Modeling luminescence behavior for phosphor thermometry applied to doped thermal barrier coating configurations

Phosphor thermometry is a promising non-destructive method for accurate temperature measurement using phosphor elements that emit temperature-dependent luminescence. The method relies on the intensity and decay of luminescence arising from the phosphor elements upon excitation by an incident laser. In this work, the classical Kubelka-Munk model has been utilized and modified to model the luminescence emitted from phosphor elements that are added into thermal barrier coatings (TBCs) to enable temperature sensing using phosphor thermometry. The collectible luminescence and its time-decay behavior emerging from a tailorable multilayer TBC configuration have been predicted for different rare-earth dopants: Dy, Er, and Sm within an yttria-stabilized zirconia (YSZ) host, and with an operational gradient of temperature acting through its depth. The configurations have been designed by varying the position and thickness of the doped layer into the coating. The decay constant of the collectible luminescence has been used to determine the position in the coating from where the luminescence decay is the same as the decay of the collectible signal. This subsurface position indicates the location at which the temperature measurement is performed using phosphor thermometry under realistic operating conditions. It has been determined that YSZ:Dy provides the highest intensity of the collectible luminescence among the three dopant materials. In the TBC configuration with a fully doped coating, using YSZ:Er as a sensor enables temperature measurement from a more in-depth position in the coating. It has been shown that this position can be tailored by adjusting the geometrical configuration of the TBCs, varying the position and thickness of the doped layer. Due to the sensitivity of the dopants to temperature, the decay behavior of the emerging luminescence is demonstrated to change for different TBC configurations. The model can be used in screening the dopants to design multilayered TBCs for their suitability in temperature sensing by phosphor thermometry.