Oxidation of divalent rare earth phosphors for thermal history sensing

Knowledge of component temperatures under the extreme conditions in industrial prime movers is of great practical importance, but very hard to obtain. Thermal indicating paints offer one possible and practical way, but they have many disadvantages. A novel concept for utilising phosphorescent coatings as thermal history sensors was proposed by Feist et al. [1] in 2007. These phosphor coatings undergo irreversible changes when exposed to high temperatures that affect their photoluminescent emission properties in such a way that off-line analysis of the emission at room temperature can reveal the temperature history of the coating. In this paper, an investigation of the thermally activated oxidation of 2+ ions in phosphors such as BaMgAl10O17:Eu2+, BaMgAl10O17:Eu2+, Mn2+ and SrAl14O25:Eu2+ is reported and used to demonstrate the potential for a phosphorescent thermal history sensor based on a new physical process. Phosphor powders were annealed at temperatures up to 1400 °C, and characterised using photoluminescence spectroscopy. An intensity ratio temperature measurand was defined and it was shown that the dynamic range of a thermal history sensor based on SrAl14O25:Eu2+ could provide a dynamic range extending from 600 °C to 1300 °C.