On the potential of Er-doped AlN film as luminescence sensing layer for multilayer Al/AlN coating health monitoring

Luminescence sensing is an attractive approach for in-situ monitoring the health and integrity of multilayered surface protective coatings on highly active metals. In this work, we demonstrate the potential of erbium (Er) doped aluminum nitride (AlN) films to be applied as luminescence sensing layer in the Al/AlN multilayered coating system. The AlN:Er films were prepared by radio-frequency magnetron sputtering from Al targets doped with varied concentrations (from 0.5 at.% to 2.5 at.%) of Er. The chemical composition, surface morphology, crystal structure, chemical state and optical properties of the deposited AlN:Er films were investigated. We found that the crystal structure, surface roughness and optical properties of the AlN:Er films have strong correlations with the Er doping level. The as-deposited AlN:Er films showed the characteristic photoluminescence emission lines of the trivalent Er ions in the visible frequency range and quenching was observed when the Er doping level increased to 2.5 at.%. This work signifies the viability of AlN:Er film as luminescence sensing layer and the optimal Er doping concentration of the Al sputtering target is 2.0 at.% for practical applications.