a means to measure temperature within the TBC and at the metal/topcoat interface, hence enabling the manufacturing of an integrated heat flux gauge. First results on yttria-stabilized zirconia co-doped with europia (YSZ:Eu) powders were published in 2000. They also demonstrated sub-surface measurements looking through a 50 μm undoped YSZ layer and detecting the phosphorescence of a thin (10 μm) YSZ:Eu layer (bi-layer system) underneath using the ESAVD technique to produce the coating. The first results on electron beam physical vapour deposition of TBCs were published in 2001. The coating tested was a monolayer coating of standard YSZ co-doped with dysprosia (YSZ:Dy). First work on industrial atmospheric plasma sprayed (APS) sensor coating systems commenced around 2002 and was published in 2005. They demonstrated the capabilities of APS sensor coatings for in-situ two-dimensional temperature measurements in burner rigs using a high speed camera system. Further, temperature measurement capabilities of APS sensor coatings were demonstrated beyond 1400 °C. Results on multilayer sensing TBCs, enabling simultaneous temperature measurements below and on the surface of the coating, were reported. Such a multilayer coating could also be used as a heat flux gauge in order to monitor the thermal gradient and also to determine the heat flux through the thickness of the TBC under realistic service conditions. Applications for thermographic phosphors in TBCs While the previously mentioned methods are focusing on the temperature detection, the inclusion of phosphorescent materials into the thermal barrier coating can also work as a micro probe to detect the aging mechanisms or changes to other physical parameters that affect the local atomic surroundings of the optical active ion. Detection was demonstrated of hot corrosion processes in YSZ due to vanadium attack. See also Fluorescence Luminescence Photoluminescence Thermometer Thermometry References Further reading Thermometers Measurement