperature measurements are made using thermocouples or optical pyrometry. However, in situations where rapid motion or reciprocating equipment is present at high temperatures, it is best to use other techniques. For certain phosphor paints,