Photoluminescence evolution in APS-deposited YSZ:Eu3+ thermal barrier coatings: mechanisms and sensitivity to thermal history over 0–800 h isothermal exposure at 1100 °C

Thermal history coatings (THCs) deposited via Atmospheric Plasma Spray (APS) offer a promising solution for recording maximum equivalent temperature maps in high-temperature environments such as gas turbines . The sensitivity of an APS-deposited Eu 3+ -doped Yttria-stabilized Zirconia (YSZ) coating to thermal history through isothermal oxidation treatments at 1100 °C for durations ranging from 10 to 800 h was investigated. The evolution of photoluminescence intensity with exposure duration was evaluated and put in relation with structural (X-ray diffractometry) and microstructural (scanning electron microscopy with energy-dispersive spectroscopy) characterizations. A comparative analysis with compressed powder pellets was also conducted to isolate the effects of the deposition process and interactions with the substrate. Photoluminescence emission measurements revealed two distinct sensitivity regimes: (1) a rapid increase in intensity during the first 30 h, driven by crystallization, reduction of crystallographic defects , and particle growth, and (2) a significant intensity decline beyond 30 h, attributed to optical property modifications caused by substrate elements diffusion (Cr, Co) to the coating surface . These findings demonstrate the capability of APS-deposited YSZ:Eu 3+ coatings to sense thermal history over extended durations of exposure, with mechanisms transitioning from crystallinity enhancement to substrate-induced effects. Those results are promising for the development of photoluminescent THCs with a capability for long-duration thermal history sensing.