Temperature measurements in harsh environments, such as those present in gas turbines, are of great importance but very hard to obtain. Sometimes, on-line measurements are not possible, and instead, the temperatures during operation are recorded using so-called thermal history sensors and read off-line. Although thermal paints have been used for many years as thermal history sensors, they present some disadvantages. Recently, a new method based on irreversible changes in the emission properties of phosphor materials when they are exposed to high temperatures has been proposed. It has been demonstrated that the process of oxidation from Eu2+ to Eu3+ is temperature sensitive up to 1400 degrees C. In this paper, we describe the manufacture of BaMgAl10O17:Eu (BAM:Eu) using a sol-gel process, and report optical properties interrogated after heat treatments in air and argon atmospheres, which confirm that after treatment in argon, the oxidation process can be reversed. This suggests a promising reusability of the phosphor as a thermal history sensor. A temperature-dependent measurand based on the change of optical properties with temperature has been defined with a dynamic range from 700 degrees C to 1100 degrees C. The effect of exposure time to a certain temperature on this measurand has also been addressed.